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Chilornycterus schoepfi (Walbaum)

Comprehensive Description

provided by Smithsonian Contributions to Zoology
Chilornycterus schoepfi (Walbaum)

A 1α is better developed dorsally than in D. hystrix, and has acquired attachment to the head of the hyomandibular and the anterolateral pterotic. This region of origin is somewhat aponeurotic, and the fibers are inseparable from those of A 2α. Insertion of the additional fibers is primarily on the ventrolateral face of the maxilla. Anteroventrally, some of the fibers arise from the dentary and articular. A 1β is also better developed, as is the A 2 complex.

The posterodorsal section of the hyohyoidei adductores has a tendon passing posteriorly over the cleithrum to attach to the postcleithrum. The pharyngoclavicularis internus is smaller, while the externus division is larger than in D. hystrix. What is apparently transversus ventralis IV is modified to form an aponeurotic sheet to basibranchial 2, i.e., it is obliquely oriented, and the fibers do not meet their antimeres.

The levatores externi are as for C. orbicularis and transversus dorsalis II is very well developed posteriorly, with a large section attaching to the dorsomedial cleithrum. Adductor III is small, and the retractor dorsalis originates from the third to seventh vertebrae. No inclinatores dorsales or anales were separable. The anterodorsal origin of the flexor dorsalis superior is more extensive. The flexor dorsalis is also larger, with a thin aponeurosis to ray D 5. The flexor ventralis is not subdivided, and originates mainly from the medial faces of the ventrolateral flanges of the second and third last vertebrae.

The anteroventral section of the obliquus inferioris from the postcleithrum attaches to the coracoid rather than joining the coracoradialis. The section over the abdominal cavity is reduced, although not to the extent seen in C. orbicularis. The posterodorsomedial section is bifid, attaching to the lateral flanges of the thirteenth and fourteenth vertebrae. The posteriormost section and the dorsal moiety of the epaxialis are much reduced.

Summary of Diodontidae

The relative development of the A 1 and A 2 sections of the adductor mandibulae varies fairly considerably, although the basic plan of the subdivisions remains constant. The sites of origin of the levatores externi and the retractor dorsalis vary, as does the relative development of the transversus dorsalis II. Other areas of the musculature showing significant variation are the flexors of the caudal fin and the development of the obliquus inferioris.

Myological Descriptions of Representative Molids

The body outline of members of this family are illustrated in Figure 11. Two out of the three genera (possibly all monotypic) were dissected for this study, no specimens of Masturus being available. The mouth is small, the dorsal and anal fins very high, and rather stiff. The caudal peduncle is aborted, so that the rays of the caudal fin lie in an almost vertical line behind the dorsal and anal fins, and appear to grade into them. The pectoral fins are short. In swimming, the dorsal and anal fins flap synchronously from side to side, steering apparently being accomplished by using the caudal fin as a rudder. The body is high and thin, the shape being ellipsoid or circular. Molids possess the powerful jaws typical of gymnodonts, although their food is reported to consist of coelenterates and pelagic tunicates (Mola) or seaweeds (Ranzania). They have a worldwide distribution (Mola itself occurring in both tropical and cold-temperate waters). Molids are thought to be pelagic, although the possibility that they are bathypelagic cannot be ruled out.

Phylogenetically, they are usually considered to be derived from the gymnodont line before separation of the tetraodontoid and diodontid stocks.
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bibliographic citation
Winterbottom, Richard. 1974. "The familial phylogeny of the Tetraodontiformes (Acanthopterygii: Pisces) as evidenced by their comparative myology." Smithsonian Contributions to Zoology. 1-201. https://doi.org/10.5479/si.00810282.155