Goniobranchus pseudodecorus, 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 : 19-22

Goniobranchus pseudodecorus sp. n. Figure 4 , Plate 7

Chromodoris maculosa - Eliot 1908: 108-109 (the beacon, Khor Dongola, Suakin, Sudan) (non Chromodoris maculosa Pease, 1871).

Chromodoris cf. decora Yonow, 1989: 294, pl. 4 (Creek, Jeddah, Saudi Arabia, Red Sea); Perrone and Doneddu 2001: 121-130, pl. 1 figs C, D (Naama Bay, Sharm el Sheikh, Egypt, Red Sea).

Glossodoris sp. 10 Debelius & Kuiter, 2007: 149 (Eilat, Israel, Red Sea).

Chromodoris sp. Yonow, 2008: 60, 186 (Jeddah, Eilat, Red Sea).

Type material.

HOLOTYPE SMF 349570: Hotel Zabargad, 120 km south of Marsa Alam, Egypt, Feb 2003, 16 mm alive (9 × 4 mm preserved), leg. and photographs J Hinterkircher. PARATYPE SMF 349571: Balena wreck, Hurghada, Egypt, 02 Aug 2012, 9 m depth, approx. 15 mm alive (10 × 3 mm preserved), leg. S Kahlbrock (SK # 19).

Other material.

Quseir , Egypt, July 2000, approx. 10 mm alive (6 × 2.5 mm preserved), leg. and photographs J Hinterkircher (jaw and radular preparations); Jeddah, Saudi Arabia, photographs only from 1980's, Pam Kemp, J Kuchinke, G Smith; Eilat, Israel, 18 Feb 2005, O Ledermann; near Hurghada, Egypt, 07 July 2012, 12 June 2016, S Kahlbrock .

Diagnosis.

Body shape rounded oblong anteriorly and rounded posteriorly. Opaque white pointed tail always longer than mantle. Dorsum translucent rose centrally and whiter marginally, with meandering longitudinal opaque white lines and round rose spots. Margin translucent orange with elongated opaque white patches.

Description.

The shape of this species is very distinctive: all photographs depict an elongated oval body of which the anterior margin is oblong and the posterior end is rounded (Plate 7 ). The pointed tail extends beyond the mantle, and is translucent white with an opaque white triangular marking centrally. The mantle is translucent rose with longitudinal interrupted opaque white lines and round pink spots that are ocellated with deeper rose. Around this area is a band of white patches that may be confluent, followed by a translucent orange band containing discrete white patches. The rhinophores are translucent orange with two inner opaque white areas; there are up to 12 lamellae and the translucent stalks issue from translucent, slightly raised sheaths. The 6-8 unipinnate gills are arranged in a simple circle; they are also translucent with opaque white cores; the orange pigment in the tips is within the translucent area.

The preserved specimens are not totally contracted, and still retain the opaque white lines on the dorsum; however, no coloured spots remain on any of the specimens. The almost black digestive gland within is clearly visible. The edges of the foot are slightly crumpled, squared anteriorly, and the oral tentacles are visible as swollen nipples (Figure 4A ). The anterior margin of the foot does not appear to be bilaminate. The 2012 specimen from Hurghada is aberrant in having two left rhinophores.

The notes made on the paratype on arrival read as follows: "dorsum dense, opaque dirty orange, glistening white lines, coloured areas still visible on rhinophores and gills (the latter were darker). Two left rhinophores but one right. Mantle margin distinct, separate, mantle glands visible posteriorly. Ventrally, the hyponotum a darker orange, foot lighter. Foot anterior margin angular with a slight median dent, large swollen oral tentacles."

The reproductive system is developed in the 6 mm specimen (collected in the summer), despite its being smaller than the types and the average recorded length, with ducts and glands clearly visible as well as the bursa copulatrix.

This same specimen has a radular formula of 27-28 × 28-33.1.33-28. There is a small (up to 15 µm long) central triangular tooth medially, crowded by the first lateral teeth (Figure 4B ). The first lateral is twisted on itself, with one or two large denticles medially and a row of four small saw-like denticles laterally (Figure 4B ). The length of the cusp increases quickly to approximately tooth 9 as does the number of denticles, also to nine. In this region, the twist of the cusp is still pronounced and forms a small knob at the top of the root/cusp junction. At approximately tooth number 13-15 until the last five teeth, the cusps are somewhat straighter on the root with a pronounced knob on the top (Figure 4C ); the denticles are saw-like. The last five teeth are stacked together and very reduced in size, flattened plates tapering towards the end with few denticles (Figure 4C ).

The jaws are composed of curved rodlets. These are bifid on the tip, with one denticle being much smaller than the other (Figure 4D ).

Remarks.

Although Eliot (1908) compares his specimen to Chromodoris maculosa Pease, subsequent records have shown it to be quite different and consistently so over time. Goniobranchus pseudodecorus sp. n. has been recorded from the Red Sea a number of times ( Yonow 1989, Perrone and Doneddu 2001, http://www.seaslugforum.net/find/13213, Yonow 2008). Goniobranchus decorus (Pease), to which this species has been compared, does not occur in the Red Sea but has a western Pacific distribution: it is similar to G. pseudodecorus sp. n. in having a translucent orange margin and pointed white foot, but there are different white markings on the dorsum, large purple patches in the orange and white marginal bands, and the rhinophore pigmentation is without banding. The body is not so obviously angular anteriorly as in G. pseudodecorus sp. n. The radular formula of a 16 mm-preserved specimen from Australia is 52 (+3) × 48.0.48 and the teeth vary similarly along the row ( Rudman 1986b: 331).

Distribution.

Endemic to the Red Sea. The first record of this species is by Eliot (1908) from the Sudanese Red Sea in which he describes the same obvious characters of shape and colour: "Elongated and rather flat: mantle broad, especially over head. Foot ends in sharp point projecting … Gills small and thick, seven in number, simply pinnate, the two hindmost smaller. … Colour translucent greyish pink. … broad undefined band of opaque white, and outside, bordering the mantle, a broad transparent orange-yellow line interrupted by opaque white spots along the edge." The species is clearly endemic to the Red Sea, and I suspect that the Maldives locality of the second photograph in Debelius and Kuiter (2008) is erroneous.

Derivatio nominis.

An unimaginative name alluding to the similarities with Goniobranchus decorus .

Figures

Figure 4. Goniobranchus pseudodecorus sp. n. A ventral view of anterior showing head, oral tentacles, and foot margin B midline area from the anterior portion of the radula C lateral teeth from the anterior section of the radula D jaw rodlets.

Plate 7. Goniobranchus pseudodecorus sp. n., photograph S Kahlbrock (non-type).