MARSENIA OKEN, 1823

(FIGS 2, 3, 5H, I, 8D, 9K, L, 10M–O, 11L)

Marsenia Oken, 1823: columns 458, 460;

type species Bulla haliotoidea Montagu, 1803 = Helix perspicua Linnaeus, 1758 by monotypy.

Included species: Marsenia herberti (Drivas & Jay, 1990) comb. nov., Marsenia perspicua (Linnaeus, 1758), Marsenia affinis Bergh, 1886 [taxon inquirendum], Marsenia cabulana Bergh, 1886 [taxon inquirendum], Marsenia dubia Bergh,1886 [taxoninquirendum], Marseniagemma Bergh, 1875 [taxon inquirendum], Marsenia isabellina Bergh, 1875 [taxon inquirendum], Marsenia perspicua var. lara Bergh, 1899 [taxon inquirendum].

Description: Body of small to medium size for the subfamily, 0.3–10.0 cm total length. Shell thin, weakly calcified; ear shaped, low to high spire, with expanded aperture; smooth or weakly sculptured by axial growth lines; completely enclosed by the mantle or presenting a small dorsal fissure. Periostracum not visible.

Protoconch of 1.2–1.6 whorls; protoconch I 0.6–0.75 whorls, nucleus diameter 100–250 μm, smooth, with subsutural axial folds; protoconch II with or without axial growth lines; protoconch–teleoconch boundary not always distinct.

Mantle flat or dome shaped, outline rounded; thick or thin, with or without tubercles on dorsum; with anterior siphon folds; texture smooth/wrinkled/jellylike; colour highly variable, almost transparent to white, grey, beige, yellow, orange, red, violet, brown, often patterned with dots, streaks or patches of colour.

Penis to the right of the right cephalic tentacle; with or without a lateral subterminal papilla. Vas deferens with or without a free loop in haemocoel.

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

Jaws short to elongated.

Distribution: Indo-West Pacific (Madagascar, Reunion, Red Sea, Taiwan, Philippines, Papua New Guinea, Tasmania, New Caledonia, Hawaii), Mediterranean Sea (Corsica and Alboran Sea), Caribbean Sea (Martinique and French Guiana); 0–214 m deep.

Remarks: The type species, Marsenia perspicua, is part of a complex of at least two cryptic species.

This widely distributed lineage is present in the tropical areas of the Indo-Pacific and the Atlantic, and in the Mediterranean Sea. It would be difficult to recognize this genus from other lamellarines with a low spire and moderately calcified shell, if it was not for its radula, characterized by a rachidian tooth bifurcated at the base, with small denticles on both sides and elongated lateral teeth with pointed, triangular and external cusps, with small denticles on both sides.

In one species (Marsenia sp. L45), a specimen with a shell not completely enclosed by the mantle but presenting a small dorsal fissure (similar to that of some Variolipallium specimens) was observed.

We think that, based on the original descriptions, several taxa inquirenda described by Bergh (1886b) from Philippines and Cape Verde material (Marsenia affinis, Marsenia cabulana, Marsenia dubia, Marsenia gemma, Marsenia isabellina and Marsenia perspicua var. lara) might belong to this genus.