ELOPIFORMES

Datovo, Aléssio & Vari, Richard P., 2014, The adductor mandibulae muscle complex in lower teleostean fishes (Osteichthyes: Actinopterygii): comparative anatomy, synonymy, and phylogenetic implications, Zoological Journal of the Linnean Society 171 (3), pp. 554-622 : 563-564

ELOPIFORMES

Descriptions

Elops lacerta ( Fig. 6 )

The segmentum facialis lacks any obvious divisions along its entirety. Origin of this muscle segment is from the preopercle, quadrate, metapterygoid, symplectic, and hyomandibula. At its insertion, the ventromedial fibres of the segmentum facialis, which presumably correspond to the stegalis, converge to a flat meckelian tendon that attaches to the coronomeckelian. The remaining facial muscle mass, which corresponds to the ricto-malaris, inserts on the mandibular tendon and retrojugal lamina that are continuous with each other.

The ramus mandibularis trigeminus nerve passes external to all of the segmentum facialis.

The segmentum mandibularis is undivided. This segment originates from the flat mandibular tendon and inserts on the dentary and angulo-retroarticular.

Megalops cyprinoides (not illustrated)

The overall morphology of the adductor mandibulae in Megalops cyprinoides is similar to that of Elops lacerta , with both taxa demonstrating the same basic position and sites of origin and insertion of the muscle. Nevertheless, the muscle sections in these taxa differ in various features. The ricto-malaris and stegalis of Megalops cyprinoides are better differentiated from each other anteriorly and the ramus mandibularis trigeminus nerve in that species passes between these muscle sections rather than external to both of them. The ventrolateral facial set of fibres of the adductor mandibulae, which corresponds to the rictalis, is more intimately associated in Megalops cyprinoides with a well-defined preangulo-paramaxillar ligament. The tendons of the intersegmental aponeurosis are more obviously separated from each other and an accessory tendon is present in this species vs. absent in Elops lacerta . This accessory tendon passes lateral to the meckelian tendon and inserts on the angulo-retroarticular and posterior tip of the coronomeckelian bone.

Remarks

Vrba (1968) provided detailed descriptions of the adductor mandibulae of elopiforms and our observations nearly universally confirm his results despite the different nomenclature applied to the muscles and ligaments in that publication. The author refers to the segmentum facialis as the adductor mandibulae and the segmentum mandibularis as the intramandibularis muscle. Paralleling the observations of the present study, Vrba (1968) also discussed the more obvious differentiation of the subunits of the segmentum facialis in Megalops than in Elops . In the case of Megalops he identified these subdivisions via specific designations, applying A 1 A 2 to the ricto-malaris and A 3 to the stegalis.

Other studies similarly reported an undivided segmentum facialis in Elops (e.g. Winterbottom, 1974; Diogo & Doadrio, 2008; Diogo, Doadrio & Vandewalle, 2008a; Diogo, Hinits & Hughes, 2008b). Contrary to Vrba (1968), these series of studies designated the entire segmentum facialis as an A2, a procedure potentially leading to the erroneous assumption that the A 1 and A 3 of Megalops were absent in Elops . As Vrba (1968) inferred, and the present study confirms, all of the facial sections found in Megalops are undoubtedly present in Elops , with the totality of the segmentum facialis exhibiting the same basic origin, insertion, and position in both genera.

Synonymy

Segmentum facialis

A2: Diogo & Doadrio (2008): Elops ; Diogo et al. (2008b): Elops ; Winterbottom (1974): Elops .

Adductor mandibulae: Vrba (1968): Elops , Megalops .

Pars ricto-malaris A 1 A 2: Vrba (1968): Megalops .

Pars stegalis A 3: Vrba (1968): Megalops .

Segmentum mandibularis

Aω: Diogo & Doadrio (2008): Elops ; Diogo et al. (2008b): Elops .

Aw: Winterbottom (1974): Elops . Intramandibularis: Vrba (1968): Elops , Megalops .

Figures

Figure 6. Adductor mandibulae and associated structures of Elops lacerta (Elopiformes: Elopidae), MZUSP 84787 (113.7 mm standard length). Left side in (A) lateral and (B) medial views. Abbreviations: AM, adductor mandibulae; BPM, buccopalatal membrane; IA, intersegmental aponeurosis; RMT, ramus mandibularis trigeminus nerve.