Nomorhamphus aenigma, Kobayashi & Masengi & Yamahira, 2020

Kobayashi, Hirozumi, Masengi, Kawilarang W. A. & Yamahira, Kazunori, 2020, A New ‘‘ Beakless’ ’ Halfbeak of the Genus Nomorhamphus from Sulawesi (Teleostei: Zenarchopteridae), Copeia 108 (3), pp. 522-531 : 2-6

Nomorhamphus aenigma , new species urn:lsid:zoobank.org:act:FB36BEB6-6BF4-4C5F-B7EA-AC75D3B5288D

Figures 1–6 , Table 1

Holotype.— MZB 25100 ( Figs. 2 , 3 ), male, 34.7 mm SL, upper reaches of Cerekang River near by Laroeha Village, Malili River basin, Sulawesi Selatan, Indonesia, 2827 0 39.7 00 S,

121804 0 03.0 00 E, K. W. A. Masengi, I. F. Mandagi, and S. A. Lawelle, 25 November 2018.

Paratypes.— MZB 25101–25104 , 4 females, 27.9–37.8 mm SL , NSMT-P 136106–136107 , 1 male, 1 female, 26.8–43.0 mm SL , WMSU 00001 , male, 28.1 mm SL, collected with the holotype ; MZB 25098–25099 , 2 females, 41.6–60.9 mm SL , NSMT-P 136102–136105 , 2 males, 2 females, 31.3–52.2 mm SL , WMSU 00002 , female, 30.1 mm SL , WMSU 00012– 00014 , 3 juveniles, 10.2–23.3 mm SL, Cerekang River near by Landangi Village, Malili River basin, Sulawesi Selatan, Indonesia, 2826 0 57.7 00 S, 121805 0 47.8 00 E, H. Kobayashi, K. W. A. Masengi, I. F. Mandagi, S. A. Lawelle , R. Kakioka, S. Ansai , and K. Yamahira, 21 November 2018 .

Diagnosis.— Nomorhamphus aenigma is distinguished from all other congeners by the absence of any elongation of the lower jaw throughout ontogeny. Nomorhamphus aenigma is also distinguished from all other congeners by a combination of the short and expanded teeth on gill rakers, 22–23 precaudal and 16–17 caudal vertebrae, 13–14 anal-fin rays, 12 segments in the male first anal-fin ray, and distal tips of the male second and third anal-fin rays having no contact with each other.

Description.— Morphometric and meristic characters are provided in Table 1. Mouth subterminal; lower jaw had no elongation or appendage, distance between distal tip of upper to lower jaw (LJLB) 0.7–1.9 [0.9]. Upper jaw longer than wide, upper jaw length/upper jaw width (UJL/UJW) 1.2–1.7 [1.4]. One row of conical teeth at the front of the upper and lower jaws, followed by irregular rows of conical teeth up to the end of the jaws. Gill rakers short, base expanded with six to nine conical teeth on the dorsal surface of the gill rakers. Eye relatively large, bony orbital diameter (ORBL) 5.9–8.2 [7.8]. Body deep, body depth on pectoral-fin base (BDP1) 15.7–19.5 [18.2] and body depth on pelvic-fin base (BDP2) 14.9–19.2 [17.0]. Caudal peduncle depth 7.6–8.6 [8.1].

Predorsal scales deeply embedded. Vertebrae number 38– 39 [38] (precaudal 22–23 [22] þ caudal 16–17 [17]). Fifth hypural fused to dorsal hypural plate. Anal-fin rays 13–14 [14]; dorsal-fin rays 10–12 [12]; pectoral-fin rays 11–12 [12]; pelvic-fin rays 6. Caudal fin truncate, principal caudal-fin rays i,5–6/6,i [i,5/6,i] (mode i,6/6,i), procurrent caudal-fin rays 6–7/6–7 [7/7] (mode 6/6).

Males have modified anal-fin fleshy covering. For a stained specimen (NSMT-P 136105), the first anal-fin ray has 12 segments. The second anal-fin ray has also 12 segments with a narrow spiculus outwards. The second anal-fin ray is shorter than the third. The second and third anal-fin rays do not contact each other. The third, fourth, and fifth anal-fin rays have 18, 8, and 10 segments.

Color in life.— Body translucent beige in base color ( Fig. 2 ); striped black in males and uniform pale black in females.

Interoperculum brilliant. Belly brilliant sky blue in holotype, others white. Throat white. Iris upper and lower parts black, middle part yellow with a yellow edge. Diffuse black pigmentation on pectoral fin and oval spot on the base of pectoral fin. Base of pectoral-fin rays dark hyaline. Pelvic fins black in males; in females translucent or black pigmentation on distal tip. Base of dorsal- and anal-fin rays black. Dorsal and anal fin black in males; pale beige with irregular black pigmentation in females. Base of caudal fin dark hyaline. Other part of caudal fin black in males; pale beige in females. Color in alcohol.— Background color beige ( Fig. 3 ) with a thin mid-lateral stripe from pectoral to caudal fin, more prominent posteriorly. Black pigment on lower anterior edge of the bony orbital. Distinct oval spot on pectoral-fin base. Uniform distribution of melanophores on the head and the dorsal and flank of the trunk; high concentration of melanophores anterior and dorsal to the distinct oval spot on pectoral-fin base. Black pigment all over dorsal-fin rays and irregularly on anal-fin rays in males. Irregular black pigment on dorsal- and anal-fin rays in females.

Sexual dimorphism.— Females grow larger than males (maximum SL recorded: 34.7 mm in males, 60.9 mm in females).

The bodies of each sex have dark coloration, but only males exhibit a striped pattern when they are in breeding condition. Males have an andropodium.

Distribution and habitat.— Nomorhamphus aenigma is known from the main stream of Cerekang River in Sulawesi Selatan, Indonesia ( Fig. 1 ). The river belongs to the Malili River basin. The holotype was collected from a locality near Laroeha Village. The type locality (2827 0 39.7 00 S, 121804 0 03.0 00 E) is approximately 10 m in width and 1.5 m in depth, partially shaded by forest canopy, and has mud and gravel as substrates ( Fig. 4 ). Nomorhamphus rex ( Fig. 7 ), Oreochromis niloticus , Oryzias dopingdopingensis , Osteochilus vittatus , Redigobius penango , and Telmatherina sp. co-occurred.

Etymology.— The specific name ‘‘aenigma,’’ from ancient Greek noun for ‘‘riddle,’’ refers to the riddle raised by this species: ‘‘why are the mandibles of most halfbeaks long?’’

Comparisons.— This new species is classified into the genus Nomorhamphus because males possess a modified anal-fin fleshy covering, it lacks notably elongate lower jaws, and it has uniserial teeth not extending medially in a concave row from the outer row of teeth ( Meisner, 2001). Nomorhamphus aenigma is distinguished from all other congeners by the complete absence of elongate lower jaws.

This new species is further distinguished from other Sulawesi-endemic congeners as follows. The new species differs from N. brembachi , N. ebrardtii , N. hageni , N. lanceolatus , N. liemi , N. megarrhamphus , and N. weberi by having fewer anal-fin rays (13–14 [14] in N. aenigma vs. more than 15 in the others; Meisner, 2001; Huylebrouck et al., 2014). It further differs from N. megarrhamphus and N. weberi by having a first anal-fin pterygiophore that is thickened and not angled anteriorly (see Meisner, 2001) and fewer precaudal vertebrae (22–23 [22] in N. aenigma vs. 24–27 in N. megarrhamphus and N. weberi ; Meisner, 2001). The new species is distinguished from N. brembachi and N. liemi by having a second anal-fin ray without further longitudinal segmentation ( Kraemer et al., 2019b). It is distinguished from N. hageni by fewer caudal vertebrae (16–17 [16] in N. aenigma vs. 18–19 in N. hageni ; Meisner, 2001). The new species also differs from N. ebrardtii , N. lanceolatus , and N. sagittarius by its characteristic straight spiculus ( Fig. 5 ); it is not lanceolate and does not contact the distal tip of the third anal-fin ray. In addition, N. aenigma is also distinguished from N. lanceolatus by more precaudal vertebrae (22–23 [22] in N. aenigma vs. 21 in N. lanceolatus ; data from 11 topotype comparative specimens in this study). It is further distinguished from N. kolonodalensis by the many conical teeth on the dorsal surface of gill rakers (vs. 1–3 teeth on the dorsal surface of some gill rakers on the second and third arches in N. kolonodalensis ; Meisner, 2001). In addition, N. aenigma is also distinguished from N. kolonodalensis by the fifth hypural plate being completely fused to dorsal hypural plate ( Fig. 6 ; vs. the fifth hypural partially separated from the dorsal hypural plate along most of its length in N. kolonodalensis ; Meisner and Louie, 2000). The new species is distinguished from N. rex by the absence of an elongate third or fourth segment in the second anal-fin ray (see Huylebrouck et al., 2012; Kraemer et al., 2019b). It differs from N. versicolor by having more segments in the first anal-fin ray (12 in N. aenigma vs. 3 in N. versicolor ; Kraemer et al., 2019a). The new species cannot be distinguished from N. celebensis and N. towoetii by most morphometric and meristic characters, except for lower jaw length: N. aenigma has clearly shorter jaws than the other two species (LJLB 0.7–1.9 [0.9] in N. aenigma , vs. 2.9–6.2 and 3.9–7.7 in N. celebensis and N. towoetii , respectively; Material Examined in this study).

The new species is also distinguished from all Philippineendemic Nomorhamphus . It differs from N. bakeri , N. manifestus , N. pectoralis , N. philippinus , N. pinnimaculatus , and N. viviparus by the second anal-fin ray being shorter than the third (vs. the second anal-fin ray being longer than the third; see Meisner, 2001). The new species is distinguished from N. bakeri and N. rossi by lacking an elongate segment in the second anal-fin ray (see Meisner, 2001). The new species is also distinguished from N. pectoralis and N. robertsi by fewer anal-fin rays (13–14 [14] in N. aenigma vs. more than 15 in N. pectoralis and N. robertsi ; Meisner, 2001; Huylebrouck et al., 2014). In addition, it differs from N. pinnimaculatus by having more precaudal vertebrae (21–22 [22] in N. aenigma vs. 20–21 in N. pinnimaculatus ; Meisner, 2001).

Figures

FIG. 1. Map showing the type locality of Nomorhamphus aenigma, new species. Map by T. von Rintelen, modified. The black and white stars indicate the type locality (holotype and seven paratypes) and locality of ten paratypes, respectively.

FIG. 2. Photographs of Nomorhamphus aenigma, new species, immediately after fixation. (A) MZB 25100, holotype (male, 34.7 mm SL), (B) MZB 25103, paratype (female, 37.8 mm SL), (C) NSMT-P 136106, paratype (female, 43.0 mm SL).

FIG. 3. Preserved specimens of Nomorhamphus aenigma. Upper: MZB 25100, holotype (male, 34.7 mm SL), lower: MZB 25099, paratype (female, 41.6 mm SL).

FIG. 4. Type locality of Nomorhamphus aenigma, Cerekang River, approximately 600 m downstream from Laroeha Village, Luwu Timur District, Regency of Wasuponda, Sulawesi Selatan. Photo taken 3 September 2019.

FIG. 5. Diagrammatic representation of the modified anal-fin rays (andropodium) of Nomorhamphus aenigma, NSMT-P 136105, 33.1 mm SL. Scale bar ¼ 1 mm, SN: spinae, SP: spiculus.

FIG. 6. Diagrammatic representation of the caudal skeleton of Nomorhamphus aenigma, NSMT-P 136105, 33.1 mm SL, male. Scale bar ¼ 1 mm. EP, epural; HY, hypural.

FIG. 7. Photographs of Nomorhamphus reX immediately after fixation. Upper: NSMT-P 136117 (male, 35.5 mm SL), lower: NSMT-P 136116 (female, 47.6 mm SL).