Phoronidae

Phoronids are a small phylum of marine invertebrates belonging to the class Phoronida. These worm-like creatures are sessile and typically live in chitinous tubes that they secrete. They are found in temperate and tropical waters worldwide, usually in shallow to moderately deep seas, often buried in sand or mud.

The most distinctive feature of phoronids is their lophophore, a circular or horseshoe-shaped structure located at the anterior end of the animal. This lophophore bears numerous ciliated tentacles that are used for both feeding and respiration. Phoronids are filter feeders, capturing small particles of food from the water column using their tentacles. The cilia on the tentacles create a current that draws water towards the mouth.

Phoronids are bilaterally symmetrical and possess a complete digestive system. They have a simple circulatory system and a nervous system consisting of a nerve ring around the lophophore and a ventral nerve cord. Reproduction can be sexual or asexual. Sexual reproduction involves the release of sperm and eggs into the water, leading to the formation of a planktonic larva. Asexual reproduction can occur through budding or fragmentation.

There are only a few known species of phoronids, with the genus Phoronis being the most common. Despite their small number of species, phoronids are ecologically significant in their habitats, contributing to nutrient cycling and serving as a food source for other marine organisms. Their sessile lifestyle and unique feeding apparatus make them an interesting subject of study in marine biology and evolutionary biology.