Cetopsis aspis, Abrahão & Mol & Pinna, 2019

Abrahão, Vitor, Mol, Jan & Pinna, Mario De, 2019, A new species of Cetopsis from the Guiana Shield (Siluriformes: Cetopsidae: Cetopsinae), Zootaxa 4664 (2), pp. 221-232 : 224-228

Cetopsis aspis , new species

Zoobank: urn:lsid:zoobank.org:pub:78CF986A-31C7-4D20-A185-CB0B2F61281A

Holotype. USNM 432561 , female, 70.96 mm SL, Suriname, Sipaliwini District, Mauritie Creek, a tributary of upper Tempati River, upper Commewijne River basin, Surgold Concession (gold mine). 05°06’12.9” N 54°35’24.9” W; J. Mol et al., 3 February 2012 ( Figure 1 ).

Paratypes. Guyana: ROM 81222 (1, 49.7 mm SL), Potaro-Siparuni, Konawaruk river , Essequibo basin, at NARIL camp along cut bank shore and on large gravel beach. 05°07’11.1”N 59°06’31.9”W; D. Taphorn et al., 13 September 2014. ROM 96811 (1, 44.1 mm SL), Potaro-Siparuni , Essequibo basin, unnamed creek, creek north of GGMC camp along road to mango landing at bridge. 05°13’19.5”N 59°02’33.8”W; D. Taphorn et al., 17 September 2014. MZUSP 125262 (1, 21.0 mm SL; 1 C&S, 26.2 mm SL), Potaro-Siparuni, Konawaruk river , Essequibo basin, near GGMC camp. 05°11’06.4”N 59°02’32.2”W; D. Taphorn et al., 16 September 2014. ROM 96922 (1, 71.4 mm SL), Potaro-Siparuni, Konawaruk river , Essequibo basin, downstream from GGMC camp active dredge. 05°12’05”N 59°02’18.4”W; D. Taphorn et al., 17 September 2014. ROM 97142 (1, 24.3 mm SL), Potaro-Siparuni, Konawaruk river , Essequibo basin, 2.6 km from Mango Landing. 05°18’23.8”N 58°55’00”W; D. Taphorn et al., 19 September 2014. ROM 97148 (4, 24– 30.2 mm SL); MZUSP 125263 (1, 28.7 mm SL), Potaro-Siparuni, Konawaruk river , Essequibo basin, above Temple Bar Falls . 05°17’54.3”N 58°55’13.1”W; D. Taphorn et al., 19 September 2014 . Suriname: USNM 432559 (1, 46.9 mm SL; Figure 2 ) collected together with holotype .

Diagnosis. Cetopsis aspis can be distinguished from all congeners, except C. montana , by the presence of a dark bilobed patch at the base of the caudal fin (vs. absent in C. amphiloxa , C. baudoensis , C. fimbriata , C. gobioides , C. jurubidae , C. motatanensis , C. othonops , C. plumbea , and C. varii ), the lack of a dark humeral spot (vs. present in C. arcana , C. caiapo , C. orinoco , C. parma and C. sarcodes ), the color pattern composed of eye-sized or larger dark spots on sides of the body (vs. small dark spots in C. pearsoni , C. starnesi , and C. umbrosa ). Individually, by the presence of a spot of dark pigmentation at the base of the dorsal fin, the dark covering of sides extending ventrally to the bases of anal-fin rays, and the presence of 41 total vertebrae with 28 caudal vertebrae (vs. dark spot absent, dark covering restricted to dorsolateral surface of body, and 42 total vertebrae with 29 to 33 caudal vertebrae in C. montana ), lack of dark pigmentation along the membrane posterior to the first dorsal-fin ray, the presence of dark spots on the ventrolateral surface of body, and the caudal fin web with dark chromatophores (vs. dark pigmentation along the membrane first dorsal-fin present, dark spots on ventrolateral surface of body absent, and caudal fin without dark chromatophores in C. sandare ), eye present (vs. absent in C.oliveirai ); conical teeth on the vomer and dentary (vs. incisiform in C. candiru ); posterior nares round and widely separated from each other by distance greater than the distance between posterior and anterior nares (vs. posterior nares slit-like, transversely-aligned and narrowly separated from eachother by distance less than the distance between posterior and anterior nares in C. coecutiens ).

Description. Morphometric and meristic data presented in Table 1 . Body moderately elongate, with some specimens preserved with distended abdomens, slightly-compressed laterally anteriorly and progressively more compressed posteriorly. Body depth at dorsal-fin origin approximately 84–95% of SL (i.e., less than HL). Lateral line on body complete, unbranched, and midlateral; extending from vertical through pectoral-fin base to vertical through last anal-fin ray, not reaching hypural plate. Dorsal profile of body slightly convex from nape to posterior insertion of dorsal-fin origin, then nearly straight to caudal-fin base. Ventral profile of body convex along abdomen, approximately straight, then posterodorsally-slanted, along base of anal fin. Caudal peduncle depth slightly greater than caudal-peduncle length in adults, opposite in juveniles.

Head acutely triangular in lateral view, with bluntly rounded snout. Dorsal profile of head convex from tip of snout to nape. Ventral profile of head slightly convex. Margin of snout rounded in dorsal view. Enlarged jaw musculature slightly protruding on dorsal surface of postorbital portion of head. Opercular membrane narrowly attaching to isthmus only anterior to vertical through pectoral-fin insertion. Branchial opening moderately-sized; slightly greater than distance from tip of snout to posterior margin of orbit. Eye situated on lateral surface of head, visible in dorsal view, located entirely dorsal to horizontal through pectoral-fin insertion. Middle of orbit located at 35-39% of HL. Eye diameter 39-46% of snout length. Interorbital width approximately equal to snout length. Anterior narial opening circular, surrounded by short, anteriorly expanded, tubular rim of skin. Opening of anterior naris located ventral to horizontal line through tip of snout and at horizontal through maxillary barbel insertion. Transverse distance between anterior nares shorter than snout length and greater than distance between anterior and posterior nares. Posterior nares nearly round, located on dorsal surface of head, at vertical through anterior margin of orbit. Anterior half of posterior naris surrounded by elongated flap of skin.

Mouth inferior, its width approximately one-half of HL (51–53%). Margin of lower jaw gently round in ventral view, its posterior limit slightly posterior to vertical through posterior margin of orbit. Premaxillary tooth patch forming gently-arched band, continuous across midline, with anterior margin convex and posterior margin concave and parallel to anterior margin. Premaxillary teeth small, conical, and sharply-pointed; arranged in three irregular rows ( Figure 6 ). Teeth in inner row of premaxilla slightly larger than teeth in other rows. Vomerine teeth arranged in single, irregular row continuous across midline. Vomerine teeth stout, conical, and larger than teeth on premaxilla and dentary. Dentary teeth comparable in shape to, but larger than, all but largest premaxillary teeth; with two irregular tooth rows near dentary symphysis, medially tapering to one row laterally.

Maxillary barbel slender, its length greater than distance from tip of snout to posterior orbit, but approximately equal to one-half of HL (48–52%). Origin of maxillary barbel located ventral to anterior margin of orbit. Mental barbels approximately equal in length and shorter than maxillary barbel. Medial mental-barbel origin at vertical through rictus. Lateral mental-barbel origin posterior to vertical through medial mental-barbel origin. Tips of mental barbels falling just short of posterior margin of opercle.

Dorsal fin base 36-45% of HL. Longest branched dorsal-fin ray, excluding distal filament of first ray, approximately three quarters of HL. Dorsal-fin spinelet absent. First dorsal-fin ray flexible, not spinous. Distal margin of dorsal fin straight, with first ray longest. Dorsal fin origin at approximately one-third of SL; on vertical line through approximately one-half of adpressed pectoral fin. Tip of adpressed dorsal fin reaching nearly to vertical through posterior tip of adpressed pelvic fin. Posterior most dorsal-fin ray adnate with posterior membranous attachment to body. Caudal fin forked, symmetrical, with tips of lobes bluntly pointed. Length of longest caudal-fin ray approximately twice as long as middle fin rays.

Anal-fin base length moderate, approximately 28–32% of SL. Anal-fin origin posterior to middle of SL and approximately in the middle of total length. Last unbranched anal-fin ray longest of fin, with subsequent fin rays gradually shorter. Anal-fin margin straight in females and immature males, slightly convex in mature males. Posterior anal-fin ray without membranous attachment to body. Pelvic fin moderately sized; its distal margin nearly straight and two anterior branched rays longest. Pelvic fin inserted anterior to middle of SL, anterior to vertical through posterior insertion of dorsal fin. Tip of adpressed pelvic fin extending beyond middle of SL and not reaching anterior margin of vent. Last pelvic-fin ray adnate, with membranous attachment to body along basal two-thirds of its length. Pectoral-fin length approximately two thirds of HL. Pectoral-fin margin sinusoidal, concave laterally and convex medially, with first ray longest and prolonged as distal filament, not spinous; filament proportionally longer in mature males.

Coloration in preservation. Dusky pigmentation covering dorsal portion of head from interorbital region to posterior of head, and from tip of snout to posterior region of head in darkly-pigmentedspecimens. Dorsal portion of body dark. Lateral surface of body pale with scattered, approximately eye-sized, dark spots. In some juveniles, spots on lateral surface of body. Dark spots more concentrated on dorsal and dorsolateral portions of body and on lateral surface of caudal peduncle. Dark spots on lateral surface of body extending until base of anal-fin rays.Ventral surface of head and body pale. Ventral surface of lower jaw with single or incomplete row of dark chromatophores in darkly-pigmented specimens. Snout margin pale from posterior nares to tip of snout, and with dark chromatophores in specimens darkly pigmented. Entire upper lip pale. Dorsal fin pale with semicircular, basally-situated, dusky region. Interradial membrane between first and second dorsal-fin rays pale. Caudal fin with dark, bilobed spot extending from base of branched fin-rays posteriorly approximately to vertical through one-third of length of inner-most fin rays. In juveniles, dark bilobed spot on caudal fin poorly defined. Anal, caudal, pectoral, and pelvic fins pale. Dark chromatophores distally along entire caudal fin in specimens retaining dark pigment. Maxillary barbel dusky on basal one-half of anterior surface, pale otherwise. Mental barbels pale or dusky on basal one-half of anterior surface, pale otherwise ( Figure 1 ).

Coloration in life. Coloration as described above in overall pattern, but with silvery sheen overlying lateral surface of head and body, with silvery coloration more intense on anterior two-thirds of body.Ventral surface of entire body whitish ( Figure 2 ).

Sexual dimorphism. Presumed mature males of Cetopsis aspis have filaments on the first rays of the dorsal and pectoral fins proportionally longer than in females and immature males. Same specimens presumed mature males also with anal-fin margin slightly convex while in females and immature males anal-fin margin nearly straight. These sexually dimorphic traits are common in several species of Cetopsinae ( Vari et al., 2005) and presumed to apply in C. aspis although specimens of the species were not directly sexed except for one c&s male specimen, a confirmation which matches the expected pattern.

Distribution. Cetopsis aspis occurs in central and northern Guyana and northern Suriname river basins ( Figure 3 ). In Guyana, it is known from the Konawaruk River and tributaries in the Potaro-Siparuni region, Essequibo River basin. In Suriname, it is known from Mauritie Creek, tributary to the Tempati River, upper Commewijne River basin, in the Sipaliwini District. This is the first species of Cetopsis known to occur exclusively in the Guiana Shield and is so far restricted to rivers draining that biogeographical region.

Ecological notes. In Suriname, specimens of Cetopsis aspis were found in medium-speed current waters in Mauritie Creek ( Figure 4 ). At the collection locality, the small and shallow stream, 5–10 m wide, 48–88 cm deep, had grey-white turbid water due to upstream activities of gold miners, with gravel, woody debris and sand substrata, and with Thurnia sphaerocephala (Rudge) aquatic macrophytes. The lateral banks were steep with high dryland forest. Specimens from Suriname were collected on 3 February 2012, around 09:00 hours, with water temperature 24.2°C, pH 5.7, 24 µS/cm of conductivity, and Secchi transparency 5 cm. Stomach contents of only one adult specimen of Cetopsis aspis contained mostly sediments, debris of plant and algae, and some allochthonous invertebrates such as ants ( Formicidae ) and beetles ( Coleoptera ). In a field aquarium, adult C. aspis ate live small tetras and pencil fishes; these prey fishes were captured at night (with aquarium lights turned off).

In pristine conditions the stream would have clear, slightly brownish water; this was observed during a recent survey in December 2017, when the miners had left the area of Mauritie Creek. The capture of the new Cetopsis in seine nets was probably related to disturbance of upstream gold miners turning the water turbid grey with high suspended sediment concentrations. After cessation of the mining activity no specimens were collected.

Syntopic species in Suriname included members of Leporinus , Cyphocharax , Chilodus , Melanocharacidium , Gasteropelecus , Astyanax , Bryconops , Charax , Hemigrammus , Hyphessobrycon , Jupiaba , Moenkhausia , Phenacogaster , Poptella , Tetragonopterus , Acestrorhynchus , Hoplias , Pyrrhulina , Ituglanis , Corydoras , Loricaria , Loricariichthys , Hypostomus , Lithoxus , Chasmocranus , Pimelodella , Pimelodus , Auchenipterus , Trachelyopterus , Gymnotus , Eigenmannia , Sternopygus , Hypopomus , Apteronotus , Krobia , Polycentrus , Potamorrhaphis , and Micropoecilia .

Etymology. The Greek word aspis means shield, in allusion to the occurrence of the new species in the Guiana Shield. A noun in apposition.

Figures

FIGURE 1. Cetopsis aspis, holotype, USNM 432561, female, 70.96 mm SL. Photo: Sandra Raredon.

FIGURE 2. Cetopsis aspis, paratype, USNM 432559, 46.9 mm SL, immediately after capture. Photo:Aniel Gangadin.

FIGURE 3. Map showing the distribution of Cetopsis aspis. Square represents the type locality, Mauritie Creek, upper Commewijne River basin, Sipaliwini District, Suriname. Circles represent the localities of paratypes, Konawaruk River and tributaries, Essequibo River basin, Guyana.

FIGURE 4. Type locality of Cetopsis aspis. Mauritie Creek, upper Commewijne River basin, Sipaliwini District, Suriname. The grey-white color of the water is caused by suspended sediments resulting from activities of gold miners 100 m upstream of the collection site.

FIGURE 6. Ventral view of the ethmoid region of skull and associated structures of Cetopsis aspis MZUSP 125262. LE: Lateral ethmoid; ME: mesethmoid; ORB: orbitosphenoid; PAR: parasphenoid; PMX: premaxilla; V: vomer. Scale bar = 1mm.