Phyllidiella striata ( Bergh, 1889 )

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 : 866-867

Phyllidiella striata ( Bergh, 1889)

(®gures 16f, 17b, 18a)

Phyllidiopsis striata Bergh, 1889: 866 , taf. 84, ®gures 23, 24.

Phyllidiopsis striata ? (sic.): Eliot, 1906a: 563.

Phyllidia nobilis: Edmunds, 1972: 79 (part), ®gures 3A, F.

Phyllidia empelia Yonow, 1984: 223 , ®gures 6, 7B, 8A, B (not P. zeylanica as per Brunckhorst, 1993).

Phyllidia mediocris Yonow and Hayward, 1991: 20 , ®gures 11C ±E, 13A (not P. rosans as per Brunckhorst, 1993).

Material. Chag96/2: 35 mm; inner reef, Ile Boddam, Salomon Atoll; 8 February 1996. Chag96/5: 18 mm; outer reef, Ile Anglais, Salomon Atoll; 10 February 1996; at 20 m depth. Chag96/8: 17 mm; outer reef, Ile Anglais, Salomon Atoll; 11 February 1996; at 8 m depth. Chag96/13 and Chag96/15: both 30 mm; inner reef between Ile Jacobin and Ile du Sel, Salomon Atoll; 12 February 1996; at 8 m and 12 m depth. Chag96/21 and Chag96/22: 26 mm and 21 mm; outer reef between Ile Boddam and Ile Poule, Salomon Atoll; 13 February 1996; at 15 m depth. Chag96/28: 26 mm; coral bommie inside Salomon Atoll; 13 February 1996; at 14 m depth. Chag96/38: 35 mm; coral bommie inside Ile Anglais, Salomon Atoll; 15 February 1996; at 12 m depth. Chag96/39d: 283 16 mm; Salomon Atoll; 13± 15 February 1996. Chag96/49: 283 12 mm; outside reef, Ile Diamante, Peros Banhos Atoll; 20 February 1996. Chag96/66: 293 8 mm; inner reef, Ile Monpatre, Peros Banhos Atoll; 25 February 1996; at 22 m depth.

Additional material. Le Morne, Mauritius, 183 5.5 mm; Grand Baie, Mauritius, 143 5 mm and 153 5 mm; Trou aux Biches, Mauritius, 18 mm (BMNH acc. no. 2350, Yonow and Hayward, 1991).

1mm

Description. Dorsum very long and thin. Three central pink tuberculate ridges, which may be broken, met behind the rhinophores; the two laterals were bent outwards to the rhinophores (®gure 16f). Single medial patch or ring of tubercles in front of the rhinophores; ring of tubercles behind the anus. First encompassing pink band may be a double row of tubercles; up to two more single rows of tubercles encircling mantle. Ventrally, the foot is pale and there is no black dusting on its top surface, although the gills are edged in black (®gure 17b). Additional internal characters are the dusty black band on the oral tube and a very thick pharynx; other details are as described for the genus ( Brunckhorst, 1993: 17). The swollen anus is black.

Geographic distribution. Western Indian Ocean: Sri Lanka (Yonow, 1984), Mauritius ( Bergh, 1889, Yonow and Hayward, 1991), Seychelles (Edmunds, 1972) and the Maldives ( Eliot, 1906a; R. C. Anderson, S. G. Buttress and N. Yonow, personal observations).

Remarks. The epithet Phyllidiella striata Bergh is correctly recognized for this species for the ®rst time since Eliot (1904a). The animal commonly called Phyllidiopsis striata is in fact Phyllidiopsis xishaensis (q.v. p. 870). Bergh’s ®gure (1889: pl. 84, ®gure 23) is identical to specimen 96/2 and both are reproduced here (®gures 16f and 18a, respectively). Eliot (1906a) recognized the similarities between his single specimen from the Maldives and Bergh’s ®gure and stated clearly that the foot and gills were lighter than the dorsum (unlike Phyllidiopsis xishaensis in which there is a black line on the hyponotum beneath the gills). Eliot described three white lines on a blackish dorsum and white patches at each end. This is similar to Bergh’s ®gure and to approximately 25 specimens recently collected from the Maldives (Yonow, unpublished). At present, we consider the variation within the species to be restricted to continuous or broken tuberculate pink ridges and either a patch or ring anteriorly; the posterior ring appears to be a constant feature in all specimens examined. Small specimens can be confused with Phyllidiella rosans but diOEer in having tuberculate ridges which are often broken, and lacking the black pigmentation on the foot and oral tentacles. Additionally, Phyllidiella striata is long and thin, while Phyllidiella rosans is broadly oval. There are several other pink and black specimens in this collection which are vaguely similar but do not have the above combination of characters; these will be considered in a further work. Bergh’ s species is re-established, and assigned to Phyllidiella , in part due to the presence of distinct oral tentacles which, as Bergh states, are`shorte r and plumper than those of Phyllidia varicosa ’ (trans., 1889: 866): these are certainly not a characteristic of Phyllidiopsis , which he de®ned as `brevissima a xa ’ ( Bergh, 1875: 661; 1876: 380). The pharynx of this Chagos specimen was exactly as in Brunckhorst’s (1993) ®gure of Phyllidiella pustulosa , the type species of the genus: a long thickened tube with a dorsal split, which con®rms this species as belonging to the genus Phyllidiella and not Phyllidiopsis . Of concern is the lack of glands on Bergh’s ®gure of the pharyngeal bulb (pl. 84, ®gure 24); however, these were very small and attached by extremely ®ne ducts in specimen 96/49; the arrangement of the digestive system was otherwise identical to that in Bergh’s ®gure.

Phyllidia empelia Yonow, 1984 is here reassigned to Phyllidiella striata: Brunckhorst (1993) correctly recognized it as Phyllidiella , but wrongly as Phyllidiella zeylanica (no colour slides of the Sri Lanka specimens exist, as stated by Brunckhorst, 1993). The elongated body shape, with anterior and posterior rings, and the rhinophores are characteristic of Phyllidiella striata and not Phyllidiella zeylanica (q.v. p. 868). The`pink tubercles tending to ridges’ are also characteristic of