There are approximately 320 described species in Aplacophora. However, it is likely there are many other species that have not been described.

Aplacophorans are found throughout the oceans over the world.

Biogeographic Regions: arctic ocean ; indian ocean; atlantic ocean ; pacific ocean ; mediterranean sea

Aplacophorans are small, cylindrical, worm-like, and usually less than 5 cm long, but can range from 1 mm to 30 cm. Like other mollusks, it has no outer shell, but the epidermis secretes calcareous spicules or scales which are embedded in dorsal mantle. These spicules give the aplacophorans a sheen. Chaetoderms have a scaly appearance. All aplacophorans have a simple mantle cavity.

The radula is not ribbon-like as in other mollusks, but is an expansion of the foregut epithelium. The teeth of the radula may be in simple plates in transverse rows, up to 50 rows with 24 teeth per row.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Exclusively marine, aplacophorans mainly burrow into the substrate in water more than 20 m deep, and may reach densities up to 4-5 per square meter. Aplacophorans in the sub-class Chaetodermomorpha are limited by a minimum salinity of 28-30%.

Habitat Regions: saltwater or marine

Aquatic Biomes: benthic

Chaetoderms burrow and feed on microorganisms and detritus while neomenioids live with and feed on cnidarians.

Primary Diet: carnivore ; omnivore ; detritivore

Neomenioids live with and feed on cnidarians but the effects on the ecosystem are unknown.

Little is known about the perception of the Aplacophora. The animals have a simple nerve ring around the esophogus and poorly developed ganglia.

Perception Channels: tactile ; chemical

Development involves metamorphosis from a trocophore larva.

Development - Life Cycle: metamorphosis

Little is known about aplacophoran lifespans.

Aplacophorans may be monoecious or dioecious with single or paired gonads. All discharge gametes through gonopericardial ducts into the pericardial (heart) chamber. Gametes then pass through gametoducts to the mantle cavity where they are then released outside the body. Animals in the Chaetodermomorpha have external fertilization while those in Neomeniomorpha are internally fertilized, and sometimes even brooded.

Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); simultaneous hermaphrodite; sexual ; fertilization (External , Internal ); ovoviviparous ; oviparous

Members of the Neomeniomorpha sometimes brood the eggs. However, most species release the gametes without further parental care.

Parental Investment: pre-fertilization (Provisioning); pre-hatching/birth (Provisioning, Protecting)

Collection Sites: world map showing specimen collection locations for Aplacophora

Barcode of Life Data Systems (BOLD) Stats
                                                             

Specimen Records:	7
Specimens with Sequences:	7
Specimens with Barcodes:	7
Public Records:	6
Species:	6
Species With Barcodes:	6

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