OSTEOGLOSSIFORMES
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publication ID |
https://doi.org/ 10.1111/zoj.12142 |
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persistent identifier |
https://treatment.plazi.org/id/03DB6116-533C-A21F-FECA-D2AC246879D5 |
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treatment provided by |
Marcus |
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scientific name |
OSTEOGLOSSIFORMES |
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OSTEOGLOSSIFORMES View in CoL View at ENA
Description
Osteoglossum ferreirai ( Fig. 11 View Figure 11 )
The ricto-malaris originates from the fascia of the levator arcus palatini, the quadrate, symplectic, hyomandibula, and preopercle. Although the rictomalaris remains fully undivided along its entirety, a partial differentiation between the dorsal malaris and the ventral rictalis is perceptible anterolaterally by the different orientations of the fibres of these sections. The dorsal set of fibres corresponding to the malaris abruptly deflects ventrally yielding a rounded anterior profile, whereas the fibres of the rictalis continue in a nearly rectilinear trajectory towards their insertion. The combined ricto-malaris inserts primarily on the mandibular tendon, with some ventrolateralmost fibres additionally inserting directly onto the angulo-articular.
The stegalis is largely continuous laterally with the ricto-malaris. However, the limits of the stegalis are easily distinguishable from a medial view by its shorter fibres and anterodorsally displaced site of origin from the metapterygoid and hyomandibula. The stegalis is partially separated dorsally from the ricto-malaris, with the ramus mandibularis trigeminus nerve passing between these two muscle sections. A distinctly less obvious, partial differentiation into an epistegalis and a substegalis is apparent medially. Anteriorly, the epistegalis joins the malaris and inserts on the dorsal portion of the intersegmental aponeurosis that differentiates anteriorly into the mandibular tendon. The substegalis converges onto the ventral region of the intersegmental aponeurosis, which in turn, differentiates anteriorly into a meckelian tendon that inserts on the coronomeckelian.
The segmentum mandibularis is not differentiated into subsections and originates from the mandibular tendon. This muscle segment inserts onto the anguloarticular and the dentary.
Arapaima gigas (not illustrated)
The segmentum mandibularis is mostly undivided along its anteroposterior expanse. The ricto-malaris arises from the quadrate, preopercle, hyomandibula, and infraorbitals 3 + 4 and 5. In the examined specimen, the ricto-malaris remains undifferentiated into subunits along most of its expanse. Near to their insertion, the dorsal fibres that correspond to the malaris, however, form a partially separate muscle bundle that abruptly deflects ventrally towards the lower jaw. The ventral set of fibres of the ricto-malaris, which is homologous to the rictalis, continues in a nearly rectilinear trajectory to its insertion. Both the malaris and rictalis insert musculously and via the mandibular tendon onto the angular and dentary.
The stegalis is continuous with the ricto-malaris but is discernible from a medial view because of its more anterior origin on the metapterygoid and symplectic and its insertion on the meckelian tendon. This tendon, which is completely separated from the mandibular tendon, splits anteriorly into a dorsal and a ventral division, both of which insert onto the coronomeckelian.
The ramus mandibularis trigeminus nerve passes medial to the segmentum facialis and then continues between the mandibular and meckelian tendons.
The segmentum mandibularis is absent.
Remarks
As in the case of many other basal groups in the Teleostei (e.g. Elopiformes and Hiodontiformes), all of the three primary facial sections of the adductor mandibulae present across the Teleostei are undoubtedly identifiable in Osteoglossum ferreirai and Arapaima gigas . These primary sections – rictalis, malaris, and stegalis – are discernible notwithstanding the pronounced degree of continuity between them ( Fig. 11 View Figure 11 ).
Several modifications of the adductor mandibulae were reported by Kershaw (1976) for taxa elsewhere in the Osteoglossiformes . Synonymization of the highly modified muscle divisions reported in that study must be considered tentative. For the osteoglossid Scleropages formosus, Kershaw (1976) described a lateral facial section (her A2) with dorsally and ventrally distinguishable sets of fibres that jointly converge to a tendon that serves as the site of origin for a mandibular segment (her Aw). Such a description is almost identical to the rictomalaris of Osteoglossum ferreirai detailed above. Kershaw’s A 3 in Scleropages formosus similarly conforms to our substegalis. Her A1 is similar in most aspects to the epistegalis in Osteoglossum ferreirai , except for its insertion on the maxilla in Scleropages formosus rather than the intersegmental aponeurosis in Osteoglossum ferreirai . These synonymies apparently also apply to the muscle divisions of Pantodon buchholzi , which has an epistegalis inserting on both the maxilla and lower jaw ( Kershaw, 1976: A1).
Kershaw’s (1976) A 1 in Osteoglossum bicirrhosum occupies the dorsolateral region of the segmentum facialis and, furthermore, has the exact same sites of origin as the malaris in Osteoglossum ferreirai (i.e. from the levator arcus palatini fascia and the vertical arm of the preopercle). Therefore, the muscle identified as the A 1 in Osteoglossum bicirrhosum by Kershaw probably corresponds to the malaris instead of the epistegalis as discussed above for Scleropages and Pantodon . Kershaw (1976) illustrated, but did not describe, the A3 of Osteoglossum bicirrhosum , which renders it impossible to precisely determine the identities of this section and of the A 2 in this species.
The segmentum facialis in the Arapaimidae inserts solely on the lower jaw (present study; Kershaw, 1976). Kershaw (1976) reported a mostly undivided segmentum facialis in Heterotis niloticus , but recognized that this muscle segment is formed by a medial A3 that originates from the metapterygoid (= stegalis) and a lateral A2 (= ricto - malaris). She identified a dorsolateral section in Arapaima gigas , termed the A2 (= malaris), and a ventromedial A3 formed by a ‘superficial layer’ of fibres with an origin from the preopercle (= rictalis) and ‘deeper fibres’ with an origin from the metapterygoid (= stegalis). In the specimen of Arapaima gigas herein examined, the malaris is only partially separated from the remainder of the segmentum facialis along their anterolateral regions. Kershaw (1976) conversely reported a malaris (her A2) that was fully separated from the adjoining facial sections in the individuals of this species that she examined. As the specimens of Arapaima gigas examined by Kershaw (1976) are distinctly larger (neurocranial length = 100 and 250 mm) than the individuals of the species herein dissected (neurocranial length = 32.2 mm), it is possible that the degree of separation of the malaris gradually increases during ontogeny, thereby accounting for the observed differences.
Munshi (1960) described the adductor mandibulae of the notopterid Chitala chitala (= Notopterus chitala ). The reported muscle is so highly modified relative to the morphology of the muscle in other known osteoglossiforms that we cannot arrive at reliable assumptions as to muscle section homologies in this species based solely on published information.
The segmentum mandibularis is absent in the Arapaimidae but present in the Osteoglossidae and Notopteridae (present study; Munshi, 1960; Kershaw, 1976).
Synonymy
Segmentum facialis A2A3: Kershaw (1976): Heterotis .
Pars malaris
A1: Kershaw (1976): Osteoglossum .
A2: Kershaw (1976): Arapaima .
Pars ricto-malaris A2: Kershaw (1976): Heterotis , Pantodon , Scleropages .
Pars rictalis Superficial layer of A3: Kershaw (1976): Arapaima .
Pars ricto-stegalis A3: Kershaw (1976): Arapaima .
Pars stegalis
A3: Kershaw (1976): Heterotis .
Deeper fibres of A3: Kershaw (1976): Arapaima .
Pars epistegalis A1: Kershaw (1976): Pantodon , Scleropages .
Pars substegalis A3: Kershaw (1976): Pantodon , Scleropages .
Segmentum facialis
Aw: Kershaw (1976): Osteoglossum , Pantodon , Scleropages .
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