Ptychogena lactea A. Agassiz, 1865 (Hydrozoa; Laodiceidae): What We Know on Taxonomy, Life-Cycle and Distribution

The hydromedusa Ptychogena lactea A. Agassiz, 1865 is a large and remarkable jellyfish; it has been found in many Arctic and even boreal localities and at various depths, from the mesopelagial to the surface. However, it is still regarded in the literature as a rare deep-water species, with an unknown polyp stage. The hydroid was reared from the medusa P. lactea in the Franz-Josef Land archipelago field laboratory. The hydroid was identified as Cuspidella procumbens Kramp, 1911: a poorly known Campanulinoidea, “Cuspidella-like” Arctic hydroid whose medusa stage was hitherto unknown. Both stages are here proposed to link taxonomically into a one nominal species. Co-distribution of the well-known medusa and the little-known hydroid is studied and mapped. Data on the distribution and ecology of both stages is added. Some data has already been published in Russian literature, but remains unknown to English-speaking scientists. New observations show that P. lactea is neither a deep-water species nor rare, and establish the continuity between medusae and polyp stages of the life cycle.