Gobiodon cobenjaminsis, Hildebrandt & & & & & Wong & Marian Y. L., 2024

Gobiodon cobenjaminsis , new species

English name: Russet Coral Goby ( Figs. 5, 6; Tables 4, 5)

Gobiodon sp. C ( Munday et al., 1999; Harold et al., 2008; Duchene et al., 2013; Herler et al., 2013)

Holotype. AMS I.51465-001, 16.0 mm SL, Shuman Island , PNG (5°17′34.3″ S, 150°05′23.3″ E), depth unknown, collected by P. Munday, 1998. GoogleMaps

Paratypes. 6 specimens from Wulai Island , PNG (5°21′02.4″S, 150°29′24.1″E) collected by P. Munday in 2002. AMS I.51466-001, 18.0 mm SL, depth unknown. AMS I.51466-002, 17.7 mm SL, depth unknown. AMS I.51466-003, 19.2 mm SL, depth unknown. AMS I.51466- 004, 17.7 mm SL, depth unknown. AMS I.51466-005, 17.7 mm SL, depth unknown. QM I.41387, 15.3 mm SL, depth unknown GoogleMaps . 2 specimens from Kimbe Bay , PNG (5°12′54.6″ S, 150°29′27.8″ E) collected by P. Munday in 1998. AMS I.51467-001, 19.2 mm SL, depth unknown. AMS I.51467- 002, 19.2 mm SL, depth unknown GoogleMaps .

Comparative material. Gobiodon brochus : AMS I.22186- 001 (1 specimen), 25.0 mm SL, Palfrey Island , GBR, Australia, collected by D. Hoese , 1975. AMS I.46739 (1 specimen), 21.0 mm SL, Ona Island , Tonga, collected by S. E. Reader , 2015. AMS I.35854-003 (2 specimens), 19.0- 19.3 mm SL, Madang, PNG, collected by K. Cole , 1994. AMS I.22187-001 (1 specimen), 23.8 mm SL, Palfrey Island , GBR, Australia, collected by D. Hoese , 1975. AMS I.22579-072, 18.5 mm SL, Escape Reef , GBR, Australia, collected by D. Hoese , 1981.

Gobiodon bicalvolineatus : AMS I.51465-001, 20.8 mm SL, Loloata Island, PNG, collected P. Munday, 2002. AMS I.51464-001, 17.6 mm SL, Loloata Island, PNG, collected P. Munday, 2002. AMS I.51464-002, 15.6 mm SL, Loloata Island, PNG, collected P. Munday, 2002. QM I.41386, 19.2 mm SL, Loloata Island, PNG, collected P. Munday, 2002. AMS I.51464-005, 11.2 mm SL (juvenile), Loloata Island, PNG, collected P. Munday, 2002.

Diagnosis. Dorsal-fin rays VI, I,10; anal-fin rays I,10; head and body naked; obvious groove between the isthmus and interopercle; body compressed and deep (depth at pelvic fin origin 39.4–45.0% of SL); head rounded in adults; dorsal fins fused with membrane. Caudal peduncle relatively deep (15.5–18.7% of SL); caudal fin long (22.2–29.3% of SL). Post symphysial teeth absent, dentary elongate and recurved; teeth of two to three various sizes in several rows. Cheek papillae elongate. Adult orange-brown in colour with black margins on all fins except pectoral fins. Black spot on the upper opercular margin ( Fig. 5). Fins lighter in colour than body, with lighter oblique patch on cheek and 3–4 lighter bands on facial area.

Description. Dorsal-fin rays VI, I,10; pectoral-fin rays 19; pelvic-fin rays I,5; anal-fin rays I, 10. Caudal-fin principal rays 9+9 or 8+8 (9+9), all branched and segmented; 5-6

procurrent rays above and below branched (all unbranched and unsegmented). Vertebrae count 26.

Head and body deep, ovoid, highly laterally compressed. Body depth maximum at pelvic fin origin. Reduced body depth at opercular margin and anal fin margin. Dorsal profile of head rounded and moderately steep. Eyes positioned dorso-laterally. Cheek papillae longer than wide. Visible dark pigmentation spot on upper opercular margin. Pigmentation of interorbital region uniform. Deep groove between isthmus and interopercle. Anterior margin of interopercle prolonged. Interopercle attached to retroarticular by short ligament. Interopercle shallow spear-like appearance. Dentary elongate recurved. Jaw dentition consists of two or three sizes. Post symphysial canine teeth absent. Multiple rows of teeth of varying sizes. Lacrimal shape elongate-narrow. Gill opening relatively narrow.

First dorsal fin origin located above or slightly anterior/ posterior to uppermost point of pectoral fin base. Posterior end of first dorsal fin base above anus. Second dorsal fin origin just behind posterior point of first dorsal fin. Dorsal fins connected via a high membrane, fused appearance. Second dorsal fin not quite reaching caudal fin. Anal fin origin posterior to urogenital papilla. Pectoral fins rounded. Pelvic fins cup shaped, fused medially with well-developed membrane. Pelvic fin posterior to pectoral fin base. Posterior point of pelvic fin not reaching behind anus. Caudal fin rounded. Head and body scaleless.

Cephalic sensory system standard for Gobiodon ( Fig. 6), consisting of anterior naris, posterior naris, first dorsal oculoscapular canal, second dorsal oculoscapular canal, three non-dorsal oculoscapular canals and three preopercular canals.

Colouration in life. Gobiodon cobenjaminsis is orange-brown in colouration during life. There are three to four lighter bands on the facial area. Pale oblique patch on cheek. Fins are slightly lighter in colour than the main body colour with a black margin and a pale line along the base of the dorsal fins. Black spot on the upper opercular margin.

Colouration post preservation. All colouration is lost upon preservation, with no remnants of the previously displayed colour. Uniformly light or dark brown. The only remaining colouration is seen in the preserved black spot on the upper opercular margin and the darker colouration on the edge of the fins ( Fig. 5).

Genetic analysis. The genetic analysis for this species has been conducted twice prior to this study. Depending on the genetic markers that were used to produce the phylogenetic tree, G. cobenjaminsis was placed in different clades within the genus. When 12S and 16S rRNA mitochondrial genes were used, G. cobenjaminsis is sister to the clade including G. okinawae , G. acicularis , G. ceramensis , and G. citrinus ( Herler et al., 2013) . However, with the addition of cytochrome b (mtDNA) and nDNA s711, the placement of G. cobenjaminsis differed ( Duchene et al., 2013). The closest sister species to G. cobenjaminsis is now G. brochus , G. aoyagii , and G. bicalvolineatus , in the same clade, while a separate adjacent clade contains the above-mentioned species seen in the Herler et al. (2013) analysis.

In this study, unfortunately G. bicalvolineatus could not be included in our phylogenetic analysis, so further confirmation of the phylogenetic relationship between G. cobenjaminsis and G. bicalvolineatus was not possible. However, our analysis does confirm the relatedness between G. cobenjaminsis and G. aoyagii / G. brochus , confirming the strong genetic signal between these species across genetic markers.

Habitat. Gobiodon cobenjaminsis has only been recorded inhabiting the coral Acropora elseyi ( Brook, 1892) , making the species highly specialised ( Munday et al., 1999).

Distribution. This species has only been recorded in the Kimbe Bay area of Papua New Guinea ( Munday et al., 1999).

Etymology. The name was chosen with the Latin “co” for ‘with’ or ‘together’ and the “benjaminsis”, with the “-sis” component derived from the Greek for a process or action, to honour the actions of the Benjamin family under the request of the specimen collector Phil Munday, especially Max Benjamin. This is due to their contribution in research, field station set-up, and marine conservation in Kimbe Bay, Papua New Guinea, that resulted in the observation and collection of this species.

Remarks. Whilst this species is closely related to G. brochus genetically, they only share limited physical characteristics and vary largely in colouration. Gobiodon cobenjaminsis has a dark pigmentation spot on the upper opercular margin, a key method for differentiation of the two species. This can be utilised for preserved specimens as the black spot on the upper opercular margin remains after the preservation process. The other major distinguishing feature is the differences in lacrimal shape; where G. cobenjaminsis is elongate and narrow, G. brochus has a more ventrally expanded lacrimal that is often triangular to quadrilateral in shape. The only other species that is known to occupy A. elseyi is G. brochus , which can be easily distinguished from G. cobenjaminsis .

This species can be easily distinguished from other genus members G. axillaris and G. atrangulatus , which may appear similar in base colouration to G. cobenjaminsis on occasion, by the lack of red markings on the face and at the base of the dorsal fins, the presence of distinctive black fin margins, fused first and second dorsal fin, and distinctive recurved lower lip observed in G. cobenjaminsis ( De Vis, 1884; Garman, 1903; Munday et al., 1999; Harold et al., 2008).

Gobiodon cobenjaminsis has a very limited range and restricted habitat niche, as it has only been observed in Acropora elseyi in Kimbe Bay, Papua New Guinea. The reasons for the limited distribution of G. cobenjaminsis are unknown, unlike its congener G. bicalvolineatus which has had genetic studies conducted focused on it ( Munday et al., 2004). Individuals matching the description of this species have not been identified elsewhere in the world. The combination of these factors makes estimating the species’ population status and relative rarity hard to determine.