Globigerina pachyderma (Ehrenberg) in the shelf-slope sediments of northern Indian Ocean

Abstract

The occurrence of specimens of @iGlobigerina pachyderma@@ (Ehrenberg) which is considered to be a typical bipolar, cooler water species, in the Recent shelf-slope sediments of the northern Indian Ocean as far north as 9, 12, 14, 19 and 23~' latitudes in the Arabian Sea and 18~' latitude in the Bay of Bengal is considered and compared with similar occurrence from other oceans of the world. Considering various factors like movement of low salinity, low temperate water masses, mixing and upwelling resulting in the occurrence of this species in the northern Indian Ocean sediments, it is proposed that the forms which occur in the low latitudes (upto 25~'N) in the norhern Indian Ocean be referred to henceforth as (1) (a) @iG. pachyderma@@ (Ehrenberg) @iforma dextralis typica@@ Setty, n. subsp. (Sensu Stricto) if the species is right-coiled, and (b) @iG. pachyderma@@ (Ehrenberg) @iforma sinistrealis typica@@ n. subsp. Setty (Sensu Stricto) if the species is left-coiled; (3) as @iG. pachyderma@@ (Ehrenberg) @iforma dextralis@@ Setty, n. subs. (Sensu Stricto) for those which occur in the mid-latitudes; and (4) all those forms which occur in the high latitudes as @iGlobigerina pachyderma@@ (Ehrenberg) (Sensu Stricto) where they are typically left coiled