Tenebrosternarchus Bernt, Fronk, Evans & Albert, 2020

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 : 64

Tenebrosternarchus Bernt, Fronk, Evans & Albert, 2020

Adductor mandibulae. The promalaris and retromalaris subsections are continuous with each other at their origin and differentiated towards their insertion sites ( Figs. 6–32 ). The posterodorsal portion of the promalaris is sectioned by the posterolateral fibers of the levator arcus palatini, being medial to the posterolateral fibers of that muscle; and with the remaining fibers located laterally to the levator arcus palatini.

The promalaris is positioned dorsolaterally to the dorsal portion of the ricto-stegalis, and arises from the mid-dorsal portion of the hyomandibula. This subsection converges to the buccopalatal membrane, with its anterodorsal fibers differentiate into an endomaxillary ligament equal to its fibrous portion; and inserting to the connective tissue between the anterior margin of the premaxilla and upper lip. The retromalaris is positioned lateroventrally to the ricto-stegalis, arising from the anteroventral portion of the preopercle and hyomandibula, with its fibers converging to the buccopalatal membrane and its ventralmost portion converging into an elongated ectomaxillary ligament, equal to one and a half of its fibrous portion, that inserts at the posterolateral face of the maxilla.

The ricto-stegalis originates in the parasphenoid, pterosphenoid, hyomandibula, sphenotic, and metapterygoid. At its origin, the lateralmost portion of the ricto-stegalis, presumably corresponding to the rictalis, is separated dorsally from the fibers of the presumed stegalis by the levator arcus palatini, becoming continuous at their mid-portion and partially differentiated towards their insertion sites. The fibers corresponding to the rictalis inserts mainly into the coronoid process; and the presumed stegalis converges into an intersegmental aponeurosis, where its ventral portion differentiates into the meckelian tendon to an insertion to the coronomeckelian bone, and the anterodorsal fibers converges into the mandibular tendon.

The segmentum mandibularis is located dorsally to Meckel’s cartilage, extending about 30% of the dorsal portion of this cartilage. The ramus mandibularis trigeminus nerve trespasses the ricto-stegalis, and lies lateral to the presumptive stegalis and mesial to the rictalis and subsections of malaris.

Levator arcus palatini. The levator arcus palatini has a roughly parallelogram shape, originating from the ventral margin of the frontal, pterosphenoid, and sphenotic; and inserting onto the hyomandibula. The origin of the levator arcus palatini is equal to its insertion. At the insertion, the posterolateral fiber bundles of the levator arcus palatini are lateral to the promalaris and ricto-stegalis, while its anterolateral, anteromesial and posteromesial bundles are medial to the promalaris and ricto-stegalis (specifically to the presumed rictalis). The anteriormost fibers of the levator arcus palatini presents an aponeurotic aspect. Only the posterodorsal fibers of the levator arcus palatini located mesially to the dilatator operculi, where the anterior margin of the dilator operculi does not exceeds the median portion of the levator arcus palatini.

Figures

FIGURE 6 | Adductor mandibulae of Tenebrosternarchus preto (Apteronotidae), MPEG 22758, 268.5 mm LEA. A. Lateral view; B. Mesial view. Median portion of the buccopalatal membrane removed. Anatomical abbreviations in Tab. 1. Scale bars = 5 mm.

FIGURE 7 | Lateral view of dorsolateral musculature of Apteronotus albifrons (Apteronotidae), MZUSP 22251, 150.1 mm LEA. Green indicates the path of recurrent ramus of anteroventral part of anterior lateral line nerve. Anatomical abbreviations in Tab. 1. Scale bar = 5 mm.

FIGURE 8 | Rhamphichthys hahni (Rhamphichthyidae), MZUSP 24736, 479.5 mm TL. A. Lateral view of adductor mandibulae, pars ricto-stegalis; B. Mesial view of levator arcus palatini. Anatomical abbreviations in Tab. 1. Scale bars = 10 mm; 2 mm.

FIGURE 9 | Mesial view of adductor mandibulae of Archolaemus janeae (Sternopygidae), MZUSP 97383, 171.0 mm LEA. Anatomical abbreviations in Tab. 1. Scale bar = 4 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.

FIGURE 11 | Lateral view of dorsolateral musculature of Hypopygus lepturus (Hypopomidae), MZUSP 91426, 55.4 mm LEA. Some fibers of the LO, anterior accidentally removed during dissections. Anatomical abbreviations in Tab. 1. Scale bar = 2 mm.

FIGURE 12 | Mesial view of suspensorium of Brachyhypopomus janeiroensis (Hypopomidae), MZUSP 22702, 80.9 mm LEA. Anatomical abbreviations in Tab. 1. Scale bar = 4 mm.

FIGURE 13 | Adductor mandibulae, pars malaris of Brachyhypopomus janeiroensis (Hypopomidae), MZUSP 22702, 80.9 mm LEA. A. Lateral view; B. Mesial view. Buccopalatal membrane dissected ventrally. Anatomical abbreviations in Tab. 1. Scale bars = 1 mm.

FIGURE 14 | Lateral view of dorsolateral musculature of Brachyhypopomus janeiroensis (Hypopomidae), MZUSP 22702, 80.9 mm LEA. Anatomical abbreviations in Tab. 1. Scale bar = 3 mm.

FIGURE 15 | Lateral view of dorsolateral musculature of Microsternarchus cf. bilineatus (Hypopomidae), MBUCV-V 7298, 59.2 mm LEA. Anatomical abbreviations in Tab. 1. Scale bar = 1 mm.

FIGURE 16 | Lateral view of dorsolateral musculature of Hypopomus artedi (Hypopomidae), USNM 408442, 202. 7 mm LEA. A= anterolateral fibers of the levator arcus palatini; P= posterolateral fibers of the levator arcus palatini. Remaining 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.

FIGURE 18 | Lateral view of dorsolateral musculature of Rhamphichthys hahni (Rhamphichthyidae), MZUSP 24736, 479.5 mm TL. Anatomical abbreviations in Tab. 1. Scale bar = 20 mm.

FIGURE 19 | Lateral view of adductor mandibulae, pars malaris of Rhabdolichops eastwardi (Sternopygidae), MZUSP 81178, 188.3 mm LEA. Anatomical abbreviations in Tab. 1. Scale bar = 5 mm.

FIGURE 20 | Lateral view of dorsolateral musculature of Japigny kirshbaum (Sternopygidae), FMNH 50185, 137.2 mm LEA. Anatomical abbreviations in Tab. 1. Scale bar = 4 mm.

FIGURE 21 | Lateral view of dorsolateral musculature of Distocyclus conirostris (Sternopygidae), MZUSP 23316, 242.2 mm LEA. Anatomical abbreviations in Tab. 1. Scale bar = 4 mm.

FIGURE 22 | Platyurosternarchus macrostomus (Apteronotidae), MZUSP 57686, 189.5 mm LEA. A. Lateral view of dorsolateral musculature; B. Mesial view of the adductor mandibulae. Anatomical abbreviations in Tab. 1. Scale bars = 10 mm; 5 mm.

FIGURE 23 | Lateral view of dorsolateral musculature of Adontosternarchus clarkae (Apteronotidae), MZUSP 30072, 79.3 mm LEA. Green indicates the path of the recurrent ramus of anteroventral part of anterior lateral line nerve. Anatomical abbreviations in Tab. 1. Scale bar = 2 mm.

FIGURE 24 | Sternarchella terminalis (Apteronotidae), MPEG 3481, 155.3 mm TL [regenerated]. A. Detail of lateral view of anterior portion of dorsolateral head muscles; B. Detail of lateral view of posterior portion of dorsolateral head muscles. Anatomical abbreviations in Tab. 1. Scale bars = 5 mm.

FIGURE 25 | Lateral view of dorsolateral musculature of Apteronotus bonapartii (Apteronotidae), MPEG 3038, 217.5 mm LEA. Anatomical abbreviations in Tab. 1. Scale bar = 5 mm.

FIGURE 26 | Lateral view of dorsolateral musculature of Sternarchorhamphus mulleri (Apteronotidae), USNM 373030, 222.2 mm LEA. Anatomical abbreviations in Tab. 1. Scale bar = 10 mm.

FIGURE 27 | Sternarchorhynchus goeldii (Apteronotidae), MPEG 1193, 1, 148.3 mm LEA. A. Lateral view of dorsolateral musculature; B. Mesial view of the adductor mandibulae. Anatomical abbreviations in Tab. 1. Scale bars = 5 mm.

FIGURE 28 | Lateral view of dorsolateral musculature of Sternarchella terminalis (Apteronotidae), MPEG 3481, 155.3 mm TL [regenerated]. Anatomical abbreviations in Tab. 1. Scale bar = 5 mm.

FIGURE 29 | Lateral view of dorsolateral musculature of Sternarchella raptor (Apteronotidae), USNM 374014, 71.9 mm LEA. Anatomical abbreviations in Tab. 1. Scale bar = 5 mm.

FIGURE 30 | Apteronotus rostratus (Apteronotidae), USNM 317229, 142.3 mm LEA. A. Lateral view of dorsolateral musculature; B. Mesial view of the adductor mandibulae. Green indicates the path of the recurrent ramus of anteroventral part of anterior lateral line nerve. Anatomical abbreviations in Tab. 1. Scale bars = 5 mm; 4 mm.

FIGURE 31 | Lateral view of dorsolateral musculature of Compsaraia compsa (Apteronotidae), MZUSP 56206, 123.4 mm LEA. Anatomical abbreviations in Tab. 1. Scale bar = 5 mm.

FIGURE 32 | Lateral view of dorsolateral musculature of Tenebrosternarchus preto (Apteronotidae), MPEG 22758, 268.5 mm LEA. A= anterolateral fibers of the levator arcus palatini; P= posterolateral fibers of the levator arcus palatini. Remaining anatomical abbreviations in Tab. 1. Scale bar = 5 mm.