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Aplacophora / æ p l ə ˈ k ɒ f ər ə / is a possibly paraphyletic taxon. This is a class of small, deep-water, exclusively benthic , marine molluscs found in all oceans of the world. [ 1 ]
There is some uncertainty regarding the phylogenetic position of the Solenogastres. Traditionally considered to be the most basal molluscan group and the sister group to the Caudofoveata, alternatives to both of these statements have been proposed. [5] Some molecular datasets plot Solenogastres as an outgroup to Mollusca. [10]
Discussion about monoplacophorans is made difficult by the slippery definition of the taxon; some authors take it to refer to all non-gastropod molluscs with a single shell, or all single-shelled molluscs with serially repeated units; whereas other workers restrict the definition to cap-shaped forms, excluding spiral and other shapes of shell. [2]
Aplacophora Aculifera (older name: Amphineura ) is a proposed clade of molluscs incorporating those groups that have no conch or shell, that is, the Polyplacophora , Caudofoveata (= Chaetodermomorpha ) and Solenogastres (= Neomeniomorpha ). [ 1 ]
This overview of orders follows the taxonomy of the Gastropoda (Ponder & Lindberg, 1997): . Order Bellerophontinaka (fossil); Order Mimospirina (fossil); Subclass Eogastropoda ...
Kulindroplax is about 2 cm (0.79 in) wide and 4 cm (1.6 in) long. [2] It is the first known mollusk showing an unambiguous combination of valves, or exterior shells, and a worm-like body. [2]
The organic pellicule is found in most polyplacophora (but not basal chitons, such as Hanleya) [15] but is unusual in aplacophora. [16] Developmentally, sclerite-secreting cells arise from pretrochal and postrochal cells: the 1a, 1d, 2a, 2c, 3c and 3d cells. [ 16 ]
The Heloplacidae are a group of plated aplacophora known from Silurian deposits. Their best understood representative, Acaenoplax, can be taken as representative of the family; it is the only genus for which soft part anatomy is known. [1] [2]