(invertebrate zoology) A subclass of vermiform mollusks in the class Amphineura characterized by no shell and calcareous integumentary spicules.
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McGraw-Hill Science & Technology Dictionary:
Aplacophora |
(invertebrate zoology) A subclass of vermiform mollusks in the class Amphineura characterized by no shell and calcareous integumentary spicules.
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McGraw-Hill Science & Technology Encyclopedia:
Aplacophora |
A class, also known as Solenogastres, of vermiform mollusks ubiquitous in the deep oceanic basins and trenches to 30,000 ft (9000 m) and common on the continental shelf and slope regions of the world, where they burrow through or creep upon the mud or wrap around alcyonarian corals. Most Aplacophora are less than 10.4 in. (10 mm) in length.
There are two distinct taxa: the subclass Chaetodermomorpha (= Caudofoveata; see illustration); and the subclass Neomeniomorpha (= Ventroplicida; Solenogastres).

Living Chaetoderma nitidulum. (Courtesy of R. Robertson)
Several features are common to all Aplacophora. The lad-derlike nervous system consists of paired lateral and ventral cords with many cross-commissures, a buccal ring, and cerebral and suprarectal ganglia. The coelom is restricted to coelomoducts, a spacious pericardium, and gonads that uniquely connect to the pericardium. There is a mantle cavity into which empty the anus and coelomoducts. Other molluscan characters present, but not common to all families, are a radula and its supports; paired gills in the mantle cavity; a mucus-secreting vestigial foot used in creeping; and a style sac containing a mucoid rod which turns against a chitinous gastric shield. See also Mollusca.
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Aplacophora |
| Aplacophora | |||||
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| Scientific classification |
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| Kingdom: | Animalia | ||||
| Phylum: | Mollusca | ||||
| Class: | "Aplacophora" | ||||
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Chaetodermomorpha (Caudofoveata)
Neomeniomorpha (Solenogastres)
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Aplacophora is a monophyletic group of small, deep-water, exclusively benthic, shell-less marine mollusks found in all oceans of the world. The group comprises the two clades Solenogastres (Neomeniomorpha) and Caudofoveata (Chaetodermomorpha), which between them contain 28 families and about 320 species. However, the relationship of these groups to the other molluscan classes and to each other is as yet unclear.
Aplacophorans are cylindrical and worm-like in form, and most very small, being no longer than 5 centimetres (2.0 in); some species, however, can reach a length of 30 centimetres (12 in).
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Caudofoveates generally burrow into the substrate while solenogasters are usually epibenthic. Both taxa are most common in water regions deeper than 20 metres (66 ft) where some species may reach densities up to 4 or 5 specimens per m². Solenogasters are typically carnivores feeding on cnidarians or sometimes annelids or other taxa while caudofoveates are mostly detritovores or feed on foraminiferans.
Aplacophorans are worm-like animals, with little resemblance to most other molluscs. They have no shell, although small calcified spicules are embedded in the skin. Caudofoveates lack a foot while solenogasters have a narrow foot which lacks intrinsic musculature. The mantle cavity is reduced in to a simple cloaca, into which the anus and excretory organs empty, and is located at the posterior of the animal. The head is rudimentary, and has no eyes or tentacles.[1]
The relationship with other molluscs, however, is apparent from some features of the digestive system; aplacophorans possess both a radula and a style. Solenogasters are hermaphroditic, but caudofoveates have two sexes, and reproduce by external fertilization. During development, the mantle cavity of the larva curls up and closes, creating the worm-like form of the adult.[1]
This class was once classified as sea cucumbers in the echinoderms. In 1987, they were officially recognized as molluscs and given their own class. This class is polyphyletic, and consists of two clades: the Solenogastres and the caudofoveata.[2]
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| Solenogastres (invertebrate zoology) | |
| Chaetodermomorpha (mollusca) | |
| Neomeniomorpha (mollusca) |
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