Mollusca is the second-largest phylum of invertebrate animals, after the Arthropoda; members are known as molluscs or mollusks (ˈmɒləsk). Around 85,000 extant species of molluscs are recognized. The number of fossil species is estimated between 60,000 and 100,000 additional species. The proportion of undescribed species is very high. Many taxa remain poorly studied.
Molluscs are the largest marine phylum, comprising about 23% of all the named marine organisms. Numerous molluscs also live in freshwater and terrestrial habitats. They are highly diverse, not just in size and anatomical structure, but also in behaviour and habitat. The phylum is typically divided into 7 or 8 taxonomic classes, of which two are entirely extinct. Cephalopod molluscs, such as squid, cuttlefish, and octopuses, are among the most neurologically advanced of all invertebrates—and either the giant squid or the colossal squid is the largest known invertebrate species. The gastropods (snails and slugs) are by far the most numerous molluscs and account for 80% of the total classified species.
The three most universal features defining modern molluscs are a mantle with a significant cavity used for breathing and excretion, the presence of a radula (except for bivalves), and the structure of the nervous system. Other than these common elements, molluscs express great morphological diversity, so many textbooks base their descriptions on a "hypothetical ancestral mollusc" (see image below). This has a single, "limpet-like" shell on top, which is made of proteins and chitin reinforced with calcium carbonate, and is secreted by a mantle covering the whole upper surface. The underside of the animal consists of a single muscular "foot". Although molluscs are coelomates, the coelom tends to be small.
The main body cavity is a hemocoel through which blood circulates; as such, their circulatory systems are mainly open. The "generalized" mollusc's feeding system consists of a rasping "tongue", the radula, and a complex digestive system in which exuded mucus and microscopic, muscle-powered "hairs" called cilia play various important roles.
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Students will learn essentials of cell and developmental biology with an engineering mind set, with an emphasis on animal model systems and quantitative approaches.
The common octopus (Octopus vulgaris) is a mollusc belonging to the class Cephalopoda. Octopus vulgaris is one of the most studied of all octopus species, and also one of the most intelligent. It ranges from the eastern Atlantic, extends from the Mediterranean Sea and the southern coast of England, to the southern coast of South Africa. It also occurs off the Azores, Canary Islands, and Cape Verde Islands. The species is also common in the Western Atlantic. Octopus vulgaris grows to in mantle length with arms up to long.
Hemocyanins (also spelled haemocyanins and abbreviated Hc) are proteins that transport oxygen throughout the bodies of some invertebrate animals. These metalloproteins contain two copper atoms that reversibly bind a single oxygen molecule (O2). They are second only to hemoglobin in frequency of use as an oxygen transport molecule. Unlike the hemoglobin in red blood cells found in vertebrates, hemocyanins are not confined in blood cells but are instead suspended directly in the hemolymph.
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 water flow is used for one or more purposes such as locomotion, feeding, respiration, and reproduction. The siphon is part of the mantle of the mollusc, and the water flow is directed to (or from) the mantle cavity.
In the aquatic environment, microplastic particles (MP) can accumulate in microbial communities that cover submerged substrata, i.e. in periphyton. Despite periphyton being the essential food source for grazers in the benthic zones, MP transfer from periph ...
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The oxygen isotope compositions of fossil biocalcites, such as foraminifera, bivalves, brachiopods, and belemnites have allowed for reconstructions of sea surface and deep ocean temperatures throughout the Phanerozoic and constitute the most important reco ...
Assessments of reef sediments in the North Ari Atoll (Maldives) were conducted in 2015 and 2018 on reefs of three islands with different management strategies: community, resort, and uninhabited. Indices applied were the Foraminifera in Reef Assessment and ...