Chiloglanis mongoensis, Schmidt & Barrientos, 2019

Schmidt, Ray C. & Barrientos, Christian, 2019, A new species of suckermouth catfish (Mochokidae: Chiloglanis) from the Rio Mongo in Equatorial Guinea, Zootaxa 4652 (3), pp. 507-519 : 510-516

Chiloglanis mongoensis sp. nov.

urn:lsid:zoobank.org:act:DFA1373D-A028-4DD8-8A0C-B91F68BBF584

Figures. 1 , 2 , 3 , 4 ; Table 2

Holotype. USNM 446973 , male ALC, 28.0 mm SL; Equatorial Guinea, Centro Sur, Rio Mongo near Mosumu , 251 m, 1.72809° N, 10.08800° W, 2017 Equatorial Guinea expedition team, 2 July 2017.

Paratypes. MRAC 2019.010 .P.0001, Male ALC, 34.8 mm SL, voucher number EqGui2017_328, collection information the same as the holotype . — USNM 446974 , female ALC, 26.0 mm SL, collection information the same as the holotype . — USNM 446975 , Female ALC, 33.1 mm SL, voucher number EqGui2017_329, collection information the same as the holotype .

Diagnosis. Chiloglanis mongoensis is readily distinguished from all other valid species of Chiloglanis with the exception of C. marlieri and C. harbinger in possessing 28–30 (14+14 – 15+15) mandibular teeth in one row. Chiloglanis mongoensis is distinguished from C. marlieri in possessing a longer dorsal spine (1.8 times into head length versus 3.1 in C. marlieri ). Chiloglanis mongoensis is distinguished from C. harbinger in having fewer premaxillary teeth (99–116 versus 150–224) arranged in fewer rows (4–5 versus 7), a longer dorsal spine (9.0–9.7 versus 7.8–9.0% SL), a deeper body at anus (14.0–16.0 versus 11.7–13.8% SL), a larger eye (3.7–4.6 versus 2.9–3.5% SL), and a higher adipose fin (2.6–3.9 versus 1.6–2.3% SL; Tables 2 and 3 ).

Description. Morphometrics and meristics for holotype and paratypes of Chiloglanis mongoensis are summarized in Table 2 . Dorsal, lateral, and ventral views ( Fig. 4 ) illustrate body shape, fin shape and placement, oral disc size and shape, size of premaxillary tooth pads and mandibular tooth row, and length of maxillary and mandibular barbels.

A moderate to diminutive Chiloglanis ; 34.8 mm maximum standard length observed in four collected specimens. Body dorsally depressed anteriorly; laterally compressed posteriorly. Pre-dorsal convex; sloping ventrally towards posterior nares; pre-orbital convex; sloping ventrally sharply anterior of nares. Post-dorsal body gradually sloping towards the caudal fin. Pre-anal profile largely horizontal to convex; post-anal profile concave. Small unculiferous tubercles present on body; concentrations higher near head. Lateral line complete; arising just dorsal to the horizontal level of orbit and sloping ventrally to midlateral along the side of the body towards the caudal peduncle. Urogenital papillae sexually dimorphic; elongated in males; reduced and separated from anus by shallow invagination in females.

Head depressed. Gill membranes broadly united. Gill openings restricted; opening near horizontal level of pectoral-fin terminus to level of orbit. Occipital-nuchal shield covered and visible through skin. Eyes moderate; located just posterior to mid-head length; horizontal axis longest; without free margins. Anterior and poster nares positioned mid-snout; anterior nares set further apart than posterior nares. Nares with raised rims; posterior nares with elongate anterior flaps.

Mouth inferior; upper and lower lips united to form oral disc. Oral disc large (width 26.3–27.2% SL); wider than long and covered in papillae. Barbels in three pairs; maxillary barbels originating from posterolateral region of the disc just past mid-length; unbranched and short (4.5–5.6% SL). Lateral and medial mandibular barbels short; incorporated into lower lip and positioned on both sides of midline cleft on posterior margin of the oral disc. Lateral mandibular barbel usually longer (1.1–1.4% SL) than medial mandibular barbel (0.8–1.0% SL). Primary premaxillary teeth “S” shaped with exposed brown tips; 99–116 teeth in 4 or 5 scattered rows on two ovoid tooth patches. Secondary premaxillary teeth small and scattered on posterior surface of premaxillae. Tertiary teeth small and needle-like; in a row near midline of dorsal edge of toothplate. Mandibular teeth “S” shaped; 1 or 2 rows; bunched near midline. Functional rows and replacement rows usually contain 14+14 or 15+15 brown-tipped teeth.

Dorsal-fin origin in anterior third of body; origin just posterior to vertical of pectoral-fin origin. Dorsal fin with small spinelet, spine, and 4 or 5 rays. Dorsal spine short (9.0–9.7% SL); anterior margin smooth with two notches distally; posterior margin smooth. Adipose fin base length long (20.7–22.5% SL) and low (height 2.6–3.9% SL); margin convex. Caudal fin forked; rounded lobes; lower lobe longer than upper lobe; count i, 7, 8, i. Anal-fin origin posterior to origin of adipose fin; extending just beyond adipose-fin terminus; margin convex; no sexual dimorphism observed; count iii, 4 or 5. Pelvic-fin origin posterior to the vertical of midpoint between dorsal-fin terminus and adipose-fin origin; margins convex; not reaching anal-fin origin; count i, 6. Pectoral fin with mostly smooth spine; two small notches on distal edge of anterior margins; relatively short (13.3–14.3% SL); count I, 8–9. Postcleithral process not sexually dimorphic. Sexual dimorphism in body size and density or shape of unculi not observed in the four type specimens.

Coloration. Live coloration: body with a light brown to cream ground color, nearly uniformly overlain with medium to dark brown melanophores. Typical coloration of preserved specimens is shown in Figure 4 . Dorsal view: cream ground color overlain with medium to dark brown melanophores; lighter areas pre-orbit, at origin of dorsal fin, and origin and terminus of adipose fin. Lateral view: Cream ground color overlain with medium brown melanophores; mostly uniformly distributed along sides above midline and sparser ventrally. Lighter small circular areas along sides just anterior to lateral line; light areas dorsal to anal-fin terminus and ventral to adipose-fin terminus. Ventral surface cream; few melanophores scattered along bases of pectoral, pelvic, and anal fins.

Pectoral and dorsal spines and rays cream-buff to translucent. Base of dorsal fin cream with scattered melanophores. Dorsal-fin rays with melanophores uniformly arranged on distal half; membranes cream to translucent. Base of pectoral fin cream with scattered melanophores; rays with scattered melanophores on distal half; membranes cream. Pelvic fin cream with few melanophores on rays. Anal-fin base cream with scatter melanophores; rays with few scatter melanophores; membrane translucent. Adipose fin cream to translucent; scattered melanophores more numerous along base. Caudal fin cream to translucent; dark brown melanophores scattered at base and in distal twothirds of upper and lower lobe.

Etymology. The specific epithet refers to the Rio Mongo, a tributary to the Rio Wele in Equatorial Guinea, where the species is presumed endemic.

Distribution. Chiloglanis mongoensis is only known for the type locality. Upstream from the bridge crossing the Rio Mongo cascades down a bedrock outcrop that is ~3-4 meters high and ~10 meters long. Standing on this very slippery bedrock we were able to collect several specimens of C. cameronensis and C. mongoensis from cracks in the bedrock with the electrofisher. After 30 to 45 minutes we collected four C. mongoensis and five C. camero- nensis specimens. Though collected in the same microhabitat; it seems likely that further, more focused, collections would reveal that these two species are occupying different habitats within the Rio Mongo. In co-occurring Chi- loglanis species from the Upper Guinea Forest streams in Guinea, Conakry one species is usually found in woody debris or submerged roots while the other occupies the cobble and larger rocks in the riffles and runs ( Schmidt et al. 2017b). Chiloglanis mongoensis or C. cameronensis specimens were not collected in a small tributary to the Rio Mongo, but the stream was shallow, substrate was mostly sand and gravel, and there was little flow.

Figures

FIGURE 1. Type localities of Chiloglanis harbinger (triangle) and Chiloglanis mongoensis (star). All other localities sampled during 2017 expedition shown in white circles.

FIGURE 2. Scatterplot of PC1 versus PC2 from principal component analysis of 44 log-transformed measurements from 12 specimens. Holotype of Chiloglanis mongoensis denoted by star.

FIGURE 3. Scatterplot of total numbers of premaxillary teeth versus PC2 from principal components analysis of 44 log- transformed measurements (A). Reduced-major axis regression of log-transformed total number of premaxillary teeth on log- transformed standard length (B). Trendlines are shown for each species; slopes for each species are equal (p-value = 0.5029) and the y-intercept (i.e., elevation) between each species are significantly different (p-value = 0.0446). Holotype of Chiloglanis mongoensis denoted by star.

FIGURE 4. Chiloglanis mongoensis, a new species, holotype, USNM 446973, male ALC, 28.0 mm SL; Equatorial Guinea, Centro Sur, Rio Mongo near Mosumu, 1.72809° N, 10.088° W; in dorsal, lateral, and ventral views. Photographs by S. Rare- don