Search results
Results from the WOW.Com Content Network
However, a growing body of molecular and biological data indicate that at least certain shell features have evolved many times, independently. [38] The nacreous layer of shells is a complex structure, but rather than being difficult to evolve, it has in fact arisen many times convergently. [ 38 ]
In some mollusks the mantle cavity is a brood chamber, and in cephalopods and some bivalves such as scallops, it is a locomotory organ. The mantle is highly muscular. In cephalopods the contraction of the mantle is used to force water through a tubular siphon, the hyponome , and this propels the animal very rapidly through the water.
Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks [a] (/ ˈ m ɒ l ə s k s /). Around 76,000 extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda . [ 5 ]
The mechanical properties of bivalve shells and their relatedness to microstructure was first published in 1969 by Stephen Wainwright at Duke University. [2] Following this, eight main categories of bivalve microsections were defined: simple prismatic, composite prismatic, sheet nacreous, lenticular, foliated, crossed-lamellar, complex crossed-lamellar, and homogenous.
A siphon is an anatomical structure which is part of the body of aquatic molluscs in three classes: Gastropoda, Bivalvia and Cephalopoda (members of these classes include saltwater and freshwater snails, clams, octopus, squid and relatives). Siphons in molluscs are tube-like structures in which water (or, more rarely, air) flows.
The radula (US: / ˈ r æ dʒ ʊ l ə /; pl.: radulae or radulas) [1] is an anatomical structure used by mollusks for feeding, sometimes compared to a tongue. [2] It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus.
The less major anterior and posterior retractor muscles extend from the shell and attach the body to a structure called the foot. [4] This muscular foot is typical of most bivalves, extending anteriorly between the valves (via an anterior protractor muscle) and aiding in locomotion , burrowing and anchorage ( holdfast ).
The girdle is often ornamented with spicules, bristles, hairy tufts, spikes, or snake-like scales. The majority of the body is a snail-like foot, but no head or other soft parts beyond the girdle are visible from the dorsal side. The mantle cavity consists of a narrow