Gymnorhamphichthys Ellis, 1912

Peixoto, Luiz Antônio Wanderley & de Pinna, Mário, 2022, Patterns of diversification and phylogenetic structure in the dorsolateral head musculature of Neotropical electric eels (Ostariophysi: Gymnotiformes), with a myological synonymy, Neotropical Ichthyology (e 210009) 20 (1), pp. 1-117 : 38

Gymnorhamphichthys Ellis, 1912

Adductor mandibulae. The malaris is fully differentiated from the ricto-stegalis and is positioned dorsolaterally to the dorsal portion of the presumptive rictalis and the lateroventrally to the stegalis ( Fig. 5 ; Peixoto, Ohara, 2019: fig. 12). The malaris has a pectinated form, originating from the mid-portion of the hyomandibula and preopercle; and converges anteriorly onto an elongated endomaxillary ligament, equivalent to twice the width of the fibrous portion of the malaris, and inserts on the posteromedial portion of the antorbital and maxilla ( Fig. 5 ), with some fibers on the buccopalatal membrane.

The ricto-stegalis is mesial to the malaris, and originates from the parasphenoid, pterosphenoid, metapterygoid, preopercle, quadrate, sympletic and hyomandibula, with its fibers restricted to the anterior margin of the preopercle. Towards its insertion, the rictalis and stegalis become gradually differentiated from each other, with the fibers of the rictalis inserting onto the coronoid process, and the stegalis converging onto the meckelian tendon which, in turn, inserts on the coronomeckelian bone. Near the insertion, a few fibers of the ricto-stegalis have a weak association with the buccopalatal membrane and posterior margin of the anguloarticular. The bundles of fibers corresponding to the presumptive stegalis are located laterally relative to the basal region of the endopterygoid and adductor arcus palatini, overlapping those elements completely. The ramus mandibularis trigeminus nerve runs through the ricto-stegalis, located mesial to the presumptive rictalis and malaris; and laterally to the presumptive stegalis.

Levator arcus palatini. The levator arcus palatini has a trapezoidal shape, originating from the ventral margin of the frontal and sphenotics and inserting mainly in the hyomandibula, with posterolateral fibers inserting on the preopercle. The relative size of its origin is half that of its insertion, with all fibers located laterally to the malaris at insertion. Only the dorsalmost fibers of the posterior portion of the levator arcus palatini are mesial to the dilatator operculi, but without reaching the median portion of the levator arcus palatini ( Fig. 17 ).

Figures

FIGURE 5 | Lateral view of adductor mandibulae, pars malaris of Gymnorhamphichthys rosemariae (Rhamphichthyidae), MZUSP 56317. Anatomical abbreviations in Tab. 1. Scale bar = 5 mm.

FIGURE 17 | Lateral view of dorsolateral musculature of Gymnorhamphichthys rosemariae (Rhamphichthyidae), MZUSP 56317, 116.3 mm LEA. Anatomical abbreviations in Tab. 1. Scale bar = 5 mm.