Aplacophora

Aplacophora is a class of worm-shaped marine mollusks without shells, with bodies covered in calcareous spicules. Its members live mainly on or within seafloor habitats.

Mollusca: Mollusca is a diverse animal phylum that includes snails, clams, cephalopods, and several less familiar groups. Aplacophora belongs to this phylum despite lacking the shell typical of many mollusks.
Solenogaster feeding: Solenogaster feeding includes capturing small prey or consuming cnidarians with a radula or other specialized structures. Many solenogasters feed on cnidarians while moving over or among their hosts.
Aculifera: Aculifera is a proposed molluscan grouping that includes Aplacophora and Polyplacophora. Shared body features have led researchers to compare aplacophorans with chitons within this grouping.
Deep-sea benthos: Deep-sea benthos comprises organisms living on or within the seafloor below the continental shelf. Many aplacophorans occur in deep-sea habitats where sampling remains challenging.
Spicule: A spicule is a small, hard skeletal element found in some animals, including mollusks and sponges. Calcareous spicules cover aplacophoran bodies in place of a shell.
Caudofoveate burrowing: Caudofoveate burrowing is movement through soft marine sediment using a tapered body and a muscular anterior end. Burrowing explains why caudofoveates are often collected from sediment rather than exposed surfaces.
Polyplacophora: Polyplacophora is the molluscan class of chitons, characterized by eight shell plates and a girdle. Chitons share a spicule-bearing girdle and other traits relevant to aplacophoran relationships.
Meiofauna: Meiofauna are small benthic animals that pass through a 0.5-millimeter mesh but are retained by finer screens. Small aplacophorans can be overlooked unless sediment samples are examined with suitable methods.
Mantle (mollusk): The mantle is a mollusk’s tissue layer that commonly secretes a shell and may enclose the body cavity. Aplacophorans retain mantle tissue even though it produces spicules rather than a shell.
Calcareous spicule: A calcareous spicule is a tiny skeletal element made primarily of calcium carbonate. Aplacophoran spicules form a protective body covering and can differ in shape across species.

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