ISSN:
0362-2525
Schlagwort(e):
Life and Medical Sciences
;
Cell & Developmental Biology
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Biologie
,
Medizin
Notizen:
Prepartum embryos obtained from old museum specimens of the ovo-viviparous fish, Oligopus longhursti, possess external intestinal appendages. They are structurally identical to the trophotaeniae described by Turner ('37) and Mendoza ('37) in goodeid fishes. This is the first report of trophotaeniae in the viviparous ophidioids. Two developmental Stages, A and B, were observed. A is a tailbud stage, 2.0-2.25 mm in length, and B is a finfold embryo, 3.0-3.25 mm in length (Wourms and Bayne, '73). Trophotaeniae occur in the form of a single median anterior process and a pair of median posterior processes. They originate from a conspicuous peduncle formed around the anus. The processes of stage A are 1.5-2.0 mm long, 0.05 mm in diameter at their base and 0.04 mm at their tip. The stage B processes are 2.75-3.00 mm long, 0.075 mm in diameter at their base and 0.050 mm at their tip. Serial sections show that the surface epithelium of the trophotaeniae is continuous with and identical to the surface epithelium of the trophotaeniae is continuous with and identical to the surface epithelium of the embryonic gut. Examination both by transmission and scanning electron microscopy confirms that the apical surface of the trophotaenial epithelium and intestinal epithelium are covered with microvilli. Trophotaeniae are considered to function in the uptake of nutrients since they are structurally identical to intestinal epithelial cells. We suggest that maternal nutrients absorbed by trophotaeniae rather than yolk reserves are the principal source of embryonic metabolites. Trophotaeniae may afford a selective advantage since their existence in O. longhursti maximizes the number of large size embryos which a female can produce at one time. Occurrence of trophotaeniae in ophidioid, goodeid and zoarcid embryos is a remarkable example of convergent evolution.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/jmor.1051470403
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