In situ observations on three species of large-finned deep-sea squids

The manned submersible Johnson Sea-Link II was used for a series of dives on the continental slope of the eastern Gulf of Mexico in September 1995. The deep-sea squids Mastigoteuthis hjorti Chun, 1913 and Octopoteuthis megaptera (Verrill, 1885) were repeatedly observed at depths of 600–850 m. Both species were videotaped alive, in situ, for the first time during these dives. These species share the characteristic of very large fins, almost as long as the mantle length, but their swimming behavior observed in the vicinity of the submersible differed greatly. Throughout most of the videotaped sequences of O. megaptera, it swam with its body oriented obliquely with the head upward, arms flexed laterally and dorsally. The fins flapped in the arc between overlapping ventrally and extending laterally, never traversing dorsally above the body plane. Conversely, the near-bottom observations of M. hjorti showed it to behave similarly to previous descriptions of Mastigoteuthis magna, orienting vertically with the head down and tentacles extended to the sediment. This orientation is maintained by gentle, complex undulation of the fins. A third species with very large fins and extremely long arms was observed near the bottom from an ROV at approximately 2200 m in January 2000. While it differed from any previously known family, it behaved similarly to a mastigoteuthid. We now believe this specimen was a 'big-fin', family Magnapinnidae Vecchione and Young, 1998. If so, this observation and a similar squid recently observed and video-taped from a submersible in the Indian Ocean extend the known distribution of the recently discovered family to deep waters in subtropical areas around the globe