The life cycle of Catablema vesicarium (A. Agassiz, 1862) (Hydrozoa, Pandeidae)

Abstract

The hydrozoan classification systems often rely on limited character sets of either polyp or medusa stages, and these classifications stay non-consistent in many cases because of lack of life cycle data. This is usual for hydrozoans with tiny inconspicuous colonies and intermittent medusae production period such as pandeid in the polar latitudes. In this study, the previously unknown life cycle of boreal-Arctic pandeid hydrozoan Catablema vesicarium was elucidated under experimental conditions. Medusae C. vesicarium were found near the Pertsov Biological Station in the White Sea and maintained in a laboratory till spawning. Morphological descriptions of development stages including medusae, eggs, planulae, polyps, and medusae buds are represented. Hydroid C. vesicarium was also collected on the shell with live Astarte elliptica. Identification of this colony was confirmed by comparing the sequences of the mitochondrial CO1, 16S, and nuclear 18S-ITS1-5.8S gene fragments of medusae and polyps. Hydroids C. vesicarium have almost sessile polyps with perisarc cup only at the base, and newborn medusae have rudimentary marginal bulbs which alternate with four marginal tentacles. Identification characters of the cultivated hydrozoan are discussed in comparison with other known pandeids. The data on temperature range of medusae appearing in experiments may be potentially useful for studying seasonality of jellyfish in the sea.