RECTAL GLAND OF FRESHWATER STINGRAYS,POTAMOTRYGONSPP. (CHONDRICHTHYES:POTAMOTRYGONIDAE)

Autor:	Todd A. Georgi, Thomas B. Thorson, Robert M. Wotton
Rok vydání:	1978
Předmět:	Potamotrygon Potamotrygonidae stomatognathic system biology South american Anatomy General Agricultural and Biological Sciences biology.organism_classification Chondrichthyes
Zdroj:	The Biological Bulletin. 154:508-516
ISSN:	1939-8697 0006-3185
DOI:	10.2307/1541076
Popis:	1. Contrary to some reports, a rectal gland is present in strictly freshwater stingrays of South American rivers (Potamotrygon spp.). 2. The gland has the location and histological features of the salt-secreting rectal gland of marine elasmobranchs, but is much reduced in size and number of tubules. 3. Its residual function, if any, is unknown. 4. The rectal gland is associated with prominent myeloid lobes, here designated as rectomyeloid bodies. 5. In the absence of potamotrygonid fossils, the atrophied rectal gland is strong evidence of marine ancestry for the freshwater rays. 6. Both the reduced gland and the loss of urea retention in potamotrygonids are indicative of a long history of freshwater adaptation.
Databáze:	OpenAIRE
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