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

Gobiodon bicalvolineatus , new species

English name: Speckle-Lined Coral Goby ( Figs. 3, 4; Tables 2, 3)

Gobiodon sp. B ( Munday et al., 1999; Munday et al., 2004; Harold et al., 2008; Duchene et al., 2013; Herler et al., 2013) Gobiodon View in CoL new species ( Munday et al., 2004)

Holotype. AMS I.51465-001, 20.8 mm SL, Loloata Island , PNG, Indo-Pacific (9°32′30.7″S, 147°17′21.1″E), depth unknown, collected by P. Munday, 2002. GoogleMaps

Paratypes. 4 specimens, all from PNG collected by P. Munday in 2002. AMS I.51464-001, 17.6 mm SL, Loloata Island , (9°32′30.7″S, 147°17′21.1″E), depth unknown; AMS I.51464-002, 15.6 mm SL, Loloata Island ; QM I.41386, 19.2 mm SL, Loloata Island; AMS I.51464-005, 11.2 mm SL (juvenile), Loloata Island GoogleMaps .

Comparative material. Gobiodon aoyagii : AMS I.27364-003 (2 specimens), 20.7–28.0 mm SL, Coast of Amitori, Ryukyu Islands , Japan, collected by H. Kishimoto , 1977. AMS I.46140-001 (1 specimen), Sakinome Beach, Oshima Straits, Amami Island , Amami Group of Ryukyu Islands , Japan (28°11.2′N, 129°16′E), 2–3 m depths, 12 September 1989, collected by M. Aizawa. GoogleMaps AMS I.1944 -076-1 (2 specimens), 18.3–30.2 mm SL, Eagle Island , GBR, Australia, collected by AMS Lizard Island Team, 1975. AMS I.22953-006 (2 specimen), 23.2–26.5 mm SL, Cebu Aquatics (Aquarium specimens), Philippines, collected by E. Murdy , 1982.

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 specimen), 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 histrio : AMS I.35859-006 (1 specimen), 23.9 mm SL, Massao Island PNG, collected by K. Cole , 1994. AMS IA.2026 (1 specimen), 22.5 mm SL, Hayman Island , GBR, Australia, collected by E. H. Rainford , 2018. AMS I. 35906-001 (2 specimens), 30.6–31.4 mm SL, Riau Islands, Indonesia, collected by P. Ng , 1993. AMS I.21578-001 (2 specimens), 32.6–34.0 mm SL, Lizard Island , GBR, Australia, collected by D. Hoese and party, 1978. AMS I.20793-079 (1 specimen), 25.1 mm SL, Clack Island , Cape York, Australia, collected by Australian Institute of Marine Science Team, 1979. AMS I.22224-001 (1 specimen), Lizard Island , GBR, Australia, collected by D. Hoese , 1975. AMS I.11773-001 (1 specimen), 33.6 mm SL, Murray Island , Torres Strait, Australia, collected by Hedly and McCulloch , 1907.

Diagnosis. Dorsal-fin rays VI, I,10; anal-fin rays I,9–10; head and majority of body naked with some squamation on caudal peduncle; body slightly laterally compressed (body depth at pelvic-fin origin 40.6–45.3% SL), typically dorsal ventrally symmetrical, head rounded; mouth small with pronounced recurved lips; groove between isthmus and interopercle present; caudal peduncle relatively deep (15.5–18.6% SL); caudal fin long (22.1–29.3% of SL). Post symphysial teeth absent, triangular dentary with various sizes of jaw dentition. Elongate cheek papillae length exceeding width. Adults with blue-green base colouration and red markings on the face and body. Facial markings as vertical bars on cheek, small spots on dorsal surface of head and unbroken horizontal lines along the length of the body beginning post pectoral fin ( Fig. 2).

Description. Dorsal-fin rays VI, I,10; pectoral-fin rays 19; pelvic-fin rays I,5; anal-fin rays I,9–10 (I,9). Caudal-fin principal rays 9+8 or 9+9 (9+9), all branched and segmented; 6 procurrent caudal-fin rays above and below branched (all unbranched and unsegmented) ( Fig. 3). Vertebral 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 origin. Dorsal profile of head steep, strongly convex. Curved profile upon approach of lips. Snout protrudes beyond upper lip, produced curved head appearance of dorsal profile. Eyes positioned dorso-laterally. Interorbital width narrow with high variation (14.0–33.2% of HL). Cheek papillae longer than wide. No visible dark pigmentation on upper opercular margin. Pigmentation of interorbital region uniform. Deep groove between isthmus and interopercle present. Anterior margin of interopercle prolonged. Interopercle attach to retroarticular by short ligament. Interopercle shallow spear-like appearance. Dentary elongate and 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 to the uppermost point of pectoral fin base. Posterior end of first dorsal fin base above anus. Second dorsal fin origin just behind posterior most point of first dorsal fin, connected via low membrane. Second dorsal fin not quite reaching caudal fin. Anal fin origin posterior to urogenital papilla. Pectoral fins elongate and obliquely pointed to dorsal surface. Pelvic fins cup shaped, fused medially with well-developed connecting membrane. Pelvic fin posterior to pectoral fin base. Posterior point of pelvic fin not reaching behind anus. Caudal fin rounded but more elongate than congeners. Head scaleless. Body mostly naked. Squamation present on caudal peduncle, large weakly ctenoid or cycloid shaped in rows (1–3 rows).

Cephalic sensory system standard for Gobiodon ( Fig. 4). 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 bicalvolineatus is light blue-green with red vertical bars on the face, red spots and lighter diagonal bars on the dorsal surface of the head, oblique pale patch on cheek, and red thin unbroken horizontal lines along the length of the body. No black spot on opercular margin.

Colouration post preservation. All colouration lost upon preservation, with no remnants of the previously displayed colour. Uniformly light or dark brown. Lines on body and face are no longer visible ( Fig. 4).

Genetic analysis. Previous genetic analyses have shown G. bicalvolineatus to be a distinct species, with its sister species being G. aoyagii ( Munday et al., 2004; Duchene et al., 2013; Herler et al., 2013; Shibukawa et al., 2013). Gobiodon bicalvolineatus and G. aoyagii consistently form a clade, but neighbouring species on the phylogenetic tree can change depending on the genetic markers used. When only mitochondrial rRNA 12S and 16S markers are used, the pair fall out alongside G. fulvus and the clade containing G. ater , G. axillaris , and G. fuscoruber ( Herler et al., 2013) . With the addition of cytochrome b (mtDNA) and nDNA S711 to the original mitochondrial markers, the pair now fall in a clade with G. brochus and G. cobenjaminsis ( Duchene et al., 2013) . Unfortunately, the DNA sample used in our genetic analysis did not yield sufficient results for the COI gene for the species to be included in the current phylogenetic tree. However, the previous analyses do strongly confirm this species′ position within a clade including G. aoyagii , G. brochus , and G. cobenjaminsis ( Duchene et al., 2013) .

Haplotype analyses have also been conducted comparing the networks seen in G. bicalvolineatus , G. aoyagii , G. brochus , G. erythrospilus , and G. histrio ( Munday et al., 2004) . Ten individuals from each species were genetically analysed to view the haplotype network present. Gobiodon bicalvolineatus was observed with only two present haplotypes, compared to the five seen in sister species G. aoyagii and even greater variation seen in the other species. The lack of genetic variation was hypothesised to be due to a strong genetic bottleneck that may have resulted from a founder event from a coral host shift in a small population ( Munday et al., 2004). The low genetic diversity is not seen in the sister species G. aoyagii despite it also only occupying a single coral species, Acropora tenuis ( Dana, 1846) . However, the distribution of G. aoyagii and its host coral are considerably larger with better coverage density ( Munday et al., 2004).

Habitat. Gobiodon bicalvolineatus has only been recorded inhabiting the branching coral Acropora caroliniana Nemenzo, 1976 , making it highly specialised ( Munday et al., 1999). Up to ten juveniles and adults have been observed living in the same coral colony at once ( Munday et al., 2004).

Distribution. The species have been primarily recorded in waters surrounding Motupore and Loloata Islands in Bootless Bay in Papua New Guinea ( Munday et al., 1999; Munday et al., 2004). There was previously quite a large population recorded within this area ( Munday et al., 2004), but the current population numbers are unknown. An image of an individual observed in Kranket Lagoon in the Madang region of Papua New Guinea during an expedition in 1987 was also identified. However, the specimen could not be confirmed.

Etymology. The name is derived from the Latin for ‘two,’ ‘bald’ and ‘lined’, representing the two pale patches at the back of the head imitating baldness and the prominent lined pattern on the body.

Remarks. Gobiodon bicalvolineatus shares physical characteristics with several species within genus Gobiodon , sharing a relatively common appearance of a teal/green/ blue base colour with red markings with G. aoyagii , G. histrio , and G. erythrospilus . Despite this commonality in appearance, only G. aoyagii is a close genetic relative within the genus phylogeny. There are both obvious and discrete differences between the two sister species. Whilst the markings of G. bicalvolineatus are relatively regular lines, G. aoyagii has a completely opposing set of markings, with the majority being cleanly broken circular patterns. More discrete differences can be seen with G. bicalvolineatus having a less pronounced and shallower interopercle than G. aoyagii . The cheek papillae are also significantly more elongated on G. bicalvolineatus specimens. The distinct differences between G. bicalvolineatus and G. aoyagii were also identified and highlighted by Shibukawa et al. (2013) in the formal description of the latter species.

The horizontal red lines seen on G. bicalvolineatus are thinner and unbroken compared to those seen in G. histrio . Additionally, the absence of spots or dots amongst broken lines separates them from Gobiodon erythrospilus . Gobiodon bicalvolineatus also lacks the black spot on the opercular margin seen in G. histrio . The oblique pale patch on the cheek, faint pale lines on dorsal surface of head, and recurved lower lip are shared with G. brochus . However, the lack of red markings on G. brochus makes them easily distinguishable. Gobiodon bicalvolineatus has only been observed occupying a single species of host coral, Acropora caroliniana , and only within a very limited geographic location. Individuals matching the description have not been identified in any other location, further suggesting a very limited range. Surveys of cryptobenthic fish species have not been recently conducted within the known geographic range of this species, and thus very little is known about the population condition.