Trichomycterus (Psammocambeva) diamantinensis, Costa & Feltrin & Mattos & Katz, 2024

Costa, Wilson J. E. M., Feltrin, Caio R. M., Mattos, Jose L. O. & Katz, Axel M., 2024, Relationships and description of a new catfish species from Chapada Diamantina, the northernmost record of Trichomycterus s. s. (Siluriformes, Trichomycteridae), Zoosystematics and Evolution 100 (1), pp. 223-231 : 223

Trichomycterus (Psammocambeva) diamantinensis sp. nov.

Figs 2 , 3 , 4A-C

Type material.

Holotype. Brazil • 1 ex., 82.2 mm SL; Bahia State: Palmeiras Municipality: Vale do Capão District: Rio da Bomba, tributary of Rio Preto, Rio Santo Antônio drainage, Rio Paraguaçu Basin; 12°39'35"S, 41°29'14"W; about 980 m a.s.l.; 15 May 2023; C. R. M. Feltrin, R. dos Santos-Junior, and G. L. Canella, leg; UFRJ 13688.

Paratypes. Brazil • 3 ex. (DNA), 39.7-60.5 mm SL; collected with holotype; UFRJ 13686; • 3 ex. (C&S), 49.4-70.0 mm SL; collected with holotype; UFRJ 13689; • 2 ex., 27.1 and 79.6 mm SL; collected with holotype; UFRJ 13690.

Diagnosis.

Trichomycterus diamantinensis is distinguished from all other species of Psammocambeva by having a unique colour pattern of adult specimens consisting of a faint brown stripe along the lateral mid-line of trunk, overlapped by a great concentration of rounded light brown spots in a more superficial layer of skin (vs. never a similar colour pattern). Trichomycterus diamantinensis also differs from its hypothesised sister species and the only other species of the CD-clade, T. tete , by having the anal-fin origin at a vertical posterior to the dorsal-fin base (vs. through the posterior portion of the dorsal-fin base), a longer nasal barbel, its tip posteriorly reaching the opercular patch of odontodes (vs. reaching area between the orbit and the opercular patch of odontodes), 39 or 40 vertebrae (vs. 36 or 37), a deeper body (body depth 14.0-17.3% SL vs. 12.5-13.2%), a deeper caudal peduncle (caudal peduncle depth 11.5-12.9% SL vs. 9.7-10.8%), a wider body (body width 11.2-12.3% SL vs. 7.3-9.0%), a wider head (head width 83.1-89.3% of head length vs. 68.7-77.5%), the anal-fin origin at a vertical through the centrum of the 25th vertebra (vs. 22nd or 23rd vertebra), the sesamoid supraorbital slender, without a lateral process (Fig. 4A ; vs. with a lateral expansion, often forming a distinctive process, Fig. 4D ), a relatively wider metapterygoid and quadrate (Fig. 4B vs. Fig. 4E ) and a minute ventral middle foramen of the parurohyal (Fig. 4C ; vs. broad, Fig. 4F ).

Description.

General morphology. Morphometric data are in Table 3 . Body moderately slender, head and trunk excluding caudal peduncle with dorsal profiles slightly convex, and ventral profile nearly straight, dorsal and ventral profiles of caudal peduncle approximately straight. Greatest body depth at vertical just anterior to pelvic-fin base. Trunk subcylindrical anteriorly, compressed posteriorly. Anus and urogenital papilla at vertical through dorsal-fin origin or just posterior to it. Head subtrapezoidal in dorsal view, snout profile slightly convex. Eye relatively small, dorsally positioned in head, nearer snout margin than opercle. Posterior nostril located nearer anterior nostril than orbital rim. Tip of maxillary barbel posteriorly reaching between posterior limit of interopercular patch of odontodes and pectoral-fin base, rictal barbel reaching posterior portion of interopercular patch of odontodes and tip of nasal barbel reaching opercular patch of odontodes. Mouth subterminal. Jaw teeth pointed, slightly curved, arranged in irregular rows. Premaxillary teeth 45-50, dentary teeth 44-50. Odontodes conical, elongate; opercular odontodes arranged in irregular transverse rows, interopercular odontodes arranged in irregular longitudinal rows. Opercular odontodes 17-19, interopercular odontodes 38-42. Branchiostegal rays 7.

Dorsal and anal fins subtriangular, anterior and posterior margins slightly convex. Total dorsal-fin rays 12 (iii + II + 7), total anal-fin rays 10 (iii + II + 5); anal-fin origin at vertical just posterior to dorsal-fin base end. Dorsal-fin origin at vertical through centrum of 20th vertebra; anal-fin origin at vertical through centrum of 25th vertebra. Pectoral fin subtriangular in dorsal view, posterior margin slightly convex, first pectoral-fin ray terminating in filament, its length about 25% of pectoral-fin length without filament. Total pectoral-fin rays 8 (I + 7). Pelvic fin subtruncate, its posterior extremity not reaching urogenital papilla, at vertical through dorsal-fin origin or immediately posterior to it. Pelvic-fin bases medially in close proximity. Total pelvic-fin rays 5 (I + 4). Caudal fin truncate. Total principal caudal-fin rays 13 (I + 11 + I), total dorsal procurrent rays 17 or 18 (xvi-xvii + I), total ventral procurrent rays 13 or 14 (xii-xiii + I).

Latero-sensory system. Supraorbital canal, posterior section of infraorbital canal and postorbital canal continuous. Supraorbital sensory canal with 3 paired pores: s1, adjacent to medial margin of anterior nostril; s3, adjacent and just posterior to medial margin of posterior nostril and s6, at transverse line through posterior half of orbit; s6 pore about equidistant from its symmetrical homologous s6 pore than orbit. Infraorbital sensory canal with 2 segments. Anterior infraorbital canal with 2 pores: i1, at transverse line through anterior nostril and i3, at transverse line just anterior to posterior nostril. Posterior infraorbital canal with two pores: i10, adjacent to ventral margin of orbit and i11, posterior to orbit. Postorbital canal with 2 pores: po1, at vertical line above posterior portion of interopercular patch of odontodes, and po2, at vertical line above posterior portion of opercular patch of odontodes. Lateral line of trunk with 2 pores just posterior to head.

Osteology (Fig. 4A-C ). Anterior margin of mesethmoid nearly straight, mesethmoid cornu rod-shaped, tip rounded. Lacrimal oval, its largest length about one third of sesamoid supraorbital length. Sesamoid supraorbital narrow, rod-like, longer than premaxilla largest length. Premaxilla sub-rectangular in dorsal view, slightly tapering laterally. Maxilla boomerang-shaped, slender, slightly shorter than premaxilla, with minute posterior process. Autopalatine sub-rectangular in dorsal view when excluding posterolateral process, its shortest width about half autopalatine length, lateral and medial margins weakly concave. Latero-posterior process of autopalatine triangular, its length about two thirds of autopalatine length excluding anterior cartilage. Metapterygoid subtriangular, deeper than long, with distinctive posterior projection; anterior margin weakly bent, posterior margin slightly sinuous. Quadrate robust, dorsoposterior outgrowth in close proximity to hyomandibular outgrowth. Hyomandibula long, anterior outgrowth with small concavity on dorsal margin. Opercle moderately elongate, opercular odontode patch slender, its depth about half length of dorsal articular facet of hyomandibula; dorsal process of opercle short and blunt. Interopercle long, its longitudinal length about three fourths of hyomandibula longitudinal length. Preopercle compact, without ventral expansion. Parurohyal robust, lateral process relatively elongate, sharply pointed. Parurohyal head well-developed, with minute anterolateral paired process. Middle parurohyal foramen small, its largest length about one fourth of distance between anterior margin of parurohyal and anterior insertion of posterior process. Posterior parurohyal process long, slightly longer than distance between anterior margin of parurohyal and anterior insertion of posterior process. Vertebrae 39 or 40. Ribs 13. Two dorsal hypural plates, corresponding to hypurals 4 + 5 and 3, respectively; single ventral hypural plate corresponding to hypurals 1 and 2 and parhypural.

Colouration in alcohol

(Figs 2 , 3 ). Dorsum and flank brownish-grey, lighter ventrally, with faint brown stripe along lateral mid-line of trunk, overlapped by great concentration of rounded light brown spots extending over flank and dorsum in more superficial layer of skin. Dorsum light brown with yellowish-grey with mid-dorsal row of small brown spots between nape and dorsal-fin origin. Dorsal and lateral portions of head brownish-grey with brown spots. Ventral surface of head and trunk white. Jaws and barbels brown. Fins hyaline, with faint brown spots on basal portion of unpaired and pectoral fins. Smallest specimen (27.1 mm SL) with flank pale yellow and narrow black stripe along lateral mid-line, which becomes paler and diffuse and overlapped by brown spots in larger specimens.

Distribution and habitat.

Trichomycterus diamantinensis is presently known only from the type locality, the Rio da Bomba, a tributary of the Rio Preto, Rio Santo Antônio drainage, Rio Paraguaçu Basin (Fig. 5 ). Rio da Bomba at the type locality is a dark-coloured small river, about 15 m wide and about 1 m at deepest places, with dense riparian forest in the river banks (Fig. 6 ). Specimens of T. diamantinensis were found amongst small and medium-sized loose stones, with diameters ranging from 1 cm to 50 cm, approximately, in shallow (about between 5 and 50 cm) and fast-flowing places, with the presence of mosses, algae and fallen leaves composing the microhabitats. They were collected both in shaded and fully sun-exposed places.

Etymology.

The name Trichomycterus diamantinensis is an allusion to the occurrence of the new species in the Chapada Diamantina, north-eastern Brazil.

Figures

Figure 2. Trichomycterus (Psammocambeva) diamantinensis sp. nov., UFRJ 13688, holotype, 82.2 mm SL: A. Left lateral view; B. Dorsal view; C. Ventral view.

Figure 3. Trichomycterus (Psammocambeva) diamantinensis sp. nov., UFRJ 13690, paratype, 27.1 mm SL: A. Left lateral view; B. Dorsal view; C. Ventral view.

Figure 4. Osteological structures of A-C. Trichomycterus diamantinensis sp. nov.; D-F. T. tete. A, D. Mesethmoidal region and adjacent structures, left and middle portions, dorsal view; B, E. Left jaw suspensorium and opercular series, lateral view; C, F. Parurohyal, ventral view. Larger stippling represents cartilaginous areas.

Figure 5. Map of geographical distribution of: 1. Trichomycterus diamantinensis sp. nov. and 2. T. tete.

Figure 6. Rio da Bomba at the type locality of Trichomycterus diamantinensis sp. nov.