BIOLOGIYA MORYA, 2014, Vol. 40, No. 4, pp. 309-318

The microscopic anatomy and ultrastructure of the contractile vessel in the sipunculan Themiste hexadactyla (Satô, 1930) (Sipuncula: Sipunculidea)

© 2014 A. V. Adrianov^{1, 2, 3}, A. S. Maiorova^{1, 2}

¹Zhirmunsky Institute of Marine Biology, Far East Branch, Russian Academy of Sciences, Vladivostok 690041;
²Far Eastern Federal University, Vladivostok 690950;
³Primorsky Oceanarium Scientific-Educational Complex, Vladivostok 690041

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The microscopic anatomy and ultrastructure of the contractile vessel of the sipunculan Themiste hexadactyla (Satô, 1930) from Vostok Bay (the Sea of Japan) were studied by histological and electron microscopic methods. The ultrastructural features of the internal (endothelium) and external (coelothelium) lining of the contractile vessel are described and illustrated. Numerous macromolecular filters, the so-called "double diaphragms", were found in the external coelothelium facing the cavity of the trunk coelom. This suggests a possible filtration from the tentacular coelom into the trunk coelom through the contractile vessel wall. The microscopic peculiarities of the main tube of the contractile vessel and its numerous lateral branches twining around some internal organs are described in detail. The contractile vessel is polyfunctional: it can act as the main reservoir for the cavity fluid during the tentacular crown withdrawing and performs the functions of the distribution system in sipunculans.

Key words: hemerythrin, double diaphragms, multicellular cells, nephridium, podocytes, Polian vessel, contractile vessel, coelothelium, sipunculan Themiste hexadactyla.