ИСТИНА

Phoronid larvae are called Actinotrocha and live in plankton for several months. Phoronid world fauna includes ten adult species only, however at least 39 “larval species” are described. In Vostok Bay (VB), the Sea of Japan phoronid larvae increase to as many as 3940 individuals/m3 and represent a significant proportion (10.5%) of the total zooplankton quantity at certain times of the year. Description of phoronid larvae and the analysis of their distribution shed light on the questions of phoronid taxonomy, which is still unclear. Larvae of three phoronid species are usual in VB: Phoronis ijimai, P. sp., Phoronopsis harmeri. Adult P. ijimai broods embryos in the lophophore until young larva. At all stages, P. ijimai larvae are opaque and have dark pigmentation of the oral field epidermis. Competent larva is very colorful and has two pairs of dark spots along the hood edge. P. sp. larvae have dark pigmented stomach diverticulum, which becomes black and prominent by metamorphosis. Competent larva is opaque, 0.35 mm long, has eight tentacles and three masses of blood corpuscles. At all stages, P. harmeri larvae are transparent and have cylindric protocoel under the apical plate. Competent larva is 1.5 mm long, has 24 tentacles and 2-6 blood masses: two main dorsolateral and 1-4 additional ventrolateral. Among phoronid there are two types of pelagic larvae: (i) small opaque with few tentacles; (ii) large transparent with more than 16 tentacles. These larval types correlate with type of development: brooding or holopelagic. Literature analysis revealed the existence of at least three competent phoronid larvae, which were found in different areas of the World Sea and whose belonging is still not established. This work was supported by RFBR grants 11-04-00690 and 12-04-33045.