Nemateleotris Fowler, 1938

Tea, Yi-Kai & Larson, Helen K., 2023, Synopsis of the ptereleotrine goby genus Nemateleotris, with description of a new species from the western and central Pacific Ocean (Teleostei: Gobiidae), Raffles Bulletin of Zoology 71, pp. 248-266 : 251-253

Genus Nemateleotris Fowler, 1938

Nemateleotris Fowler, 1938: 131 (type species Nemateleotris magnifica Fowler , by original designation).

Diagnosis. Nemateleotris is readily distinguished from all other gobioid genera in having the following combination of characters: dorsal-fin rays VI, I,27–33; first three dorsal-fin spines elongate and pennant like, filamentous in one species, first spine longest, 1.4–3.9 in SL; anal-fin rays I,25–32; pectoral-fin rays 18–21 (usually 20); pelvic-fin rays I,5; pelvic fins separate, not connected to each other by frenum or to body by membrane; total caudal-fin rays 37–45; scales in longitudinal series 110–190; no visible lateral line; total gill rakers 19–25; branchiostegal rays 5.

Description. Dorsal-fin rays VI, I,27–33, all segmented rays unbranched; anal-fin rays I,25–32, all segmented rays unbranched; pectoral-fin rays 18–21, upper and lowermost 3–4 unbranched, all other rays usually branched (sometimes all rays unbranched); pelvic-fin rays I,5; segmented caudalfin rays 17; upper procurrent caudal-fin rays 9–14; lower procurrent caudal-fin rays 10–14; total gill rakers = 19–25.

Mouth strongly oblique, forming an angle of about 50° to horizontal axis of body; maxilla reaching a vertical through centre of eye; upper jaw with an outer row of four to six, widely spaced, moderately large, incurved canines on each side, and a medial band of small villiform teeth that narrows posteriorly; lower jaw slightly protruding when mouth closed, with two to four enlarged recurved canines at corner of each side of jaw, the more posterior tooth largest, a middle band composed of two to four rows of low villiform teeth narrowing to a single row posteriorly, and an inner pair of enlarged recurved canines at front corner of each side; no teeth on vomer or palatines; tongue truncate, set far back in mouth.

A low median fleshy ridge on top of head from interorbital space to origin of first dorsal fin; no opercular or preopercular spines; preopercular margin free only ventrally; upper end of gill opening at or slightly dorsal to level of middle of eye, the ventral end extending to below posterior margin of preopercle; anterior and posterior nasal pores separated by a distance about equal to half the pupil diameter; anterior nasal pore small, rounded and terminating in a short fleshy tube; posterior nasal pore larger, rounded, with little or no rim.

No visible lateral line on body; pores of cephalic lateral line system in two main series, a preopercular canal of three large pores on upper margin of preopercle, the uppermost pair at approximately level of lower edge of pupil, the lowermost slightly below level of lower edge of eye, and an anterior oculoscapular canal of five large pores, the anteriormost immediately above nostril, the second above centre of eye or slightly ahead of this point, the third slightly above eye and slightly anterior to a vertical at posterior edge of eye, the fourth slightly behind eye on a horizontal with about middle of pupil or slightly above, and the last slightly higher than the fourth and nearly in line with a projection from the two preopercular pores; a single median pore of moderate size situated at about mid-interorbital, connected to the left and right oculoscapular canals by a coronal commissure (see N. magnifica in Akihito [1984: fig. 62] and N. helfrichi [ Fig. 1 ]).

Scales very small, non-imbricate, numbering 110–190 in longitudinal series; scales on body ctenoid dorsoposteriorly to about posterior third of dorsal fin, cycloid elsewhere, those anteriorly frequently embedded; no scales on head; no median predorsal scales, but embedded scales extend anteriorly on side of nape to level of gill opening or slightly beyond; prepelvic area of thorax with embedded scales; anterior portion of isthmus naked; no scales on fins except for approximately basal half of caudal fin.

First dorsal fin elevated anteriorly, the first three spines elongate and pennant like, filamentous in one species, the first spine longest, 1.4–3.9 in SL; the second and third spines only slightly shorter, the fourth, fifth, and sixth shorter than second; caudal fin truncate or weakly emarginate, round in one species; pectoral fins moderately pointed, pattern of branching variable, usually the upper and lowermost 3–4 rays unbranched (sometimes all rays unbranched), the middle rays longest, 4.7–6.1 in SL; pelvic fins separate, not connected to each other by frenum, not connected to body by membrane, their origin directly below pectoral-fin base, 3.6–7.4 in SL. remaining pterygiophores of second dorsal fin with autogenous middle and proximal radials. First anal-fin pterygiophore bearing one supernumerary spine and one serial ray, inserting anterior to first hemal arch; subsequent anal-fin pterygiophores each bearing one serially associated segmented ray; proximal tips of all pterygiophores of medial fins cartilaginous.

Osteology. Vertebral column with 10 precaudal and 16 caudal vertebrae ( Fig. 2); all vertebrae, except compound ural centrum, with neural spines; neural spines 1 through 20–21 with one or two foramina; epineurals on vertebrae 1 through 15–16, the posteriormost 3–4 sometimes weakly ossified; ribs present on precaudal vertebrae 3 through 10; vertebrae 24 (=PU3) and 25 (=PU2) with modified haemal and neural spines. Neural and haemal spine of PU3 only slightly broader than those of preceding. Haemal spine of PU2 broad proximally, blade-like distally, its flat anterior margin distally articulating with ventral procurrent cartilage, its cylindrical posterior margin articulating with two segmented caudal rays. Terminal vertebral (compound ural) centrum and hypurals 3–4 not differentiated; hypural 5 slender, about half the length of hypurals 1+2, well separated from ural centrum. Hypurals 1+2 undifferentiated and platelike with anteroventral flange. Parhypural autogenous, truncated proximally, with anterior flange, inserting distally in groove on anteroventral flange of hypurals 1+2. Anterior to hypural 5 a single, large epural with a cylindrical core near posterior margin, its flat anterior margin distally articulating with dorsal procurrent cartilage.

Typically, 9–14 unsegmented procurrent rays articulating with each dorsal and ventral procurrent cartilage; total number of segmented caudal-fin rays 17; one segmented ray articulating with epural and hypural 5, respectively; seven branched rays articulating with hypurals 3+4; six branched rays articulating with hypurals 1+2, the ventralmost sometimes displaced slightly below plate; one segmented ray articulating with parhypural and haemal spine of PU2 respectively.

First dorsal fin with six spines. No supraneurals. Two pterygiophores between neural spines 3 and 4, two between neural spines 4 and 5, one between neural spines 5 and 6, one between neural spines 6 and 7, followed by vacant interneural space (interneural gap) between neural spines 7 and 8 (formula 3-22110); proximal and medial radial of first two pterygiophores of second dorsal fin undifferentiated; Etymology. Combination of the Greek nemat meaning thread, and the eleotrid genus Eleotris . Genus is feminine. Species of Nemateleotris are known by a variety of common names, including firefish, firegoby, and dartfish. To maintain consistent terminology with other members of the ptereleotrinae , we use dartfish as the preferred common name, but provide alternative names wherever appropriate.

Habitat and biology. Small (rarely exceeding 70 mm total length), elongate and moderately compressed fishes frequently found hovering close to the substrate near or in coral reefs at depths between 6–100 m, especially in areas replete with sand channels and loose coral rubble ( Fig. 3 ). Diet primarily plankton and other small invertebrates which they pick out of the water column. All species brightly coloured (see key below) and with an elongate pennant-like first dorsal fin which they flick back and forth repeatedly, often in synchrony with their pelvic fins. Most frequently observed singly or in pairs, juveniles sometimes in small groups, often mixed with other plankton feeders. When startled they quickly dart into small holes or crevices in the substrate, emerging a few minutes later when the threat has passed.

Figures

Fig. 1. Laterosensory pores and neuromasts based on holotype of Nemateleotris helfrichi (BPBM 11595). A, lateral view; B, dorsal view. Letter codes (in blue) for laterosensory pores follow Akihito et al. (1984). ANP, anterior nasal pore; PNP, posterior nasal pore; AOC, anterior oculoscapular canal; PC, preopercular canal; FDF, first dorsal fin. Arrowhead indicates position where gill membranes are attached to the isthmus.

Fig. 3. A pair of Nemateleotris magnifica (middle) in habitat typical of the genus, consisting of sand channels and loose coral rubble. Note the presence of other fishes frequenting this habitat, including Pomacentrus auriventris and Meiacanthus grammistes. Underwater photograph from 15 m, central Sulawesi. Photograph by: V. Chalias.