Glossodoris kahlbrocki, Yonow, 2018

Yonow, Nathalie, 2018, Red Sea Opisthobranchia 5: new species and new records of chromodorids from the Red Sea (Heterobranchia, Nudibranchia, Chromodorididae), ZooKeys 770, pp. 9-42 : 13-18

Glossodoris kahlbrocki sp. n. Figure 2 , Plate 5

Glossodoris sp. 10 Debelius and Kuiter 2007: 189 (El Quseir, Egyptian Red Sea).

Glossodoris sp. 6 Gosliner et al. 2008: 238 (Red Sea).

Glossodoris sp. nov. Yonow 2015: fig. 540, fig. 21 (holotype; Hurghada, Red Sea).

Type material.

HOLOTYPE SMF 349567: Dahara Wadi Gimal, near Hurghada, Egypt, 18 May 2010, 13 m depth, one specimen 25 × 10 mm preserved, leg. and photographs S Kahlbrock. PARATYPE SMF 349568: Dahara Wadi Gimal, near Hurghada, Egypt, 10 Jul 2012, 10 m depth, one specimen approx. 40 mm alive (27 × 10 mm preserved, bent), leg. and photographs S Kahlbrock (SK # 6). PARATYPE SMF 349569: Dahara Wadi Gimal, near Hurghada, Egypt, 13 Oct 2016, 12 m depth on rock during night dive, one spcm 15 × 9 mm preserved, leg. and photographs S Kahlbrock (SK # 3; radular and jaw preparations).

Other material.

The Creek, Jeddah, Saudi Arabia, 1970s, photographs of one individual only, W Pridgen (Plate 5 ).

Diagnosis.

Uniformly white to cream mantle with no markings. Mantle colour bleeding into a more opaque white submargin. Bright blue border same thickness as opaque white band with clear distinct boundaries on both sides. Thin marginal line deep blue to black, present on both dorsal and ventral surfaces. Gills and rhinophores white, gill lamellae may tend to ochre.

Description.

This distinctive glossodorid is essentially white with a bright blue margin. The marginal pigmentation is identical in all three specimens (and the few available photographs, see Material above), and present on both sides of the mantle margin: an opaque creamy white band is followed by a light blue band and a deep blue to black marginal line. The gills are retracted into a small pocket in all but one photograph: in only one photograph of a series of photographs of the paratype specimen, the nine gills are extended: they are unipinnate with white rachides and ochre lamellae; in Plate 5 they are also extended and number at least five. They are arranged in a circlet and the last two gills are smallest. The rhinophores are tall and parallel-sided, white with faintly ochre lamellae: there are 21 lamellae in the paratype and 18 lamellae can be counted on the photograph of the 2016 non-type specimen. The rim of the rhinophore pocket is barely raised above the notum.

The body is solid and the thick mantle margin is held in three permanent folds. The hyponotum and top of the foot are identical in colour to the mantle, and there is no colour what-so-ever on the foot margin or oral tentacles.

The preserved holotype is fairly well relaxed and soft. It is elongated and slightly tapered at each end. The dorsum is of almost equal width and height. The mantle margin is very thin and flexible, with the permanent folds visible in the photographs present only as undulations. The foot is much longer than the mantle, and the posterior end is curled over the dorsum. The gill and rhinophore pockets are visible only as puckered holes. Viewed dorsally, the notum is pale pinkish white, the mantle margin is translucent cream. The digestive gland is visible as a dark patch halfway along the body to the left. In ventral view, it is visible as a large sphere spanning the width and depth of the body, therefore visible both dorsally and ventrally. The anterior margin of the foot is rounded and bilaminate; neither lamina is notched. The oral tentacles are two simple swellings each with a terminal nipple (Figure 2A ). The type specimens are identical in their preserved states, but the smallest third specimen has a proportionately larger mantle margin. There is no hint of the blue margins on any of the preserved specimens except where the mantle was folded over in the paratype. Mantle glands are visible in a submarginal band on the posterior half of the mantle of the paratype (which also has the front of the foot and head partly damaged).

The reproductive organs of the small 15 mm preserved specimen dissected for the radula preparation were in a relatively underdeveloped state. This is not unexpected as the type specimens are twice the size.

The radular formula of the small specimen is 55 × ~60.0.~60. There is no central tooth in the row; the first tooth in each row bears five or six small rounded denticles on the inner face of the curved cusp (Figure 2B ). The remaining teeth have a straight root, longer than the cusp, and a small projection on the top. The teeth are the same shape and dimensions along the row until the last four or five, where they become very reduced in size and stacked in a line (Figure 2C ).

The jaws comprise curved rodlets that are conical at the tips, which taper abruptly. They are relatively long, nearly 80 µm in length (Figure 2D ).

Remarks.

There is absolutely no species of chromodorid resembling this new species, in either the Red Sea or the western Indian Ocean: the pure white dorsum with startling blue marginal bands is unique.

Distribution.

Endemic to the Red Sea. The first photograph of this species was taken in the 1970s, in the vicinity of Jeddah, Saudi Arabia (see Material above). Since then, it has only been photographed a few times, indicating its rarity in the Red Sea: the collected specimens are from the same locality years apart. Despite the numerous books and websites on nudibranchs, there are no records of this distinctive species anywhere else in the world.

Derivatio nominis.

This species is in honour of Sven Kahlbrock, who searched many years for specimens of this beautiful but rare species. In addition, he has tirelessly supplied photographic records and many specimens in the last eight years.

Figures

Figure 2. Glossodoris kahlbrocki sp. n. A ventral view of anterior showing head, oral tentacles, and foot margin B midline area from the posterior portion of the radula C lateral teeth from the middle section of the radula D jaw rodlets.

Plate 5. Glossodoris kahlbrocki sp. n., photograph E Pridgen (non-type).