The foot is narrow and trilobed or with a terminal disc which can be protruded through the oral opening of the shell. Aplacophora or Solenogastres: 1. In shelled mollusks, this foot is usually the same size as the opening of the shell. General Characters of Molluscs 2. Here we interpret the to form branching nerves that innervate the mantle tissue at foot to be ventral, which is the most parsimonious arrange- the ventral aperture of the shell and surround the muscular ment and facilitates comparisons with other classes. The morphological distance between an aplacophoran mollusc (Figure 6) and, for example, a cephalopod mollusc stretches anyone's concept of the rank of phylum.Aplacophora were the last class to be placed in the Mollusca and have until recently been one of the least studied groups. hus, the foot stalk (Lacaze-duthiers 1856). Solenogastres (Aplacophora) is a small clade of marine, shell-less worm-molluscs with close to 300 valid species. Aplacophora is a monophyletic group of small, deep-water, exclusively benthic, marine molluscs found in all oceans of the world. 2. In mussels the foot is not used for digging and is much smaller than the foot of an infaunal bivalve. Scallops ( Pecten, Chlamys ) have a row of small blue eyes along each mantle edge (Figure 16-25). The foot is a retractable as well as an extendable organ. Classification of Molluscs 3. The foot has a longitudinal byssal groove along its posterior margin. The group comprises the two clades Solenogastres (Neomeniomorpha) and Caudofoveata (Chaetodermomorpha), which between them contain 28 families and about 320 … Mollusks have a muscular foot, which is used for locomotion and anchorage, and varies in shape and function, depending on the type of mollusk under study. 4. The body is soft, un-segmented, bilaterally symmetrical and consists of head, foot, mantle and visceral mass. The body is elongated and worm-like and enveloped by the mantle. General Characters of Molluscs: 1. The small wormlike foot is located in about the middle of the ventral margin of the visceral mass. ADVERTISEMENTS: In this article we will discuss about Molluscs:- 1. The shell is absent and the body is covered with a cuticular mantle enclosing spicules of calcified material. Molluscs are essentially aquatic mostly marine, few freshwater and some terrestrial forms. They include a pair of statocysts in the foot, a pair of osphradia of uncertain function in the mantle cavity, tactile cells, and sometimes simple pigment cells on the mantle. […] Foot-extends along entire ventral surface-covered by overlying shell and girdle-locomotion due to subtle waves of muscular activity called "pedal waves" ... A sense organ consisting of a sac enclosing sensory hairs and particles of sand, lime, etc., that functions in maintaining equilibrium, serving to indicate position in space. Aplacophora(Aplacophorans) Phylum MolluscaClass AplacophoraNumber of families 30Thumbnail description Vermiform (worm-shaped) marine mollusks lacking shells and living in the zone between the seashore and the edge of the continental shelf Source for information on Aplacophora (Aplacophorans): Grzimek's Animal Life Encyclopedia dictionary. The class Aplacophora contains two subclasses: Neomeniomorpha (also called Solenogastres) and Chaetodermomorpha (also called Caudofoveata). All known modern forms are shell-less: only some extinct primitive forms possessed valves. Its function is the formation and manipulation of byssal threads. Most neomenioids creep by means of a narrow foot with a ventral groove that begins as a pedal pit toward the front of the animal. The pallial cavity, containing multiple pairs of small gills, surrounds the foot with which the animal typically clings to hard surfaces. Most are small (0.5-5 cm, but one species reaches over 30 cm in length). 2. The plates are greatly reduced or even internal in a few species, these species sometimes having an elongate, somewhat worm-like body. Economic Importance.
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