Calcarea

Calcarea, commonly called calcareous sponges, is a class of the phylum Porifera. Members produce skeletons of calcium carbonate and lack silica-based spicules. They range from a few millimeters to several centimeters and can be found in a variety of shapes, from tube-like to encrusting forms. The canal system among Calcarea spans simple asconoid to more complex syconoid and leuconoid architectures, reflecting diversity in body organization.

Spicules are calcareous and may be monaxons (one ray) or multiradiate (three or more rays). Sponges of Calcarea are mostly marine, inhabiting shallow coastal waters to deeper seas on rock, coral, or sediment, and can tolerate a range of salinities; freshwater sponges belong to other classes.

Calcarea reproduce both asexually by budding and sexually, with many species being hermaphroditic. Eggs and sperm are produced in the mesohyl; fertilization often occurs with free-swimming larvae that settle to form new individuals.

Ecology and evolution: Calcareous sponges are among the oldest animal lineages with a fossilizable calcium carbonate skeleton; their calcareous skeletons aid in paleontological studies of early metazoans. They contribute to benthic habitats as filter feeders and can form communities on reefs and rocky substrates.

Taxonomy: Calcarea is divided into two subclasses, Calcinea and Calcaronea, encompassing several orders and many genera, united by the presence of calcium carbonate spicules rather than silica.