At hatching, Heterobranchus longifilis does not display any primordia of the cephalic skeleton. The latter appears 12 h post-hatching and develops in three stages up to day 16. The first stage (12 h to 2 days) involves almost exclusively the development of the chondrocranium. During the second period (days 3-8), dermal elements of the splanchnocranium appear. The final stage is marked by resorption of the cartilages, progressively replaced by ossifications (days 10-16). At their appearance the elements of the splanchnocranium are fused together, as are the first neurocranial elements. Later, the splanchnocranium splits up. By the time the yolk sac is completely resorbed, the buccal and pharyngeal jaws are present, the suspensoria and hyoid bars are partially developed, and the parasphenoid partially closes the hypophyseal fenestra. These structures delimit a buccal cavity that is probably functional, i.e. capable of participating in the intake of exogenous food. Next to continue its development is principally the splanchnocranium, completing the walls of the buccal cavity. Cartilage resorption parallels the appearance of endochondral ossifications (except for the trabecular bars). Braincase closure begins to accelerate once the buccal system is complete. 1997 The Fisheries Society of the British Isles No cephalic skeletal structure is visible.
Day 1The first cartilaginous structures have appeared [ Fig. 1(a)]. They all belong to the splanchnocranium. These structures are: the hyosymplectic, the interhyal, the hyoid bar, the pars quadrata of the palato-quadrate, and Meckel's cartilage.
Pomacentrids display a significant biodiversity through a variety of sympatric species with various feeding habits. The use of ecomorphological methods, based on the study of skeletal and muscular structures of the feeding apparatus could result in a better understanding of the adaptive radiation of this family. Significant differences in teeth and in the shape and thickened areas of the different bones were observed. The strongest structures occur in species which had teeth characteristic of suction feeding, and the weakest structures in species with biting teeth.
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