BIOLOGIYA MORYA, 2011, Vol. 37, No. 6, pp. 423-429

The structure of the proboscis musculature of the nemertean Baseodiscus delineatus (Delle Chiaje, 1825) (Heteronemertea) and a comparative analysis of the proboscis musculature among the heteronemerteans

© 2011 T. Yu. Magarlamov¹, A. V. Chernyshev^{1, 2}

¹A.V. Zhirmunsky Institute of Marine Biology, Far Eastern Branch, Russian Academy of Sciences, Vladivostok 690059;
²Far Eastern Federal University, Vladivostok 690600

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The proboscis musculature of the nemertean Baseodiscus delineatus was examined by confocal laser-scanning and transmission electron microscopy. The proboscis wall consists of three muscular layers: outer longitudinal, diagonal, and inner circular. The endothelium consists of two cell types: apically situated supportive cells with rudimentary cilia and subapical myocytes forming the inner circular musculature. Thin cytoplasmic processes of the supportive cells reach into the basal extracellular matrix; their perikaryons cover the apical surface of the myocytes. The distinguishing features of the endothelium in B. delineatus are the folded basal layer of the extracellular matrix and the different height of the myocyte processes, which gives the appearance of the multi-layer endothelial musculature. A comparative analysis shows that the diagonal musculature of Baseodiscus is not homologous to that of other heteronemerteans. An endothelial origin of the inner circular muscles of all heteronemerteans is proposed.

Key words: nemerteans, proboscis, diagonal musculature, endothelium.