Dermal Skeleton

Dermal Skeleton

 

a system of bony formations that develops in the connective-tissue layer of skin, or derma, of vertebrates.

The dermal skeleton performs protective and supportive functions. It is most highly developed in fish and loricate Agnatha. The original type of dermal skeleton was the placoid scale (dermal denticles), which covered the head and body of the animal evenly (fossil telodonts and Euselachii). The dermal denticles could fuse into more or less large plates, forming a shell. In the evolution of fish, the dermal skeleton differentiated into a cephalic section, consisting of large ossifications forming a dermatocranium, and a truncal section, consisting of rows of scales (cosmoid and ganoid). Vertebrate phylogeny has shown a gradual sinking of the elements of the dermal skeleton beneath the skin, bringing the dermatocranial ossifications into closer contact with the cranium and gradually reducing the shell of truncal scales (well developed in many fossil vertebrates). In extant terrestrial vertebrates the rudiments of the primitive dermal skeleton are preserved in the form of bony scales in apodal amphibians and ventral ribs in tuataras and crocodiles. In certain vertebrate forms, such as turtles and armadillos, a heavy dermal skeleton developed secondarily. The skeletal formation in certain invertebrates is sometimes called a dermal skeleton, but such formations differ from the dermal skeleton of vertebrates in content (for example, calcareous plates and the spines of echinoderms).

V. N. IAKOVLEV

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References in periodicals archive ?
Pharyngeal dentic1es (placoid scales) of sharks, with notes on the dermal skeleton of vertebrates.
Protective and hydrodynamic function of the dermal skeleton of elasmobranchs.
However, the fish that belonged to these groups presented a delay in the dermal skeleton regenerative process (lepidotrichia and actinotrichia) of the tail fins (Figure 3b, Figure 4b, Figure 5b and Figure 6b).
Although there was a delay of approximately 4 days in the regeneration of the tail fin dermal skeleton of the fish treated with doses of 20 and 30 mg.
However, these fish presented a delay in the process of dermal skeleton regeneration (lepidotrichia and actinotrichia) of the tail fins.
Although the doses here used delayed the regeneration of the dermal skeleton of the tail fin, they did not interfere with the migration of the epidermal cells and consequently with the formation of the epidermal cap.
This is the first evidence showing that in the dermal skeleton of Andreolepis (A.
It also seems to be true that in these two taxa the lateral line canals are situated differently in the dermal skeleton.
Sytchevskaya on the dermal skeleton of early actinopterygians were very useful.