Actinotrocha, the larva of PHORONIDA

The characteristic larva of the Phoronida has been described near Helgoland (Germany) by Müller (1846) who considered them as an adult form, he named 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 (see Silén, 1952), corroborated through Nielsen (2013).

  • Consequently, the actinotroch keeps it name Actinotrocha followed by a "specific" name which is sometimes still different from the adult species name, however without author's name and year (see Silén, 1952; Nielsen, 2013).

  • This use has to be followed, but sometimes forgotten in recent papers on Phoronida, perhaps the authors did know this use. Others have the ingenuity to consider the specialists of Phoronida as responsible for the maintain of abnormality in the use of the nomenclature or yet the overconfidence to consider the specialists of Phoronida, from more than 150 years, to have a devil-may-care attitude and to misuse of the International Code of Zoological Nomenclature. See the drawing.

The Actinotrocha  bears an anterior preoral lobe on which is located the nervous ganglion (on the apical area), a tentacular ridge, a pair of protonephridia, and posteriorly a ciliated ring around the anus. The larvae undergo a planktotrophic development and settle after about 20 days.
The metamorphosis is "catastrophic" occurring within less than 30 minutes and leads to a slender young phoronid.

Phoronids generally breed from spring to autumn over a fairly long period (until 8 to 10 months). The peak of reproduction occurs in late spring and summer. Individuals which metamorphosed in spring may show a reproductive period in autumn.
In several species brooding occurs until the first larval stages.

Emig C. C., 1982. The biology of Phoronida. Adv. mar. Biol., 19, 1-89.

See also the recent references - click on...1995, 1996, 1997, 1998.