Marseniella, BERGH, 1886

Fassio, Giulia, Stefani, Matteo, Russini, Valeria, Buge, Barbara, Bouchet, Philippe, Treneman, Nancy, Malaquias, Manuel António E., Schiaparelli, Stefano, Modica, Maria Vittoria & Oliverio, Marco, 2023, Neither slugs nor snails: a molecular reappraisal of the gastropod family Velutinidae, Zoological Journal of the Linnean Society 197 (4), pp. 924-964 : 957

MARSENIELLA BERGH, 1886

Marseniella Bergh, 1886a: 14 ;

type species Marseniella borealis Bergh, 1886 by monotypy.

Included species: Marseniella borealis Bergh, 1886 .

Description: Body of medium size for the subfamily, 2.2 cm total length. Shell thin, membranaceus, weakly calcified; ear shaped, low spire, last whorl wide and detached from the spire at the back, with expanded aperture; completely enclosed by the mantle. Periostracum unknown.

Protoconch unknown.

Mantle flat, outline rounded; with coarse and fine knots on the dorsum; with anterior siphon folds; texture unknown; colour unknown.

Penis to the right of the right cephalic tentacle; with a lateral subterminal papilla. Vas deferens with a free loop and several folds in the haemocoel.

Radula reduced taenioglossate, formula 0:1:1:1:0; rachidian tooth base bifurcated; rachidian cusp with several denticles on both sides; lateral tooth elongated, with a pointed triangular external cusp, with several denticles on both sides.

Jaws short.

Distribution: Known only from Florø, north of Bergen ( Norway); depth unknown.

Remarks: Bergh (1886a, b, 1887) described this monotypic genus from a single specimen collected in Norwegian waters. Bergh described it as very similar to velutinids that we call here Lamellaria and Marsenia , but different enough to deserve a separate name. The radular formula and the ‘V’-arched rachidian tooth confirm that it belongs to the Lamellariinae . The rachidian tooth with denticle on both sides and a lateral tooth elongated, with a pointed triangular external cusp, with several denticles on both sides might be compatible with the genus Marsenia (but we have not found any Marsenia in Norwegian waters, from where we have examined only Lamellaria specimens). The vas deferens producing several folds in the haemocoel has been observed in the genus Lamellaria , but we do not consider this character as diagnostic at the genus level. Above all, Bergh (1886a, b, 1887) described for Marsenia borealis a very unusual corneous shell, only partly calcified, somehow similar in texture to that of Onchidiopsis . The described shape is also unusual, flatter than Lamellaria and Marsenia , with a very wide last whorl detached from the spire at the back (a shell shape not observed in any other velutinid examined so far) ( Bergh 1887: pl. X figs 1, 2).

For these reasons, pending further analysis, we provisionally keep Marseniella as a valid genus in the subfamily Lamellariinae , not present in our molecular dataset.