LOCOMOTION MODES OF DEEP-SEA CIRRATE OCTOPODS (CEPHALOPODA) BASED ON OBSERVATIONS FROM VIDEO RECORDINGS ON THE MID-ATLANTIC RIDGE

The behaviour of cirrate octopods of the genera Cirroteuthis and Grimp oteuthis in their natural habitat was studied using video recordings. Sequences were filmed during the French cruise ''Faranaut'', from the manned submersible ''Nautile'' at depths between 2702 and 4527 m, in t wo zones in the Fifteen-Twenty Fracture Zone on the Mid-Atlantic Ridge . Four different modes of active locomotion, namely crawling, takeoff, fin-swimming, and pumping, and one apparently passive mode of locomot ion, umbrella-style drifting, were observed. Jet-propulsion, a charact eristic mode of locomotion typically employed by cephalopods, was not observed in the cirrate octopods filmed, although breathing movements of the mantle to aerate the gills were assumed to generate some slight propulsion through the funnel. Fin-swimming was the mode of active lo comotion most frequently observed. Neutral buoyancy was confirmed in o ne individual after capture. This buoyancy enables passive drifting in the umbrella-style attitude observed in Cirroteuthis spp., possibly u sing near-bottom ocean currents. Pumping, a mode of slow locomotion ge nerated by peristaltic waves in the primary and intermediate webs, als o observed in Cirroteuthis sp., is described here for the first time. The take-off mode of locomotion, a sudden, single contraction of the b rachial crown and web, is also described; it was always followed by fi n-swimming. No medusoid swimming of the type previously described for opisthoteuthid cirrates was observed. A flight response to the approac h of or contact with a strange object, i.e. the submersible, using the crawling, take-off, or fin-swimming modes was observed. A ballooning response was observed in a high-stress situation when a C. magna indiv idual was captured.