Lacantunia, Rocío Rodiles-Hernández, Dean A. Hendrickson, John G. Lundberg & Julian M. Humphries, 2005

Rocío Rodiles-Hernández, Dean A. Hendrickson, John G. Lundberg & Julian M. Humphries, 2005, Lacantunia enigmatica (Teleostei: Siluriformes) a new and phylogenetically puzzling freshwater fish from Mesoamerica., Zootaxa 1000, pp. 1-24 : 6-10

Lacantunia n. gen. Rodiles-Hernández, Hendrickson & Lundberg

Figs. 1-2, 4-7

Type species. Lacantunia enigmatica n. sp.

Diagnosis: Lacantunia is distinguished from all other siluriforms by five uniquely derived and anatomically complex characteristics.

1) Fifth infraorbital bone relatively wide and thick-walled, boomerang-shaped and anteriorly convex, and remote from a markedly prominent sphenotic process (Fig. 4). A long, naked span of the infraorbital sensory canal traverses the bone-free gap between IO5 and the sphenotic process. Primitively in catfishes the infraorbital sensory canal is almost completely surrounded by thin tubular ossicles separated by short gaps, the largest infraorbital bone (fifth or sixth) posterior to eye is simple and anteriorly concave, contacting or close to the sphenotic process that is small or lacking (Lundberg 1982, Mo 1991).

2) Lateral margin of skull thickened along frontal bone and adjacent parts of lateral ethmoid and sphenotic bones at origins of much enlarged adductor mandibulae and levator arcus palatini muscles (Fig. 4). Also, skull roof medial to muscle origins severely constricted, flat, lacking crests and fossae. Most catfishes have smaller jaw and hyoid arch muscles with limited cranial attachments (Lundberg 1982, Grande & de Pinna 1998) and broader, arched skull roofs across the frontals and sphenotics. Other catfishes with enlarged jaw and hyoid arch muscles (e.g. diplomystids, modern ictalurids, most cetopsids, some amblycipitids, bagrids, clariids and heptapterids) have different patterns of muscle arrangement and attachment sites dorsally on skull roof (Arratia 1987, de Pinna & Vari 1995, Grande & de Pinna 1998, Bockmann 1998).

3) Pair of cone-shaped "pseudo-pharyngobranchial" bones at anterior tips of enlarged accessory cartilages medial to first and second epibranchials (Fig. 5). Many catfishes have small, paired accessory cartilages medial to the cartilaginous caps on the epibranchials(Bockmann 1998), but without ossification. The "pseudo-pharyngobranchial" bones and accessory cartilages of Lacantunia are not homologous with first or second pharyngobranchials that are primitively retained in a few siluriforms as rod-shaped bones anteriorly adjacent and parallel to their companion epibranchials (Arratia 1987).

4) Hypertrophied, axe-shaped uncinate process on third epibranchial (Fig. 5). Primitively the third epibranchial of catfishes lacks an uncinate process. Some catfishes have a low process or, if enlarged, a process of markedly different shape (de Pinna 1993).

5) Gas bladder with paired spherical, unencapsulated diverticulae protruding from anterodorsal wall, each extending dorsad before anterior limb of fourth transverse process, lateral to first centrum and anterior limb of tripus, and posterior to occiput and ossified Baudelot's ligament (Fig. 6). Diverticulae walls of tough connective tissue containing silvery guanine crystals as in wall of main gas bladder chamber; without heavy vascularization. Catfishes primitively lack gas bladder diverticulae, though a few have different unpaired or multiple diverticulae posterior or lateral to main bladder(Chardon 1968).

Other characters useful for identification. Anterior and posterior nostrils widely separated (cf. nostrils adjacent in sympatric species of Ariidae); nasal barbel present on anterior rim of posterior nostril (cf. nasal barbel absent in sympatric species of Ariidae and Heptapteridae); maxillary barbel inserted above lip remote from corner of mouth (cf. maxillary barbel inserted on corner of lip in sympatric species of Ictaluridae); upper lip without accessory folds parallel to premaxillary teeth (cf. upper lip with a fold parallel to premaxillary teeth in sympatric species of Heptapteridae); palate edentulous (cf. palate toothed in sympatric species of Ariidae); eye without a free orbital rim (cf. eye with a free orbital rim in sympatric species of Ictaluridae, Ariidae and Heptapteridae); supraoccipital process very short and remote from dorsal-fin base (cf. supraoccipital process projecting well beyond skull, often reaching dorsal-fin base in sympatric species of Ictaluridae, Ariidae and Heptapteridae); dorsal-fin soft rays 8 to 10 (cf. dorsal-fin soft rays 6 or 7 in sympatric species of Ictaluridae, Ariidae and Heptapteridae); pelvic rays 6 (cf. pelvic rays greater than 6 in sympatric species of Ictaluridae); caudal fin slightly rounded to truncate with rounded corners, its principal caudal rays 1,7,9,1 (cf. caudal fin distinctly lobed or forked, its principal caudal rays 1,7,8,1 in sympatric species of Ictaluridae and Heptapteridae, and 1,6,7,1 in Ariidae).

Etymology. Lacantunia , from the Río Lacantún in Chiapas, the tributary river of Río Usumacinta inhabited by the new catfish, gender feminine.