Some Aspects of the Morphology of Four Species of the Neogastropod Family Marginellidae with a Discussion on the Evolution of the Toxoglossan Poison Gland

Abstract

The living animal, alimentary canal and reproductive system of Mesoginella (Sinuginella) pygmaea (Sowerby), Volvarina (Haloginella) mustelina (Angas), Volvarinella cairoma (Brookes) from New Zealand and Diluculum sp. from the New Hebrides are described. V. cairoma has the duct of the gland of Leiblein opening into the buccal cavity and has no buccal mass or radula, whereas the other species have a well developed buccal mass and the gland of Leiblein discharges into the oesophagus behind the nerve ring. An unusual feature of the oesophagus of M. pygmaea, V. mustelina and Diluculum sp. is a tube, derived largely from the ventral channel of the anterior oesophagus, which by-passes the valve of Leiblein and then opens into the mid-oesophagus just behind the valve. The male genital system has a large prostate gland which is closed except for a small posterior opening, and the female system has no gonopericardial canal and has vesicular seminal receptacles that do not ingest soerm. The albumen and capsule glands are similar to those of other Rachiglossa. An hypothesis is presented on the possible evolution of the toxoglossan poison gland from the combination of the gland of Leiblein, glandular dorsal folds of the mid-oesophagus and ventral channel of the anterior oesophagus.