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Bio Lab Wksht & HW Questions 86

Bio Lab Wksht & HW Questions 86 - absent(octopods...

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81 Class Gastropoda (snails, slugs, sea slugs) Molluscs with a single spiral shell (absent in slugs and nudibranchs), bodies show torsion (twisting). Snails and slugs secrete mucus that aids in locomotion. Note how the foot is used for creeping along a substratum. All gastropods use a radula for feeding. Class Bivalvia (bivalves: clams, oysters, scallops, mussels, etc.) Paired lateral shells (valves) hinged dorsally; head reduced, radula absent, gills enlarged for filtration of food, bivalves are suspension feeders. Note that the foot in many of these animals is used to dig into the sand. Class Cephalopoda (nautiluses, squids, octopuses) Head and foot fused; carnivorous, shell may be multi-chambered and external (nautiloids), internal and calcareous (cuttlebone in cuttlefishes), internal and proteinaceous (pen in squids) or
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Unformatted text preview: absent (octopods). In these animals part of the head is modified into tentacles for capture of prey and manipulation of objects, and the foot forms a siphon for jet-propelled locomotion. ECDYSOZOA: These animals, like the Lophotrochozoa (seen in earlier in the semester), are grouped on the basis of molecular evidence. However, both phyla in this group display ecdysis , or molting of the outermost layer. Phylum Nematoda (round worms) Nematodes are pseudocoelomate, unsegmented, round in cross section, tapered at both ends, covered by a resistant, secreted cuticle , and lacking in appendages. Nematodes are widespread and common; they can be either free-living or parasitic. On display are Enterobius (pinworm) and Ascaris . In both species, the male is smaller and has a hooked posterior end....
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