Black Coralgoby
Figs. 5, 6, 10 & 11; Tables 1, 6, 7 & 10
Gobiodon sp. 2 Herler and Hilgers 2005: 121, Fig. 14; Niedermüller et al. (2009): 1501, Fig. 2; Herler et al. (2009): 733, Fig. 4.
Holotype. NMW 94612, female, 26.5 mm SL, Gulf of Aqaba, Egypt, Dahab, “Napoleon Reef” (28 ° 28 ’ 15 ” N, 34 ° 30 ’ 33 ” E), 1 m, coll. J. Herler, 18 November 2005.
Paratypes. Five specimens. NMW 94613, female, 26.4 mm SL, 14 November 2005, other data same as holotype. BMNH 2012.3. 20.1, male, 23.1 mm SL, other data same as NMW 94613. BMNH 2012.3. 20.2, female, 24.6 mm SL, other data same as NMW 94613. MNHN 2012 -0110, female, 25.4 mm SL, other data same as holotype. MNHN 2012 -0111, male, 15.9 mm SL, northern Red Sea, Egypt, Marsa Alam (25 °03’ 59 ’’ N, 34 ° 54 ’05’’ E), 1 m, coll. J. Herler, 29 November 2005.
Additional material. CH 232 - 42 -001, 18.2 mm SL, Egypt, Dahab, coll. J. Herler, 30 November 2003; CH 232 - 42 -003, 18.5 mm SL, Egypt, Dahab, coll. J. Herler, 26 May 2004; CH Mal 243 (DNA sample and photograph), 19.1 mm SL, Indian Ocean, Maldives, Gulhi Island, coll. J. Herler, 27 March 2007; CH Tai 0 0 7 (DNA sample), 18.2 mm SL, southern Taiwan, Kenting, coll. J. Herler, 0 4 December 2008.
Comparative material. Gobiodon ceramensis (Bleeker, 1853): OMNH P 34042 (Fig. 9 H), 35 mm SL, Japan, Ryukyu Islands, Ishigaki Island, coll. T. Suzuki and M. Suzuki, 17 August 1997.
Diagnosis. Dorsal-fin rays VI + I, 10; anal-fin rays I, 8; head and body naked; deep curved groove on isthmus; body and caudal peduncle slender (depth 37–41.2 % and 13.8–14.7 % SL, respectively); head rounded in juveniles, large adults slightly hump-headed. Juveniles and adults uniformly black, including iris. Very small species (<28 mm SL); females of breeding pairs usually significantly larger than males, smallest highly gravid female 18.5 mm SL.
Description (based on 6 types and several non-types (for osteology)). Large, compressed head; body rather cylindrical. Body proportions and meristics for types are provided in Tables 6 and 7, respectively. Unusual for the genus, the sexes differ in size: females of breeding pairs are usually significantly larger than the males. Dorsal-fin rays VI + I, 10 (n = 6); anal-fin rays I, 8 (n = 6); pectoral-fin rays 19 –20 (19:5, 20: 1); pelvic-fin rays I, 5; caudal fin with 16–17 branched and segmented rays. First dorsal-fin short and rounded. Second dorsal- and anal-fin with long posterior rays, rhomboid in shape. Pelvic disc well-developed, with frenum between spines. No scales. Gill opening as wide as pectoral-fin base, ending ventrally in opposite of 1 st or 2 nd lower pectoral-fin ray. Gill rakers 0– 1 + 6–7. Deep curved groove present between interopercle and isthmus. Mouth terminal, bending downwards posteriorly, upper jaw reaching to below anterior margin of orbit or mid-orbit. Upper lip more curved down than lower lip. A few rows of small, slender and recurved teeth in both jaws behind the outer row, which has 10 larger and slightly recurved teeth in upper and lower jaw. In lower jaw, one pair of large, postsymphysial canines on each side; one or both of these teeth often smaller or absent, probably due to tooth loss and replacement. Anterior and posterior nasal openings at the end of short tubes. Head sensory canals typical for Gobiodon (Winterbottom & Harold 2005), with anterior oculoscapular (pores NA (paired), AI, PI (unpaired), SO, AO and IT (paired)) and preopercular (three pores on each side) canals present.
Life colouration. Uniformly black, including iris; thus eye hardly visible in living fish in the field (Figs. 5 A, 6 A). When stressed, black colouration can turn into grey.
Preserved colouration. After formalin fixation and ethanol preservation, the general colour is dark brownishgrey to black, eyes opaque. Some patches on the cheek, pectoral and median fins may appear lighter (Fig. 5 B, 6 A, 6 C).
Molecular genetics. The present analysis includes the sequence of the a: paratype MNHN 2012 -0111 (as G.sp. 2 _RN 1) from the northern Red Sea (see Table 1 for Genbank accession numbers). Derived from the present analysis, the genetically closest species are G. axillaris and G. fuscoruber. The p -distance between G. ater and G. fuscoruber in the present study ranges from 0.023 to 0.032 (Table 10), making up a genetic difference of more than 2 %. Gobiodon axillaris seems genetically even closer to G. ater, but since the NJ-bootstrap value between the two was very low (21), this relationship is highly questionable and requires a more detailed genetic and morphological analysis.
Habitat. Gobiodon ater is highly specialized and prefers fine-branched corals such as Acropora selago and small tabulate colonies of A. hyacinthus. Less often, it also occurs in other Acropora species, such as A. acuminata, A. samoensis, A. eurystoma and A. valida (Dirnwoeber & Herler 2007). The species is found in shallow water regions such as protected reef flats and reef crests. Due to its black colouration it is sometimes difficult to detect this species within the dark interstices of narrow-branched Acropora colonies.
Distribution. So far this species is known from the Red Sea, the central Indian and the western Pacific Ocean.
Etymology. This species is named after its uniformly black life colouration (“ ater ” = Latin word for “black”), which even includes the eye. Suggested common name: Black Coralgoby.
Remarks. This species was designated as Gobiodon sp. 2 by Herler and Hilgers (2005) and these authors assumed that it may be identical with one of the other entirely black species from the western Pacific, in particular with G. ceramensis. The syntypes of G. ceramensis cannot be identified from the more than 100 specimens collected by Bleeker (Ronald de Ruiter, pers. comm.), but when compared with the original description of Bleeker (1853), G. ceramensis has a higher fin-ray A count (9–10 rays versus 8), a lower P count (17 versus 19–20) and larger eyes (25 versus 21 % of head length) than G. ater. The fin meristics of Bleeker (1853) are corroborated by specimens from Japan, which are considered to represent G. ceramensis (Fig. 9 H) by one of us (TS); these also have fin-ray counts of D 2 I, 10 and A I, 9, the range recorded by Bleeker (1853). Furthermore, according to Harold et al. (2008), G. ceramensis does not have a deep curved groove on isthmus, as it is present in G. ater. Other nominal species with an entirely black colouration (at least when adult) include G. heterospilos Bleeker 1856, G. spilophthalmus Fowler 1944, G. albolineatus Smith 1959, G. albofasciatus Sawada and Arai 1972, G. acicularis Harold and Winterbottom 1995, G. winterbottomi Suzuki, Yanao and Senou 2012 and a potentially new species from the Maldives (Herler et al. 2009; as G. sp. 4). Apart from the possibility that some of the four former species may be synonymous with each other, most of these species represent a genetical clade (tested for G. acicularis, G. ceramensis and G. spilophthalmus by Harold et al. 2008; Herler et al. 2009; Duchene et al. 2013 and herein (Fig. 11)), which is distant from G. ater and its genetically closest relatives G. fuscoruber and G. axillaris. Morphologically, G. ater differs from most members of the other genetic clade in that it is entirely black already when juvenile, and by a rounded first dorsal fin, shaped by a short first fin spine. By contrast, the first dorsal spine is the longest in several species of the other genetic clade. This results in a rather rectangular or even triangular first dorsal fin shape. Also typical for G. ater is the presence of a groove between interopercle and isthmus: a comparison with other species having such a groove is given in the remarks section of G. fuscoruber sp. nov. below. Gobiodon ater is genetically closely related to G. axillaris (Fig. 11, Duchene et al. 2013), although they have very different life colouration, and to G. fuscoruber sp. nov, to which it is phenotypically more similar. These species are in a clade together with another undescribed black species from the Indian Ocean (Gobiodon sp. 4, Herler et al. 2009), which has a very elongate body, and with G. histrio and G. erythrospilus Bleeker 1875. Considerable morphological similarities between G. ater and G. fuscoruber sp. nov. have also been revealed by the geometric morphometric analysis, in which the former in particular overlaps with western Pacific specimens of the latter (Fig. 10). MANOVA, however, confirmed significant shape differences between all three populations. Species discrimination was also supported by the PCA of body proportions of the Red Sea type specimens (adults only): G. ater mainly differs from G. fuscoruber sp. nov. by its longer abdomen (V—A: 30.6–34.3 versus 25.0– 29.8 % SL) and lower posterior body depth (D 2 —A: 29.5–32.3 versus 33.6–37.2 % SL). They can further be distinguished by life colour and maximum size. Inferred from this morphological comparison and from a previous, more elaborate genetic analysis (Herler et al. 2009) that included sequences of cytochrome b, it is evident that G. ater and G. fuscoruber sp. nov. are very closely related but distinct species. The genetic distance between the two species calculated herein exceeds the level of 2 % accepted for species delineation (Harold et al. 2008). The genetic distance to G. unicolor sensu Harold et al. (2008) from the Great Barrier Reef, being synonymous with G. fuscoruber sp. nov. (see below for details), is even greater (0.032).