BIOLOGY OF THE WHITE SEA HYDROZOAN TUBULA RIA-INDIVISA (HYDROZOA, ATHECATA)

The hydroid Tubularia indivisa L. is represented by two different morp hs in the Kandalaksha Bay of the White Sea. These morphs vary in their size, proportions and seasonality of life cycles. T. indivisa from sh allow-water zones has larger polyps carrying more gonophores and sitti ng on short and thick stems attached to stones by branching supporting stolons. In autumn, after autotomy of hydranths, hydroids go on to th e winter dormant stage with undeveloped but real polyps inside the per isarcal tubes. T. indivisa from deep-water zones has smaller polyps wi th few gonophores on shorter peduncules, but with higher stems (of 580 mm high) attached to smooth stones by small perisarcal discs. The hig h morphological variability of T. indivisa is a result of environmenta l influence, temperature fluctuations and hydrodynamics in particular. Development, release and settlement of hydrozoan actinula larvae are described in details. These processes are similar in both morphs. The ecologically dependent morphological plasticity and solitary life mode , along with the actinula stage in T. indivisa are considered as primi tive traits in Hydrozoan evolution.