Glossogobius mahalonensis, Hoese & Hadiaty & Herder, 2015

Hoese, Douglass F., Hadiaty, Renny Kurnia & Herder, Fabian, 2015, Review of the dwarf Glossogobius lacking head pores from the Malili lakes, Sulawesi, with a discussion of the definition of the genus., Raffles Bulletin of Zoology 63, pp. 14-26 : 17-20

Glossogobius mahalonensis , new species

(English common name: Mahalona Bluefin Goby)

( Figs. 4 A–E, Table 1 )

Material examined. Holotype: MZB 21382, (50 mm SL), male, Indonesia, Sulawesi, South Sulawesi Province, Lake Mahalona, inshore habitat of north-western Lake Mahalona at 2°34.751’S, 121°29.068’E, Larona (Malili Lakes) drainage, F. Herder & A. Nolte, 28 November 2002 . Paratypes: (all collected with the holotype, except for ZRC specimen) - AMS I.46210-001, 50 mm SL female; AMS I.46210-002, 46 mm SL female ; MZB 22199, females (43 mm SL, 44 mm SL, 48 mm SL, 49 mm SL, 49 mm SL) and males (47 mm SL, 52 mm SL) ; NTM S.17645-001, 48 mm SL female; SAMA F. 13953, 43 mm SL female; ZFMK 67403, 56 mm SL male; ZFMK 67404, 48 mm SL female; ZFMK 67405, 50 mm SL female; ZFMK 67406, 44 mm SL female; ZFMK 67407, 47 mm SL female; ZFMK 67408, 52 mm SL female; ZFMK 67527, 50 mm SL male; ZFMK 67528, 47 mm SL female; ZFMK 67529 47.7 mm SL female ; ZFMK 67530 , 54.7 mm SL female ; ZFMK 67531, 49 mm SL female; ZRC 45757, 50 mm SL male, D. Wowor et al., 27 January 2010 ; ZSM 43116, 47 mm SL male .

Additional non-type material. The following specimens are excluded from the type series due to abnormalities, data not recorded or poor condition of specimens: ZFMK 56307 , 1 (56) ; ZFMK 67409, 47 mm SL; MZB 22110 , 50 mm SL, 44 mm SL, 52mm SL; ZFMK 56308, 34 mm SL, all collected with the holotype .

Diagnosis. A species of Glossogobius lacking all head pores, with mental fraenum indistinct and covered by sensory papillae; cheek naked; operculum with few embedded small scales dorsally; predorsal scaled to near eye; pectoral base scaled; prepelvic area partly scaled, naked anteriorly; second dorsal fin-rays usually I,9; anal-fin rays usually I,8; pectoral rays 14–16; predorsal scale count 17–24; pelvic fin oval, length about twice width, rays not thickened; gill opening broad, reaching to a point below end of pupil to posterior end of eye; midsides with horizontally elongate small brown spots (smaller than pupil length) forming a broken horizontal line, often indistinct, not visible in dark specimens; first dorsal fin blue in life; cheek papilla lines composed of multiple rows of papillae, forming distinct lines.

Description. Based on 28 specimens, 42–56.6 mm SL. First dorsal spines 6(28*); second dorsal rays I,8(3), I,9(25*); anal rays I,7(1), I,8(27*); pectoral-fin rays 14(5), 15(16), 16(9*); gill rakers on outer face of first arch 1+1+7(4), 1+1+8(2), 1+1+9(4), 2+0+8(1); gill rakers on outer face of second arch 0+7(9), 0+8(4); segmented caudal-fin rays 17(32*); branched caudal rays 6/6(28*); vertebrae 10+17(13); predorsal scale count 17(1), 18(1), 19(4), 20(1), 21(4*), 22(5), 23(5), 24(3); longitudinal scale count 27(1), 22(2), 28(2), 29(18*), 30(8), 31(1); transverse scale count (TRB) 8.5(1), 9(5), 9.5(8), 10(4), 10.5(12*).

Head slightly compressed, depth subequal to width at posterior preopercular. Cheeks not bulbous. Interorbital narrow, about three-quarters pupil diameter. Snout elongate, acutely pointed in dorsal view, slightly concave in side view, with distinct hump formed by ascending processes of premaxilla. No small bump below anterior nostrils. Anterior nostril at end of short tube, just above and almost in contact with upper lip. Posterior nostril a large pore just above and behind anterior nostril and separated by 1–2 posterior nostril diameters from anterior nostril. Posterior preopercular margin without spine or bony projection. Preoperculum short, distance from end of eye to upper posterior preopercular margin less than eye length. Mental fraenum indistinct without fleshy projections. Mouth moderate; reaching to below or just behind anterior margin of pupil; jaws forming an angle of 15–25° with body axis, upper margin of upper jaw in line with lower quarter of eye. Postorbital long, distance from end of eye to posteriormost margin of operculum subequal to distance from tip of snout to middle to posterior margin of pupil. Gill opening very broad reaching to below a posterior quarter of pupil to near posterior end of eye, well before posterior preopercular margin. Teeth in upper jaw: outer row of teeth conical, enlarged and wide set, three-five inner rows of smaller depressible, inwardly directed teeth, innermost row larger than middle rows. Teeth in lower jaw: teeth in outer row conical, slightly enlarged and wideset anteriorly to about half of dentary, two-three inner rows of smaller depressible teeth. Basihyal tip bilobed. Gill rakers on outer face of first arch short and broad, becoming smaller anteriorly; subequal to or slightly shorter than filament length below each raker, anterior part of arch connected to inner face of gill cover without rakers. Rakers on inner face of first arch and other arches short and denticulate. Predorsal area scaled forward almost to eyes at sides of nape, with large triangular naked area between dorsoposterior margins of eyes. Cheek naked. Operculum with 2–4 rows of scales near dorsal margin. Pectoral base covered with small cycloid scales, two rows dorsally and three ventrally in about 13 vertical rows. Prepelvic fully scaled to isthmus where opercula meet, some specimens with a small naked patch where opercula meet. Belly fully scaled, with scales on midline cycloid. Body covered mostly with large ctenoid scales, cycloid on predorsal area before a line from dorsal origin to upper pectoral fin insertion, one row of scales below dorsal fins cycloid, pectoral base, scales on prepelvic area and 3–4 rows on midline of belly cycloid. Body slender. First dorsal fin with second dorsal spine usually prolonged into a filament in both sexes reaching from third segmented dorsal ray in second dorsal fin to basal quarter of caudal fin; one male with deformed and poorly developed second spine not prolonged. Second dorsal fin subequal in height to first spine in first dorsal fin. Anal fin subequal in height to dorsal fins. Pectoral fin with pointed to acutely rounded margin, reaching to or just beyond anus. Pelvic disc oval, rays not thickened, length of fin 1.5–2 times greater than width; pelvic rays with few dichotomous branches, fifth ray with 4 terminal tips; fin reaching to or slightly behind anus.

Head pores. Absent.

Sensory papillae. A line of papillae along posterior margin of eye, extending between eyes, often becoming two rows of papillae or each side, meeting Line 1 before eye. Line 1 (medial to nostril), continuous with interorbital lines, expanding near lip into multiple rows, curving toward midline. Line 2 (medially between nostrils) absent. A transverse line behind each eye. Inner preopercular mandibular line composed of 2–3 rows of papillae along lower jaw. Other papillae not discernible, due to fixation in alcohol, but some scattered papillae on cheek suggest a pattern similar to that of G. flavipinnis .

Colouration in alcohol. Colouration variable. Head and body uniformly light to dark brown, without distinctive markings on body or with small faint dark brown spots on midside, spots normally covering only a single scale row, but extending onto two or more longitudinal scales, forming a faint stripe on the midside in some specimens; spot much smaller than eye diameter; first spot below first dorsal fin, second below front of second dorsal fin, third spot below end of first dorsal fin, fourth spot and in some specimens a fifth spot on caudal peduncle and last at end of caudal peduncle extending onto caudal fin base; spots on side in many specimens run together and number of spots variable. Head usually with a dark brown stripe (less than pupil diameter in depth), extending from anteroventral margin of eye to near upper lip. Head uniformly coloured or often with a stripe from anteroventral margin of eye to middle of upper lip; some specimens with large irregularly shaped blotches, one below anterior half of eye, but above horizontal line from posterior tip of lower jaw and second composed of small brown spots extending obliquely downward and posteriorly from posterior quarter of eye, reaching posterior end of preoperculum in some specimens; operculum in some specimens with faint brown blotches and some specimens with a dark mark on anterodorsal margin of opercular membrane. Branchiostegal membranes externally pale to dark brown in both sexes. Pectoral fin base dark brown dorsally, forming a horizontal stripe in most specimens, extending onto anterior bases of pectoral-fin rays; followed ventrally by a light brown stripe, curving anteroventrally on pectoral fin base and with a dark brown spot ventrally extending onto anterior parts of ventral pectoral-fin rays.

Life colouration. See Fig. 4a . Life colouration similar to colour in alcohol; head and body uniformly light brown to light reddish brown, belly white. The small faint lateral spots are dark brown to reddish brown, the stripe on head from anterorventral margin of eye to middle of upper lip dark brown; irregularly shaped dark brown blotches on lateral head. Eye brown, iris black. Membranes of unpaired fins hyaline to light brownish. First fin ray and the prolonged part of the second fin ray in first dorsal fin dark reddish brown, following fin rays in first and second dorsal fin hyaline to light brownish with 5 to 6 rows of small dark reddish brown spots. Spots more distinct in first than in second dorsal fin. Rays in caudal and anal fin reddish brown. Anal fin with conspicuous bluish iridescent sheen. Pectoral fin membranes light yellowish hyaline, pectoral fin rays faint blackish. Pelvic disc membranes hyaline, pelvic rays hyaline to light grey.

Distribution and habitat. The species is known only from the specimens examined here. It is endemic to Lake Mahalona, and has so far only been recorded at a single site at the north-western shoreline of the lake on 28 November 2002. The type locality is a moderately steep inshore habitat characterised by mangroves over gravel substrate in the shallows, turning to predominantly rocks alternating with sand and mud in about two meters depth. In addition to gravel, rocks and submerged branches and roots of mangroves in the shallows, the habitat was also structured by submerged dead wood, especially in less than two meters depth. At time of sampling, the water was rather cloudy compared to other habitats in the Malili Lakes, with only a few meters visibility. Glossogobius mahalonensis was recorded and caught in the shallows down to approximately two meters depth, but not present in depths between two and 12 m, the maximum depth visited by diving at this site. Sympatric fish species recorded are the sailfin silversides Telmatherina celebensis , Paratherina striata and P. wolterecki , the ricefish Oryzias marmoratus , and the gobies Mugilogobius latifrons , M. rexi , and another two species of Glossogobius ( G. intermedius and G. matanensis ).

Similarity to other species. This species is most similar to G. flavipinnis in lacking all head pores and in having the anterior nostril almost in contact with the upper lip. These are the two smallest sized species from the Malilli Lakes with a maximum size of 56 mm SL. This species differs from G. flavipinnis in having more numerous second dorsal and anal rays (second dorsal rays usually I,9, versus usually I,8, anal rays usually I,8 versus I,7), the second dorsal filamentous in females and when present, and small horizontally elongate spot on the midside, rather than round spots.

Etymology. Named for the type locality Lake Mahalona, Sulawesi.

Remarks. Meeting expectations arising from Aurich’s notions on the “stupidity” of dwarf Glossogobius in the Malili Lakes (see above), G. mahalonensis could even be caught by hand. This behaviour clearly exceeded observations in G. flavipinnis , the type species of (the non-valid) genus Stupidogobius – G. mahalonensis were at the time of sampling much more easy to obtain than the shyer G. flavipinnis .

Figures

Fig. 4. Glossogobius mahalonensis, new species. A, life specimen, directly after catch; B, MZB 21382, holotype, male, 50 mm SL; C, ZFMK 67404, paratype, 48 mm SL, female; D, radiograph of MZB 21382, holotype; E, radiograph of ZFMK 67404, paratype.