The Phoronida is an exclusively marine group of lophophorate animals: infaunal, suspension-feeders, with a vermiform body enclosed in a slender, chitinous tube in which it moves freely and it is anchored by the ampulla, the end-bulb of the body. The tube is embedded in hard or soft substrates.
 

Currently the PHORONIDA are constituted by only two genera, without any intermediate hierarchical level (see Emig, 1971, 1979, 1982):

• Phoronis, Wright, 1856, without epidermal invagination at the base of the lophophore. This genus is recognised with seven species.


• Phoronopsis, Gilchrist, 1907, has an epidermal invagination at the base of the lophophore, and three well-defined species.

Phoronids are found in all oceans and seas (except the Antarctic) and are not uncommon in favourable situations. In some habitats they are very abundant, reaching several tens of thousand individuals per square metre.
Phoronids occur at depths ranging from the intertidal zone to about 400 m depth, but mainly between 0 to 70 m.
Almost all species have wide geographical ranges and most are probably cosmopolitan.

Diagnosis of the Phoronida

• three body parts in the adult forms, each containing its own coelomic cavity, while only two cavities occur in the larva;


• presence of a lophophore which is defined as a tentacular extension of the mesosome (and of its cavity, the mesocoelom) that embraces the mouth, but not the anus, and its main functions are feeding, respiration and protection (Hyman, 1959; Emig, 1976).


• U-shaped digestive tract;


• nervous centre between mouth and anus, a ring nerve at the basis of the lophophore, one or two giant nerves fibres;


• one pair metanephridia;


• a closed circulatory system with red blood corpuscules;


• internal fertilization and a radial and total development.