The calcareous sponges of

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently ...

Calcarea are members of the animal phylum

Porifera Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...

, the cellular sponges. They are characterized by

spicule Spicules are any of various small needle-like anatomical structures occurring in organisms Spicule may also refer to: *Spicule (sponge), small skeletal elements of sea sponges *Spicule (nematode), reproductive structures found in male nematodes ( ...

s made of calcium carbonate in the form of

calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratc ...

aragonite Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including pre ...

. While the spicules in most species have three points, in some species they have either two or four points.

Biology

All sponges in this class are strictly marine, and, while they are distributed worldwide, most are found in shallow tropical waters. Like nearly all other sponges, they are sedentary

filter feeder Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feedin ...

s. All three sponge body plans are represented within class Calcarea : asconoid, syconoid, and leuconoid. Typically, calcareous sponges are small, measuring less than in height, and drab in colour. However, a few brightly coloured species are also known. Calcareous sponges vary from radially symmetrical vase-shaped body types to colonies made up of a meshwork of thin tubes, or irregular massive forms. The skeleton has either a mesh or honeycomb structure.

Classification

Of the 15,000 or so species of Porifera that exist, only 400 of those are calcareans. Calcarean sponges first appeared during the

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ...

, and their diversity was greatest during the

Cretaceous period The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of t ...

. Recent molecular analysis suggests the class Calcarea should be designated as a

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature ...

, in particular the first to have diverged in the

Animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...

ia. The calcareous sponges are divided into two subclasses and six orders: Class Calcarea * Subclass Calcinea ** Order Clathrinida ** Order Murrayonida * Subclass Calcaronea ** Order Baerida ** Order Leucosolenida ** Order Lithonida ** Order Pharetronida† Clathrina clathrus Scarpone 055

References

External links

UCMP: Calcarea
{{Taxonbar, from=Q209924 Taxa named by James Scott Bowerbank