MURAENINAE, Rafinesque, 1815
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publication ID |
https://doi.org/ 10.1643/CI-19-211 |
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persistent identifier |
https://treatment.plazi.org/id/C74B87A5-8C30-4912-FCAC-FC62E252A8FB |
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treatment provided by |
Felipe |
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scientific name |
MURAENINAE |
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Gill-arch skeleton
Figures 1–4 View Fig View Fig View Fig View Fig
The pharyngeal apparatus of muraenid eels is notably reduced compared to most teleosts, including other anguilliform eels (see Nelson, 1966: figs. 41–44). There are no hypobranchials or basibranchials. There are four epibranchials and ceratobranchials, the first three of which are relatively thin and delicate and apparently serve only to support the gill filaments. The fifth ceratobranchial (Cb5) is absent, and the rod-like fourth ceratobranchial (Cb4) supports the lower pharyngeal toothplate (LPT), which is usually supported by Cb5. The fourth epibranchial (Eb4) is robust and rod-like and, as described and illustrated by M&W (fig. 4) and illustrated by Nelson (1966: figs. 43–44), articulates at its anterior end with the medial surface of a dorsal process (‘‘horn-shaped process’’ of M&W) on the single toothed element in the dorsal complex, the large, elongate upper pharyngeal toothplate (UPT).
Extrinsic gill-arch muscles
External levators (LE).— ( Fig. 1B View Fig ) There are three relatively thin external levators (LE1-3). As with levators in most teleosts, they have a common origin along with the internal levators on the occipito/otic region of the braincase and insert on their respective epibranchials. A fourth external levator occurs in only four species placed in the subgenus Neomuraena (not illustrated). As is typical for LE4, it originates together with the other levators but bypasses UPT medially to insert on the dorsal surface of Eb4 near its articulation with Cb4 as is the case in uropterygiines.
Internal levators (LI).— ( Figs. 2C View Fig , 3–5 View Fig View Fig View Fig , 7 View Fig , 10 View Fig ) There are two internal levators (LI1-2). Levator internus 1 (LI) originates in the epaxialis directly above UPT and inserts on the anterior portion of its dorsal surface ( Figs. 1B View Fig , 2C View Fig , 3–5 View Fig View Fig View Fig , 7 View Fig ). It is identified as such as follows. Most pre-acanthomorphs have three internal levators, the most posterior being the third, which is lost at the level of Ctenosquamata (sensu Rosen, 1973) concomitant with the loss of the fifth upper pharyngeal toothplate (UP5; Johnson, 1992). UP5 is also absent in several pre-ctenosquamate clades. A third internal levator (LI3) has been lost independently in Anguilliformes , where there is also no UP5. Identity of the two internal levators of most eels is obvious, as one (LI1) inserts on Pb2 (second pharyngobranchial) and the other (LI2) on Pb3. Nelson (349) noted briefly that in Conger LI 1 extends between the fascia of the trunk and Pb2, and, because he only discussed differences between Conger and the other families he described, the implication is that this also characterizes those other families. I agree, and I know of no group of teleosts outside anguilliforms in which an internal levator originates from the epaxial musculature rather than the braincase. S&J and Springer and Johnson (2015) did not consider the point of origin of internal or external levators. However, I have confirmed the origin of LI1 to be as Nelson described it for Conger (from the epaxialis) in anguillids, muraenids, ophichthids, and chlopsids, and I illustrate it for muraenines in Figures 1B View Fig and 7. I View Fig have not examined the condition in all anguilliform families, but I can confirm that it exhibits the primitive state (origin on the braincase) in protanguillids and synaphobranchids. Additionally, when LI1 originates in the epaxialis, it is broad and strap-like vs. roughly cylindrical (e.g., in Springer and Johnson, 2015, compare LI 1 in figs. 4, 5 of Conger and Anguilla to that in figs. 2, 8 of Protanguilla and Synaphobranchus ).
Levator internus 2 (LI2) originates on the occipito/otic region of the braincase together with the external levators and gives rise to two separate sections, which are continuous at their origin. The anterior section inserts on the dorsomedial surface of the anterior end of UPT and the posterior section on the dorsolateral surface of its posterior end ( Figs. 2C View Fig , 3A View Fig , 4 View Fig , 5 View Fig ). Muraenids have no separate Pb2, the normal insertion site of LI1, but because the third muscle bundle inserting on UPT is very broad and strap-like and originates in the epaxial musculature, it is readily identifiable as Nelson’s LI1. Thus, the remaining two muscle bundles are most parsimoniously interpreted as subdivisions of LI2, a condition unique among eels to the Muraeninae . The four species currently placed in the subgenus Neomuraena (not illustrated) are exceptional in having an undivided LI2.
Dorsal retractor (DR).— ( Figs. 2C View Fig , 3–6 View Fig View Fig View Fig View Fig ) Nelson (362) reported the presence of both dorsal and ventral retractors (DR, VR) in all eels (wherein the latter are unique among teleosts), essentially continuations of the inner longitudinal muscle layer of the sphincter oesophagi (SO) muscle fibers. These extend anteriorly from the esophageal wall and attach to the posteriormost portion of UPT (DR) and that of LPT (VR), which is associated with the fourth ceratobranchial (Cb4; Fig. 5 View Fig ). Posterior to the attachments of the retractors, the outer transverse or circular esophageal muscle layer surrounds the longitudinal layer. Nelson observed that only in muraenines does a portion of the dorsal retractor attach to the vertebral column, and he and others (e.g., Winterbottom, 1974; Springer and Johnson, 2015) have made clear that this muscle is not equivalent to Rosen’s (1973) retractor dorsalis (a synapomorphy of neoteleosts, Rosen, 1973; Johnson, 1992), which also originates on anterior vertebrae but is largely outside the sphincter oesophagi (see also S&J). My observations of the dorsal retractor of muraenines agree with Nelson’s and indicate that its attachment to the vertebral column ranges from robust direct muscular attachment (e.g., in Gymnomuraena , Fig. 6 View Fig ) to connective tissue suspension in other muraenine genera, except Rhinomuraena , where I found it lacking. As reported by Nelson and M&W, all uropterygiines also lack this attachment.
Recti dorsales (RecD).— These are the muscles Nelson called obliquii inferiores (see Winterbottom, 1974: 259 and S&J: 26). They connect adjacent epibranchials. As described by Nelson (table 2, fig. 11) muraenines have RecD1-3 and uropterygiines have only RD2-3. M&W did not mention these muscles, and they are not illustrated or discussed further here.
Subpharyngealis (Sph).— ( Figs. 1 View Fig , 2C View Fig , 7 View Fig ) As described and illustrated by Nelson (358, fig. 10), the ventral muscles of muraenine eels primarily comprise numerous subdivisions (Nelson’s interbranchial attractors) of the subpharyngealis.
These are represented by fan-like arrays of muscle fibers lying dorsal to the ventral-arch elements connecting adjacent ceratobranchials, some of which extend forward to insert on the hyoid arch (by which he apparently meant specifically ceratohyal) These muscles are unusual in that they lie dorsal to the skeletal elements of the ventral arches (see Nelson: 249 and Springer and Johnson, 2015: 615). The most robust of these subdivisions originates on the dorsal surface of Cb4 near its articulation with Eb4 ( Fig. 7C View Fig ).
Intrinsic gill-arch muscle
Adductor dorsalis 4 (AD4).— ( Figs. 2–4 View Fig View Fig View Fig , 7C View Fig ) Adductor dorsalis 4 is a large ovoid to triangular muscle that originates on the dorsal surface of the posterior quarter of Cb4 and inserts along the ventral surface of most of the length of Eb4 with some fibers continuing onto the lateral surface of the dorsal process of UPT.
Sternohyoideus (Sh)
Figure 7A, B View Fig
The sternohyoideus, not part of the gill-arch musculature, is described here because of its obvious activity during pharyngeal jaw movement (see Functional Summary). It is an elongate muscle originating primarily along the lateral surface of the hypaxialis and inserting along the ceratohyal ( Eagderi, 2010: figs. 6.13c, 6.16c). In most teleosts and other eels, it inserts on the urohyal, which is lacking in muraenids.
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