The genus Thyasira Leach, 1817 in the Magellan Region and adjacent Antarctic waters (Lucinoidea: Thyasiridae)

ZELAYA D. G.

Monterrey, USA

Congreso; 38th Annual Western Society of Malacologists – 71st annual Americal Malacological Society; 2005

Americal Malacological Society - Western Society of Malacologists

Thyasira Leach, 1817 is a worldwide genus of infaunal bivalves, occurring from shallow to abyssal waters, including oxygen-poor and hydrogen sulfide-rich environments. Five species of the genus were reported from the Magellan Region and adjacent Antarctic waters: Thysira falklandica Smith, 1885, Thyasira fuegiensis (Dall, 1889), Thyasira magellanica Dall 1901, Thyasira bongraini (Lamy, 1910) and Thyasira debilis (Thiele, 1912). At present, there is confusion on their identity, arising from the unprecise original descriptions, based on few, subtle and widely variable shell characters. Soft part anatomy of the species is completely unknown. In this study a revision of the thyasirids occurring in the Magellan Region and adjacent Antarctic waters is performed by studying shell and gross external anatomy. The study is based on material collected during several field trips at the Magellan Region and the Scotia Arc Islands. Shell morphology was studied by SEM and anatomy by dissection under stereoscopic microscopy. In addition to the five species of Thyasira previously reported for the area, 3 species new to science were found during this study. Most of the species here examined showed great intraspecific variability in shell morphology. This fact is in contrast with the soft part anatomy (e.g. the morphology of the gill and food) which proved to be appropriated to recognize different species.