Electrophorus Gill, 1864

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 : 27-28

Electrophorus Gill, 1864

Adductor mandibulae. The stego-malaris originates in the hyomandibula, metapterygoid, endopterygoid, quadrate, parasphenoid, frontal and sphenotic. Its component subsections are increasingly differentiated towards its insertion, where dorsolateral fibers, presumably corresponding to the malaris, converge towards the coronoid process and dorsomesial fibers converge on a thick mandibular tendon inserted on the mesial surface of the coronoid process. The middle fibers, presumably correspond to the stegalis, diverge in a thick meckelian tendon inserted on the dorsal margin of the coronomeckelian bone ( Fig. 3 ). Dorsomesial fibers corresponding to the stegalis are disposed laterally relative to the posterolateral region of the basal portion of the endopterygoid, not completely overlapping it but totally covering laterally the adductor arcus palatini ( Fig. 2 ).

The rictalis originates in the preopercle, quadrate and hyomandibula, with lateral fibers surpassing the anterior margin of the preopercular fossa, but not reaching the posterior margin of the bone, being restricted to its medial portion. The rictalis inserts mainly on the coronoid process, but with a few lateral fibers on the buccopalatal membrane. The dorsal portion of the rictalis is disposed mesially to the stego-malaris, with anterior fibers close to its insertion fully differentiated from the latter. The ramus mandibularis trigeminus nerve is arranged mesially to the rictalis and laterally to the stego-malaris (n = 1) or mesially to all sections of the adductor mandibulae (n = 1).

Levator arcus palatini. The levator arcus palatini anterior originates in the anteroventral margin of the sphenotic and is inserted on the hyomandibula. The levator arcus palatini posterior originates in the posteroventral margin of the sphenotic and inserts onto the hyomandibula and preopercle. In the region of origin, the two sections are partially continuous and sectioned by the truncus hyomandibularis nerve, which is lateral to the anterior section and mesial to the posterior one ( Fig. 10 ). At the insertion, fiber bundles of the levator arcus palatini anterior are mesial to the malaris and those of the levator arcus palatini posterior are lateral to the malaris and posterolaterally to the rictalis. The origin of the levator arcus palatine is narrower than its insertion and only its posterodorsal fibers are mesial to the dilatator operculi.

Dilatator operculi. The dilatator operculi ventralis has a roughly rectangular shape, originating in the posterior margin of the preopercle and inserting on the anterodorsal portion of the dorsal process of the opercle. The dilatator operculi dorsalis is approximately conical and originates in the ventral margin of the pterotic, sphenotic and dorsal portion of the hyomandibula. The fibers of dorsal and ventral sections are partially continuous near their insertion on the anterodorsal and dorsal part of the dorsal process of the opercle ( Fig. 10 ).

Levator operculi. The origin of the levator operculi anterior occurs in the posteroventral margin of the pterotic and exoccipital, while its insertion is into a ridge on the dorsal margin of the opercle, posterior to the anterodorsal process of that bone. The origin of the levator operculi posterior is in the postotic canal segment corresponding to the supracleithrum and it inserts along a crest at the posterolateral margin of the opercle, with fibers surpassing the dorsal margin of that bone ( Fig. 2 ).

Figures

FIGURE 2 | Lateral view of dorsolateral musculature of Electrophorus cf. electricus (Gymnotidae), MZUSP 85509, 488.2 mm TL. Anatomical abbreviations in Tab. 1. Scale bar = 10 mm

FIGURE 3 | Adductor mandibulae of Electrophorus cf. electricus (Gymnotidae), MZUSP 85509, 488.2 mm LEA. A. Lateral view; B. Mesial view. Anatomical abbreviations in Tab. 1. Scale bar = 10 mm.

FIGURE 10 | Electrophorus cf. electricus (Gymnotidae), MZUSP 85509, 488.2 mm LEA. A. Lateral view of dorsolateral head muscles; B. Posterior portion of dorsolateral head muscles. Adductor mandibulae dissected in B. LO, anterior not visible in lateral view. Anatomical abbreviations in Tab. 1. Scale bar = 10 mm.