Systematic Zoology

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Diploma Thesis

"Computer-aided 3D-microanatomy of the rhipidoglossate heterobranchs Hyalogyrina glabra Marshall, 1988 and Hyalogyrina grasslei Warén & Bouchet, 1993 (Gastropoda: Ectobranchia)"

haweIn 1985 and 1988 Haszprunar reintroduced the concept of the Heterobranchia, Gray 1840 as a monophyletic taxon of all higher gastropods. This thesis was confirmed in most publications afterwards (at last by Dinapoli & Klussmann-Kolb 2010). Since the work of Rath (1988) the Valvatidae, Gray 1840 (Heterobranchia: Ectobranchia = Valvatoidea) are an inherent part of this group – until then they were counted as prosobranch molluscs for a long period of time due to an incorrect presumption of a primary bipectinate ctenidium. A nearly related taxon is Hyalogyrinidae Warén & Bouchet, 1993. Species of this family are in possession of a basal rhipidoglossate radula and as yet were mostly classified as Skeneidae (Vetigastropoda).

In the present diploma thesis two species of Hyalogyrinidae, Hyalogyrina glabra Marshall, 1988 and Hyalogyrina grasslei Warén & Bouchet, 1993 were investigated according to their inner anatomy based on histological semi-thin-slices and 3D-surface reconstruction. The new characters achieved here were used for morphological, functional and phylogenetic discussion.

The type species H. glabra, with a length of 1.7 mm, possesses a heterostrophic shell with a hyperstrophic protoconch. There are no epipodial tentacles on the soft body. Though propodium and snout have bilobate ends. Three tentacles are present: two nearly identical cephalic tentacles and a single pallial tentacle on the right side. Furthermore there is a single pedal gland in the anterior part and seven bigger calcium cells in the posterior part of the foot. The deep mantle cavity is in possession of two pallial glands, a ciliated secondary gill with a single connection to the cavity roof and no PMO (= pigmented mantle organs. Two ducts for genital and digestive system are present. The kidney is located in front of the heart and behind the gill. The pharynx with some well developed jaws has no longitudinal folds or alimental groove. The oesophagus is ciliated and lacks in gland cells. The short, s-shaped radula is supported by a distinct muscle odontophore. The stomach with a single ciliated sorting field owns two separate ducts to the anterior and posterior digestive gland. In addition, the intestine is short in contrast to the rectum. This species is a simultaneous hermaphrodite. There is no penis or other copulation organ in addition to a complex genital tract. The nervous system is epiathroid, the fusion of cerebral with pleural ganglia is complete. The osphradium is located in the left anterior mantle roof. This species has no eyes.

In its outer appearance H. grasslei is very alike H. glabra but with a length of 2.6 mm it is much bigger. In addition, this species has two small bumps between the cephalic tentacles. The right cephalic tentacle is furthermore in possession of a smaller, posterior tentacle appendix. There is no exactly defined pedal gland but a small amount auf calcium cells is found in the metapodium. The mantle cavity is deep and glandular - here the discrimination of different glands fails. The gill is once again ciliated but has two connections to the mantle roof. The position of kidney and heart are identical to that of H. glabra. Differences are found in the connection between stomach and digestive glands. They are fused and bear a single tooth for sorting. This hermaphroditic species lacks a penis. Instead it probably uses the small tentacle appendix on the right side for copulation. There are no obvious differences between nervous systems and sense organs in the two species.

Both species were confirmed in their position within the basal heterobranchs in recognition of the new characters investigated. In addition with the diploma thesis of Speimann (2007) this work gives an extensive overview over almost all known species within the Hyalogyrinidae and near phylogenetic neighbours. Whereas H. glabra was first assigned to the Skeneidae, the results of this study clearly state a close phylogenetic relation of all investigated species (summed up as Hyalogyrinidae) within the basal heterobranch molluscs together with Cornirostridae, Xylodisculidae and Valvatidae.