ANGUILLIFORMES
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publication ID |
https://doi.org/ 10.1111/zoj.12142 |
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persistent identifier |
https://treatment.plazi.org/id/03DB6116-5320-A21B-FB9E-D39D20677FA2 |
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treatment provided by |
Marcus |
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scientific name |
ANGUILLIFORMES |
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ANGUILLIFORMES View in CoL View at ENA
Description
Anguilla reinhardti ( Fig. 9 View Figure 9 )
At its origin, the segmentum facialis is divided into an outer much expanded ricto-malaris and two inner sections – the epistegalis and substegalis. The rictomalaris has a broad origin from the preopercle, hyomandibula, pterotic, frontal, parietal, the epaxialis and supracarinalis fasciae, and a midsagittal tendinous raphe shared with its antimere. Fibres of the rictomalaris attach solely to the cited structures; however, this muscle section extends without attachment over multiple additional bones and muscles. The combination of a broad origin and narrow insertion of this compound section result in the fibres becoming gradually arranged into several bundles that are partially segregated from each other by internal fasciae as they approach the insertion. Three main bundles are more prominent and superficially readily distinguishable. Positionally, the ventral bundle seems to correspond to the rictalis, and the two upper bundles to the retromalaris posteroventrally and promalaris anterodorsally. Most fibres of the rictalis insert on the posterolateral region of the coronoid process of the dentary; however, a few ventrolateral fibres insert onto an inconspicuous preangulo-paramaxillar ligament that attaches to the maxilla. The retromalaris and promalaris insert jointly on the anterior portion of the coronoid process of the dentary, primarily via a robust mandibular tendon.
The stegalis is totally subdivided into two separate subunits, both of which insert on the meckelian fossa along the medial surface of the lower jaw. The epistegalis originates from the pterosphenoid, sphenotic, and pterotic and inserts onto the dentary and anguloarticulo-retroarticular. The substegalis arises from the quadrate and hyomandibula and converges to a conspicuous meckelian tendon that passes lateral to the epistegalis and inserts on the coronomeckelian.
The path of the ramus mandibularis trigeminus nerve could not be determined.
The segmentum mandibularis is absent.
Ariosoma sp. (not illustrated)
The adductor mandibulae is mostly similar to that of Anguilla reinhardti . The ricto - malaris has the same origin in the two taxa; however, in Ariosoma the rictalis and malaris can only be differentiated from each other anteriorly. In this genus, the fibres of the rictalis attach to a lateral laminar tendon that inserts on the dorsolateral region of the coronoid process of the dentary. There is no connection of the rictalis with the welldifferentiated preangulo-paramaxillar ligament. The malaris converges onto a stout mandibular tendon that inserts on the dorsomedial region of the coronoid process of the dentary and the dorsal portion of the coronomeckelian.
The stegalis is completely divided into an epistegalis and a substegalis, both of which are partially continuous with the ricto-malaris at their origins. The substegalis arises from the preopercle, quadrate, and hyomandibula and converges onto a strong meckelian tendon that attaches to the coronomeckelian. The epistegalis originates from the sphenotic and pterosphenoid, passes medial to the substegalis and inserts musculously on the coronomeckelian and angulo-articulo-retroarticular.
The path of the ramus mandibularis trigeminus nerve could not be determined.
The segmentum mandibularis is absent.
Remarks
Homology propositions for the bones of the suspensorium in the Anguilliformes remain unsettled. The metapterygoid that serves as a typical site of origin for the stegalis elsewhere in the Teleostei, is not present as an autogenous element amongst anguilliforms, but is rather possibly fused to the hyomandibula ( Belouze, 2001). This fact, in conjunction with other cranial modifications amongst anguilliforms, yields ambiguity in the identification of the stegalis in the anguillid Anguilla reinhardti and the congrid Ariosoma sp. examined herein, as these species exhibit two distinct shorter inner sections – an anterodorsal section originating from the neurocranium and a posteroventral component arising primarily from the hyomandibula ( Fig. 9B View Figure 9 ). Adams (1919) reported, however, that Anguilla sp. has a single shorter inner facial division that bifurcates posteriorly into an anterodorsal bundle with an origin mainly on the neurocranium and a posteroventral bundle with an origin from the suspensorium (his Adm 3). A single, short, medial division of the segmentum facialis that arises from both the hyomandibula and neurocranium is also present in the nettastomatid Hoplunnis ( Eagderi & Adriaens, 2010b: A3). Based on its internal position and shorter fibres relative to the external facial sections, the single medial division reported by Adams (1919) for Anguilla sp. and Eagderi & Adriaens (2010b: A3) for Hoplunnis seems to correspond to the entire stegalis. Given that arrangement, the stegalis in the examined material of Anguilla reinhardti and Ariosoma sp. is interpreted as being completely subdivided into an epistegalis that arises solely from the neurocranium and a substegalis with an origin on the suspensorium. Two inner sections with the same general morphology were also reported for Anguilla anguilla ( Eagderi & Adriaens, 2010a: A 2m and A3) and Conger conger ( Eagderi & Adriaens, 2010b: A2β and A3).
Only one inner facial section has been reported for Heteroconger (Congridae) and Pythonichthys (Heterenchelyidae) , and in this configuration this section arises solely from the neurocranium ( De Schepper, De Kegel & Adriaens, 2007a; Eagderi & Adriaens, 2010a). This inner section may correspond solely to the epistegalis or equate with the entire stegalis. The former hypothesis implies the incorporation of the substegalis into the outer facial sections and the latter proposal requires the migration of the origin of the stegalis to the neurocranium. We surmise that the hypothesis of this muscle being the epistegalis is the more likely; however, both propositions are equally parsimonious in light of the limited available information on adductor mandibulae morphology in taxa closely related to Heteroconger and Pythonichthys . Consequently, we were unable to incorporate these taxa in our synonymy. Data from De Schepper, Adriaens & De Kegel (2005) and De Schepper, De Kegel & Adriaens (2007b) are difficult to interpret because of the highly modified muscles of the described taxa and, in the case of the first of these publications, also because of some limitations of the associated illustrations.
A tenuous connection of the ventrolateral fibres of the rictalis with the preangulo-paramaxillar ligament is present in at least some components of the Anguillidae ( Fig. 9 View Figure 9 ), Heterenchelyidae , and Nettastomatidae . In Hoplunnis (Nettastomatidae) the rictalis is differentiated into the ectorictalis and endorictalis ( Eagderi & Adriaens, 2010a, b).
Forms of the adductor mandibulae reported in the literature across the Anguilliformes share some notably distinctive features such as the extreme hypertrophy of the superficial portion of the segmentum facialis, which originates from the neurocranium, and the drastic reduction of the segmentum mandibularis ( Fig. 9 View Figure 9 ; Adams, 1919; De Schepper et al., 2005, 2007a, b; Eagderi & Adriaens, 2010a, b). More extreme modifications of the adductor mandibulae occur in subsets of anguilliforms (A. Datovo pers. observ.; De Schepper et al., 2005, 2007b). Thus, future broadly based comparative analyses within the Anguilliformes are necessary to properly elucidate the homologies of the muscle components in many groups within this order.
Synonymy
Segmentum facialis A2: Wu & Shen (2004): Echidna .
Pars rictalis
A2α: Eagderi & Adriaens (2010b): Conger , Hoplunnis . A2v: Eagderi & Adriaens (2010a): Anguilla .
Pars ectorictalis
A2α ventralis or A2αv: Eagderi & Adriaens (2010b): Hoplunnis .
Pars endorictalis
A2α dorsalis or A2αd: Eagderi & Adriaens (2010b): Hoplunnis .
Pars ricto-malaris
A 1 + A 2: Eaton (1935): Anguilla .
Adm 1: Adams (1919): Anguilla . Pars malaris
A1: Eagderi & Adriaens (2010b): Conger .
A2β: Eagderi & Adriaens (2010b): Hoplunnis .
Pars promalaris
A2β anterior or A2βa: Eagderi & Adriaens (2010b): Hoplunnis .
A2a: Eagderi & Adriaens (2010a): Anguilla .
Pars retromalaris
A2β posterior or A2βp: Eagderi & Adriaens (2010b): Hoplunnis .
A2d: Eagderi & Adriaens (2010a): Anguilla .
Pars stegalis
A3: Eagderi & Adriaens (2010b): Hoplunnis . Adm 3: Adams (1919): Anguilla .
Pars epistegalis
A3: Eagderi & Adriaens (2010a): Anguilla ; Eagderi & Adriaens (2010b): Conger .
Pars substegalis
A3: Eagderi & Adriaens (2010a): Anguilla .
A2β: Eagderi & Adriaens (2010b): Conger .
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