Author:
Alibardi Lorenzo,Thompson Michael B.
Abstract
Formation of the scutes and dermis of the embryonic shell of the turtle
Emydura macquarii was studied using light and electron
microscopy. Shell morphogenesis begins at embryonic stage 15 and the shape of
the shell is mostly completed by embryonic stage 19. The carapace anlagen
arises as a thickening of the skin in the dorsal part of the mid-trunk region
between the anterior and posterior limbs. This thickening extends
ventro-laterally to form ridges at the margins of the carapace. Each ridge
forms as a thick epidermal placode over a condensation of mesenchymal cells.
The epidermis behind the advancing margins of the carapace is cuboidal or
columnar but does not form placodes. The margins of the carapace expand
rapidly in all directions. The plastron anlagen is derived from epidermal
cells localised in the latero-ventral regions between the fore- and
hind-limbs. Plastron placodes are present laterally, while the mid-ventral and
central epidermis remains cuboidal or columnar but does not form placodes at
embryonic stage 16. The plastron thickening rapidly moves from a
latero-ventral position to a flat ventral position between embryonic stages 16
and 19. Dermal–epidermal anchoring complexes occur throughout placodes
of both the carapace and plastron, but are rare in non-placode areas. The
accumulation of a dense mesenchyme beneath the shell epidermis forms a dermal
cushion that surrounds the body cavity. The superficial dermis close to the
epidermis is made of mesenchymal fibroblasts at embryonic stage 19, although
the inner-most areas contain bipolar fibroblasts and extracellular fibrils.
Scutes with serrations at their borders form as invaginations of the epidermis
into the dermis in the mid-dorsal areas of the embryo at embryonic stages
18–19. Dermal–epidermal anchoring complexes are located around the
infoldings that form the scutes of the hinge region. The epidermis of the
shell has 2–3 suprabasal cells at embryonic stages 19–22, and
lacks keratinisation before embryonic stage 22 when it has 4–6
suprabasal layers with 2–3 external layers made of flat cells. The
dermis thickens and has numerous collagen fibrils after embryonic stage 19.
The formation of dermal bones begins at embryonic stage 18–19 in the
plastron. Only small areas of the carapace near to the bridge have begun to
form dermal bone at embryonic stage 19. Calcification begins at embryonic
stage 19, but is still incomplete at embryonic stages 24–25.
Subject
Animal Science and Zoology,Ecology, Evolution, Behavior and Systematics
Cited by
28 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献