Mastiglanis durantoni, Pinna & Keith, 2019

Pinna, Mário De & Keith, Philippe, 2019, Mastiglanis durantoni from French Guyana, a second species in the genus (Siluriformes: Heptapteridae), with a CT scan survey of phylogenetically-relevant characters, Cybium 43 (2), pp. 125-135 : 127-132

publication ID	https://doi.org/ 10.26028/cybium/2019-423-002
DOI	https://doi.org/10.5281/zenodo.10493327
persistent identifier	https://treatment.plazi.org/id/03B4B01B-0822-0232-FE9C-FA81FE53FBF7
treatment provided by	Felipe
scientific name	Mastiglanis durantoni
status	sp. nov.

Treatment

Mastiglanis durantoni , new species

( Figs 1-2 View Figure 1 View Figure 2 )

Megalonema cf. platycephalum View in CoL ; Le Bail et al., 2000: 95.

Mastiglanis aff. asopos View in CoL ; Le Bail et al., 2012: 304, 316.

Holotype. – MNHN 2015-244 View Materials , 63.7 mm SL, Tampok River , tributary to Maroni stream, French Guiana, coll. P. Keith, P.Y. Le Bail, 17 Nov. 1998.

Paratypes. – MNHN 2015-245 View Materials , 3 ex, 43.9-64.9 mm SL, same data as holotype ; MNHN 2015-0248 View Materials , 2B, 54.7-70.7 mm SL, same data as holotype . MZUSP 118118 View Materials , 2 ex, 46.9- 67.1 mm SL, same data as holotype ;. MNHN 2015-246 View Materials , 2 ex, 46.3-50.6 mm SL, Grand Inini , tributary to Maroni stream, French Guiana, coll. P.Y. Le Bail, P. Keith, M. Jégu, E. Vigneux, M. Duranton, 30 Sep. 1997 ; MZUSP 118119 View Materials , 2 ex (1BC), 41.2-44.9 mm SL, same data as MNHN 2015- 246.

Diagnosis

Distinguished from its only congener, M. asopos , by the following characteristics: 1) slender caudal peduncle ( Fig. 1 View Figure 1 ; caudal peduncle depth 4.3-5.3% of SL vs. 5.6-6.3%); 2) upper jaw protruding markedly beyond lower, resulting in long snout ( Fig. 3 View Figure 3 ; 36.5-42.0% of HL vs. 23.4-33.6%); 3) head depressed ( Fig. 1 View Figure 1 ; head depth 34.0-44.4% of HL vs. 44.4-53.0%); 4) procurrent caudal fin rays 12 dorsally and ventrally (vs. 14-17); 5) dorsal margin of adipose fin concave (vs. variably convex, straight or gently sinusoidal); 6) occipital process deeply notched, distally V-shaped, forming an acute angle ( Fig. 4 View Figure 4 ; vs. distal margin of occipital process variably-shaped, with distal concavity, when present, semicircular or not deep, forming an obtuse angle); 7) mesethmoid cornu widest at its midlength ( Fig. 5 View Figure 5 ; vs. gradually narrower from base to tip).

Description

Morphometric data provided in table I View Table I . Refer to figures 1 and 2 for general aspect. Dorsal profile of body sloping from tip of snout to orbit, less so from that point to dorsal-fin origin, nearly straight from that point to adipose-fin origin and then slightly concave towards caudal fin. Ventral profile straight to anal-fin origin, gently concave along caudal peduncle. Body elongated, slightly depressed at dorsal-fin origin, gradually more compressed toward caudal peduncle. Concentration of adipose bodies on axillary region, immediately dorsoposteriorly to base of pectoral fin, composed of globular corpuscles, opaque-white in preserved specimens. Lateral line complete, extending posteriorly to basal third to half of caudal fin, between upper and lower lobes. Myomeres visible through skin along most of body. Head depressed, dorsally covered by thin skin. Cheeks formed by muscular mass of adductor mandibulae, dorsally forming well-defined groove accommodating basal portion of maxillary barbel. Snout long and strongly depressed, semicircular in dorsal view. Posterior nostrils well separated from anterior nostrils (internarial length about twice posterior internarial width), partially occluded with flexible anterior skin flaps. Eyes large, closely positioned in dorsal view, with orbital rim subtly invaginated anteroventrally. Mouth inferior, crescent-shaped, with flat fleshy rictal fold. Upper jaw markedly longer than lower, with premaxilla extending considerably anteriorly to mandibular symphysis ( Fig. 3A View Figure 3 ), forming nearly spatulate snout ( Figs 2 View Figure 2 , 3A View Figure 3 ). Premaxilla ( Fig. 6 View Figure 6 ) with approximately 40 tiny viliform teeth arranged in 3-4 irregular rows, its posterior comer gently curved posteriorly. Lower jaw delicate, with anguloarticular widely trabeculate on lateral surface, with similar dentition disposed in 2-3 rows ( Fig. 7 View Figure 7 ). Vomer edentulous ( Figs 5 View Figure 5 , 8 View Figure 8 ). Barbels nearly ovoid or round in cross section. Maxillary barbels long, extending posteriorly beyond origin of anal fin. Outer and inner mental barbels long, extending posteriorly slightly beyond bases of pelvic- and pectoral-fins, respectively. Branchiostegal membranes medially overlapping, joined to isthmus region only at anteriormost portion. Seven branchiostegal rays (5 on anterior ceratohyal, 1 on posterior ceratohyal, 1 on intervening cartilage). Eleven slender gill rakers on first branchial arch, ten on first ceratobranchial plus one at angle formed with first epibranchial (sometimes a vestigial one on epibranchial, near its articulation with ceratobranchial). Cranial fontanel long, interrupted by epiphyseal bridge just behind eyes ( Fig. 8 View Figure 8 ). Width of fontanel mostly even along its length, slightly narrower near anterior end. Supraoccipital process large and wide, with parallel lateral edges and strongly concave, v-shaped distal margin. Bones of cranial roof thin, without ornamentation ( Fig. 8A, B View Figure 8 ). Frontals, sphenotics, pterotics, and supraoccipital joined via overlapping joints. Nasal bones very elongate, anteriorly reaching anterior portion of mesethmoid and then curved laterally along anterior margin of mesethmoid cornua. Infraorbital bones composed of five elements: first infraorbital (with tiny transversal ossified canal medially-directed), and three subsequent long tubular infraorbitals (posteriormost onestrongly angled). Dorsal fin large, quadrangular in overall shape with distal margin gently concave, with I + 6 (*) rays. First dorsal-fin element (homologous to second dorsal-fin spine in the generalized siluriform condition) segmented, rigid proximally for as long as first branched element, and with distal portion produced into long and flexible filament reaching to anterior third of adipose-fin. First and second branched dorsal-fin elements also longer than others. Locking element (spinelet, or first dorsal-fin spine in generalized siluriform condition) absent ( Fig. 8A, B View Figure 8 ). Seven dorsal-fin pterygiophores articulating with bifid neural spines of vertebrae 6 through 12-13. Pectoral fin scythe-shaped with I + 8(2*) or I + 9 (1). First element unfused, segmented, non-serrated, with basal portion (equivalent to length of first branched element) rigid and distal portion filamentous ( Figs 1 View Figure 1 , 2 View Figure 2 ), the tip of which extends beyond vertical though anal-fin origin or to anterior third of adipose fin. Postcleithral process small, straight and spine-like, with very fine tip. Pelvic fin large, with I + 5 rays, its origin at vertical though middle of dorsal-fin base. Anal-fin rays: ii + 7 (3*), (plus 1 rudimentary anterior ray); anal fin with rounded margin in lateral profile. Nine blade-like pterygiophores between hemal spines of vertebrae 22 through 28. Adipose fin large, isosceles-triangle shaped, with smallest side leading, its origin slightly anterior to vertical through origin of anal fin ( Fig. 1 View Figure 1 ). Posterior edge of adipose fin slightly concave, with small posterior free flap. Caudal fin deeply forked, its lobes equal in length. Principal caudal rays 8/9 (*) and procurrent caudal rays 12 dorsal and 12 ventral (confirmed in 2 c&s paratypes). Hypurals 1 and 2, and 3, 4, and 5 fused. Parahypural separate. One large epural. Six pairs of pleural ribs associated with parapophyses of vertebrae 6 to 11. First complete haemal spine on vertebrae 13. Distal extremities of four anterior pleural ribs strongly expanded, with scythe-like aspect ( Fig. 8B View Figure 8 ). Total vertebrae 38.

Pigmentation in alcohol

Overall body colour pale yellowish (translucent in life and white immediately after preservation), with very reduced dark pigment, restricted to dorsal half of body and head. Dorsal trunk region with indistinct disperse scattering of individual dark chromatophores. Seven concentrations of dark pigment on body: one between head and dorsal fin (just behind nape), one in front of dorsal-fin origin, one along bases of last three branched dorsal-fin rays (one in each ray base in some specimens), one between dorsal and adipose fin, one just behind the adipose-fin origin, one on the posterior point of adipose-fin base, and one on caudal peduncle. Laterally, sparse cloud of chromatophores concentrated along the horizontal septum, forming faint longitudinal band, expanded as dark triangle over hypural plate. Some scattered melanophores on top of head region, along path of infraorbital canals and over cheek, forming thin dark outline of olfactory chamber. Dorsal part of maxillary barbels with some dark pigment. Adipose fin with few irregularly distributed melanophores. Dorsal-, pectoral-, and caudal-fin rays with few isolated dark chromatophores on some rays, with interradial membranes hyaline.

Pigmentation in life (based on photographs of one live specimen; Fig. 9 View Figure 9 )

Body partly translucent, dusky tan-yellowish. Well-defined elongate dark fields along base of dorsal fin, anterior third of base of adipose fin and posterior three-quarters of base of anal fin. A round dark spot at base of caudal fin, slightly displaced towards ventral lobe. Faint irregular dark fields on sides of body, formed by concentrations of internal dark chromatophores on sagittal plane visible by transparency. Barbels iridescent white. Fins transparent, with first ray of dorsal fin light tan. Dorsal aorta visible by transparency as thin dark midlateral line along most of body.

Etymology

The species name is dedicated to Michel Duranton, who collected with the second author the first specimens of the species, in recognition of his fascinating work on the fauna of French Guiana.

Distribution

Preserved specimens come from two small unnamed creeks, one tributary to the Tampok River and the other to the Grand Inini River ( Le Bail et al., 2000). Additionally, the species was seen and photographed in the Waki River ( Melki, 2016), but no specimens were preserved from that locality. All sites are within a ca. 60 km radius. The Tampok, Waki and Grand Inini are independent tributaries to the Maroni River in French Guiana ( Fig. 10 View Figure 10 ).

Ecological notes

The species was found in the dry season in small clear water tributaries (depth 30-50 cm) on substrate composed of pebbles and sand, with slow current. It co-occurred with 39 to 49 other species, several of which are catfishes: Chasmocranus longior Eigenmann, 1912; Pimelodella cristata (Müller & Troschel, 1849) ; Pimelodella geryi Hoedeman, 1961 ; Pimelodus ornatus Kner, 1858 ; Ituglanis amazonicus (Steindachner, 1882) ; Bunocephalus amaurus Eigenmann, 1912 ; Callichthys callichthys (Linnaeus, 1758) ; and Corydoras guianensis Nijssen, 1970 .

The feeding habits of M. durantoni are unknown at present. Its closest relative, M. asopos , is a carnivore, which feeds on trichopteran, ephemeropteran, chironomid and ceratopogonid larvae and small adult beetles ( Zuanon et al., 2006). Oral structure and dentition, as well as habitat, suggest that a similar diet is expected for M. durantoni . Mastiglanis asopos is reported to employ a peculiar sit-and-wait foraging tactic: poised on the bottom and supported by a tripod formed by its pelvic and anal fins, the fish spreads its long barbels and the filamentous dorsal and pectoral-fin rays, thus forming a “drift-trap” which helps it to intercept and lunge at passing food items ( Zuanon et al., 2006). In view of the similar morphology of the relevant anatomical parts in M. durantoni , it is expected to display the same behaviour. Mastiglanis asopos often co-occurs with Imparfinis pristos , Characidium pteroides , Pygidianops amphioxus and species of Gymnorhamphichthys in its psammic habitat. All those associated taxa are absent from the localities of M. durantoni and have so far not been recorded from the Maroni system or French Guiana ( Le Bail et al., 2000). So, it seems that M. durantoni is the only narrowly specialized psammophilic fish species in its habitat.