NOTACANTHIFORMES

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 : 566-568

publication ID	https://doi.org/ 10.1111/zoj.12142
persistent identifier	https://treatment.plazi.org/id/03DB6116-5322-A205-FEF6-D7EA269D7DD7
treatment provided by	Marcus
scientific name	NOTACANTHIFORMES
status

Treatment

NOTACANTHIFORMES View in CoL View at ENA

Description

Halosaurus pectoralis ( Fig. 8 View Figure 8 )

The retromalaris is superficially distinguishable from the remainder of the segmentum facialis, especially in its distinctly posteriorly displaced origin. The retromalaris arises from the preopercle and hyomandibula and inserts on the subocular tendon and buccopalatal membrane. The promalaris is totally separate from all other facial sections. It arises from a posterodorsal expansion of the metapterygoid and inserts on the retrojugal lamina and more so on the welldifferentiated endomaxillar ligament that attaches to the anteromedial region of the maxilla.

The rictalis and stegalis are fully continuous along their expanses, thereby forming a compound ricto- stegalis originating from the metapterygoid, quadrate, and preopercle. The lateral set of fibres of the ricto-stegalis, probably corresponding to the rictalis, inserts on the mandibular tendon, whereas the medial set of fibres, representing the stegalis, converges to the meckelian tendon. This tendon attaches to the posterior portions of Meckel’s cartilage.

Posteriorly, the ramus mandibularis trigeminus nerve traverses the segmentum facialis between the promalaris and retromalaris and then proceeds anteriorly between the coronalis dorsally and the ricto-stegalis and mentalis ventrally.

The segmentum mandibularis originates from the mandibular tendon and is well differentiated into the coronalis and mentalis sections. The coronalis extends posteriorly distinctly beyond the posterior border of the lower jaw and is laterally enclosed by the vaultshaped posterodorsal portion of the buccopalatal membrane. Both the coronalis and mentalis insert onto the angulo-articulo-retroarticular.

Remarks

Determination of the homology of the dorsomedial facial section inserting on the maxilla via the endomaxillar ligament is complicated in Halosaurus pectoralis ( Fig. 8B View Figure 8 ). At first sight, this muscle section might be considered to represent a dorsal subdivision of the stegalis as proposed by Diogo et al. (2008a; their A3-MAX). Comparisons with other species of the Notacanthiformes and Albuliformes cast doubt on that hypothesis of homology. In Albula , a partially differentiated medial promalaris has the same basic features as the section in question in the Notacanthiformes : an origin aligned with that of the stegalis and an insertion on the endomaxillar ligament ( Fig. 7B View Figure 7 ). These features suggest that the dorsomedial facial section inserting via the endomaxillar ligament onto the maxilla in Halosaurus pectoralis is rather an anteromedial subdivision of the malaris, i.e. the promalaris ( Fig. 8B View Figure 8 ). Further supporting this supposition is the fact that the notacanthiforms Notacanthus and Polyacanthonotus have the dorsomedial (= promalaris) and dorsolateral (= retromalaris) facial sections sharing an anterior tendinous connection ( Greenwood, 1977).

The adductor mandibulae of other halosaurids, although largely similar to that of Halosaurus pectoralis ( Greenwood, 1977) , demonstrates some notable differences. According to Greenwood (1977), other halosaurids have the stegalis fully or partially separated from the rictalis and, at least in Halosaurus guentheri , the posterior margin of the retromalaris is aligned with that of the rictalis. Consequently, the two latter sections cannot be discerned from each other in Halosaurus guentheri and jointly form a ricto-retromalaris.

The adductor mandibulae of notacanthids demonstrates some notable differences relative to the condition in the Halosauridae : the segmentum mandibularis is absent (vs. present); the rictalis inserts on the maxilla (vs. the mandibular tendon); and the promalaris originates medial to the levator arcus palatini (vs. anteroventral to the levator arcus palatini; Greenwood, 1977). In Polyacanthonotus africanus and Notacanthus , the retromalaris is divided into a dorsolateral retromalaris superioris and a ventromedial promalaris inferioris. Notacanthus additionally has a rictalis subdivided into a large ectorictalis and a small endorictalis ( Trotti, 1945; Greenwood, 1977).

Synonymy

Pars rictalis

A1α: Greenwood (1977): Lipogenys , Notacanthus , Polyacanthonotus .

Pars ectorictalis

A1α 1: Greenwood (1977): Notacanthus .

a 1 β: Trotti (1945): Notacanthus .

Pars endorictalis

a 1 α: Trotti (1945): Notacanthus .

A1α 2: Greenwood (1977): Notacanthus .

Pars ricto-retromalaris

A2: Greenwood (1977): Aldrovandia , Halosauropsis , Halosaurus .

Pars retromalaris