Publication Date:
2015-07-15
Description:
A morphological study revealed that the NW American soft-bottom bivalve Nutricola tantilla is dioecious, not a protandric hermaphrodite as previously reported. We base this conclusion on the smaller males having highly specialized, glandular sperm ducts, while the larger females have simple oviducts and no transition between the two ducts occurs. The females are brooders and retain their ova in a marsupium within the dorsal part of the inner demibranchs. Sperm cells were present and associated with a mesh-like tissue among the ova or early-stage embryos. How this tissue originates is still unknown. We suggest that sperm cells dissociate from this pool and fertilize the oocytes as soon as they are ovulated. The mode of sperm storage in N. tantilla represents a unique case in that the sperm are presumably nurtured within a nonepithelial tissue. We describe the ultrastructure of the sperm cells in N. tantilla. Large, spherical cytophores become associated with a multitude of acrosomes of spermatozoa and probably represent the precursors of the spermatozeugmata that have been described previously.
Print ISSN:
0260-1230
Electronic ISSN:
1464-3766
Topics:
Biology
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