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The Body Wall and Musculature of the Marine Triclad Palombiella stephensoni (Palombi, 1938): Part One: General Tissue Structure as seen with the Light Microscope



This paper describes the morphology of the body wall and muscles of Palombiella stephensoni (Palombi, 1938), a marine triclad of the family Bdellouridae. It was first described by Palombi (1938) under the name of Synsiphonium stephensoni. More recently it has been assigned to the genus Palombiella by Westblad (1951). Specimens have been recorded from South Africa, Tristan da Cunha, Banks Peninsula, New Zealand (Nurse, 1955) and Wellington, New Zealand (the present study).

The Wellington material fits almost exactly the description given by Westblad (1951) for specimens from Tristan da Cunha. However, 3 differences are apparent. Firstly, the Wellington specimens have 28 testes, whereas those described by Westblad had 24. Nurse (1955) records specimens of P. stephensoni from Banks Peninsula, New Zealand with 36-38 testes. Secondly, the shape of the anterior end is blunt and not pointed, an observation also made by Nurse regarding the Banks Peninsula specimens. Thirdly, a variety of colour-patterns occurs. Most specimens are dark grey on the dorsal surface with irregular patches of pale cream as described by Nurse, but the colour varies from light grey to black, and there is also a form which is red-orange on the dorsal surface. Westblad described the Tristan da Cunha material as being mostly dark brown on the dorsal surface. Ciliated protozoans in the pharynx sheath and gut of the Wellington specimens are similar to those of the same regions in the animals from Tristan da Cunha and Banks Peninsula.