Rissoella venezolanicola, Caballer, Manuel, Ortea, Jesus & Narciso, Samuel, 2011

Caballer, Manuel, Ortea, Jesus & Narciso, Samuel, 2011, Description of two new species of Rissoella Gray, 1847 (Mollusca, Gastropoda, Heterobranchia) from Venezuela, with a key to the Caribbean species known for the genus, ZooKeys 115, pp. 1-18 : 7-9

Rissoella venezolanicola sp. n. Figs 6 –811–1218– 22Tabs 134

Description.

Shell very small (Tab. 3), smooth and translucent (Fig. 18); protoconch about half a whorl after the nucleus (Fig. 19); teleoconch of two whorls and three quarters; aperture oval, with the columella slightly bowed and arched; umbilicus narrow and deep, slightly closed by the expansion of the columellar edge; preumbilical cord extended, with an angle delimiting and closing the umbilicus forming a trapezoid (Figs 11-12, 20); average height of the last whorl, 82.9% of shell length; average height of the aperture, 49.6% of shell length (Tab. 3); Shell length/width ratio = 1.52; spiral angle = 58°; umbilical angle = 23°-25°.

Operculum oval, translucent with an amber tinge, membranous consistence; head, flanks, oral lobes and cephalic tentacles translucent white with scattered black to greenish brown dots (Fig. 6); eyes black; foot translucent white (Fig. 7); hypobranchial gland translucent white with scattered blotches black to greenish brown and a distinctive yellow design quaver-shaped (Fig. 8); visceral mass in the first whorls, black; protoconch with fuchsia highlights in live animals.

Odontophoral cartilages kidney-shaped, with large uncini placed longitudinally (Fig. 21); radular formula of an specimen 0.96 mm shell length, 16 × 1.1.R.1.1; rachidian tooth wide, with bilobed apex forming two smooth cusps (Fig. 22), slightly larger than marginal tooth; lateral tooth triangular, 28.3 µm long, with the apex hooked and smooth; imbricated with the opposite tooth above the rachidian; marginal tooth triangular and curved, 16.3 µm long, with blunt apex.

Types.

Holotype, 1.02 µm × 0.66 µm, collected alive (August 2, 2010), preserved dry and deposited in FUDENA (CFRFSIA0002). Paratype 1, 0.96 × 0.64 µm, SOM-IVIC (IVICCMT008), used to get the radula, shell preserved dry. Paratype 2, 0.54 × 0.46 µm, preserved dry, SOM-IVIC (IVICCMT009).

Type locality.

Leeward patch reef, Isla de Aves, Venezuela (15°39'54.2"N, 63°37'17.6"W), on Dictyota spp., 10 m depth.

Further localities.

Paratypes: Northern end, Isla de Aves, Venezuela, (15°40'24.7"N, 63°37'11"W), on Dictyota spp., 10 m depth.

Etymology.

venezolanicola latinization of venezolana, inhabitant of Venezuela.

Remarks.

Due to the presence of the preumbilical cord, Rissoella venezolanicola sp. n., is comparable to Rissoella zaidae , Rissoella florae , Rissoella elsae , Rissoella taniae (Ortea and Espinosa 2004) (listed above) and Rissoella morrocoyensis sp. n. But it is different because in none of them the preumbilical cord delimits and closes the umbilicus, neither the hypobranchial gland has a yellow quaver-shaped design. Additionally, Rissoella venezolanicola sp. n. differs from all these species by:

- Rissoella zaidae : (shell length/width ratio = 1.63, spiral angle = 50°, umbilical angle = 30°) the whorls of the spire are more angled and tilted, the umbilicus is in the middle of the last whorl, the head, oral lobes, cephalic tentacles and the visceral mass in the first whorls are lilac and the hypobranchial gland is kidney- shaped, pale violet with lilac blotches and bounded by a yellow ribbon with transverse bands.

- Rissoella florae : (shell length/width ratio = 1.35, umbilical angle = 18°) the head and oral lobes are black, the cephalic tentacles are different in colour than the oral lobes, the eyes are located in lighter areas of orange hue, the visceral mass in the first whorls is brown or orange and the hypobranchial gland is lemon-yellow without any design on it.

- Rissoella elsae : (shell length/width ratio = 1.69, spiral angle = 45°) the shell is more conical, the preumbilical cord is higher than the columellar wall, the head, oral lobes and cephalic tentacles are lilac, the mantle is green and hides the eyes, and the hypobranchial gland has large patches of dark green and is enclosed by a white ribbon with transverse bands.

- Rissoella taniae : (shell length/width ratio = 1.4, spiral angle = 65°, umbilical angle = 43°) the shell is spherical with slightly globose whorls, the umbilicus is very open, the head, oral lobes, cephalic tentacles and visceral mass in the first whorls are dark green, there are no eyes apparently and the hypobranchial gland is white with green spots.

- Rissoella morrocoyensis sp. n.: (shell length/width ratio = 1.32) the umbilicus is deeper and more closed by the expansion of the columellar edge and the head, oral lobes and cephalic tentacles are black.

Two species from Africa have a design on the hypobranchial gland similar to Rissoella venezolanicola sp. n.: Rissoella luteonigra Rolán & Rubio, 2001 and Rissoella trigoi Rolán & Hernández, 2004. Rissoella venezolanicola sp. n. differs from these species in:

- Rissoella luteonigra ;is bigger (1.8 mm), with a narrower and longer shell, lacking preumbilical cord. Animals are black homogeneous ( Rolán and Rubio 2001).

- Rissoella trigoi ; has a rough protoconch with cavities in the suture, the preumbilical cord parallel to the expansion of the columellar edge until it converges (divergent in Rissoella venezolanicola sp. n.) and the animals are black with a white drawing in the hypobranchial gland ( Rolán and Hernández 2004), very simple and very different.