World Congress of Malacology Antwerp ... - Unitas Malacologica

presumed discrepancy between molecular age estimates and first fossil occurrences of vesicomyids
emphasized earlier disappears in the light of our evaluation. Of Oligocene age are the new
Archivesica from Alaska, which is shorter and more oval than other known Archivesica species, and
a possible Pliocardia? sp. from cold seeps in Washington. From the early Miocene of Washington
Isorropodon is described and represents the first certain record of this genus from outside the Atlantic
realm. The new middle Miocene Adulomya is so far only known from a whale-fall community in
Hokkaido and may have been endemic to this type of habitat. The timing of the occurrences of these
taxa show no correlation to the evolution of whales in this area, shedding further doubt on the ‘whale
stepping-stone’ hypothesis for the origin of vesicomyids.
Ultrastructural study of the spermatogenesis of a protandric neogastropod, Coralliophila
meyendorffii (Muricidae, Coralliophilinae)
Amor, Maria Jose 1 ; Richter, Alexandra 2 ; Montserrat, Ramón 3 ; Dufort, Mercedes 4
1. Universidad de Barcelona, Av. Diagonal, 645 08028 Barcelona, Spain,
Email: mamor@ub.edu
2. Università degli Studi della Sapienza, viale dell’Università, 32, I-00185 Rome,
Italy,
Email: alexandra@acett.org
3. Instituto Oceanográfico de Baleares, Muelle del Poniente, s/n Apdo. 291, 07015
Palma de Mallorca, Spain,
Email: montserrat.ramon@ba.ieo.es
4. Universidad de Barcelona, Av. Diagonal, 645 08028 Barcelona, Spain,
Email:mdurfort@ub.es
The spermatogenesis of a protandric neogastropod, Coralliophila meyendorffii (Muricidae,
Coralliophilinae) has been studied with electron microscopy and light microscopy. As in other
neogastropod species, males of Coralliophila meyendorffii develope in the testis two types of
spermatoza, fertile eusperm and sterile apyrene parasperm, both of which are ejaculated in the
seminal fluid. Mature parasperm are similar to that of other muricid species. They are worm shaped,
motile, lack nucleus, present multiple axonemes arranged peripherically under the plasma membrane
and contain degenerated mitochondria, glycogen granules and larger cytoplasmic electrodense
granules with polysaccharides. A nutritive role of the parasperm for the eusperm while they are
stored in the female oviduct is suggested. The ultrastructure of the mature eusperm and the processes
during maturation conform with those observed in other caenogastropod. Primary spermatocytes are
characterized by the presence of rod shaped and large mitochondria in a scarce cytoplasm and a
nucleus with a granulose chromatin showing the initial synaptoneme complexes and one or two
nucleolus. Early spermatid have a nucleus with a still a granulose chromatin forming small amounts
on the periphery. The nucleolus are often detected in this phase. The cytoplasm, with mitochondria
and the Golgi body, is scarce, and the axoneme starts developing. The next phases are chatacterized
by the progressive chromatin condensation, the mitochondria fusion and the beginning of their
twisting around the axoneme at the level of the middle piece. In the part of the tail near the middle
piece, the axoneme is surrounded by numerous glycogen granules decreasing progressively in
number toward the tip of the tail. In the head region, the Golgi body is highly active and secretes
granules to form the acrosome which ascends towards the top of the nucleus. The rests of cytoplasm
are excreted as a vesicle.
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