Anacanthus barbatus Gray 1830

Anacanthus barbatus Gray

Various modifications are apparent in the adductor mandibulae complex. A 1α′ originates from the lateral and medial ethmoid. It is partially covered by A 1α posteriorly, and has a long, thin aponeurosis which crosses the upper jaw to insert in the anterior tissues of the barbel. A 1α arises from the ethmoid behind A 1α′ and from the prefrontal. It also develops a long aponeurosis, which fades into the tissues of the barbel at its posterior base. These sections are only connected to the upper jaw by connective tissue. A 1β is fairly well developed, and has its normal relationships. A 1β′ is absent, and A 1γ is poorly developed, originating from the prefrontal and the infraorbital ligament. The fibers of the latter section soon become aponeurotic, and insert on the ethmoid and parasphenoid posterior to the retractor arcus palatini. A 2α and A 2β are not separated posteriorly, but are so anteriorly, where the ramus mandibularis V passes between them. The orbital process of the sphenotic almost reaches the hyomandibular. The levator operculi and levator arcus palatini are very small, but the dilatator operculi remains well developed. The adductor arcus palatini is confined to a region in front of the orbit, but behind the retractor arcus palatini. The latter muscle is very well developed.

Both the hyohyoidei abductores and the hyohyoidei adductores are well developed, the latter muscle attaching to three of the four branchiostegal rays. The hyohyoideus inferioris meets its antimere in the ventral midline, and is not attached to the urohyal.

Rectus ventralis II is single, with the fibers passing anteromedially to the midline, where they join to form two tendons to the urohyal. Obliquus ventralis III is absent, as is the ventral section of rectus IV.

The dorsal ends of the gill arches lie beneath the prootic shelf at the level of the prefrontal. Levatores externus IV inserts only on epibranchial 4. The levatores interni arise from the prootic just before the start of the shelf at the rear of the orbit. They course the length of the orbit before inserting on the infrapharyngobranchials.

The levator pectoralis is very well developed, originating from the elongated ventral process of the pterotic and sphenotic, the medial fibers arising from the posteromedial face of the hyomandibular. It inserts on the supracleithrum and anterodorsal cleithrum. The protractor pectoralis is less well developed, but also more anterior in position.

There is a single dorsal spine, the depressor dorsalis being larger than the erector dorsalis. The supracarinalis medius is musculous at its attachment sites, but aponeurotic in the middle twothirds, where it attaches to the tips of the neural spines. The infracarinalis anterior has partially fused in the midline. The residual inclinator of the anal fin is very well developed, grading into the infracarinalis medius anteriorly and the obliquus inferioris dorsally. The interradialis is well developed, but both the hypochordal longitudinalis and the transversus caudalis are absent.

Summary of Monacanthidae

The monacanthids exhibit a wide range of variation and progressive specialization, which may or may not be obviously related to the body form. The adductor mandibulae is very variable in both the number of subdivisions and in the relative development of these sections. The basic plan is, however, fairly consistent, with two subdivisions of A 1α and A 1β, and a single section of unknown function, A 1γ. Section A 2 usually has two subdivisions, separated by the path of ramus mandibularis V, the posterodorsal surface of A 2α sometimes reaching the prefrontal. The levator arcus palatini may be well developed or almost absent, or it may be visible laterally owing to a breakdown in the lateral wall of the dilatator fossa. The adductor arcus palatini may be well or poorly developed, confined to the region in front of the orbit, stretch half way across it, or it may reach the rear of the orbit. The retractor arcus palatini is well separa ted from the above muscle, and may be well or poorly developed.

The protractor hyoidei may have a superficial section arising from the fascia overlying the ventral tips of the cleithra, and the hyohyoideus inferioris may arise partially, totally, or not at all from the ventrolateral face of the urohyal. There are minor variations in the extent of development and number of the sections of the branchiostegal ray musculature. The amount of separation and consolidation of the ventromedial section of the sternohyoideus varies, as does the insertion of the sternobranchialis. The retractor interoperculi is sometimes absent.

The pharyngoclavicularis externus is often bifid, and rectus II shows progressive specialization and subdivision. The ventral fiber bundle of rectus ventralis IV may be absent, and the relative positioning and development of the sections of transversus ventralis IV differs.

The position of origin of the levatores externi depends on the location of the prootic shelf, while that of the levatores interni seems independent of this variable. The muscles serving the fin ray elements of the pelvis are variously developed or absent, the ray elements themselves being absent in certain genera. Muscles attaching to the dorsal spines vary in sites of origin and relative development. The anterodorsal portion of the obliquus inferioris may be musculous or largely aponeurotic, and the sites of origin of the spinalis vary.

At least some of the variation in monacanthids is attributable to the large number of species and genera and the great variety of body form. They would appear to have undergone “explosive” evolution, and form the apomorph sister group of the balistids.

Myological Descriptions of Representative Aracanids

The general body form of these fishes is illustrated in Figure 5. In his review of the genera of ostracioid fishes, Fraser-Brunner (1935) recognized six genera in what was originally a subfamily, but which he later raised to familial rank (1941b). Representatives of two of these six genera have been dissected for the present study. The fishes are encased in a bony cuirass of modified scales from the snout to the level of the posterior margin of the dorsal and anal fins. Neither this family, not the succeeding one (Ostraciidae) show any evidence of pelvic fins or girdle. They are presumably slow swimmers, but virtually nothing is known about their life habits. They appear to live in deepish water (down to 100 fathoms). The gut contents of the specimens dissected for this study indicate a diet of small crustacea and worms.

The aracanids are usually considered, in effect, as the plesiomorph sister group of the next family, the Ostraciidae, and derived originally from a common ancestor with the balistids (although it has also been suggested that they arose from a neotenic molid ancestor).