Systematic Zoology

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Diploma Thesis


"Computergestützte 3D-Rekonstruktion und vergleichende Anatomie skeneimorpher Gastropoden an Bathyxylophila excelsa Marshall, 1988 und Ventsia tricarinata Warén & Bouchet, 1993"

Computer-aided 3D-reconstruction and comparative anatomy of the skeneimorph Microgastropods Bathyxylophila excelsa Marshall, 1988 and Ventsia tricarinata Warén & Bouchet, 1993


The family Skeneidae (Vetigastropoda, Trochoidea/Turbinoidea) is currently regarded as a polyphyletic lumping pot for small (max. 3 mm), rhipidoglossate gastropods ("skeneimorph") showing signs of internal fertilisation. Recent methodological progress including serial semithin sectioning combined with computer-aided (software AMIRA) 3D-reconstruction enables the detailed anatomical investigation of such small, helicoid gastropods. Here I describe the microanatomy of the small (max. 1.5 mm) Bathyxylophila excelsa Marshall, 1988, found on sunken wood (800 m depth) near Chatham Rise, New Zealand, and the hot-vent inhabitant Ventsia tricarinata Warén & Bouchet, 1993, (max. 2.5 mm) from the Lau Basin, Fiji (1800 m depth). Both species were placed originally inside the family Skeneidae.

Ventsia tricarinata has papillate cephalic and epipodial tentacles, a single left monopectinate ctenidium with skeletal roots and bursicles, a monotocard heart penetrated by the rectum, a left papillate and a right excretory organ, a rhipidoglossate radula with one pair of radula cartilages, two intestinal loops, a papillate oesophagus a hypoathroid nervous system, two statocysts with several statoconia, a single left osphradium, a subradulary organ and one pair of ESO-tentacles. The sexes are separated, the female genital systems consists of an ovary with big yolky eggs covered by a vitellin layer, a simple urinogenital duct, and a separated receptaculum seminis.

Bathyxylophila excelsa differs as follows: The heart does not encircle the rectum, the oesophagus lacks papillae. Due to insufficient fixation, many histological details could not be cleared up.

All anatomical data strongly suggest a position of both species inside the Vetigastropoda. The distinct appearance of epipodial tentacles and the lack of a combined epipodial sense organ strictly argues against an inclusion into Trochoidea/Turbinoidea and Skeneidae, where combined epipodial tentacles are always present. However, the combination of characters exclude both species from all currently defined subclades of the Vetigastropoda. Until more data on possibly related forms are collected they remain as Vetigastopoda "incertae sedis".