Alviniconcha hessleri Okutani & Ohta, 1988 PROVANNIDAE -3610m, Alice Springs Hydrothermal Field, Mariana Trough, 48.5mm, F+++, 1980s The Hairy Gastropod is one of the most famous representatives of hydrothermal vent endemic molluscs and unmistakable with its heavily hirsute periostracum. It houses chemosynthetic endosymbionts in greatly enlarged gill and relies on these for nutrition, the digestive system is reduced as a consequence. Although once thought to be widely distributed from Mariana Trough (its type locality) to Kairei Field in the Central Indian Ridge, genetic studies have revealed at least three cryptic species (Mariana, North Fiji to Manus, and Central Indian Ridge); and thus only populations from Mariana Trough should be referred to as the species A. hessleri. It is best known from Alice Springs field (about -3600m) and Forecast field (-1470m), where individuals form dense aggregations on vent chimneys dominating areas closest to the vent effluent. It uses both hemocyanin and hemoglobin for oxygen carrier. It often co-occurs with another large provannid Ifremeria nautilei Bouchet & Warén, 1991, whose aggregations frequently surround that of A. hessleri. The typical shell length is around 45mm, large specimens may approach 60mm. The other species ranging from North Fiji to Manus basin is much larger and may exceed 80mm. Like most other vent endemic molluscs, it is virtually unobtainable for shell collectors due to its extremely inaccessible habitat.
Posted on: Sat, 29 Mar 2014 16:11:28 +0000
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