Hyalogyra expansa Marshall, 1988

Hess, Gerhard Haszprunar Erika Speimann Andreas Hawe Martin, 2011, Interactive 3 D anatomy and affinities of the Hyalogyrinidae, basal Heterobranchia (Gastropoda) with a rhipidoglossate radula, Organisms Diversity & Evolution (New York, N. Y.) 11 (3), pp. 201-236 : 228-229

Hyalogyra expansa Marshall, 1988

Anatomy and histology

Because of the very poor preservation of the specimens available, only a superficial description can be provided which focuses on differences to the species described above.

There is only a single pedal gland, which is quite large and lies in the anterior foot.

The single (left) ctenidium is quite large, bipectinate, and lacks skeletal support. Its anterior half reaches free into the mantle cavity. Again there is a monotocardian heart and a single (left) kidney lying in the pallial roof. The single (left) hypobranchial gland shows three distinct regions differing in histology. In addition, a huge medio-dorsally placed pallial gland (brood pouch?) with various cell types is present. More posteriorly a separated, glandular (much narrower), tubular vas deferens (prostate gland) opens into the mantle cavity.

This species represents another simultaneous hermaphrodite, and again the genital apparatus as a whole is a very complex system. The hermaphroditic gland shows distinct regions of sperm (outwards) and egg (inwards) production. The eggs are very large (more than 200 μm in diameter) and yolk-rich. There is a receptaculum below and posterior to the heart on the left side; a ciliated duct connects the receptaculum to the mantle cavity. A copulatory organ is situated behind the right cephalic tentacle and is supplied by a nerve from the cerebropleural connnective. The posterior basis of the copulatory organ is provided with another short appendix.

The entire buccal apparatus resembles those in the Hyalogyrina species, but each buccal retractor clearly shows a nerve inside. The anterior oesophagus has two main dorsal folds and shows torsion, and there are true, separate oesophageal glands (not pouches). The posterior oesophagus is not folded. The stomach is again equipped with gastric shield and ciliary fields. Intestinal loops are found only below the posterior mantle cavity; there is no anterior loop. The very thick pallial gonoduct shifts the pallial rectum far to the left side of the mantle cavity.

The nervous system is again epiathroid and streptoneurous and strongly resembles those in the Hyalogyrina species. A so-called juxtaganglionar organ (e.g. Clare 1987; Herbert 1982; Martoja 1965a, b; Switzer-Dunlap 1987) lies at the dorsal side of the short cerebral commissure. The statocysts are attached at the posterior-ventral side of the pedal ganglia and again contain a single statolith each.