FAMILY VELUTINIDAE GRAY, 1840

Velutinidae Gray, 1840: 90;

type genus Velutina J. Fleming, 1820.

Included subfamilies: Hainotinae Fassio, Bouchet, Schiaparelli & Oliverio subfam. nov., Lamellariinae d’Orbigny, 1841, Marseniopsinae Fassio, Bouchet, Schiaparelli & Oliverio subfam. nov., Velutininae Gray, 1840.

Description: Small to medium size for the superfamily, 0.5–11.5 cm total length. Shell exposed to completely enclosed by the mantle, thin to very thin, from strongly calcified to membranaceus; ear, shield or cap shaped, low to high spired, with expanded aperture; smooth or weakly sculptured by axial growth lines. Periostracum from thick and hairy to not visible.

Protoconch of 0.76–2.10 whorls; protoconch I of 0.25–1.20 whorls, smooth or with microgranules, with or without subsutural axial folds, nucleus diameter 54–875 μm; protoconch II with or without marked axial ribs or growth lines; protoconch–teleoconch boundary not always distinct.

Echinospira planktotrophic larva with double larval shell: the outer periostracal planispiral, smooth and rounded or strongly carinate, the inner helicoid.

Mantle flat (Fig. 4C) or dome shaped (Fig. 4A), outline from above rounded (Fig. 4J) or polygonal (Fig. 4B, H); thick or thin, with or without dorsal warts or tubercles; with or without anterior (inhalant) and right lateral (exhalant) siphon folds; texture smooth, wrinkled, jelly-like or velvet-like; colour highly variable, almost transparent to white, grey, beige, yellow, orange, red, violet, blue, dark green, brown, black, often patterned.

Penis to the right of the right cephalic tentacle; with or without a lateral subterminal papilla; with or without tip of the seminal duct protruding from the penis tip. Vas deferens with or without a free loop in haemocoel.

Radula taenioglossate (with formula 2:1:1:1:2) or reduced taenioglossate (if lacking marginal teeth, formula 0:1:1:1:0); rachidian tooth base rectangular (broad or elongated) or bifurcated (inverted V-shape), rachidian cusp with or without several external denticles; lateral teeth broad or elongated, with a pointed, triangular, internal or external cusp or one external cusp plus one truncated projection, with or without denticles; marginals, when present, narrow, with or without denticles.

Jaw s of v a r i a b l e s h a p e, s h o r t t o e l o n g at e d; homogeneous or composed of scale-like elements; with or without uniform masticatory denticles.

Distribution: Worldwide, from shallow to abyssal waters (0–4500 m).

Remarks: Velutinids differ from the other two velutinoidean families (Triviidae and Eratoidae) chiefly in their thin to very thin, helicoid shell, with expanded aperture (vs. solid, cowry-like, with narrow aperture in triviids and eratoids) and the planispiral outer layer of the echinospira larval shell (vs. helicoid in triviids and eratoids). Also, the siphon is proportionally shorter in velutinids than in triviids and eratoids.

Many velutinid species are reported to live and feed on ascidians (Wilson, 1998), and the colour and texture of the dorsal mantle can mimic the ascidian host. Both hermaphroditic and gonochoristic species are reported (Wilson, 1998). Egg capsules are flask shaped (Diehl, 1956; Fretter & Graham, 1962) and are laid in holes in the tunic of the ascidians (Peck et al., 2006; Fassio et al., 2019).