Phascolosoma

Phascolosoma is a genus of marine peanut worms in the phylum Sipuncula. Members are unsegmented, worm-like animals that possess a retractable introvert at the anterior end, which bears a crown of tentacles around the mouth. The trunk is typically swollen and contains the main body cavity. Individuals range in size from millimeters to several centimeters depending on species, and coloration varies from pale to brownish, often with a translucent appearance.

Distribution and habitat: Phascolosoma species are found in oceans worldwide, from shallow intertidal zones to deeper continental shelves. They inhabit soft substrates such as sand, mud, and silt, often living in burrows or concealed among detritus, rocks, or coral rubble.

Ecology and biology: They are deposit feeders, using their tentacular crown to collect organic matter and microorganisms from sediment. food is drawn toward the mouth by ciliary action and mucus. Gas exchange and excretion occur across the body wall, as there are no specialized respiratory or circulatory organs. They lack true segmentation and move slowly, retreating into their burrows when threatened.

Reproduction and development: Reproduction is primarily sexual, with separate sexes and external fertilization in many species. Larval development is typically pelagic for a period before settlement, though there can be species-specific variations. Some species may brood eggs or show direct development.

Taxonomy: Phascolosoma belongs to the phylum Sipuncula and the family Phascolosomatidae. The genus comprises multiple described species, which vary in size, morphology, and habitat preferences.