Chromodoris cavae Eliot, 1904

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 : 26-29

Chromodoris cavae Eliot, 1904 Fig. 10Plates 37, 38

Chromodoris cavae Eliot, 1904a: 388, pl. 23 figs. 7, 8 (Zanzibar): Debelius and Kuiter 2007: 141 (South Africa).

Chromodoris vicina Eliot. - Gosliner 1987: 75, fig. 109 (South Africa) (non Chromodoris tennentana Kelaart).

Chromodoris cf. leopardus Rudman. - Yonow et al. 2002: 854, figs. 4f, 10b, 12C, D, 13b (Chagos).

Chromodoris sp. 1. - Debelius & Kuiter 2007: 141 (Oman, Kenya, Mozambique, South Africa).

Chromodoris leoparda (sic. in error for leopardus). - Debelius & Kuiter 2007: 141 (Oman, Thailand: middle left and lower two photos only).

Material.

La Réunion: 60 mm (25 × 15 mm pres., #1), Bassin des Hirondelles, St. Gilles les Bains, 05 November 2006, 1-2 m depth, leg. P Bidgrain; 76 mm (37 × 20 mm pres., #2), Bassin des Hirondelles, St. Gilles les Bains, 17 September 2009, 1-2 m depth, leg. P Bidgrain; 75 mm (34 × 17 mm pres., #3), Bassin des Hirondelles, St. Gilles les Bains, 17 September 2009, 1-2 m depth, leg. P Bidgrain [all in permanent shallow pool on granite coast]; numerous photographs as Chromodoris cf. geminus on http://seaslugs.free.fr/nudibranche/a_intro.htm. - Sri Lanka: photographs of two individuals, Unawatuna, S of Galle and Negombo, N of Colombo, 30 December 2010 and 12 January 2011, S Kahlbrock.

Description.

The three specimens are well preserved, accompanied by 10-20 photographs each. They were all similar in life, with an ochre dorsum extending towards a white band around the edge of the mantle; the purple margin normally present in the species was lacking in all three. The first specimen (60 mm) was rusty orange, deeper along central dorsum and fading toward edge; creamy white band along margin but no purple edge. Some photographs are of the hyponotum as the animal flapped its margin, and there was no purple crescent or line ventrally. Six large wine-red patches with white annulus outside and white speckles inside. Around edge of rust-coloured area was a ring of small round wine red spots, each also with white ring. Rhinophores white, distal part of frontal surfaces and tips purple: 35 lamellae on right rhinophore, very faint purple wash at tips remaining on preserved specimen. 25 pinnate gills arranged with two ends of an arc spiralling inwards: each is triangular, flat surface white and translucent pinnae on other two surfaces. Both branchial and rhinophoral pockets slightly raised, orange in life. Foot and digitate oral tentacles white, but upper lamina of foot very faintly purple; no spots ventrally.

Specimen 2 (76 mm) was deeper orange in life, with more brown centrally and more yellow-orange marginally than specimen 1; faint submarginal band of yellow-orange before white margin. 13 large brown-red spots encircled with white, few smaller ones arranged irregularly around central patch. Additionally, this specimen had some white patches outside and amongst the small spots. 22 gills all had purple tips; rhinophores had more extensive purple pigment than those of specimen 1. Foot yellow-orange posteriorly followed by white band around margin. Ventrally foot bilaminate for its entire anterior margin (Fig. 10A). This specimen was dissected to remove the radula: body wall of foot thick and rose-red internally, digestive gland dark brown-pink while buccal mass white with pink tint. Muscles were very strong, glistening pink; reproductive system opaque white. The radula is large, but the teeth are minute: the largest laterals measure 100 μm (Fig. 10C). The formula is 58 (+2) × 56.1.56. There is a much reduced median thickening in some of the older rows (Fig. 10D). The first lateral bears a small rounded denticle on each side of a sharp cusp. The next 12 laterals have 10-12 weak denticles along the cusp (Fig. 10D). The remaining teeth are simply hook-shaped, blunt and rounded at the old end of the radula (Fig. 10E) but with extremely long sharp cusps at the newer end. Most of the jaw elements are simple unicuspid structures, with a single slightly curved cusp; very few are bicuspid.

Specimen 3 (75 mm) was dark like specimen 2, with 19 gills tipped in purple; rhinophores dark violet, with many closely spaced lamellae (Plate 37). Orange raised rhinophoral pocket rims can be seen in the plate. Ventrally, top of foot white with dark spots, violet margin on upper lamina of foot, white oral tentacles; orange-yellow marking posteriorly but no purple margin; faint orange line in crease between hyponotum and foot. Conical oral tentacles of preserved specimen visible in Fig. 10B, although left one is difficult to see. Margin of anterior foot distinctive, with the two laminae quite separated and extending across entire margin.

Remarks.

Many photographs of additional individuals from La Réunion as well as those from Sri Lanka (Plate 38) clearly belong to the same species. Variations range from large to small spots with solid to diffuse pigmentation, wine-red to almost black-red in colour, all with white ocelli; the presence or absence of smaller spots with a very broad to ‘normal’ white marginal band; a violet margin is very rarely present in the La Réunion individuals but present on the Sri Lanka individuals. Ventrally, there is also some variability, from pure white to having a (faint or dark) rusty orange line along the crease between the foot and the hyponotum, from no spots to few spots on the foot below this line, and there may or may not be an orange patch on the tail. The Sri Lanka individuals had a very faint purple line on the foot margin.

The specimens are all distinctive in preservative, either alcohol or formaldehyde: they are violet-purple to plum red-violet, and all have a thick undulating mantle skirt (including that from Chagos, see Yonow et al. 2002: 854). The gills spiral inwards at their ends and are triangular in section, with lamellae on two sides. The foot is broad anteriorly. No mantle glands are visible in any of the specimens.

Rudman (1987) initially synonymised Eliot’s species Chromodoris cavae with Kelaart’s Chromodoris tennentana (p. 44) but subsequently separated them into two species (http://www.seaslugforum.net/showall/chrotenn). Gosliner et al. (2008) retain this species as distinct from both Chromodoris tennentana and Chromodoris leopardus . Willan, based on 21 photographs on NudiPixel (http://www.nudipixel.net/species/chromodoris_tennentana/) decided that all variations belong to one species which is simply very variable from the western Indian Ocean to the West Pacific. However, the preserved specimens (including the one from Chagos, Yonow et al. 2002) are violet when preserved while all preserved tennentana (p. 44 and Yonow et al. 2002: 845) and leopardus ( Yonow 2001: 23) are translucent. The gills in tennentana are flattened and simply pinnate (see p. 44) or sub-quadrangular ( Rudman 1987: 364) while the gills of leopardus are triangular ( Rudman 1987: 388); the gills of cavae are triangular. The gills and rhinophores of tennentana are coloured ochre with white tips, those of leopardus are tipped in violet (the gills rarely have an ochre rachis), and those of cavae are violet or tipped with violet. No mantle glands are visible in the preserved specimens of cavae, whereas they are obvious in tennentana (p. 44 and Fig. 11) and form a band around the mantle in leopardus ( Rudman 1987).

Comparison of the radulae of tennentana, vicina, leopardus, cf. leopardus, and one La Réunion specimen show only slight variations in morphology but large differences in tooth size; the sizes listed are of the same dimension of a lateral tooth - from the tip of the cusp to the flange where the cusp meets the base.

20 mm alive (Rudman, tennentana) 40(+2) × 37.0.37 40 µm

36 mm alive (Edmunds, vicina = tennentana) 52 × 49.1.49 60 µm

59 mm alive (Rudman, leopardus) 74(+2) × 61.0.61 90 µm

34 mm alive (Yonow et al., cf. leopardus = cavae) 52 × 62.1.62 25 µm

80 mm alive (this paper, cavae) 58(+2) × 56.1.56 100µm

The three specimens examined from La Réunion belong to a form of Chromodoris cavae in which the violet mantle margin is lacking; of the additional photographs of a further 25 individuals from La Réunion and Mauritius (P Bidgrain, pers. comm., H. Flodrops, pers. comm., and http://seaslugs.free.fr/nudibranche/a_intro.htm) all but one individual lack the violet margin on both the mantle and the foot. The Chagos specimens both had a pale purple margin to the mantle ( Yonow et al. 2002) as did the individuals from Sri Lanka (Plate 38). Chromodoris cavae differs from both Chromodoris tennentana and Chromodoris leopardus in numerous features, all discussed above, and it is here removed from the synonymy of Chromodoris tennentana . Chromodoris cavae is recorded from Chagos, Sri Lanka, La Réunion, Zanzibar, and South Africa, indicating a western Indian Ocean distribution.