UROPTERYGIINAE, Fowler, 1925

Johnson, G. David, 2019, Revisions of Anatomical Descriptions of the Pharyngeal Jaw Apparatus in Moray Eels of the Family Muraenidae (Teleostei: Anguilliformes), Copeia 107 (2), pp. 341-357 : 344

UROPTERYGIINAE

Figures 8–10

The gill-arch skeleton of uropterygiines comprises the same elements in the same configuration as that of muraenines, with some minor differences. As described by M&W, uropterygiines lack a dorsal process on UPT, and thus the connection to the fourth epibranchial is dorsal rather than medial. M&W also reiterated Nelson’s observations that LPT lacks a lateral groove for insertion of the pharyngocleithralis, and the fourth ceratobranchial attaches to its ventral rather than lateral side. In addition, some uropterygiines have first and second hypobranchials (Nelson, M&W).

The extrinsic gill-arch muscles of uropterygiines differ from muraenines in several ways. As illustrated by Nelson (fig. 9) and noted by M&W, the first three external levators are reduced, and there are no longitudinal fibers of the sphincter oesophagi attached to the vertebral column. There are in addition three significant differences. First, unlike muraenines, with the exception of Neomuraena (see above), there is an LE4, originating on the braincase with the other levators and inserting on the posterior end of EB4. Second, LI2 comprises only a single bundle that inserts on the anterior end of UPT. Finally, the most striking difference is the presence of an additional dorsal retractor that finds its origin in the hypaxial musculature in the region of the extremely reduced cleithrum ( Figs. 9 , 10 ). This is a relatively large oblong to trapezoidal muscle that tapers anteriorly to insert by a strap-like tendon on the fourth epibranchial near its articulation with the fourth ceratobranchial. I term this muscle hypaxial retractor (HR). In lateral view, this large muscle is well hidden medial to the pharyngocleithralis, sternohyoideus, and particularly the anteriormost portion of the hypaxialis.

Figures

Fig. 8. Uropterygius alboguttatus, USNM 338657, 350 mm. (A) Left lateral view of left fourth gill arch and associated musculature, removed from body, circular fibers of SO removed to expose longitudinal fibers of DR, hypaxial retractor removed. (B) Medial view of A. Note insertion of single branch of LI2 on anterior end of UPT and posterior insertion point of LE4 near Eb4-Cb4 articulation. AD, adductor dorsalis; Cb, ceratobranchial; DR, dorsal retractor; Eb, epibranchial; LE levator externus; LI, levator internus; LPT, lower pharyngeal toothplate; UPT, upper pharyngeal toothplate.

Fig. 9. Uropterygius alboguttatus, USNM 338657, 310 mm. Left lateral view of left fourth gill arch and associated musculature in situ, posterior end of pharyngocleithralis and anterior end of hypaxialis excised at red lines to expose hypaxial retractor; LE4 passes medial to the insertion of HR to insert more posteriorly (see also Fig. 10). AD, adductor dorsalis; Cb, ceratobranchial; Eb, epibranchial; Ep, epaxialis; HR, hypaxial retractor; Hy, hypaxialis; LE levator externus; LI, levator internus; Pcl, pharyngocleithralis; SO/DR, sphincter oesophagi/dorsal retractor; Sph, subpharyngealis.

Fig. 10. Uropterygius alboguttatus, USNM 338657, 340 mm. Left lateral view of left fourth gill arch and associated musculature, removed from body. Note insertion of hypaxial retractor on Eb4. AD, adductor dorsalis; Cb, ceratobranchial; DR, dorsal retractor; Eb, epibranchial; HR, hypaxial retractor; LE levator externus; LI, levator internus; LPT, lower pharyngeal toothplate; SO/DR, sphincter oesophagi/dorsal retractor; UPT, upper pharyngeal toothplate.