Thursday, June 2, 2011

Brooded ophiuroid juveniles

Amphopholis squamata is a common small intertidal ophiuroid (brittle star) in the Pacific NorthWest. Unlike many larger species of ophiuroids which produce large numbers of eggs, free-spawn them and have pelagic development, this small species produces few eggs at a time and broods its young in specialized pouches, called the genital bursa, located in the central disc. The juveniles may be removed from the brooding adult by opening the genital bursa from the oral side. The juveniles dissected from a single adult are often at different developmental stages and of different size. They may range from fertilized egg to a juvenile ready for self-sufficiency. The different stages may be found within a single brooding pouch. These are dark-field photomicrographs of two juveniles dissected from a single adult taken at the same magnification. The top picture is of a small juvenile that was still connected to the brood pouch of the adult brittle star, so that it may receive necessary nutrients for development. Because the embryos receive nutrition from the mother, they grow inside the brood pouches. The bottom picture shows a larger juvenile which has developed arms.

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