Phyllidiella rosans (Bergh, 1873)

Yonow, Nathalie, Anderson, R. Charles & Buttress, Susan G., 2002, Opisthobranch molluscs from the Chagos Archipelago, Central Indian Ocean, Journal of Natural History 36 (7), pp. 831-882 : 864-865

Phyllidiella rosans (Bergh, 1873)

(®gures 16e, 17a)

Phyllidia nigra Pease, 1868: 80 , pl. 9, ®gure 5 (pre-occupied by P. nigra van Hasselt, 1824 ).

Phyllidia rosans Bergh, 1873b: 139 (67), pl. 9, ®gures 1±4, pl. 10, ®gures 1±18.

Phyllidia soria Marcus and Marcus, 1970: 174 , ®gures 53, 54.

Phyllidiella rosans: Brunckhorst, 1993: 56 , pl. 6a±D.

NOT Phyllidia bourgini Risbec, 1928: 57 , ®gure 2, pl. 1, ®gure 1; 1953: 12, ®gure 3 (same specimen as Risbec, 1928).

NOT Phyllidiopsis cf. striata: Edmunds, 1972: 83 (part), ®gures 3D, G. (as per Brunckhorst, 1993) (5 Phyllidiella zeylanica , q.v. p. 868).

NOT Phyllidia mediocris Yonow and Hayward, 1991: 20 , ®gures 11C±E, 13A (as per Brunckhorst, 1993) (5 Phyllidiella striata , q.v. p. 866).

Material. Chag96/9: 20 mm; outer reef, Ile Anglais, Salomon Atoll; 11 February

1996; at 12 m depth. Chag96/23: 17 mm; outer reef between Ile Boddam and Ile

1mm 1mm

(a) (b)

Poule, Salomon Atoll; 13 February 1996; at 10 m depth. Chag96/39a, b: 13 mm, 15 mm; Salomon Atoll; 13± 15 February 1996. Chag96/48a, b: 13 mm, 15 mm; outer reef, Ile Diamant, Peros Banhos Atoll; 20 February 1996; at 22 m depth. Chag96/72b: 163 6 mm; outer reef, Peros Banhos Atoll; 27 February 1996; coll. A. JolliOEe.

Description. Body with three longitudinal raised but smooth pink ridges and four black lines; surrounding low pink ridges up to three in number, coalescing anteriorly and posteriorly. The median extended to just in front of the rhinophores, where it expanded slightly. Rhinophores black with pink sheaths. Ventrally, most of the specimens had a dusting of black along the top edge of the foot, and a black patch on the posterior end of the sole. The head and oral tentacles were also dusted with black (®gure 17a).

Geographic distribution. Indo-West Paci®c: the Maldives and ReÂunion to Hawaii and Tahiti ( Brunckhorst, 1993).

Remarks. It appears that Phyllidiella rosans ( Bergh, 1873b) and Phyllidiella nigra (Pease, 1868) are not as tuberculate as their original descriptions indicated, and (with Phyllidiella soria Marcus and Marcus, 1970 ) are in fact one species originating from Tahiti. This species is characterized by the smooth pink ridges bearing a crest in larger specimens: three central longitudinal ones and up to three encompassing rings which converge anteriorly and posteriorly. Large specimens can be almost round in shape. The grey spots on the sole noted by Brunckhorst (1993) are concentrated submarginally, and there is frequently a black patch on the distal end of the sole. Brunckhorst (1993) had additional material from the Maldives and ReÂunion; certainly this species is extremely common in the Maldives (Yonow, unpublished). The specimens from Chagos range from 13 to 20 mm and are smaller than those from the Paci®c, which are 18±35 mm ( Brunckhorst, 1993). It is noteworthy that despite many earlier collections in the Indian Ocean, this species was only recently recorded, despite being abundant when present.