Key Vocab 13. Classification of Invertebrates

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Sessile

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Describes an organism that is fixed in place and does not move freely (e.g., corals, barnacles, sea sponges).

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Porifera

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A phylum of simple, multicellular, aquatic invertebrates that lack true tissues and organs. They have porous bodies and rely on filter feeding (e.g., sponges).

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Sea Sponges

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Marine or freshwater invertebrates belonging to the phylum Porifera, characterized by a porous body structure that allows water to flow through for feeding and respiration.

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Cnidaria

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A phylum of aquatic invertebrates with radial symmetry, specialized stinging cells (cnidocytes), and two main body forms: polyp and medusa (e.g., jellyfish, corals, sea anemones).

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Hydra

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A small, freshwater cnidarian that exists in polyp form and reproduces asexually by budding or sexually through gametes. It has tentacles with stinging cells for capturing prey.

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Polyp

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A body form of cnidarians that is sessile (attached to a surface) and tubular, with the mouth and tentacles facing upward (e.g., corals, sea anemones, hydra).

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Annelida

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A phylum of segmented worms with a body divided into ring-like segments, a complete digestive system, and a closed circulatory system (e.g., earthworms, leeches).

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Earthworm

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A terrestrial annelid that plays a crucial role in soil aeration and nutrient recycling by burrowing and feeding on organic matter.

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Mollusca

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A large phylum of invertebrates with soft bodies, often protected by a calcium carbonate shell, and a muscular foot for movement (e.g., snails, clams, octopuses).

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Cephalopod

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A class of highly developed mollusks with tentacles, a well-developed brain, and the ability to squirt ink for defense (e.g., octopuses, squids, cuttlefish).