CHARACIFORMES (Datovo & Castro, 2012)

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 : 585-589

publication ID	https://doi.org/ 10.1111/zoj.12142
persistent identifier	https://treatment.plazi.org/id/03DB6116-5331-A228-FEF0-D4DB27B67D82
treatment provided by	Marcus
scientific name	CHARACIFORMES
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CHARACIFORMES View in CoL View at ENA

Description

Xenocharax spilurus ( Fig. 17 View Figure 17 )

The rictalis and malaris are continuous with one another at their origins from the quadrate, preopercle, and hyomandibula. Anteriorly, these sections gradu- ally separate and have distinct insertions. The malaris converges onto the dorsal portion of the intersegmental aponeurosis that, in turn, differentiates anteriorly into a mandibular tendon. The rictalis further subdivides anteriorly proximate to its insertion into a small ectorictalis and a larger endorictalis. The ectorictalis attaches to the posterolateral region of the retrojugal lamina, whereas the endorictalis inserts on the coronoid regions of the dentary and angulo-articular.

The ramus mandibularis trigeminus nerve passes between the endorictalis and malaris.

At its origin, the dorsal portion of the stegalis is separated dorsally from the malaris, with the levator arcus palatini passing between these two sections. Ventrolaterally, the stegalis is continuous with the remainder of the segmentum facialis. The fibres of the stegalis arise mainly from the metapterygoid and converge onto the ventral portion of the intersegmental aponeurosis, which separates anteriorly into a meckelian tendon attaching to the coronomeckelian.

As it proceeds distally, the mandibular tendon assumes an aponeurotic form and serves as the site of origin for the entire, undivided segmentum mandibularis. An inconspicuous accessory tendon runs along the posteroventral region of the segmentum mandibularis and is anchored to the angulo-articular. The segmentum mandibularis inserts on the anguloarticular, dentary, and Meckel’s cartilage.

Remarks

The adductor mandibulae of the Characiformes was recently reviewed in detail by Datovo & Castro (2012). These authors described the forms of the adductor mandibulae for representatives of all characiform families and clarified the homologies of the muscle divisions within that order. Based on obvious positional correspondence and comparability of attachment sites of the muscle sections detailed in Datovo & Castro (2012), their A1 corresponds to the rictalis, the A1α to the endorictalis, the A1β to the ectorictalis, the A2 to the malaris, the A2α to the promalaris, the A2β to the retromalaris, the A3 to the stegalis, the A3α to the epistegalis, the A3β to the substegalis, and the Aω to the segmentum mandibularis. Datovo & Castro (2012) further hypothesized that the A1γ section, found exclusively in the Acestrorhynchidae and Ctenoluciidae , represents an expansion of what they termed the A1, rather than a subdivision of this section into an A1α and A1β, as is the case elsewhere in the Characiformes . Nevertheless, as discussed in Datovo & Vari (2013), evolutionary events of muscular expansion are almost always associated with events of muscle subdivision and the adoption of distinct terminologies for each of these evolutionary processes is unnecessary. Further research is necessary in order to better determine the precise homologies of the A1 and A1γ in the Acestrorhynchidae and Ctenoluciidae , in particular the possible derivation of the A1γ from the malaris in the Acestrorhynchidae (see Datovo & Castro, 2012: 107). Pending that, and in the interest of nomenclatural simplicity, A1 and A1γ in the Acestrorhynchidae and Ctenoluciidae are herein provisionally synonymized with the ectorictalis and endorictalis, respectively.

The malaris and stegalis are associated anteriorly with the intersegmental aponeurosis across the entirety of the Characiformes ( Alexander, 1964; Howes, 1976; Vari, 1979; Gosline, 1989; Datovo & Castro, 2012; Mattox & Toledo-Piza, 2012). The origin of the malaris extends onto the neurocranium in the Acestrorhynchidae , Ctenoluciidae , Cynodontidae , Erythrinidae , Hepsetidae and the characids Agoniates , Acestrocephalus , Brycon , Bryconops , Lignobrycon , Salminus , and Serrasalmus ( Howes, 1976; Vari, 1995; Datovo & Castro, 2012; Mattox & Toledo-Piza, 2012). In many basal lineages of characiforms (most members of the Distichodontidae and Anostomidae ), the rictalis is partially divided into an endorictalis and ectorictalis ( Vari, 1983; Datovo & Castro, 2012; Mattox & Toledo-Piza, 2012). In these taxa, the rictalis is associated with both the retrojugal lamina and the lower jaw. Hemiodontidae and Parodontidae are unique within the Characiformes in having the entire rictalis inserting on the maxilla ( Datovo & Castro, 2012). All remaining lineages in this order have the rictalis inserted primarily on the lower jaw, although a few fibres of the section occasionally also attach to the infralabial membrane ( Alexander, 1964; Winterbottom, 1974; Howes, 1976; Vari, 1979; Lauder, 1981; Machado-Allison, 1983; Gosline, 1989; Datovo & Castro, 2012: 102; Mattox & Toledo-Piza, 2012).

Datovo & Castro (2012) compared their results with all known prior publications dealing with the adductor mandibulae in the Characiformes . The evidence underlying the synonymization of different components of the muscle in earlier studies is consequently not repeated in this paper.

Pronounced modifications of the adductor mandibulae characterize a few of the characiform taxa reported in the literature (e.g. the distichodontids Eugnatichthys and Ichthyborus ; Vari, 1979) or in some instances the morphology of the system was only partially described. In such instances, the homologies of all muscle divisions could not be confidently elucidated and these taxa are not included in the following synonymy.

Synonymy

Pars rictalis

A 1: Alexander (1964): Anisitsia notata (= Hemiodus unimaculatus ), Brycon , Creatochanes (= Bryconops ), Hoplias , Myleus rubripinnis (= Myloplus rubripinnis ), Pyrrhulina , Serrasalmus ; Howes (1976): Acanthocharax , Charax , Cynodon , Cynopotamus , Hydrolycus , Rhaphiodon , Roeboides , Roestes ; Machado-Allison (1983): Piaractus ; Vari (1979): Citharidium , Citharinus ; Vari (1983): Prochilodus .