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Smithsonian National Museum of Natural History
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Roper, C.F.E. and M. Vecchione

1997
In situ observations test hypotheses of functional morphology in Mastigoteuthis (Cephalopoda, Oegopsida).
Vie et Milieu 47:87-93.

ABSTRACT: Mastigoteuthis magna observed in situ has a characteristic "tuning fork" posture that can be used as an aid for identification, even for very small squids. Observations of living Mastigoteuthis from submersibles in the western Atlantic Oceanenabled us to test formerly proposed hyotheses concerning functional morphology of these deep sea squids. Hypotheses supported by observations on live animals include: 1) The large fins provide propulsion; simple and double sinusoidal waves move anteriorly or posteriorly, fins flap powerfully, fins roll together ventrally to squeeze water out anteriorly or posteriorly. 2) Tentacular suckers have weak release mechanism; tentacular clubs on live animals feel very sticky, like fly paper, and must be firmly pulled off observer's skin and aquarium wall. 3) Tentacular suckers have sensory function; tentacular tips skim along bottom to allow animal to maintain position in food-rich benthic boundary layer. Observations do not support these hypotheses: 1) Vacuolated arms and head induce head-upwards posture; observations confirm a head-downwards posture maintained by constantly maneuvering fins. 2) Ventral arms lock together to form "gutter" for feeding; live animals hold long ventral arms far apart with proximal part of tentacles enveloped in tentacular sheaths, allowing them to serve as non-tangling trolling lines fishing for minute prey. 3) Well developed eyes and ink sac indicate photic zone habitat; all observations of Mastigoteuthis from submersibles are close to the bottom below 500 m, never in photic zone. We suggest Mastigoteuthis evolved from a Chiroteuthis-like ancestor; its adaptive characters enable it to inhabit the unique trophic zone immediately above the deep sea bottom, feeding on small zooplankters with trolled, non-tangling tentacles.

Mastigoteuthis magna

Mastigoteuthis magna In typical head-down posture. Fins show double sine wave undulation. Mucous strands (white blobs) attached to posterior end of mantle. Corresponds to Pl. 1A.
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Mastigoteuthis magna Drifting just above bottom in typical head-down, tuning fork posture with elongate tentacles and their shadows converging on the bottom,correponds to Pl. 1D.
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Mastigoteuthis magnaDrifting in typical tuning fork posture through expanded tentacles of anemone, corresponds to Pl. 1E.
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Mastigoteuthis magnaIn typical tuning fork posture with tentacles greatly elongate as animal suddenly drifts over steep drop-off of sea floor, corresponds to Pl. 1F.
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Mastigoteuthis magnaWith single sinusoidal undulation of fins originating at posterior end. Animal somewhat above bottom with tentacles contracted into tentacular sheaths of arms IV. Corresponds to Pl. 2A.
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Mastigoteuthis magnaWith fins overlapping ventrally and motionless. Corresponds to Pl 2C.
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Mastigoteuthis magnaWith fins rolling together along ventral midline, squeezing water out posteriorly in a low-velocity jet. Corresponds to Pl. 2D and 2E.
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