Test 2 Study Guide

Test 2 Study Guide - Test 2 Study Guide I. Phylum Cnidaria...

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Test 2 Study Guide I. Phylum Cnidaria General Characteristics: Radial symmetry with 2 body forms o Polyp – feeding orientation of the cnidarians, anchored to the substrate, mouth and tentacles point upward o Medusa – feeding orientation of the cnidarians, free floating, mouth and tentacles point downward Tissues – 2 layers (no totipotent cells) o Gastrodermis – digestive layer o Epidermis o Mesoglea Cnidoblasts – nematocysts – stinging cells in the tentacles, used to kill or stun prey Mostly marine Many colonial, some solitary Many attached, some free living Colored, transparent, colorless Incomplete digestive system; mouth, digestive cavity (enteron), tentacles No respiratory, excretory, nervous (partial), muscular (mesentaries only; folds in the organisms body wall, increases the surface area to aid in absorption and digestion), circulatory system, or anus Calcareous or organic skeleton may be present Evolutionary Model: Ciliated, colonial protozoan – ancestor * Protomedusa – earliest body form; protomedusa instead of polyps o Feeding and locomotion o Protective layer
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o Circulation and reproduction o Motion o Specialization o Blind gut Polyploid line o Sensory and food o Reorientation o Radial symmetry o Two tissue layers with middle region Class hydrozoa – emphasizes polyp Class scyphozoa – emphasizes medusa Class Anthozoa – only polyps can divide; reproduce sexually Classification: Class Hydrozoa – PC to recent, radial symmetry. Most species have both medusoid and polyploid stages. Coelenteron not partitioned; mesoglea gelatinous, noncellular. Solitary or colonial, mostly marine, pelagic, sessile benthos o Order hydroida – PC to recent. Polyploid stage well developed, colonial or solitary. Marine and fresh water; pelagic, sessile benthos. o Order milleporina – Late cretaceous to recent. Polyploid colony with massive to encrusting calcareous skeleton with pores through which polyps protrude. Medusoid generation reduced. Marine, predominantly sessile benthos o Order stylasterina – late cretaceous to recent. Massive to encrusting skeletons with pores for polyps. Non-medusoid. Marine, sessile benthos o Order siphonophora – ordivician to recent. Colonial. Polyps with medusa attached to stem or disk. Supported by swimming bell or float. Marine, pelagic. Rare as fossils. Class scyphozoa – Precambrian to recent. Solitary. Coelenteron divided in some by mesentaries. Radial symmetry. Polyp much reduced, highly modified or lost. Mesogloea cellular. Entirely marine, predominately pelagic.
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o Subclass scyphomedusa – Precambrian? Cambrian? Late jurassic to recent. True jelly fish. Marine, predominately pelagic. Rare as fossils. o
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Test 2 Study Guide - Test 2 Study Guide I. Phylum Cnidaria...

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