Panaqolus purusiensis (LaMonte, 1935)

Cramer, Christian Andreas, 2014, Redescription of Panaqolus purusiensis (LaMonte, 1935) (Siluriformes: Loricariidae) with identification key to the species of the genus, Neotropical Ichthyology 12 (1), pp. 61-70 : 62-67

Panaqolus purusiensis (LaMonte, 1935) Figs. 1a , 2-4

Diagnosis. The presence of dark bars on the trunk (in specimens smaller than 85 mm SL) and bands on the fins alternating with light interspaces distinguishes Panaqolus purusiensis from all congeners except P. changae , P. maccus , and P. gnomus . Panaqolus purusiensis can be distinguished from P. changae by the dorsal-adipose distance (16-25% of SL vs. 14-17% of SL [n = 8]), by the coloration of its head (straight light lines vs. worm lines) and the dark bars on body and fins (dark bars wider than light interspaces vs. dark bars as wide as or thinner than the lighter interspaces) and the larger adult size (130 mm SL vs. 86 mm SL). Panaqolus purusiensis differs from P. gnomus by the posterodorsal to anteroventral orientation of bars on the trunk (vs. anterodorsal to posteroventral [n = 30]) and the larger adult size (130 mm SL vs. 70.8 mm SL). From P. maccus it can be separated by a shorter head length (33-39% SL vs. 37-42% [n = 8]), the smaller cleithral width (31-36% SL vs. 34-44%), the greater dorsal-pelvic depth (22-32% SL vs. 19-23%), and the larger adult size (130 mm SL vs. 87.6 mm SL).

Panaqolus purusiensis can be distinguished from P. albomaculatus by its body and fin coloration (alternating dark and light bars or uniformly brown body [in large specimens] vs. small, white or yellowish spots on body and fins [n = 26]), by the position of the dentaries (touching in the middle forming a V with approximately 70° angle vs. normally not touching, forming a very acute angle or being nearly parallel [ Fig. 1 ]), by the mouth width (42-50% HL vs. 32-44%) and the longer maxillary barbel length (10-18% HL vs. 2-10%). As P. dentex do not pass a size of 74 mm SL, a size where P. purusiensis still shows its banded pattern on body and fins, these two species can easily be separated as the former species never shows bands on body or fins (n = 20).

The lines on the head and trunk may be faded in large specimens (> 85 mm SL) of P. purusiensis . In this case, these specimens are especially difficult to distinguish from large P. nocturnus ( Fig. 5 ). Panaqolus purusiensis usually has a higher caudal peduncle than P. nocturnus (11-14% SL vs. 10-12% [n=30]), large individuals (> 85 mm SL) have a lower thorax length to pelvic-dorsal depth ratio (86-98% SL [mean 93%] vs. 86-125% SL [mean 103%), and a lower dorsal-pectoral depth to dorsal-pelvic depth ratio (107-116% SL [mean 111%] vs. 110-142% SL [mean 122%]). Panaqolus koko (n = 1) has uniformly dark body and fins (vs. banded) and nearly quadrate teeth with strong lateral cusps (vs. round teeth without or with small lateral cusps).

Description. Counts and proportional measurements in Table 1 . Medium-sized loricariid with standard length of measured specimens up to 130.4 mm SL. Dorsal profile of head and snout strongly convex from snout tip to posterior tip of supraoccipital, straight and posteroventrally slanted between dorsal-fin origin and adipose-fin origin, gently concave through caudal peduncle to posterior tip of last procurrent caudal fin ray. Dorsal orbit margin slightly raised, forming a gentle ridge, narrowing anteriorly, from anterior orbit margin to area lateral to nares. Dorsal surface of trunk transversely flattened from dorsal-fin origin to adipose-fin base. Ventral profile of head and body flat from oral disk to anal-fin origin. Caudal peduncle oval in cross-section and relatively deep (11-14% SL).

Greatest body depth at dorsal-fin origin. Pectoral-fin origin just posterior to orbit; pelvic-fin origin at vertical through origin of second dorsal-fin ray; anal-fin origin shortly posterior after vertical through origin of last dorsal- fin ray. Adipose fin with well-ossified leading spine bearing odontodes.

Dorsal fin II,7-8 (holotype II,8), pectoral fin I,6, pelvic fin i,5, anal fin i,4, caudal fin i,13-14,i (holotype i,13,i). Spinelet V-shaped, dorsal-fin spine lock functional, posterior fin margin straight, margin of last two rays rounded. Dorsal-fin origin closer to vertical line passing through pelvic-fin origin than to vertical line passing through pectoral fin origin; not reaching adipose fin when adpressed. Adipose fin triangular; adipose-fin spine slanted posteroventrally, tip straight to curved ventrally, pointed; posterior margin of adipose-fin membrane concave to nearly vertical. Pectoral-fin spine robust, membrane of interspace between spine and first ray may bare fleshy extension in large individuals, posterior fin margin straight, when depressed reaching 1 / 3 of pelvic fin. Pelvic-fin spine robust, posterior margin slightly rounded, when adpressed reaching mid-length of anal fin. Caudal fin forked.

Head and body entirely plated except for small naked area around dorsal-fin base, snout without naked area near tip. Abdomen of adults ranging from incompletely plated (plates only in skin ventral to pectoral girdle, along sides, and in skin posterior to pelvic fin) to completely covered by small irregularly arranged platelets (specimens> 85 mm SL). Abdomen of juveniles unplated. Area dorsal to pelvic-fin base below ventral margin of inframedian plate row usually with 1-3 small plates, without smaller platelets and with large intervening naked space. Supraoccipital bordered posteriorly by 2-3 (mode 2) scutes on each side. Body with pronounced lateral ridge extending from cleithrum to posterior margin of fifth or sixth plate of the inframedian plate row; ridge gradually decreasing in prominence posteriorly. Trunk without elevated ridges.

Head and body covered by odontodes of uniform size and distribution. Enlarged odontodes on anterodorsal border of pectoral-fin spine. Cheek odontodes hypertrophied with tips recurved laterally, longest odontode extending to posterior cleithrum margin. Interorbital space straight or slightly convex. Eye moderately large, dorsolaterally placed; orbit diameter 14-22% HL. Iris diverticulum present. Nares small and ovoid, slightly longer than wide.

Oral disk round, distal margin of upper lip well separated from maxillary barbel base. Maxillary barbels of moderate length (10-18% HL). Lips moderately rugose, small patch of elongate fleshy papillae medial to each tooth row. Border of lips smooth.

Teeth spoon-shaped and normally unicuspid; sometimes a very small lateral cusp is present that may be reduced to a lateral dent ( Fig. 6 ). Premaxillary teeth 5-7 per ramus (mode 5), mandibular teeth 4-7 per ramus (mode 6). Premaxillae angled at approximately 90°, dentaries at approximately 70° ( Fig. 1 ).

Color in alcohol. Base coloration on body, head and fins light brown or olivaceous in large specimens (> 85 mm SL) or dark brown if smaller ( Fig. 4 ). Fins showing dark and light bands in all sizes. Small individuals (<25 mm SL) with four clear light bands on trunk, nearly as wide as the dark interspaces; fine light lines on head, going from eyes to the margin; abdomen light without dark markings. Medium sized specimens (25-85 mm SL) with 5 to 9 light bands on trunk. Number of bands increasing with size. Anterior bands very thin, slightly thickening towards the caudal fin. Markings on head only visible in smaller individuals. Abdomen dark brown with irregular white worm lines. Large specimens without bands on trunk and light markings on abdomen or with only some faint traces of them. Coloration light brown or olivaceous with darker or lighter shadows.

Sexual dimorphism. No clear sexual dimorphism could be observed in the specimens examined.

Distribution and Habitat. The species is known from the upper Purus drainage ( Fig. 7 ). Some of the specimens were caught at night with a cast net on stony bottom in strong current (MCP 45733). Others had been picked by hand from holes in rotten wood in low current (UFRO-I 17720).

Figures

Fig. 1. Mouth of a) Panaqolus purusiensis (MUSM 39425) and b) P. albomaculatus (UFRO-I 17825) with the different angles of the dentaries.

Fig. 2. Dorsal, lateral, and ventral views ofPanaqolus purusiensis, holotype, AMNH 12600, 106.7 mm SL, Brazil,Acre, Purus drainage, vicinity of the mouth of rio Macauã, a tributary of rio Iaco.

Fig. 3. Lateral views of the topotypes of Panaqolus purusiensis collected by Krukoff: a) USNM 94665, 110.6 mm SL; b) MSNM Pi43, 126.4 mm SL. Photo by G. Bardelli.

Fig. 4. Lateral views of recently collectedPanaqolus purusiensis to show the different size-dependent color patterns: a) 15.5 mm SL; b) 42.8 mm SL; c) 83.3 mm SL (all UFRO-I 17720); d) 130.4 mm SL (MUSM 39425). Photos by B. S. F. Barros.

Fig. 5. Lateral view of an adult Panaqolus nocturnus (AUM 45528, 137.4 mm SL) to show the similarity between adult P. nocturnus and P. purusiensis. Photo by B. S. F. Barros.

Fig. 6. Teeth ofPanaqolus purusiensis: a) Teeth without lateral dent (UFRO-I 17720, premaxilla); b) teeth with rudiment of a lateral cusp in form of a small lateral dent (MUSM 39425, dentary); c) tooth with small lateral cusp (MCP 45733, dentary).

Fig. 7. Distributions of Panaqolus purusiensis (hexagon) and P. nocturnus (triangle). Open symbol: type locality. Symbols may represent more than one locality or lot.