Phyllidiella zeylanica (Kelaart, 1858)

Yonow, Nathalie, 2020, Red Sea Opisthobranchia 6: Phyllidiidae and their paradorid mimic: new species and new records (Heterobranchia, Nudibranchia, Doridina), ZooKeys 1006, pp. 1-34 : 1

Phyllidiella zeylanica (Kelaart, 1858) Plates 4-8 ; Figures 3-6

Phyllidia zeylanicus Kelaart, 1858: 120 (Sri Lanka).

Phyllidiella zeylanica : - Yonow 1996: 502, fig. 10A-G (Maldives, Seychelles, Thailand); Yonow et al. 2002: 868, fig. 19a (Chagos); Domínguez et al. 2007: 105, fig. 12 (Papua New Guinea); Yonow 2012: 71, pls 72, 73 (Seychelles. Maldives, Sri Lanka) and references therein.

Material.

Egypt - Hurghada. Sept 2009, one specimen 10 × 5 mm (pres., alcohol), leg. and photograph S. Kahlbrock; Sha’ab Dorfa, 07 Sept 2010, 14 m depth, one specimen 10 × 5 mm (pres., alcohol), leg. and photograph S. Kahlbrock; 2014, one specimen 13 × 6 mm (pres., formaldehyde), leg. S. Kahlbrock; April 2015, one specimen 9 × 5 mm (pres., alcohol), leg. S. Kahlbrock; Abu Kafan, 14 July 2015, 7 m depth, one specimen 10.5 × 4 mm (pres., alcohol), leg. and photographs S. Kahlbrock (SK #13).

Photographic records.

Egypt - Hurghada, 16 July and 15 Aug 2010, three individuals, photographs S. Kahlbrock; Dahab, 2017, photographs of one individual, C. von Mach (H. Blatterer, Vienna, pers. comm.).

Description.

These five specimens and the additional photographs all bear a single dorsal black band enclosing both the rhinophores and the anal orifice (Plates 4-8 , Figs 3A-6A ); it is not quite complete in one specimen and bears a transverse mark in three specimens (Plates 4 , 5 , Figs 3A , 4A ). Critically, in all five specimens, the anterior section of this black band is squared, a feature unique to this species. All specimens bear a second thin black line submarginally and faint black markings within the central black ring. The individual tubercles in the central black ‘square’ and the multiple tubercles in the wide marginal pink band are as described previously: the pink areas are tuberculate with some faint or distinct black markings between them. Between the two black rings is a double or triple row of tubercles, which appears to be another diagnostic character of P. zeylanica . The thin mantle margin is pink. The rhinophores are long and straight in all photographs, black with a white stalk and few white lower lamellae. Photographs of three individuals are also similar and clearly identifiable; the one with slightly higher and more defined tubercles is probably larger than the others (Plate 8 ), virtually identical to the specimen illustrated from the Maldives ( Yonow 2012: pl. 73) that measured 38 mm in length.

None of the preserved specimens were relaxed before preservation, but they are moderately flat with the margins slightly curled (as reported previously for preserved specimens) and their rhinophores are all retracted. Of the photographic series of living specimens, SK #13 has a few that are focused on the rhinophores, and there are 12-14 lamellae on each clavus with the lower three or four lamellae being white. This lower white portion is visible on all photographs of all animals even if they are not sharp enough to count the individual lamellae. Ventrally, the foot sole has no black line nor are there any other markings on it or on the hyponotum (Figs 3B , 4B , 5B , 6B ). In four specimens the anterior foot margin is notched and the margin and ‘lips’ are separated with the triangular oral tentacles set at an angle. In one less relaxed specimen, the ‘lips’ and margin are contracted around the mouth. In three specimens (Figs 3B , 4B , 5B ), black pigment is visible on the oral tentacles.

Remarks.

A careful search of all photographic records in the author’s archives from Pam Kemp, Woody Pridgen, and Jürgen Kuchinke who were in Saudi Arabia and diving during the 1980s revealed no photographs of Phyllidiella zeylanica ; size is presumably not the issue as they all had photographs of Phyllidia dautzenbergi Vayssière, 1912 (<20 mm alive), which is similarly small. Is it reasonable to conclude that Phyllidiella zeylanica is a recent migrant? Given that there is no previous photographic evidence of this species in the Red Sea, in this work, it is considered a recent introduction from the Indian Ocean, where it is frequently recorded. Some authors (e.g., Brunckhorst 1993, Gosliner et al. 2008) have a different view on the identity of P. zeylanica based on Pacific specimens, but to date, having examined hundreds of specimens of species of phyllidiids from both the Indian Ocean and the West Pacific, this consistent colour pattern bears no resemblance to some specimens in the author’s collection from the Indian Ocean, currently unidentified, whose dorsal patterns match those illustrated by Brunckhorst (1993) and Gosliner et al. (2008) identified as P. zeylanica . Given these external morphological differences, these are not simply much larger specimens of P. zeylanica . Domínguez et al. (2007) recorded P. zeylanica from Papua New Guinea which has the same dorsal pattern, and anterior foot with prominent ‘lips’ and triangular tentacles so the species is known to occur in the western Pacific. However, neither Domínguez et al. (2007) nor Brunckhorst (1993) described the black tips on the oral tentacles for P. zeylanica as they did for ' P. pustulosa '.

Figures

Plates 4 - 8. Phyllidiella zeylanica, variations in dorsal pattern 4 Hurghada, April 2009 5 Abu Kafan, 14 July 2015, SK 13 6 - 8 three individuals not collected, near Hurghada (all photographs S. Kahlbrock).

Figures 3 - 6. Phyllidiella zeylanica, four specimens. Upper row (A) showing the dorsal pattern and lower row (B) illustrating their ventral sides 3 Hurghada, April 2009, S. Kahlbrock 4 Abu Kafan, 14 July 2015, S. Kahlbrock SK 13 5 near Hurghada, 2014, S. Kahlbrock 6 Hurghada, April 2015, S. Kahlbrock.