Aplysia parvula Guilding in Moerch , 1863

Yonow, Nathalie, 2012, Opisthobranchs from the western Indian Ocean, with descriptions of two new species and ten new records (Mollusca, Gastropoda), ZooKeys 197, pp. 1-130 : 7-8

Aplysia parvula Guilding in Moerch, 1863 Plates 1011

Aplysia spuria Krauss. - Macnae 1955, 235, figs.1d, 2d, 3d, 6a, b (South Africa).

Aplysia parvula . - Gosliner 1987: 46, fig. 24 (South Africa); Yonow and Hayward 1991: 5, figs. 4E, 5D (Mauritius); Yonow 2008: 98 (Red Sea); Apte 2009: 165, fig. 1h (Laccadive Islands).

Aplysia fasciata . - Yonow 1994a: 104, fig. 4G (Maldives); Yonow 2000: 94, fig. 3, plate 7 (Red Sea) (non Aplysia fasciata Poiret).

Aplysia cf. parvula . - Yonow et al. 2002: 837, figs. 2d, 3a, b (Chagos).

Aplysia sp. - Yonow 2008: 100 (Red Sea).

Material.

Pale form: Socotra: 10 mm × 5 mm pres. (IT-084, N-171), Rhiy di-Irisal, SE site, 2-8 m depth, 24.II.1999, leg. N Simões. - La Réunion, photographs of numerous individuals http://seaslugs.free.fr/nudibranche/a_intro.htm.

Dark form: Maldives: two specimens approx. 14 mm in length, Hulhulé Island, North Malé Atoll, 12 m depth on orange encrusting sponge on outer reef, 30 July 1995, leg. RC Anderson & SG Buttress ("dark brown with numerous tiny white dots, brown tending to orange, greyish white at margins"); two specimens both 14 mm, Old Shark Point, Thilafalhu Reef, North Malé Atoll, 16 m depth, 18 November 1995, leg. RC Anderson & SG Buttress ("dark brown with numerous fine pale dots; edges of [parapodia] and tentacles pale"); 20 mm (MDV/AB/96/13), Fulidhoo Channel, Felidhoo Atoll, 9 m depth, 07 May 1996, leg. RC Anderson & SG Buttress ("no white spots"). - La Réunion, photographs of several individuals http://seaslugs.free.fr/nudibranche/a_intro.htm. - Tanzania: photo of one individual, Mafia Island, shallow water, May 2009, A de Villiers.

Description/Remarks.

The dark colour form is common in the Red Sea and western Indian Ocean ( Yonow 1994a, Yonow et al. 2002, Yonow 2008) and also occurs in the western Pacific ( Gosliner et al. 2008), albeit less frequently. The pale Socotra specimen is well relaxed and preserved: the body is cream coloured with black edging to the rhinophores, oral tentacles, foot, and parapodia. Both colour forms are small, and one is the reverse colour pattern of the other. Although pale Aplysia parvula are recorded to grow to 120 mm ( Marshall and Willan 1999), the largest size recorded for the dark colour formis the Maldives specimen listed above at 20 mm. Consistent differences occur in the colour patterns: Aplysia parvula sensu strictu is usually pale green or greenish brown with white marbling and spots, and dark purple-to-black margins on the tentacles and parapodia (Plate 10). The black form is very dark brown or black, sometimes with white speckles, and with pale pink or violet edging to the parapodia and tentacles (Plate 11). The pale form is found in shallow tidal areas with seaweed, while the dark form is found on coral reefs in more exposed areas. Several other colour patterns have been illustrated on the La Réunion website.

The radula of the Socotra specimen has the formula 29 (+2) × 4.7.1.7.4. It is comparable in formula and size to those of the dark form previously examined from the Red Sea (26 (+1) × 4.6.1.6.4: Yonow 2000) and Chagos (26 (+3) × 3.6.1.6.3: Yonow et al. 2002), although it must be stressed that the radulae are not very good diagnostic features for differentiating between species of Aplysia . The shell is also similar in both forms but again, it is variable and therefore not a particularly useful character for determining species of aplysiids.