28.E: Invertebrates (Exercises) - Biology

28.E: Invertebrates (Exercises) - Biology

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28.1: Phylum Porifera

The simplest of all the invertebrates are the Parazoans, which include only the phylum Porifera: the sponges. Sponge larvae are able to swim; however, adults are non-motile and spend their life attached to a substratum.

Review Questions

Cnidocytes are found in _____.

  1. phylum Porifera
  2. phylum Nemertea
  3. phylum Nematoda
  4. phylum Cnidaria


Cubozoans are ________.

  1. polyps
  2. medusoids
  3. polymorphs
  4. sponges


Free Response

Explain the function of nematocysts in cnidarians.

Nematocysts are “stinging cells” designed to paralyze prey. The nematocysts contain a neurotoxin that renders prey immobile.

Compare the structural differences between Porifera and Cnidaria.

Poriferans do not possess true tissues, while cnidarians do have tissues. Because of this difference, poriferans do not have a nervous system or muscles for locomotion, which cnidarians have.

28.2: Phylum Cnidaria

Phylum Cnidaria includes animals that show radial or biradial symmetry and are diploblastic, that is, they develop from two embryonic layers. Nearly all (about 99 percent) cnidarians are marine species. Cnidarians contain specialized cells known as cnidocytes (“stinging cells”) containing organelles called nematocysts (stingers). These cells are present around the mouth and tentacles, and serve to immobilize prey with toxins contained within the cells.

Review Questions

Annelids have a:

  1. pseudocoelom
  2. a true coelom
  3. no coelom
  4. none of the above


Which group of flatworms are primarily ectoparasites of fish?

  1. monogeneans
  2. trematodes
  3. cestodes
  4. turbellarians


A mantle and mantle cavity are present in:

  1. phylum Echinodermata
  2. phylum Adversoidea
  3. phylum Mollusca
  4. phylum Nemertea


The rhynchocoel is a ________.

  1. circulatory system
  2. fluid-filled cavity
  3. primitive excretory system
  4. proboscis


Free Response

Describe the morphology and anatomy of mollusks.

Mollusks have a large muscular foot that may be modified in various ways, such as into tentacles, but it functions in locomotion. They have a mantle, a structure of tissue that covers and encloses the dorsal portion of the animal, and secretes the shell when it is present. The mantle encloses the mantle cavity, which houses the gills (when present), excretory pores, anus, and gonadopores. The coelom of mollusks is restricted to the region around the systemic heart. The main body cavity is a hemocoel. Many mollusks have a radula near the mouth that is used for scraping food.

What are the anatomical differences between nemertines and mollusks?

Mollusks have a shell, even if it is a reduced shell. Nemertines do not have a shell. Nemertines have a proboscis; mollusks do not. Nemertines have a closed circulatory system, whereas Mollusks have an open circulatory system.

28.3: Superphylum Lophotrochozoa

Animals belonging to superphylum Lophotrochozoa are protostomes, in which the blastopore, or the point of involution of the ectoderm or outer germ layer, becomes the mouth opening to the alimentary canal. This is called protostomy or “first mouth.” In protostomy, solid groups of cells split from the endoderm or inner germ layer to form a central mesodermal layer of cells. This layer multiplies into a band and then splits internally to form the coelom.

28.4: Superphylum Ecdysozoa

The superphylum Ecdysozoa contains an incredibly large number of species. This is because it contains two of the most diverse animal groups: phylum Nematoda (the roundworms) and Phylum Arthropoda (the arthropods). The most prominant distinguising feature of Ecdysozoans is their tough external covering called the cuticle. The cuticle provides a tough, but flexible exoskeleton tht protects these animals from water loss, predators and other aspects of the external environment.

The embryonic development in nematodes can have up to __________ larval stages.

  1. one
  2. two
  3. three
  4. five


The nematode cuticle contains _____.

  1. glucose
  2. skin cells
  3. chitin
  4. nerve cells


Crustaceans are _____.

  1. ecdysozoans
  2. nematodes
  3. arachnids
  4. parazoans


Flies are_______.

  1. chelicerates
  2. hexapods
  3. arachnids
  4. crustaceans


Free Response

Enumerate features of Caenorhabditis elegans that make it a valuable model system for biologists.

It is a true animal with at least rudiments of the physiological systems—feeding, nervous, muscle, and reproductive—found in “higher animals” like mice and humans. It is so small that large numbers can be raised in Petri dishes. It reproduces rapidly. It is transparent so that every cell in the living animal can be seen under the microscope. Before it dies (after 2–3 weeks), it shows signs of aging and thus may provide general clues as to the aging process.

What are the different ways in which nematodes can reproduce?

There are nematodes with separate sexes and hermaphrodites in addition to species that reproduce parthenogentically. The nematode Caenorhabditis elegans has a self-fertilizing hermaphrodite sex and a pure male sex.

Describe the various superclasses that phylum Arthropoda can be divided into.

The Arthropoda include the Hexapoda, which are mandibulates with six legs, the Myriapoda, which are mandibulates with many legs and include the centipedes and millipedes, the Crustacea, which are mostly marine mandibulates, and the Chelicerata, which include the spiders and scorpions and their kin.

Compare and contrast the segmentation seen in phylum Annelida with that seen in phylum Arthropoda.

Arthropods have an exoskeleton, which is missing in annelids. Arthropod segmentation is more specialized with major organs concentrated in body tagma. Annelid segmentation is usually more uniform with the intestine extending through most segments.

28.5: Superphylum Deuterostomia

The phyla Echinodermata and Chordata (the phylum in which humans are placed) both belong to the superphylum Deuterostomia. Recall that protostome and deuterostomes differ in certain aspects of their embryonic development, and they are named based on which opening of the digestive cavity develops first. The word deuterostome comes from the Greek word meaning “mouth second,” indicating that the anus is the first to develop.

Review Questions

Echinoderms have _____.

  1. triangular symmetry
  2. radial symmetry
  3. hexagonal symmetry
  4. pentaradial symmetry


The circulatory fluid in echinoderms is _____.

  1. blood
  2. mesohyl
  3. water
  4. saline


Free Response

Describe the different classes of echinoderms using examples.

The Asteroidea are the sea stars, the Echinoidea are the sea urchins and sand dollars, the Ophiuroidea are the brittle stars, the Crinoidea are the sea lilies and feather stars, the Holothuroidea are the sea cucumbers.

Invertebrate Worksheet

1. Approximately what percentage of animals are invertebrates?

3. Name the phyla of invertebrates and members of each phyla.

4. __________ are in the phylum Porifera. There are about _____ different species & most of these are _________ organisms found in oceans & seas. A few sponges are found in __________, but these are small and not brightly colored.

5. Sponges are _____________ that trap __________ from water as it flows through them.

6. Sponges have no basic body arrangement and are said to be ________________.

7. Sponges live attached to one spot as adults so they are __________.

8. The skeleton of sponges is made of a flexible protein called ___________ and hard fibers called __________ which are composed of calcium carbonate or silicon dioxide.

9. Sponges are full of holes called __________ through which water flows into their __________ bodies.

10. Sponges are the simplest animals and lack the __________ level of specialization like all other animals. Sponges do have some specialized _________ in their bodies.

11. Special cells called choanocytes line the pores and have __________ that spin to pull in water.

12. __________cells at the base of choanocytes capture plankton from the water & start digesting it.

13. _______________ are special cells that carry this food to all other parts of the sponge.

14. Wastes and excess water leave a sponge through a large opening at the top called the __________.

15. Sponges reproduce asexually by internal or external __________ and by _______________ whenever a piece of a sponge breaks off. This last method helps sponges form _____________.

16. Sponges reproduce sexually also and are _______________ producing both eggs and sperm. Sponges __________ sperm with each other and do not fertilize their own eggs.

17. Internal buds or ____________ form if the freshwater supply evaporates and are release when the sponge __________ and become ___________ when freshwater returns.

17. The phylum Cnidaria includes what organisms?

18. All cnidarians are _______________ organisms except for the __________ which is found in freshwater.

19. Cnidarians all have _______________ symmetry and _____________ or arms that have stinging cells called _______________. These stinging cells shoot out like a _______________ and contain a __________ that can kill or paralyze their prey.

20. Cnidarians have _____ body layers an inner _______________ and an outer ____________.

21. Cnidarians have _______ opening into their hollow bodies called the __________ so food enters and wastes leave through this same opening. This is called a ________________ digestive system.

22. The hollow cavity the mouth opens into is called the ____________________ cavity.

23. Cnidarians have 2 body forms. ___________ forms have the mouth & tentacles located at the top like Hydra, corals, and sea anemones. _____________forms like the jellyfish have their tentacles and mouth located at the bottom.

24. Some cnidarians like the _______________ go through both polyp and medusa forms in their life cycle.

25. Cnidarians have a simple nerve _________ and can reproduce both _____________ and _____________.

26. Corals build _____________ cases that make underwater ___________.

27. Flatworms are in the phylum _______________ and are flattened ______________ with __________ symmetry.

28. Flatworms are said to be _________________ because of their solid body.

29. ___________and ____________ are parasitic flatworms having only _______ body opening called the _____________.

30. Specialized _____________ cells remove wastes.

31. The ______________ is the most common free living flatworm. It is found in __________ or _____________ places.

32. Planarians produce both eggs and sperm and are said to be ________________ however, they _____________ sperm with other planarians. Planarians also reproduce asexually by _________________.

33. Flukes and tapeworms usually live in their host’s ______________ tract resistant to digestive _______________ allowing the __________ to digest their food.

34. Tapeworms are divided into sections called _________________ with complete _________________ structures. The head is called the _______________ and has both _________________ and ______________ to attach to the host.

35. Tapeworms are ___________________ and ______________ their own eggs which pass out of the host’s body in ripe ____________________ along with feces.

36. Humans get tapeworms from eating _______________________, while children pick up tapeworm eggs from ________________ boxes.

37. _______________ are in the phylum Nematoda and are _________________ in shape and ________________ at both ends.

38. Roundworms are ____________________ because their body cavity or ________________is not fully lined. The body cavity is filled with fluid giving them a ____________________ skeleton against which _______________can contract.

39. Roundworms have a complete gut with both a ______________ and an _____________ giving them a ________________ digestive tract.

40. Roundworms have no ____________ and no ___________ but can digest food.

41. Most roundworms are _________________ with ________________ symmetry and no _____________________. They are found in _______________________.

42. A protective __________________covers them and must be _____________.

43. Roundworms reproduce _________________.

44. The roundworm called Trichinella causes the disease _______________ and is picked up when someone eats ________________________. This disease affects the ______________ and _______________.

45. The roundworm Ascaris parasitizes human _____________________. __________________ and _________________ are common parasites of humans, and the Filaria worm attacks the _________________ system causing great swelling.

46. Rotifers are ___________________ worms found in terrestrial & aquatic habitats.

47. Rotifers have a crown of ______________ surrounding their mouth for ________________ and ______________________. Their bodies are covered with ________________.

48. Rotifers have separate _____________, but some species reproduce by _______________________.

49. Describe parthenogenesis.

50. Name several organisms in the phylum Mollusca.

51.Mollusks have a durable shell made of ________________ and are found ________________.

52. List several economic importance’s of this group.

53. Name the 2 largest invertebrates.

54. Mollusks have ________________ symmetry and a ___________________ containing their body organs. Mollusks also have a muscular ____________ for movement which can be modified into arms or _________________.

55. Mollusks breathe through ________________ or________________ located below a protective layer called the _______________. This layer can also form an external _____________.

56. The ______________ is a rough tongue for scraping food.

57. Mollusks have a ___________________ heart and an ______________________circulatory system.

58. Mollusks reproduce ___________________ and go through a free swimming larval stage called the _______________________.

59. ____________________ mollusks have a muscular foot on their belly and include the shelled _______________ and the unshelled ________________.

60. ___________________ mollusks have a 2 part hinged shell that is opened and closed by _________________ muscles. They move by ___________________ or by extending their muscular _______________, and they respire through __________________.

61. Name some bivalve mollusks.

62. _____________________ are head-foot mollusks that have a _______________ and ________________, arms or ___________________, and ____________________ to move by jet propulsion.

63. Name some cephalopod mollusks.

64. What is the only shelled cephalopod?

65. Cephalopods breathe through _______________ .

66. Cephalopods are the most ________________________ mollusks.

67. The _____________________ & ________________ can secrete an inky substance into the water to escape predators and have an __________________ shell.

68. Annelids are ____________________ worms found in _________________.

69. External segments correspond to internal segments called _______________.

70. Give two ways that segmentation is an advantage for an organism.

71. Annelids have a tube within a tube body plan called the ___________________ where the body _______________ are located. This tube runs from the _________________ to the _______________ and is fully _______________.

72. Annelids show ______________________ by having bilateral symmetry with an anterior head where most sense organs are found.

73. Coelomic fluid gives annelids a ______________________ skeleton.

74. The best known member of this group is the ____________________ which moves by external bristles called _________________ on each body segment. These bristles are made of _________________. Earthworms respire through their ________________________ and have a ___________________ circulatory system and _____________ pairs of hearts or aortic arches.

75. Describe how an earthworm feeds and tell how this helps the environment.

76. What are castings and where can they be found?

77. ______________ are annelids with _____________ at both the anterior and posterior end. Anterior suckers are used to __________________________ , while posterior suckers help to ____________________________.

78. Most leeches are _______________________ or ____________________, but blood sucking leeches are collected for ___________________________.

79. Both leeches and earthworms produce eggs and sperm and are called _______________________ however, leeches lack ________________ and are flattened _________________________.

80. ___________________ are marine annelids whose setae are modified into paddle like ____________________ for movement and more area for _______________________.

81. Polychaetes live commensally with what other organisms?

82. Arthropod means _________________ appendages.

83. Give 5 characteristics of all arthropods.

84. What is ecdysis and why is it necessary?

85. What is the exoskeleton of arthropods composed of?

86. What is meant by an open circulatory system?

87. Arthropods are divided on the type of _____________________ they have. ______________________ have chelicerae or fangs and no_________________, _______________________ have pincers called ___________________, and _______________________ have mandibles or jaws.

88. ___________________ are extinct, marine arthropods with a_____________ and segmented _____________________ with a pair of legs on each section.

89. ________________________ arthropods like insects, centipedes, & millipedes breathe through hollow air tubes called _____________________ aquatic chelicerates like the ____________________ crab have ___________________ to breathe spiders, ticks, and scorpions use _____________________ to get air and crustaceans breathe through ______________________.

90. Terrestrial mandibulates are ____________________ with one-branched appendages while aquatic crustaceans are _______________________ with two-branched appendages.

91. Arthropods have a nervous system with an anterior ___________________ and sensory organs that include compound eyes or simple eyes called _______________ ______________________ membranes for hearing and ___________________ for smelling, feeling, or tasting.

92. ______________________ tubules filter wastes in arthropods.

93. The subphylum Chelicerarta contains the class ______________________ with the horseshoe Crab and the class ____________________ with spiders, ticks, scorpions, & mites. Both classes have ___________ body regions, the ___________________ and abdomen, no ___________________, ____________________ legs, and ___________________ or fangs.

94. Appendages on the head of chelicerates called _____________________ are used for sensing the environment and getting food into the mouth.

95. Spiders have posterior glands called ________________ that help make their silken webs to get prey. Spiders detect movement whenever their prey gets caught in their ________________ and by sensory ________________ on their body. Spiders produce _______________ to kill their prey & are beneficial because they feed mainly on ____________________.

96. Spiders are unlike insects in that they have _____________ not ___________ legs, only ___________________ eyes and not compound, and _________ body regions and not _____________.

97. Name the body regions of insects and spiders.

98. The ____________________ and ____________________ are two poisonous spiders in our area.

99. The class Crustacea is in the subphylum _______________________ and includes _________________, ________________, ________________, _________________, _________________, and the terrestrial __________________ & ___________________.

100. Crustaceans have a pair of sensory __________________ and a pair of shorter ___________________ for balance. The head also contains three types of mouthparts – _____________________, _____________________, and _______________________. They also have pincers called __________________ to help catch and eat food.

101. Aquatic crustaceans have an external shell or __________________ that must be molted, and they are used by man for ___________________.

102. The class _____________________ contains predators called centipedes with ________________, _________________ glands, posterior_______________, & ________________ pairs of legs per body segment.

103. The class ____________________ contains millipedes which are ____________________ with _______________ pairs of legs per body segment.

104. The largest and most successful group of arthropods are the __________________.

105. Insects have _______ body regions, _________ legs, a pair of sensory ________________, and a pair of ________________ for flight. ___________________ & ___________________ are wingless insects, while flies have their second pair of wings modified into balancing organs called ____________________.

106. Insects have 4 mouthparts which include the jaw or ________________, the _______________, the lower lip or _________________, and the upper lip or __________________.

107. Insect mouthparts are modified according to their ___________________. Butterflies have ___________________ mouthparts, flies have _________________ mouthparts, mosquitoes have ________________ mouthparts, and grasshoppers have ___________________ mouthparts.

108. Wings and legs are both attached to the _________________ on insects, and some female insects have an egg laying tube or ____________________ on the end of their abdomen.

109. Name 2 ways insects communicate.

110. Insects detect sound by _________________ membranes on the abdomen and sensory _______________ that cover their body.

111. _________________ along the abdomen of insects open into their breathing tubes or ___________________.

112. Insects with _________________ metamorphosis go through egg, larva, pupa, & adult stages while those with incomplete metamorphosis go through ________________, ___________________, and _________________ stages.

113. Give examples of insects with complete and incomplete metamorphosis.

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28.E: Invertebrates (Exercises) - Biology

This is one of many exercises available from Invertebrate Anatomy OnLine , an Internet laboratory manual for courses in Invertebrate Zoology. Additional exercises can be accessed by clicking on the links to the left. A glossary and chapters on supplies and laboratory techniques are also available. Terminology and phylogeny used in these exercises correspond to usage in the Invertebrate Zoology textbook by Ruppert, Fox, and Barnes (2004). Hyphenated figure callouts refer to figures in the textbook. Callouts that are not hyphenated refer to figures embedded in the exercise. The glossary includes terms from this textbook as well as the laboratory exercises.

Eumetazoa, Triploblastica, Ctenophora P , Cydippida O , Pleurobrachiidae F (Fig 8-15)

Ctenophores, or comb jellies, are delicate, transparent, mostly pelagic, marine carnivores. They have biradial symmetry, oral-aboral axis of symmetry, and triploblastic organization with a thick cellular mesoglea. Some true organs are present. About 80 species, ranging in size from millimeters to over a meter, are known (Fig 8-1, 8-12, 8-13, 8-14).

Comb jellies are gelatinous zooplankters that superficially resemble scyphomedusae but differ from them in several important respects. There have no alternation of generations, no equivalent of the polyp generation, no dimorphism, and no colonial (modular) organization. Cnidocytes are absent and cilia, rather than muscles, are used for locomotion. The gut is complete, with openings at both ends. Ctenophores were long thought to be allied with cnidarians and included in the now defunct group Coelenterata. We now believe the similarities to be convergences and ctenophores are probably closer to Bilateria than to Cnidaria (Fig 8-15).

Digestion begins extracellularly but is completed intracellularly. The gut is divided into digestive and distributive regions similar to the situation in scyphozoans. Cilia are well developed and used for a variety of purposes. Locomotion is accomplished by eight longitudinal rows of paddles, each paddle being composed of thousands of cilia. Cilia are also involved in sensory reception and some function in a mechanical, rather than neuronal, communication system. The connective tissue compartment is a mesoglea containing cells of several types, especially muscle. Ctenophores are hermaphroditic (unlike scyphomedusae) and many are bioluminescent.

Ctenophores should be studied alive if possible but preserved material must be used in most laboratories. Because of their delicacy, living ctenophores are difficult to ship and their study is a luxury possible only at coastal laboratories. Observation of living comb jellies is an altogether different experience than the study of preserved animals.

Cydippid ctenophores, such as the sea gooseberry Pleurobrachia (Fig 1, 8-1B), are more or less typical. Pleurobrachia pileus is the species usually provided in preserved condition by biological supply companies. It is a small animal, about 1 cm in diameter.

Figure 1. The comb jelly, Pleurobrachia pileus, drawn from a preserved specimen. The tentacular plane coincides with the plane of the paper (or screen). The pharyngeal plane is perpendicular to it. The tentacles are shown extended, as they would be in life but not when preserved. Some ctenes have been omitted to reveal structures beneath them. Cten12L.gif

Place a preserved specimen in a small dish of tapwater . Examine it with the dissecting microscope. If your specimen is transparent, you will find transmitted light preferable to incident. Handle your specimen carefully as it is delicate and easily broken.

The ctenophore body wall consists of a thin, bilayered, outer epidermis and a thin inner gastrodermis lining the coelenteron. Between the two is the thick, gelatinous, cellular, collagenous mesoglea.

Pleurobrachia is a slightly ovoid sphere weakly flattened on two opposite sides. The two ends of the ovoid are the oral and aboral poles (Fig 1, 8-1A). In preserved material the aboral pole is often recessed in a depression whereas the oral pole may protrude somewhat. The mouth is a transverse slit at the oral pole. In preserved specimens it may be elevated above the body surface by the partial eversion of the pharynx. Two anal pores are present at the aboral pole.

Figure 2. Aboral polar view of the cydippid larva of an unidentified ctenophore (probably Mnemiopsis) from Beaufort, North Carolina. The diameter is about 0.5 mm. cten13L.gif

The oral-aboral axis is the axis of symmetry around which is arrayed the biradial symmetry characteristic of ctenophores. Two planes, both including the axis of symmetry and at right angles to each other, are the planes of symmetry (Fig 2). One, the tentacular plane, passes through the two tentacle sheaths on opposite sides of the body. Another, the pharyngeal plane, passes through and includes the plane of the flattened pharynx. These two planes, and no other, divide the jelly into equal, mirror image halves.

The most conspicuous features of a ctenophore are its eight comb rows, which are arranged like meridians, or lines of longitude, on the surface of the sphere (Fig 1, 8-3, 8-2). Each row is composed of a number of successive plates of large, fused cilia. Each plate functions as a paddle and is known as a ctene (= comb).

The two tentacle sheaths (Fig 1, 8-9) are deep ectodermal invaginations opening on the surface of the aboral hemisphere. They extend into the interior to terminate on opposite sides of the pharyngeal region of the gut. The sheaths and tentacles lie in the tentacular plane of the animal.

A single tentacle arises from a large, opaque tentacle bulb (=tentacle base) at the bottom of each sheath. The tentacles extend from the sheath and trail through the water where they fish for zooplankton. The tentacles are branched, unlike those of cnidarians, and the branches, known as tentilla, bear colloblasts. Colloblasts are cells reminiscent of cnidocytes and, like them, arise from epidermal interstitial cells. They release mucus rather than toxins when discharged onto the prey and they do not penetrate.

The tentacles are muscular and can be retracted into the sheaths. Completely extended tentacles of Pleurobrachia may be 25 cm in length but in preserved specimens the tentacles are partly or completely retracted.

The mouth opens into a large, wide, flat, epidermal pharynx where extracellular digestion begins. The pharynx is strongly flattened in the pharyngeal plane.

The pharynx extends aborally from the mouth and empties into the small stomach near the center of the animal (Fig 1, 8-9). Unlike the pharynx, the coelenteron, including the stomach, is endodermal (i.e. gastrodermal) and is lined with ciliated, secretory, phagocytic gastrodermis.

An extensive system of ciliated endodermal canals arises from the stomach and distributes food to the tissues (Fig 1, 8-9). It includes eight meridional canals (one below each comb row), two tentacular canals (one to each tentacle sheath), two pharyngeal canals to opposite sides of the pharynx, a pair of transverse canals, and an aboral canal extending vertically to open to the exterior via two anal pores at the aboral pole. Notice that all metabolically active tissues have a canal in close proximity.

As is the case in Scyphozoa and Anthozoa, the gut is divided into a central digestive region where extracellular digestion occurs and a peripheral distributive portion. The pharynx is the major extracellular digestive chamber and the canals are the distribution, or fluid transport, system. The gastrodermis lining the distributive canals is composed of both ciliated and phagocytic cells. Extracellular digestion begins in the pharynx with the secretion of hydrolytic enzymes. Partially digested food moves into the stomach and from there into the canal system, propelled by ciliary currents. In the canals the partially digested material is phagocytized or pinocytosed (endocytosed) and digestion is completed intracellularly. Undigested material passes through the aboral canal and is voided through one of the two anal pores at the aboral pole.

The epithelial walls of the canals include cells specialized for light production (bioluminescent photocytes), osmoregulation (rosettes), endocytosis and intracellular digestion, gametogenesis (gonads), and fluid transport (monociliated cells).

" If the body wall is opaque and obscures your view of the interior, your instructor may direct you to dissect the animal. Do this by cutting from pole to pole through the epidermis on one side with fine scissors. Look into the interior through the cut. The pharynx, tentacle sheaths, and tentacles should be easier to see now. Relocate these structures and look once more for the canals of the gastrovascular cavity. "

" Remove a small piece of a comb row and make a wet mount with it. Your instructor may designate a damages specimen for use by several students for this purpose. Examine the wetmount with the compound microscope. Find a ctene and note its composition. Look for the individual cilia of which it is composed. Do you understand now why these plates are called "combs"?

The aboral organ (= apical organ) can be seen as a small spot at the aboral pole (Fig 1, 8-4). It is a center for gravity detection and control of the comb rows. It contains a calcareousstatolith, which is easily seen with magnification (Fig 8-7). The statolith rests on four tufts of balancer cilia (Fig 8-4B). From each balancer run two ciliary grooves, one each to the aboral ends of each pair of side-by side comb rows. Tilting the body away from its vertical orientation increases the pressure of the statolith on one or two of the balancers. Pressure of the statolith on a balancer changes the beating rate of its cilia. This change is transmitted mechanically, not by neurons, to the cilia of the ciliary groove and thence to the cilia of the ctenes. The ctenes of those comb rows beat faster and return the animal to vertical.

" If instructed to do so, use fine scissors to excise the aboral pole being sure to include the aboral organ. Carefully arrange the apical organ on a slide and prepare a wetmount. Be sure the epidermis is not folded over the apical organ.

Look for the statolith, four balancer tufts of cilia upon which the statolith rests, and a ciliated groove extending to each comb row. This is the apparatus that controls the beating of the ctenes in the comb rows.

>Test the composition of the statolith by drawing 8% HCl (See Techniques chapter) under the coverslip. Watch the response of the statolith. If it is calcareous, it will react with the HCl, release carbon dioxide, and disappear. <

Reproduction and Development

Ctenophores are hermaphroditic and gonads of both sexes are located in the lining of the meridional canals but they are usually not evident in preserved specimens (Fig 8-4A). Gametes are shed to the sea through numerous tiny gonopores in the comb rows. In most species fertilization is external.

Development is direct without metamorphosis but includes a characteristic cydippid larva (Fig 2) which resembles the adult (Fig 8-11).

*Hyphenated call-outs, such as this one, refer to figures in Ruppert, Fox, and Barnes (2004). Those without hyphenation refer to figures embedded in this exercise.

Hernandez-Nicaise, M-L. 1991. Ctenophora, pp 359-418 in Harrison, F. W. & J. A. Westfall (eds.). 1991. Microscopic Anatomy of Invertebrates vol. 2 Placozoa, Porifera, Cnidaria, and Ctenophora. Wiley-Liss, New York. 436p.

Horridge, G. A. 1965. Relations between nerves and cilia in ctenophores. Am. Zool. 5:357-375.

Horridge, G. A. 1974. Recent studies on the Ctenophora. in Muscatine, L. and H.M. Lenhoff (eds) Coelenterate Biology. Academic Press, New York. pp. 439-468.

Mayer, A. G. 1912. Ctenophores of the Atlantic coast of North America. Carnegie Inst. Washington Pub 162:1-58, 17 pls.

Ruppert EE, Fox RS, Barnes RB. 2004. Invertebrate Zoology, A functional evolutionary approach, 7 th ed. Brooks Cole Thomson, Belmont CA. 963 pp.

28.E: Invertebrates (Exercises) - Biology

This is an exercise from Invertebrate Anatomy OnLine , an Internet laboratory manual for courses in Invertebrate Zoology. Additional exercises can be accessed by clicking on the links to the left. A glossary and chapters on supplies and laboratory techniques are also available. Terminology and phylogeny used in these exercises correspond to usage in the Invertebrate Zoology textbook by Ruppert, Fox, and Barnes (2004). Hyphenated figure callouts refer to figures in the textbook. Callouts that are not hyphenated refer to figures embedded in the exercise. The glossary includes terms from this textbook as well as the laboratory exercises.

Panarthropoda SP , Arthropoda P , Mandibulata, Tracheata, Myriapoda SC , Chilopoda C , Notostigmophora SO , Scutigeromorpha O , Scutigeridae F (Fig 6-15, 20-14A, 20-15)

Panarthropoda includes Onychophora, Tardigrada, and Arthropoda. These taxa share segmentation, a hemocoel, saccate nephridia, ecdysis of a secreted chitinous but non-collagenous exoskeleton, loss of locomotory cilia, a tubular, dorsal, ostiate heart in a pericardial sinus, a coelom reduced to end sacs and gonocoel, and paired segmental legs.

Arthropoda, by far the largest and most diverse animal taxon, includes chelicerates, insects, myriapods, and crustaceans as well as many extinct taxa. The body is segmented and primitively bears a pair of jointed appendages on each segment. The epidermis secretes a complex cuticular exoskeleton which must be molted to permit increase in size. Extant arthropods exhibit regional specialization in the structure and function of segments and appendages. The body is typically divided into a head and trunk, of which the trunk is often itself divided into thorax and abdomen.

The gut consists of foregut, midgut, and hindgut and extends the length of the body from anterior mouth to posterior anus. Foregut and hindgut are epidermal invaginations, being derived from the embryonic stomodeum and proctodeum respectively, and are lined by cuticle, as are all epidermal surfaces. The midgut is endodermal and is responsible for most enzyme secretion, hydrolysis, and absorption.

The coelom is reduced to small spaces associated with the gonads and kidney. The functional body cavity is a spacious hemocoel divided by a horizontal diaphragm into a dorsal pericardial sinus and a much larger perivisceral sinus. Sometimes there is a small ventral perineural sinus surrounding the ventral nerve cord.

The hemal system includes a dorsal, contractile, tubular, ostiate heart that pumps blood to and from the hemocoel. Excretory organs vary with taxon and include Malpighian tubules, saccate nephridia, and nephrocytes. Respiratory organs also vary with taxon and include many types of gills, book lungs, and tracheae.

The nervous system consists of a dorsal, anterior brain of two or three pairs of ganglia, circumenteric connectives, and a paired ventral nerve cord with segmental ganglia and segmental peripheral nerves. Various degrees of condensation and cephalization are found in different taxa.

Development is derived with centrolecithal eggs and superficial cleavage. There is frequently a larva although development is direct in many. Juveniles pass through a series of instars separated by molts until reaching the adult size and reproductive condition. At this time molting and growth may cease or continue, depending on taxon.

Mandibulata includes arthropods in which the third head segment bears a pair of mandibles. As currently conceived this taxon includes myriapods, hexapods, and crustaceans. Appendages may be uni- or biramous and habitats include marine, freshwater, terrestrial, and aerial.

Myriapods and hexapods share tracheae and a single pair of antennae and are sister taxa in Tracheata. Crustaceans, which have gills and lack tracheae, are excluded and form the sister group.

The body consists of a head and trunk with numerous segments but no tagmosis into thorax and abdomen. Trunk segments bear paired segmental appendages, always in excess of three pairs. Myriapoda includes the familiar centipedes and millipedes, as well as symphylans and pauropods. Median ocelli have been lost but lateral eyes are present in some taxa. The nervous system is arthropodan with little tendency to cephalization.

Chilopods are commonly known as centipedes. Each trunk segment has one pair of legs. The first trunk appendages are modified as fanglike forcipules equipped with poison glands. The gonopores are posterior (opisthogoneate), typically on the penultimate trunk segment, unlike those of all other myriapods. Unlike millipedes (and pauropods) centipedes are trignathous and have three pairs of mouthpart appendages mandibles, first maxillae, and second maxillae. About 2800 extant species are known. Centipedes are nocturnal raptors. Respiration is via tracheae with paired lateral, or unpaired dorsal, spiracles. The excretory system consists of a single pair of Malpighian tubules.

Notostigmorphs have unpaired dorsal spiracles on the posterior margin of the tergites. These serve only the dorsal blood vessel and their tracheae do not ramify throughout the body as do. Scutigeromorpha is the only notostigmorph taxon. All other chilopods belong to Pleurostigmorpha and have paired lateral spiracles serving trachea extending to the tissues, rather than the blood.

Scutigeromorphs have long antennae, with as many as 400 flagellar articles, eight large terga, and fifteen pairs of long legs. The extreme length of the legs is due to proliferation of secondary tarsal articles. Scutigeromorphs are swift cursorial predators that rely on speed and quick reflexes to capture prey. The unpaired spiracles are dorsal and open into short tracheae which supply oxygen to the dorsal blood vessel. This highly unusual tracheal system is probably not homologous to that of other tracheates. Unlike that of all other chilopods, the blood contains hemocyanin. The eyes are pseudofaceted, and although they resemble the compound eyes of insect are probably not homologous to them. Scutigeromorpha contains a single family, Scutigeridae. Scutigera coleoptrata is about 2-3 cm in length but one South American species reaches 5 cm with a legspread of 12 cm.

Scutigera coleoptrata, the house centipede, is a common, harmless inhabitant of houses and their basements and environs. It is often seen scurrying rapidly across the floor or trapped in a smooth-sided bathtub. Scutigera requires a relatively moist habitat to avoid desiccation. It is native to Europe but, like so many other inhabitants of human homes and gardens, it has been introduced to and is now widespread in North America. It feeds on small household arthropods such as flies, spiders, silverfish, bedbugs, and juvenile cockroaches. Although all centipedes have fangs and poison glands, Scutigera is not aggressive and rarely bites humans, its fangs being barely capable of penetrating human skin. The non-lethal bite is comparable to a bee sting. Far from being undesirable, house centipedes are beneficial housemates.

Specimens are not available from the major biological supply companies, either preserved or alive, but occasional individuals for laboratory study can be captured, with skill and luck, and preserved in 40% isopropyl alcohol. They can also be studied alive after anesthetization with carbon dioxide or chloroform. Only the external anatomy is considered in this exercise.

Typical of myriapods, the body is divided into only two tagmata. The anterior head is relatively short but the trunk is long and segmented (Fig 20-1C, B). Because careful examination of the mouthparts destroys the head and is likely to damage the anterior trunk, it is best to study the trunk first and the head last. The following account begins at the posterior end of the animal and works its way anteriorly.

Most of the centipede body is a linear series of homonomous segments extending posteriorly behind the head and known as the trunk. The contractile dorsal blood vessel, or heart, can be seen through the translucent tergites. It lies on the dorsal midline (Fig 1, 20-3).

The true segmentation of the trunk is not immediately apparent from the dorsum because of the disparity in the number of tergites and segments. The trunk consists of 18 segments including a terminal so-called telson (segment 18) but only 11 tergites are present (Fig 2). The first trunk segment bears a pair of poison fangs, or forcipules, and the next 15 (segments 2-16) each have a pair of long legs. The last pair of legs, borne on segment 16, are especially long, antenniform, and have a sensory function, as do the cerci of some insects (Fig 20-1C).

Figure 1. Head and anterior trunk of a female house centipede, Scutigera coleoptrata, from Greenwood, South Carolina. T = tergite. Centipede18L.gif

Dorsally the trunk bears a linear series of 10 tergites but these are not arranged in a one to one correspondence with the segments (Table 1). Most tergites cover more than one segment but segments 1, 2, 16, 17, and 18 cover individual tergites. All other segments share a tergite with one or two additional segments. Trunk segment 1 has a small tergite visible as a narrow collar posterior to the head (Fig 1). The first tergite is followed by a series of eight much larger, quadrate or slightly oval tergites. These tergites cover varying numbers of segments as indicated in Table 1. The 10 th and 11 th tergites are less well developed.

The spiracles are dorsal, median and unpaired (Fig 1, 4). Each opens into a median air-filled atrium from which radiate hundreds of short, tubular, branched tracheae. The tracheae extend to the nearby dorsal blood vessel, or heart. Spiracles are present on tergites 2-8. In non-scutigeromorph centipedes the spiracles are paired and their tracheae deliver blood directly to the tissues rather than to the blood.

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    Given some of the difficulties associated with conservation status evaluation of invertebrates outlined above, it is perhaps not surprising that compared with vertebrates and vascular plants in which numerous species have been listed under national legislation and for which a number of national Action Plans and Recovery Plans have been prepared, only 62 species of invertebrates (21 insects, 21 molluscs, 14 crustaceans, 3 worms, 2 seastars and 1 spider) are currently listed under the EPBC Act. Indeed, relatively few invertebrates are listed globally as threatened (<1% of all described taxa have been evaluated), and there is bias even here, with most listed invertebrate species comprising butterflies, dragonflies, molluscs and freshwater crabs (Cardoso et al. 2011b ). In other words, many orders of invertebrates simply have no representation on conservation schedules (Taylor et al. 2018 ). Some of the bias in listing is partly because these groups have a relatively high public profile and better taxonomic knowledge, but it is also related to the zeal of individual proponents prepared to draft and submit nominations (New 2009 ).

    Approaches to threatened species conservation

    There are three main approaches in which the profile of invertebrate threatened species conservation could be raised. The first approach is to prepare national Action Plans for higher taxonomic groups to determine which species are at risk. For instance, rather than targeting individual species, several higher taxonomic groups of invertebrate could be targeted for comprehensive Action Plans in Australia, including camaenid land snails (Mollusca) (Stanisic 1999 Slatyer et al. 2007 ), millipedes (Diplopoda) (Car 2016 ), trapdoor spiders (Mygalomorphae) (Churchill 1997 Harrison et al. 2016 Rix et al. 2017 ), springtails (Collembola) (Greenslade 2007 ), dragonflies (Odonata) (Watson 1982 Hawking 1999 Clausnitzer et al. 2009 Bush et al. 2013 Khelifa et al. 2017 ), certain Orthoptera (Rentz 1993 Cranston 2010 ), dung beetles (Scarabaeinae) (Spector 2006 Monteith 2015 ), stag beetles (Lucanidae) (Meggs & Munks 2003 Munks et al. 2004 ), ground beetles (Carabidae) and jewel beetles (Buprestidae) (F. Douglas, pers. comm. 2017), some diurnal moths (e.g. Castniidae) (Williams et al. 2016 ) and butterflies (Papilionoidea) (New et al. 1995 New & Sands 2004 New 2011 ). Some of these taxa are reasonably well known taxonomically, or at least morphospecies have been circumscribed and are supported by well-curated reference collections and are known to be informative as bioindicators for inventory and/or monitoring (Braby & Williams 2016 ).

    The second approach is to select and promote a relatively large set of threatened ecological ‘indicator’ taxa (

    10–100 species) that are indicative of two critical issues: (1) threatened ecological communities, habitats or biomes and/or (2) key threatening processes. That is, Action Plans are prepared for a suite of threatened indicator taxa that reflect a specific threat impacting on a particular ecological community/habitat in urgent need of protection, conservation management and/or ecological restoration. This approach appears to have received little attention in the conservation arena as far as invertebrates are concerned (Yen & Butcher 1997 ), but it could take several different directions.

    For instance, at the ecological community or habitat level, there are currently 69 terrestrial threatened ecological communities listed under the EPBC Act, of which 33 are classified as Critically Endangered, 34 as Endangered and two as Vulnerable (Commonwealth Department of the Environment and Energy 2017c ). Most of these ecological communities have been heavily impacted by habitat loss through conversion for agriculture or urbanisation, and the small habitat remnants are threatened by multiple factors including isolation and fragmentation, invasive species (particularly weeds), inappropriate fire regimes and climate change (Sands 2018 ). However, apart from a few threatened ecological indicator Lepidoptera (e.g. Pale Imperial Hairstreak Jalmenus eubulus Miskin for old growth acacia woodlands dominated by brigalow Acacia harpophylla and A. melvillei, Richmond Birdwing Ornithoptera richmondia (Grey) and Pink Underwing Moth Phyllodes imperialis smithersi Sands for subtropical rainforest, Golden Sun-moth Synemon plana Walker for temperate grasslands and grassy woodlands, and Graceful Sun-moth Synemon gratiosa Westwood formerly listed for banksia woodland of the Swan Coastal Plain) (Taylor et al. 2018 ), there is a general lack of information on the extent of threatened invertebrates, and their management requirements, that are indicative of these threatened ecological communities.

    At a finer scale, a species' guild could be targeted according to their ecological function (e.g. saproxylic invertebrates associated with dead branches and logs in areas where firewood removal is a threatening process). Another option is to target species that are co-dependent on host species known to be threatened (Moir et al. 2016 ), such as specialised detritivores dependent on the faeces of threatened mammals or birds (e.g. Antbed Parrot Moth of the endangered golden-shouldered Parrot, Zborowski & Edwards 2007 ) or specific insect pollinators of endangered plants (e.g. thynnine wasps of terrestrial orchids, Phillips et al. 2015 ). Another possibility is to protect under legislation taxa with exceedingly small distributions (short-range endemics), including stygofauna and troglofauna, such as the model developed in Western Australia (Harvey et al. 2011 ). Although such species may not be threatened per se, they are particularly susceptible to impacts of habitat loss and degradation from development proposals because an exceptionally high proportion of their occupied area may be adversely affected.

    The third approach is to promote on behalf of local communities and recovery teams a relatively small set (

    5–10 species) of ‘flagship’ taxa (i.e. threatened species or ‘iconic’ species of high scientific and/or social value) within particular geographical regions, such as the examples developed for butterflies in the urban areas of Melbourne and Brisbane (New 2018 ) or the model developed for the South Coast Threatened Invertebrates Group in Western Australia (Moir et al. 2015 ). Although the intention of the South Coast Threatened Invertebrates Group, which was established in 2001, is to acquire data on the distribution, endemism and spatial turnover of all potentially threatened species in this biodiversity hotspot (Moir et al. 2009 ) and to nominate species for listing and develop regional management plans specifically for threatened invertebrates (Moir et al. 2015 ), the key point of this approach is the collaboration of a diverse array of stakeholders, including scientists, park managers, non-government organisations and local communities. Taylor et al. ( 2018 ) have proposed that this approach ought to be scaled nationally using citizen scientists so that flagship taxa are represented in each of the various bioregions of the continent (e.g. IBRA regions) and in each of the major different ecological communities or habitats, particularly those that are under threat, within those bioregions. Such a strategy would ensure spatial representativeness of invertebrate conservation across the entire Australian landscape.

    All of these approaches are complimentary and the first two hinge on entomologists or invertebrate biologists being prepared to draft a series of dedicated Action Plans. These plans would provide the foundation for a national overview of threatened invertebrates in conservation need. Such a national list would then form the basis for formal (legal) listing and further recovery action and management, building on the short list of 25 species evaluated by Clarke and Spier-Ashcroft ( 2003 ) and potentially provide a more strategic approach than listing single species on an ad hoc basis.

    Conservation triage

    Because resources for conserving biodiversity assets are grossly inadequate, with only a small proportion of threatened species ever managed for recovery globally, it is essential that species are prioritised so that scarce funds are optimised and allocated wisely (Bottrill et al. 2008 Joseph et al. 2009 ). In other words, given that not all species threatened with extinction can be saved, triage – the efficient allocation of conservation resources to maximise conservation and persistence of valuable biodiversity assets (e.g. species, habitats) – is essential. Conservation triage is a difficult exercise, and New ( 1991 , 2009 , 2011 ) summarised the criteria that are typically used to set priorities for threatened insect species. These criteria include conservation status (level of threat or extinction risk), phylogenetic distinctiveness (evolutionary history), ecological importance (role in ecosystem function), social significance (economic value, cultural value), taxonomic status (species, subspecies, significant population or evolutionary significant unit) and the extent to which the species is spatially restricted (endemism). However, in addition to these values and benefits to biodiversity, it is crucial that two other criteria are considered, namely the likelihood of successful recovery and the cost of management (Bottrill et al. 2008 Joseph et al. 2009 ). Data on biodiversity values/benefits, probability of success and management costs can then be combined and analysed to rank or prioritise threatened species so that return on conservation investment is maximised. For instance, sites supporting the co-occurrence of multiple threatened species (invertebrates, plants and/or vertebrates) have high biodiversity value (Britton et al. 1995 ), and provided that the recovery actions for such ‘threatened communities’ have a high probability of succeeding and the cost of recovery is low, would score a high level of ‘efficiency’ in the prioritisation process (Joseph et al. 2009 ).

    Intelligent Invertebrate: The Octopus!

    An eight legged creature with over a hundred suction cups on each of its tentacles lurking among the great depths of the ocean is not only one of the ocean’s top predators but also one of the most intelligent invertebrates undersea.

    The octopus is a unique marine animal that has caught the interest of many individuals due to its ability to learn from others and change its behaviors to adapt to the environment in order to survive. The octopus is known as one of the ocean’s most intelligent invertebrates due to its communication skills, defense mechanisms, and learning capabilities.

    Cephalopod Communication

    Cephalopods exercise several methods of communication, the most common method being visual signals. Visual signals involve an array of movements of the arms, fins, and body. Octopi are also capable of displaying a variety of color changes to communicate by sending signals to other animals. Special cells called chromatophores cause the many color changes that octopi display. These specialized cells contain pigment granules that help disperse the color changes throughout the body. The different color changes serve as danger signals, protective coloring, and courtship rituals.

    Octopi are capable of using their chromatophores to display a variety of color changes and patterns.

    Cephalopods rely heavily on their chemical senses rather than their surface structures or capabilities, but this hasn’t stopped them from re-creating their own type of visual signals. They have evolved over the years and have learned to use their intricate luminescent organs to their advantage⁵. The color changing characteristics that octopi display is significant to their survival and has helped them catch prey as well as flee from predators.

    Defense Mechanisms

    Octopi have learned defense mechanisms that have been advantageous to their survival. The octopi warns its predators by changing its chromatophores to a wide range of colors by discriminating different surfaces and textures with their tentacles, and using their chemical senses to imitate a similar pattern to help camouflage themselves for hunting or escaping from predators.

    A well-known defense mechanism that cephalopods use to their advantage is their ink sac. This sac empties into the rectum and contains sepia, a dark fluid containing the pigment melanin. When a cephalopod is alarmed, it releases the sepia, which serves as a protective cloud to distract the predator. The cloud helps the cephalopod flee from the scene to escape from the harmful predator⁵.

    Another defense mechanism that has showcased the intelligence level of octopi is their ability to mimic other marine animals to escape predators. In the waters of Indonesia, scientists have studied the ability of the mimic octopus (Thaumoctopus mimicus) to impersonate several marine animals to escape the predation of other animals. This master of disguise octopus has been known to imitate toxic flatfish, lionfish, and sea snakes by arranging its limbs and adapting similar movements and behaviors of various animals. The octopus changes its color to similar patterns and also displays similar spots to completely impersonate the marine creature to fool predators. This defense mechanism has allowed this species of octopus to swim openly in the ocean with more freedom from potential predators¹.

    Brainy Invertebrate

    Octopi have been known as one of the ocean’s brainiest invertebrates. This is due to their ability to learn from imitation, observation, and positive reinforcement, as well as their problem solving capabilities. There have been numerous experiments that have proved that octopi have an impressive intellectual capacity for example cephalopods can be taught to distinguish between certain shapes-such as a rectangle and a square and can also remember the distinction for quite a period of time.

    Octopi have also displayed certain beneficial behaviors that are not seen in other marine creatures. Australian researchers conducted a study on octopi in which they found an octopus collecting coconut shell halves by stacking them and carrying them with quite some difficulty. When the octopus stopped in an open area in the ocean, it would use the coconut shells as a type of protective shield². Octopi have also been known to pick locks and take apart cages while in captivity³.

    These creatures have also been known as problem solvers. They can apply different methods to a situation to reach their goal. At Chicago’s Shedd Aquarium, biologist Ernie Sawyer conducted an experiment in which she dropped a jar of frozen shrimp in a tank for a ten-pound octopus. The octopus first changed from a calm brown color to an irritated red, as a warning signal or territorial defense mechanism. The octopus finally stretched out an arm and wrapped its tip around the jar, and pulled it underneath its body. The octopus then used the strength of its suction cups and took the lid off⁴. Observational studies have shown what these intelligent creatures are capable of with their given resources.

    Octopus Survival

    The best way to study the full intelligence if these creatures is to observe them in their natural habitat.

    Octopi have used their strengths to their advantage to adapt and survive. Their intricate nervous and sensory systems, methods of communication, defense mechanisms, and learning capabilities all play an important role in understanding this creature’s intelligence. Unfortunately, it is difficult to understand the true intelligence of octopi because they are mostly studied while in captivity rather than in their natural habitat. We can only hope that in the years to come we’ll be able to gain more information about the intelligence of these fascinating creatures.

    1. California Academy of Sciences (2012, January 5). Fish mimics octopus that mimics fish. ScienceDaily. Retrieved March 20, 2014, from

    2. Clemmitt, Marcia. “Do Animals Think?” CQResearcher. N.p., 22 Oct. 2010. Web. 20 March 2014.

    3. Goldberg, Cait. “The Octopus and the Orangutan: More True Tales of Animal Intrigue, Intelligence, and Ingenuity.” ProQuest. N.p., 9 Nov. 2002. Web. 20 March 2014.

    4. Newman, Alexander A. 󈫺 Smart Animals.” ProQuest. N.p., July-Aug. 2004. Web. 20 March 2012.

    5. Roberts, Larry S., Susan L. Keen, Allan Larson, Helen I’Anson, and David J. Eisenhour. “Molluscs.” Integrated Principles of Zoology. By Cleveland P. Hickman. 14th ed. Boston: McGraw-Hill/Higher Education, 2008. 353-56. Print.

    Vertebrates & Invertebrates Free Games & Activitiesfor Kids

    If you are an animal in the possession of a back bone or spinal column you are a vertebrate. They compromise many species of animals and fishes, reptiles and birds. If you do not have a backbone you are called an invertebrate. There are over 50,000 species of vertebrate. That sounds like a lot but there are far more invertebrates. Vertebrates are usually much larger than invertebrates. Vertebrates are smart, some of them are very smart, like humans. Most vertebrates have an advanced nervous system, muscles and skeleton.

    Evolution is a theory that explains why animals and plants are so good at surviving in their environments. Evolution explains why species change over time. The theory of evolution was developed by Charles Darwin in 1859. Darwin believed that evolution occurs through natural selection. Animals and plants that are best able to survive also fit better into the ecosystem are far more likely to live.

    Watch the video: Vertebrate and Invertebrate animals. Video for Kids (August 2022).