Hypoptopoma guianense Boeseman, 1974

Aquino, Adriana E., 2010, Systematics Of The Genus Hypoptopoma Günther, 1868 (Siluriformes, Loricariidae), Bulletin of the American Museum of Natural History 2010 (336), pp. 1-110 : 28-32

Hypoptopoma guianense Boeseman, 1974 Figure 20 , table 2

Hypoptopoma guianense Boeseman, 1974: 259 , 1 fig., 1 pl., tables 1–2 (original description; Surinam: left tributary of the Nickerie river, a few km upstream from the Stondansi Falls).— Isbrücker, 1980: 87 (list of loricariid species).— Nijssen et al., 1982: 54 (catalog of type specimens at Zoölogische Museum Amsterdam).— Ferraris and Vari, 1992: 27 (catalog of type specimens at NMNH).— Eschmeyer and Ferraris, 1998: 688 (catalog of fishes).— Machado Allison et al., 2000: 17 ( Venezuela: Río Cuyuní).— Isbrücker, 2002: 28 (list of loricariid species).—Schaefer, 2003: 323 (list of hypoptopomatine species).— Ferraris, 2007: 250 (list of catfish species).—Vari et al., 2009: 38 (list of freshwater fishes of Guiana Shield).

HOLOTYPE: RMNH 26919 (61.5 mm SL)

Suriname, left tributary of the Nickerie

River, a few kilometers upstream from the Stondansi Falls; collected by H. Boeseman, 30 January 1971 (not seen).

PARATYPES: RMNH 26922 (1 ♀ + 3 ³, 47.0–56.0 mm SL) Suriname, Nickerie River, below Blanche Marie Falls ; collected by H. Boeseman, 11 February 1971. USNM 213484 (2 ♀, 48.9–51.6 mm SL) Surinam, left tributary creek upper Nickerie River ; collect- ed by H. Boeseman, 30 January 1971.

OTHER MATERIAL EXAMINED: Guyana, Cuyuni-Mazaruni: INHS 49274 (1 ♀, 27.6 mm SL) 1.5 mi. SW Rockstone [ Essequibo river ] ; INHS 49366 (1 juvenile, 29.3 mm SL) 31.9 mi. SSW Rockstone. Potaro-Siparuni: INHS 49402 (1 juvenile, 23.3 mm SL) Essequibo River drainage, Tumatumari Cataract, S bank, below old hydroelectric plant. Upper Demerara-Berbice: AMNH 13341 (2 ♀, 35.5– 40.7 mm SL) Malali ; AMNH 13666 (1 ♀ + 1 ³, 38.5–39.2 mm SL) Rockstone, Essequibo River drainage ; AMNH 220509 (2 ♀, 46.3– 47.5 mm SL) Essequibo River drainage ; INHS 49660 (10 ♀ + 2 juveniles, 25.2– 63.4 mm SL) Rockstone. Upper Takutu– Upper Essequibo: BMNH 1983.7.26:12–28 (16 ♀ + 1 ³, 2 cs, 28.5–47.8 mm SL) Rupununi River ; BMNH 1983.26 :49–54 (6 ♀, 37.2–46.1 mm SL) Rupununi River, Kamarang ; FMNH 69962 (3 ♀, 37.3– 42.1 mm SL) Moco Moco River .

DIAGNOSIS: Hypoptopoma guianense is distinguished from all congeners by the presence of an elongated dark spot along the median caudal-fin branched rays, involving the lanceolate plates at the base of the fin. The spot is typically extended over an equal number of branched rays of both the upper and lower lobes and along more than twothirds of the ray length (fig. 17C).

DESCRIPTION: Morphometric and meristic data presented in table 2. Body moderately elongate and low. Dorsal profile of head and body slightly convex from tip of snout to dorsal-fin origin; straight from dorsal-fin origin to anteriormost caudal-fin procurrent ray. Head moderately depressed and narrow. Lateral process of lateral ethmoid dorsally not visible. Snout rounded to slightly spatulate in dorsal view; smoothly rounded in dorsal view; dorsally variably concave anteri- or to naris. Posterior surface of bony pit of nasal organ sharply inclined. Body cross section between pectoral- and pelvic-fin origins horizontally ovoid, posterior to dorsal fin changing from ovoid to rounded, posterior to adipose-fin base progressively compressed.

Eyes moderately large, positioned closer to posterior tip of compound pterotic than to tip of snout. Ventral margin of orbit located close to ventral surface of head. Dorsal interorbital distance shorter than ventral interorbital distance.

Total plates in lateral medial series 23–24 (23). Dorsal series 20–21 (20); middorsal series 3–4 (4); midventral series 13–15 (13), with four plates (rarely five) anterior of first plate of ventral series; ventral series 19–21 (20). Second plate of midventral series contacting single plate of medial lateral series.

Abdomen covered by paired series of lateral sickle-shaped plates, with unequal number of plates between left and right series, 4–10 each; medial series of 3–8 (5) roughly squared plates; anterior azygous plate absent. Single anal plate present. Thoracic plates absent. Preopercular canal absent. Posterolateral margin of canal-bearing plate and lateral margin of fourth infraorbital smooth; pore between canalbearing ventral plate and fourth infraorbital absent.

Small odontodes evenly distributed on trunk and head. Odontodes ventral and dorsal to tip of snout not arranged in aligned series. No odontode-free discontinuity between ventral and dorsal odontodes; odontodes dorsal to tip of snout slightly larger than those on head. Lamina of trunk plates with longitudinal lines of odontodes, becoming progressively smoother ontogenetically; distinct column of marginal odontodes on posterior plate border in mature adults.

Total vertebrae 27. Premaxillary teeth 21– 26 (23), dentary teeth 17–24 (20). Maxillary barbels short; reaching to anterior margin of ventral canal-bearing plate in adults.

Dorsal-fin origin located slightly posterior of vertical through pelvic-fin origin. Depressed dorsal fin reaching to vertical through midpoint of anal-fin base length. Pectoral fin reaching to vertical through midpoint of pelvic-fin length. Extension of serrae along pectoral spine margin except for short basal segment; serrae of oblique type. Pelvic fin short, 2–3 longest branched rays slightly longer than spine. Depressed fin reaching to plate anterior to anal-fin spine. Caudal-fin margin forked; upper and lower lobes equal and elongate. Adipose fin variably present; when present, minute.

COLOR IN ALCOHOL: Ground color tan and pale ochre. Melanophores dark brown, on trunk and head clustered resulting in mottled appearance; distinct light spot dorsally on each lateral rostral plate. Melanophores slightly more concentrated on anterior surface of lip, along narrow area among compound pterotic, cleithral process and dorsal tip of opercle, at base of dorsal and pectoral fins. Deep-lying melanophores arranged in narrow transverse bands posterior to dorsal-fin base, noncoincident with posterior margin of plates. Midlateral stripe situated along trunk variably defined. Ventral surface of body mostly unpigmented except for scattered melanophores on posterior portion of trunk, soft tissue along base of pectoral and anal fins, anterolateral margin of cleithra, and lateral portions of lateral abdominal series. Paired and dorsal fins with dark brown bars. Caudal-fin bars variable defined (fig. 17C). Presence of elongated dark spot along middle caudal-fin branched rays; spot typically extending over equal number of upper- and lower-lobe rays and along more than two-thirds of ray length; spot connected to lanceolate plates at base of fin. Tip of upper and lower lobes slightly pigmented with reddish-brown melanophores.

SEXUAL DIMORPHISM: Male urogenital papilla well developed, pointed, joined at base to anterior flaplike anus. Males with patch of tightly arranged small odontodes oriented as a swirl, variably covering first to fourth plates of ventral series, lateral to urogenital papilla. Female anus tubular,

TABLE 2 Morphometric and Meristic Data for Hypoptopoma guianense Paratypes: RMNH 26922 . Nontypes: AMNH 13666 , 220509 ; BMNH 1983.7.26:12–28 ; FMNH 69962 ; INHS 49960 .

without separate urogenital papilla. In females, size and arrangement of odontodes on plates lateral to anus similar to adjacent plates, without distinct patch of differentially arranged odontodes.

DISTRIBUTION: Known from of the basins of the Essequibo ( Guyana) and Nickerie ( Surinam) rivers (fig. 19).

TAXONOMIC REMARKS: Prior to the present revision, Hypoptopoma guianense was the only nominal species of Hypoptopoma to be established on the basis of a relatively large number of individuals (approximately 31). The species is most similar to H. psilogaster Fowler, 1915 , which has been reported from the Ríos Ampiyacu, Itaya, Nanay, Napo, and Yaguas in Amazonian Peru. Valid taxonomic status of both species is supported on the basis of differences in the caudal-fin pigmentation: both species possess an elongate spot along the middle caudal-fin branched rays, but in H. guianense the spot is continuous with the dark spot on the lanceolate plates, versus discontinous in H. psilogaster . Further differences are shown in an analysis of the overall morphometric variation among H. guianense , H. psilogaster , and H. thoracatum . In a sheared principal component analysis on 18 distance variables (fig. 21; table 3), the scatter plot of the component scores on sheared PC2 and PC3 shows near complete separation among the three species. The second and third components represent 3.1 % and 0.9 % of the total morphometric variance, respectively. The morphometric variance explained by PC2 reflects differences in the elongation of the body (caudal-peduncle length, trunk length, caudal-peduncle depth); likewise, PC3 appears to reflect differences in head width at the level of the eyes (least distance between orbit and naris).

Figures

Fig. 20. Hypoptopoma guianense, paratype, RMNH 26922, in dorsal, lateral, and ventral views.