Systematics

Several authors regard Phoronida as constituting a separate phylum; but others, including myself (Emig, 1977, 1997), consider them as a class within the phylum Lophophorata, which also includes the Bryozoa and Brachiopoda. Recently, Cohen (2000) included the Phoronida in a subphylum named Phoroniformea within the Brachiopoda. The Phoronida are particularly distinguished from the other two lophophorate groups on the basis of its cylindrical body form living in a tube which can be compared to the shell of the Brachiopoda and to the exo-skeleton in the Bryozoa.

Currently only two genera, Phoronis, Wright, and Phoronopsis, Gilchrist, are recognised, together with respectively seven and three well-defined species (Emig, 1971, 1979, 1982). The name Phoronis, given by Wright (1856) from the genus name, is one of the numerous epithets of the Egyptian goddess Isis (Wright, 1856). The genus Phoronopsis has an epidermal invagination at the base of the lophophore.

The characteristic larva of the Phoronida, named actinotroch or Actinotrocha, has been described near Helgoland (Germany) by Müller (1846). He considered it as an adult form, and named it Actinotrocha branchiata. The transformation of the actinotroch into an adult phoronid was described for the first time by Kowalevsky (1867) who, following the metamorphosis, realised that the Actinotrocha was a larval stage of Wright's Phoronis species.

Separate names for larval and adult forms are still used in taxonomy. Despite the priority of the larval name Actinotrocha, the International Commission of Zoological Nomenclature accepted also as valid the name Phoronis. Consequently, the actinotroch keeps a separate "generic" name considered as a technical term under Actinotrocha (see Silén, 1952) which is sometimes still different from the adult species name.

Distribution

Phoronids are found in all oceans and seas 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 occuring in European waters have wide geographical ranges and most are probably cosmopolitan.

From data of recent ecological surveys in Europe, mainly in the south of the Iberian Peninsula, the Chafarinas Islands and Canary Islands (Emig et al. 1999a, 199b, 2000), the number of phoronid species occuring in the European waters increased to 9 of 10 species known in the world. The species not recorded in Europe, Phoronis ijimai, is presently known from Pacific and N. W. Atlantic waters. The Iberian Peninsula and the surrounding islands represent a privileged area for the Phoronida because all 9 species has been recorded along their coasts.

For more detailed information on Phoronida see the website at http://www.com.univ-mrs.fr/DIMAR/Phoro/.

References