Histioteuthids observed from submersibles characteristically have the mantle oblique with all arms curled above the head which, in long-armed species, can give the impression that the squid is tied in a knot (see photograph below). Presumably this posture is in response to disturbance by the submersible. In addition to the usual function of fins, the small fins at the posterior tip of the mantle form a circle and swimming waves from one will continue onto the other causing the squid to rotate about its axis (Hunt, 1996).
Figure. Left - In situ video frames of a histioteuthid (probably H. reversa), depth unknown. Right - Two video frames of Stigmatoteuthis arcturi, 800 m, Bahamas, show a hovering S. arcturi with "knotted arms" on the left, then the same squid slowly swimming away on the right. Pictures provided by M. Vecchione.
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