Abstract:
Razor clams (Pharidae and Solenidae, Mollusca) are ecologically and economically important deep-burrowing bivalves. They are distributed in shallow waters of the tropical, subtropical, and temperate seas. The North-West and the Indo-West Pacific has the highest species richness (about 85% of all species) mostly in the Sea of Japan, China Sea, the Gulf of Thailand, and the Andaman Sea. Their species composition forms 16 biogeographic regions which concur with existing marine biogeographic hypotheses. More than half of the species are endemic to these biogeographic regions. This is an exceptionally high rate of endemicity in the oceans and suggests little gene flow between populations. Species richness increases from the cold temperate to intermediate latitudes and dips near the equator following the mean sea surface temperature. Species richness decreases with temperature range, chlorophyll-a concentration, and primary productivity over all latitudes, but increases with ocean area in the Northern Hemisphere. Most species are predicted to shift their distribution ranges poleward in the future due to global warming. Thus the mid-latitude peaks of species richness will move further apart, increasing the dip in richness near the equator.