GONORYNCHIFORMES
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publication ID |
https://doi.org/ 10.1111/zoj.12142 |
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persistent identifier |
https://treatment.plazi.org/id/03DB6116-5339-A212-FED8-D41E21DA7B03 |
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treatment provided by |
Marcus |
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scientific name |
GONORYNCHIFORMES |
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GONORYNCHIFORMES View in CoL View at ENA
Description
Chanos chanos ( Fig. 14 View Figure 14 )
The rictalis and malaris are continuous with each other at their origins from the quadrate, symplectic, hyomandibula, and preopercle. Slightly anterior to their origins, the rictalis and malaris become completely separated from each other. The rictalis inserts via a tendon on the anteromedial region of the maxilla. Proximate to its insertion, the muscle fibres of the rictalis become organized into two differentiated, but continuous, bundles that correspond to the ectorictalis (lateral) and endorictalis (medial). The buccopalatal membrane is poorly differentiated from the surrounding connective tissues, but the collagenous reinforced band connecting the insertional tendon of the rictalis to the coronoid process of the lower jaw is presumably derived from connective tissues corresponding to the buccopalatal membrane. This ligament cannot be homologized with any of the main buccopalatal ligaments described in Datovo & Vari (2013) and is herein named the postcoronoid ligament.
The fibres of the malaris converge onto an elongate intersegmental aponeurosis, mainly onto its posterodorsal portion that corresponds to the subocular tendon. The intersegmental aponeurosis runs from the subocular region towards the lower jaw.
The stegalis is well separated from the remaining facial sections along most of its extent. The section arises from the metapterygoid and the palatoquadrate cartilage and inserts along the ventral margin of the intersegmental aponeurosis. The intersegmental aponeurosis bifurcates anteriorly into a ventral meckelian tendon that attaches to the coronomeckelian, and a dorsal mandibular tendon that serves as the site of origin of the segmentum mandibularis.
In the examined specimens, the ramus mandibularis trigeminus nerve passes lateral to the entire segmentum facialis of the adductor mandibulae before continuing onto the medial side of the lower jaw.
The segmentum mandibularis is undivided, but its bipinnate configuration permits the recognition of a coronalis dorsally and mentalis ventrally. Anteriorly these sections cannot be differentiated from each other and the entire segmentum mandibularis inserts on the dentary.
Remarks
Howes (1985a) provided a comprehensive summary of the cranial muscles of representatives of all extant genera of the Gonorynchiformes . In the monotypic Chanos , he identified a ventrolateral muscle section (his A 1 /a 1) that clearly corresponds to the rictalis ( Fig. 14A, C View Figure 14 ). Howes (1985a) mentioned that this section had two insertional tendons: one that attaches to the maxilla and ‘another tendon [that] branches off from the dorsal face of the muscle to join an aponeurosis from which extends Aw’ (addition in brackets ours). This latter tendon apparently corresponds to the poorly differentiated postcoronoid ligament that we describe above in Chanos (see Fig. 14B, C View Figure 14 ). Howes (1985a) did not refer to the differentiation of the rictalis in that genus into ectorictalis and endorictalis sections as documented in some subsequent studies (Diogo & Doadrio, 2008; Diogo et al., 2008a; Diogo, 2008b) and herein ( Fig. 14A View Figure 14 ). Amongst all other gonorynchiforms, the rictalis is more obviously subdivided with its subunits explicitly named by Howes (1985a) as the a 1 o (= ectorictalis) and a 1 i (= endorictalis). According to Howes (1985a), Gonorynchus has the endorictalis inserting onto the ‘thick connective tissue surrounding the coronoid process’ (? = buccopalatal membrane), whereas in all other gonorynchoids, the endorictalis attaches to the maxilla in conjunction with the ectorictalis.
Although the separation of the stegalis from the malaris is somewhat subtle, the stegalis is clearly discernible in the specimens of Chanos that we dissect- ed ( Fig. 14B, C View Figure 14 ). One possible consequence of this subtle separation was that the stegalis was not identified as a separate element in any prior analysis of Chanos ( Howes, 1985a; Diogo & Doadrio, 2008; Diogo et al., 2008a; Diogo, 2008b). Thus, the term A2 of prior studies ( Howes, 1985a; Diogo & Doadrio, 2008; Diogo et al., 2008a; Diogo, 2008b) was applied to both the stegalis and malaris – that is, the stego-malaris of gonorynchiforms. In addition to its insertion on the lower jaw, the stego-malaris according to Howes (1985a) also connects with the lacrimal in Gonorynchus , the maxilla and autopalatine in Cromeria , and the antorbital, rictal cartilages, and endorictalis in Phractolaemus .
The kneriid Grasseichthys gabonensis is a miniaturized freshwater fish that exhibits some notable reductive features ( Howes, 1985a; Britz & Moritz, 2007). Howes (1985a) identified only one single facial division (his?A 1) in this species with this section having an origin on the ventral portion of the preopercle and with ‘the majority of fibers appearing to insert into the tissue covering the maxilla’. According to Howes ‘there is, apparently, no inner muscle (A 2)... attaching to the lower jaw’ of Grasseichthys . Cromeria , the sister group of the monotypic Grasseichthys ( Grande & Poyato-Ariza, 1999) , alternatively has an insertion of the ricto-malaris on the maxilla. In light of the qualifications and doubts as to the condition of the muscle in Grasseichthys gabonensis expressed by Howes (1985a), it is possible that his?A 1 might actually refer to the entire segmentum facialis with undifferentiated subdivisions and/or that the connection of this muscle segment with the lower jaw was not noticed by him as a consequence of the very small size of the examined specimens. Additionally corroborating this supposition is the fact that an absence of facial sections of the adductor mandibulae was not encountered in any other teleost either in this study or in that of Datovo & Vari (2013). Thus, if Howes’ (1985a) hypothesis proves correct, then Grasseichthys gabonensis would be the sole known case of a teleost lacking a connection of the segmentum facialis with the lower jaw and in which some facial sections are in fact lost. Neither condition seems probable in light of the current knowl- edge of the ontogeny of the adductor mandibulae, in which facial muscle sections are derived from subdivisions of the single muscle mass attached to Meckel’s cartilage present in earlier developmental stages ( Edgeworth, 1929, 1935; Hernandez, Patterson & Devoto, 2005; Diogo et al., 2008b; Konstantinidis & Harris, 2010; Staab & Hernandez, 2010).
The whole adductor mandibulae of the monotypic Phractolaemus is modified to a pronounced degree as a function of its highly derived, dorsally opening mouth ( Howes, 1985a). Given these striking modifications, the synonymy presented below for this genus is based primarily on the interpretations of Howes (1985a) and should be considered to be tentative.
Within the Gonorynchiformes , a segmentum mandibularis occurs solely in the monotypic Channidae ( Howes, 1985a) . In the two examined specimens of Chanos chanos , the ramus mandibularis trigeminus nerve passes external to the entire segmentum facialis. Howes (1985a), however, reported a passage of this nerve between the rictalis and malaris in this species.
Synonymy
Pars rictalis
A 1 or a 1: Howes (1985a): Chanos , Cromeria , Gonorynchus , Kneria , Parakneria , Phractolaemus .
A1-OST: Diogo (2008b): Chanos , Cromeria , Parakneria , Phractolaemus ; Diogo & Doadrio (2008): Chanos ; Diogo et al. (2008a): Chanos .
Pars ectorictalis
A 1 o or a 1 o: Howes (1985a): Cromeria , Gonorynchus , Kneria , Parakneria , Phractolaemus .
A1-OST-L: Diogo (2008b): Chanos , Cromeria , Parakneria , Phractolaemus ; Diogo & Doadrio (2008): Chanos ; Diogo et al. (2008a): Chanos .
Pars endorictalis
A 1 i or a 1 i: Howes (1985a): Cromeria , Gonorynchus , Kneria , Parakneria , Phractolaemus .
A1-OST-M: Diogo (2008b): Chanos , Cromeria , Parakneria , Phractolaemus ; Diogo & Doadrio (2008): Chanos ; Diogo et al. (2008a): Chanos .
Pars stego-malaris
A 2 or a 2: Howes (1985a): Chanos , Cromeria , Gonorynchus , Kneria , Parakneria , Phractolaemus .
A2: Diogo (2008b): Chanos , Cromeria , Parakneria , Phractolaemus ; Diogo & Doadrio (2008): Chanos ; Diogo et al. (2008a): Chanos .
Segmentum mandibularis
Aω: Diogo & Doadrio (2008): Chanos .
Aw: Howes (1985a): Chanos .
AW: Diogo (2008b): Chanos .
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