Magdalenichthys mompox DoNascimiento, Villa-Navarro, Albornoz-Garzón, Méndez-López & Conde-Saldaña, 2025

Magdalenichthys mompox DoNascimiento, Villa-Navarro, Albornoz-Garzón, Méndez-López & Conde-Saldaña sp. nov.

( Figs 5–6 View Figure 5 View Figure 6 ; Table 1 View Table 1 )

ZooBank registration: urn:lsid:zoobank.org:act:.

Holotype: CZUT-IC 25911 (38.0 mm SL); Colombia, Antioquia, Cáceres, Cauca River ; 07°41’12”N 75°16’30”W, 100 m a.s.l.; D. Montoya-Ospina & D. Bedoya, 8 Feb 2019. GoogleMaps

Paratypes: Colombia: CIUA 8149 (1, 37.7 mm SL); Tolima, Ortega, río Tetuan , 03°51’10.3”N 75°16’24.2”W; J.G. Ospina Pabón, D. Restrepo Santamaría, J.L. Londoño López, 6 Mar 2023 GoogleMaps . CZUT-IC 15098 (10, 24.7–34.2 mm SL, 1 c&s, 30.9 mm SL); Cesar, El Copey, río Ariguaní , tributary of río Cesar ; 10°16’05”N 73°59’14”W, 163 m a.s.l.; J.G. Albornoz-Garzón & G. Beltrán, 22 Oct 2015 GoogleMaps . CZUT-IC 20495 ( 1, 33.2 mm SL, 1 c&s, 33.4 mm SL); collected with holotype. GoogleMaps IAvH-P 21928 (3, 21.1–31.5 mm SL); Colombia, Antioquia, Cáceres , Cauca River at Puerto Bélgica, 07°41’25.6”N 75°16’22.34”W; D. Montoya-Ospina, 4 Feb 2019 GoogleMaps .

Diagnosis: Magdalenichthys mompox differs from all its congeners by having a rectangular contour of the head in dorsal view, with lateral profiles straight (vs. parabolic, with lateral profiles convex); more numerous gill rakers on first arch (7–8 vs. 3–5 in M. lundbergi , 5–6 in M. poira , 3–4 in M. yariguies ); fewer vertebrae (32–33 vs. 36–37 in M. lundbergi , 38–39 in M. poira , 40 in M. yariguies ); first dorsal-fin pterygiophore inserted posterior to neural spine of vertebra 9 (vs. vertebrae 10–12); first anal-fin pterygiophore inserted posterior to hemal spine of vertebra 21 (vs. vertebrae 23–25); caudal-fin lobes subequal (vs. upper-caudal fin lobe distinctively longer than lower lobe); and more numerous caudal-fin branched rays (15 vs. 14 or fewer). Magdalenichthys mompox can be additionally distinguished from M. lundbergi and M. poira by having the adipose-fin origin posterior to the anal-fin origin (vs. origin of both fins at same vertical); narrower mouth (28.7–36.3% of HL vs. 36.1–43.7% in M. lundbergi , 41.3–53.5% in M. poira ); longer maxillary barbel (22.8–32.1% of HL vs. 17.5–23% in M. lundbergi , 17.5–23% in M. poira ); and longer inner mental barbel (12.5–15.8% of HL vs. 8.6–12% in M. lundbergi , 8.4–12.9% in M. poira ). Magdalenichthys mompox can be recognized from M. lundbergi and M.yariguies by having a longer prepelvic length (42–47.9% of SL vs. 35.1–42.6% in M. lundbergi , 35.4–41.5% in M. yariguies ); shorter adipose-fin base (17.5–20.9% of SL vs. 22.9–29.8% in M. lundbergi , 26.2–28.9% in M. yariguies ); and longer caudal-fin lower lobe (21.9–24.9% of SL vs. 16–20.5% in M. lundbergi , 16.3–19.4% in M. yariguies ). Magdalenichthys mompox can be recognized from M. poira and M. yariguies by having a longer head (22.9–25.1% of SL vs. 18.4–22.1% in M. poira , 16.7–20.4% in M. yariguies ). Magdalenichthys mompox further differs from M. poira by having more ribs (eight vs. six to seven) and fewer number of ventral procurrent caudal-fin rays (12–14 vs. 15–16). Magdalenichthys mompox further differs from M. yariguies by having fewer principal anal-fin rays (9–10 vs. 11–12); greater cleithral width (15.3–19.1% of SL vs. 12.8–15.2%); and shorter anal-fin base (9.9–13.5% of SL vs. 15.6–18.1%).

Description: Morphometric data in Table 1 View Table 1 . Refer to Figure 5 View Figure 5 for general appearance.Small heptapterine catfish (largest specimen 38 mm SL), with elongated body, elliptical in cross-section at dorsal-fin origin (longest axis vertical), progressively more compressed to caudal region. Dorsal profile straight from snout tip to occipital region, straight and slightly ascending immediately posterior to this point to dorsal-fin origin, straight along dorsal-fin base to adipose-fin origin, sloping ventrally along adipose-fin base and slightly ascending along dorsal membrane supported by procurrent caudal-fin rays. Ventral profile of head slightly convex, then straight to anal-fin origin, dorsally sloping along anal-fin base to origin of procurrent caudal-fin rays and slightly descending along membrane supported by procurrent caudal-fin rays.

Head depressed, roughly rectangular in dorsal view, dorsally covered by thin skin. Cheek filled with muscular mass of adductor mandibulae, but muscle not reaching dorsally onto skull roof. Snout short and rounded. Mouth slightly prognathous. Premaxillary teeth arranged in a rhomboidal patch of 4–5* medial and 8*–9 lateral irregular rows of minute conical teeth. Lower jaw slightly longer than upper jaw. Dentary teeth in 4*–5 irregular rows of minute conical teeth, similar to those on premaxilla. Maxillary barbel reaching base of innermost pectoral-fin ray. Conspicuous groove accommodating anterior part of maxillary barbel along sides of head and delimiting dorsal and lateral regions of head. Bases of outer and inner mental barbels in a straight line. Outer mental barbel reaching pectoral-fin origin. Inner mental barbel reaching branchial opening. Small subcutaneous eye, dorsal in position and almost circular. Anterior naris tubular. Posterior naris closer to anterior margin of eye than to anterior naris, anteriorly bordered by a low fleshy margin. Anterior and posterior internarial widths equal. Nares disposed in a squared arrangement. Branchiostegal membrane free, supported by 7 or 8 rays and joined to isthmus only at anteriormost point. Gill rakers of first arch 7–8, located along anterior margin of ceratobranchial.

Lateral line canal complete, reaching caudal skeleton. Supraorbital pore s1 medially adjacent to anterior naris; s2 + i2 pore slightly closer to anterior naris ( Fig. 6 View Figure 6 ), at distal end of posteriorly directed membranous tubule, originating from commissure connecting supraorbital and infraorbital canals, closer to supraorbital canal; s3 pore not visible externally, inside posterior naris, adjacent to its posterior margin, at notch of cutaneous membrane. Contralateral supraorbital canals connected medially by epiphyseal membranous branch, dorsal to middle of anterior fontanel, without superficial pore; s8 pore (parietal branch) arising from a posteriorly directed membranous canal, externally located posterior to eye, at level of medial margin of eye; s4 and s7 branches and pores absent. Infraorbital pore i1 laterally adjacent to anterior naris, between naris and maxillary barbel base; i3 pore posterior to maxillary barbel base; i4 pore approximately at vertical through posterior margin of posterior naris; i5 pore at vertical through posterior margin of eye; i6 pore posterior to eye, aligned with ventral margin of eye. Pterotic branch (po2) at posterolateral corner of pterotic. Dentary with seven pores of preoperculo-mandibular canal. Submental pores (pm1) paired. Sixth and seventh mandibular pores approximately at same vertical level. Subpreopercular ossicle with one pore (pm8). Preopercle with two pores, anterior pore (pm9) originating from membranous tubule lateral to interopercle and posterior pore (pm10) from membranous tubule passing lateral to ventral portion of opercle. Last preopercular pore (po1 + pm11) at end of membranous tubule, dorsal to dorsoposterior portion of opercle. Axillary branch (ll1) ventral, running posterior to supracleithrum.

Precaudal vertebrae 9 (1)–10 (1), thoracic vertebrae 7(1) or 8 (1), and caudal vertebrae 23, totalling 32–33 vertebrae. Ribs eight (last rib shortest). Pectoral fin with i,7* (8)–8 (1) rays. First pectoral-fin ray (unbranched) soft and shorter than first branched ray. First branched ray longest. Distal margin of pectoral fin convex. Pelvic fin with i,5 rays. First pelvic-fin ray (unbranched) thick and shortest, second and third branched rays longest. Pelvic-fin origin at level of first branched ray of dorsal fin, at vertical through vertebrae 13 or 14. Dorsal fin lacking spinelet, with one unbranched and six branched rays (one c&s specimen with five branched rays), supported by seven pterygiophores. Dorsal-fin margin convex, its unbranched ray as long as first branched ray; first three branched rays subequal. First dorsal-fin pterygiophore inserted posterior to neural spine of vertebra 9 and last pterygiophore anterior to neural spine of vertebra 15. Adipose fin long, almost rectangular with attenuated ends and posterior lobe free. Adipose-fin origin at vertical through second unbranched ray of anal fin. Anal fin with 2 (1)–3 (1) procurrent (unsegmented) rays, and 2 (4)–3* (5) unbranched and six* (3) or seven (5) branched rays for a total of nine (5) or ten (3) principal rays. Posteriormost one or two rays (branched) associated with last pterygiophore. Anal-fin distal margin rounded. Anal fin supported by nine pterygiophores. First anal-fin pterygiophore posterior to hemal spine of vertebra 21 and last pterygiophore anterior to hemal spine of vertebra 27. Caudal fin deeply forked with i,7 + 8,i principal rays. Caudal-fin lobes subequal, with lower lobe slightly longer than upper lobe, both lobes pointed. Procurrent caudal-fin rays 13 (1) or 14 (1) dorsal and 12 (1) or 14 (1) ventral, located posterior to vertebra PU 5 (dorsal rays) and to PU 5 or PU 6 (ventral rays). Posteriormost two procurrent caudal-fin rays segmented. Caudal skeleton PH + 1 + 2,3 + 4 + 5. Long epural present.

Pigmentation in alcohol: Overall ground coloration light brown. Minute and numerous melanophores clustered at humeral region. Dorsal surface of head and predorsal area darker than remaining of body surface. Dark streak extending dorsally on surface of snout, between base of maxillary barbel and anterior margin of eye. Conspicuous and narrow pale band posterior to head, between dorsal corners of branchial openings. Cheeks and maxilar groove lighter than remaining surface of head, peppered with sparse chromatophores. Basal portion of maxillary barbel darkly pigmented on dorsal surface. Pale transversely oval spot at dorsal-fin origin. Base of dorsal fin and adipose fin with a dark band along sides. Ventral surface of head and body pale. Adipose fin with sparse chromatophores. Rays of fins with chromatophores. Interradial membrane of fins hyaline.

Distribution: This species has a patchy distribution in three disjunct areas of the Magdalena basin, the lower course of the main channel of the Cauca River, the río Ariguaní, a tributary of the lower basin of the río Cesar, and in the río Tetuan, a tributary of the río Saldaña that drains directly in the upper basin of the Magdalena River ( Fig. 4 View Figure 4 ). It is expected that this distribution pattern simply reflects an artifact of sampling.

Etymology: The species name refers to the Cacique Mompoj of the Malibú tribe that once inhabited the region today corresponding to the municipality of Santa Cruz de Mompox, within the so-called Momposina Depression. This indigenous group was exterminated by the Spanish armies of Gerónimo Lebrón and Alonso Martín, during the Cesar massacre of 1540. Used as a noun in apposition.