Homalopteroides modestus ( Vinciguerra 1890 )

Randall, Zachary S. & Page, Lawrence M., 2012, Resurrection of the genus Homalopteroides (Teleostei: Balitoridae) with a redescription of H. modestus (Vinciguerra 1890), Zootaxa 3586, pp. 329-346 : 337-343

Redescription of Homalopteroides modestus ( Vinciguerra 1890)

( Figs. 4, 5, & 6)

Helgia modesta Vinciguerra 1890: 330 , Pl. 11 (fig. 12); Annali del Museo Civico di Storia Naturale di Genova (Serie 2) v. 9.

Lectotype. MSNG 15173 A; Myanmar, Meekalan, Tenasserim; L. Fea, 1887. Designated by Tortonese 1961: 188; Catalogo del tipi de pesci del Museo Civico di Storia Naturale di Genova. (Parte I). Annali del Museo Civico di Storia Naturale `Giacomo Doria' v. 72: 179–191.

Paralectotypes. BMNH 1893.2 .16.50, 1 ALC; Myanmar, Meetan, Tenasserim; L. Fea, 1887 .— MSNG 15173 B, 1 ALC (1, now 3); same collection data as BMNH 1893.2.16.50— ZMA 100982 , 2 ALC; same collection data as BMNH 1893.2.16.50.

Homaloptera modesta: Hora 1932: 288 ; Memoirs of the Indian Museum, v. 12 (2).

Homalopteroides modestus was placed in the genus Helgia along with Homaloptera (Homaloptera) bilineata Blyth 1860 by Vinciguerra (1890). Jordan (1920) subsequently designated H. (Homaloptera) bilineata as the type species of Helgia , making Helgia Vinciguerra 1890 a synonym of Homaloptera van Hasselt 1823 . Fowler (1905) designated Homaloptera wassinkii Bleeker 1853 as the type species for Homalopteroides to which H. modestus belongs.

Homalopteroides modestus originally was described from the Meekalan and Meetan rivers, Tenasserim Division (now known as the Tanintharyi Region, Mon State and southern Kayin State) of southern Myanmar, and type specimens subsequently were designated by Tortonese (1961). The only type specimen examined in this study (due to availability) was a paralectotype, BMNH 1893.2.16.50. This specimen is in extremely poor condition and only pectoral fin and pelvic-fin ray counts could be made. Vinciguerra (1890) gave a total pectoral-fin ray count of 13 (v, 8) and a total pelvic-fin ray count of 8 (ii, 6). However, the paralectotype examined has a total pectoral-fin ray count of 15–16 (v, 10–11) (only one side could be counted) and a total pelvic-fin ray count of 9 (ii, 7). Since its original description, H. modestus has been redescribed by Silas (1953), Menon (1987), and Selim and Vishwanath (1998). Silas (1953) gave a total pectoral-fin ray count of 13–14 (v–vi, 8) and the same pelvic-fin ray count given by Vinciguerra (1890). Menon (1987) gave the same counts as Silas (1953), whereas Selim and Vishwanath (1998) followed the original description. Based on all material examined in the present study, H. modestus has a total pectoral-fin ray count of 14–16 (iv–vi, 8–10, i) with a modal number of 15 (v, 9, i). Silas (1953), Menon (1987), and Selim and Vishwanath (1998) gave a lateral-line scale count of 47 although Vinciguerra (1890) states “11 numero delle squame della linea laterale non si può precisare con esattezza: esse sono circa 47” (11 Number of the scales of the lateral line cannot be precise: there are about 47). The 68 individuals sampled in this study had a lateral-line pore count of 38–42 +1–2. Vinciguerra (1890) gave a pharyngeal tooth count of 8 and described the 2 nd to 4 th teeth as being well developed, and the other five as rudimentary. In one of the specimens examined in this study, the pharyngeal tooth count was 8, the first six teeth being large and the last two small ( Fig. 4).

Diagnosis. Homalopteroides modestus is distinguished from all other members of Homalopteroides (Table 3) by the combination of its caudal-fin color pattern that consists of a black proximal bar, a black distal bar and a black median blotch, 15 pectoral-fin rays (v, 9, i), a pectoral-fin length greater than the head length, 5–6½ scales above and 5–6 scales below the lateral line (to the pelvic fin), a total lateral-line pore count of 39–44, absence of an axillary pelvic lobe, pelvic fin not extending to the anus, orbital length less than the interorbital width (an adult character, see Discussion), and a maxillary barbel that reaches to or slightly past the anterior orbital rim.

Homalopteroides modestus is morphologically most similar to H. nebulosus , H. rupicola , and H. tweediei . It is distinguished by having 15 pectoral-fin rays vs. 13–14 in H. nebulosus , 16 in H. rupicola , and 13 in H. tweediei . It can be distinguished further from H. nebulosus and H. tweediei by a pectoral-fin length greater than head length vs. pectoral-fin length less than head length, and from H. rupicola by an interorbital width greater than the orbital length vs. interorbital width less than or equal to the orbital length. Homalopteroides smithi and H. wassinkii are distinguished from H. modestus by the presence vs. absence of an axillary pelvic lobe. Homalopteroides indochinensis , H. stephensoni , H. weberi , and H. yuwonoi are distinguished from H. modestus by a pelvic fin that extends to or past the anus.

Description. Dorsal, lateral, and ventral views of an adult are shown in Figures 5A and 6. Measurements and meristic counts are given in Table 1. Homalopteroides modestus is a moderate-sized species reaching 44 mm SL. The body has a flattened ventral surface, is arched predorsally and tapers posteriorly to the caudal base. The head is conical when viewed dorsally and covered with tubercles. The orbits are small, ovoid, positioned dorsolaterally, and smaller in length than the interorbital width. The nostrils and orbital rim are in close proximity but are not in contact.

The mouth ( Fig. 6) is inferior with both upper and lower jaws slightly visible. The lips are thin, smooth, crescent-shaped, and continuous around the corners of the mouth. The lateral portion of the lower lip is broad and the medial portion is thin. The chin extends anterior to the lateral portion of the lower lip. Posterior to the lower lip is a series of large tubercles that extend onto the operculum. Rostral and postlabial grooves are present. Two pairs of rostral barbels and a pair of maxillary barbels are present at each corner of the mouth. The medial-rostral barbels are separated from one another by a large lobe. The rostral barbels are separated by a small lobe with a distance about equal to the length of the medial-rostral barbel. The lateral-rostral barbel reaches the base of the maxillary barbel, and the maxillary barbel reaches horizontally to a vertical at or slightly posterior to the anterior orbital rim. The gill opening extends to the ventral surface of the body, and the gill membrane is united to the isthmus with a large central furrow where the gills meet. The opercle reaches to or past the 2 nd pectoral-fin ray.

Body scaled except for the ventral surface anterior to pelvic-fin; scales between the anal-fin origin and pelvic insertion are deeply embedded. In the cleared and stained specimen a medial row of scales from the pelvic fins reached to a small patch of scales between the pectoral fins. Most scales, especially above the lateral line and at the dorsal-fin origin, have a small nipple at their posterior extremity; up to six nipples are present on a scale. The total lateral-line pore count is 39–44.

Variations in fin counts are given in Table 1; modal numbers are given here. Dorsal fin has 3 simple and 7 branched rays (iii, 7 ½) and originates over the pelvic fin, closer to the caudal-fin base than to the snout. Pectoral fin has 6 simple and 9 branched rays (v, 9, i), is longer than the head length and reaches past the pelvic-fin origin. Pelvic fin has 2 simple and 7 branched rays (ii, 7), lacks an axillary pelvic lobe, and does not reach the anus which is located closer to the anal-fin origin than to the pelvic-fin insertion. Anal fin has 1 simple and 5 branched rays (i, 5 ½). The caudal fin is forked with rounded lobes and has a total of 17 branched rays; the lower lobe slightly longer than the upper. Total number of vertebrae is 31, comprising 15 abdominal and 16 caudal. The fifth ceratobranchial ( Fig. 4) bears a large transverse ventralis process and has a single row of 8 teeth. Positioning of the teeth varies in the left and right ceratobranchials in the cleared and stained specimen examined.

Lateral view of a juvenile is shown in Figure 5B. Measurements and meristics for juveniles (individuals with an orbital length greater than or equal to the interorbital width) are given in Table 1. The maximum size is 27 mm. Characters not shared with adults are discussed. The body lacks a well-defined predorsal arch and lobes between the barbels. Few tubercles may be present by and between the nares. Nipples on the scales are not prominently found. The pectoral fin reaches the pelvic fin, but does not always reach past it.

Coloration. In 70% Ethanol: The general color is shown in Figures 5 and 6. The color pattern varies slightly between adults and juveniles. In dorsal view, the base color is cream with small mottled brown spots. There are five black dorsal saddles. The 1 st saddle may have smaller, incomplete saddles surrounding it and is between the supraoccipital and dorsal-fin origin; 2 nd is located at the dorsal-fin origin; 3 rd is located at the dorsal-fin insertion between the dorsal-fin and anal-fin origins; 4 th is dorsal to the anal fin; and 5 th wraps the caudal-fin base. The saddles often are faint and hard to distinguish in juveniles. A black bar extends from the lateral-rostral barbel base through the orbit and to the supraoccipital, which is outlined in black.

The lateral view shares the same base color pattern as the dorsal view. A black bar extends from the medialrostral barbel base to or just before the nares. Another black bar extends from the orbit to the posterior edge of the opercle just below the origin of the lateral line. The lateral line is marked by a solid black stripe that may contain circular blotches. One–4 large pigmented blotches may be present below the black stripe between the pectoral-fin origin and the anterior edge of the orbit. The 3 rd and 4 th saddles usually commence at the lateral line. Mottled brown spots sometimes coalesce to form distinct lines above and below the lateral line and may form large spots between the pelvic and anal fins.

In ventral view, the base is cream and, when mottled spots are present, they are restricted to a band at the analfin origin. The barbel bases are black, and the lips are occasionally pigmented between the rostral barbels and at the maxillary barbels.

All of the fins have black bands; the dorsal fin has 3–4 in adults and 2–3 in juveniles. The pectoral fin has 2–3 bands, the pelvic fin has 1–2, and the anal fin has 1–2 in adults and 1 in juveniles. The caudal fin has 2 bars, a proximal bar and a distal bar, and a median blotch that may fuse to the distal bar. The lower lobe of the caudal fin is pigmented only at the caudal bars. The paired fins are black at their bases, and the unpaired fins have a black spot at their origins. All fins have hyaline tips.

Distribution. Homalopteroides modestus occurs in the Salween, Mae Khlong, and Tenasserim basins ( Fig. 7). The latter two basins drain the Tenasserim Range, a large mountain chain between Thailand and Myanmar. The eastern part of the Tenasserim Range is crossed by the Mae Nam Kwae Noi River (Mae Khlong basin) and the southwestern part gives rise to the Tenasserim River. The Salween River flows north of the Tenasserim Range. Other species that have a distribution in both the Mae Khlong and Salween basins are Schistura mahnerti ( Kottelat 1990; Plongsesthee et al. 2011), and Acanthocobitis pictilis ( Kottelat 2012) . Most individuals of H. modestus have been collected in mountain streams in rubble and gravel riffles ( Fig. 8).

Homalopteroides modestus has been reported from Borneo by Boulenger (1894) and Popta (1906); however, these populations were subsequently described as H. weberi and H. stephensoni by Hora (1932). The description given for H. modestus from Manipur, India ( Selim and Vishwanath 1998), does not agree with the data from this study and probably refers to a different species.