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The family Magnapinnidae was originally based on a single species, Magnapinna pacifica. However, the discovery of a second species, M. atlantica, and the realization that other known specimens and species belong in the family indicate that this poorly known deep-sea family may have as many as five species based on only eleven specimens. However, as only three of the species are well-described, and four of them are weakly separated from one another, we cannot infer yet that this is a highly speciose family.
Vecchione et al. (2002) described the occurrence of a strange, large squid recorded only by submersible or ROV observations (see title photograph). The authors suggested that these squid belong in the family Magnapinnidae. With the discovery of more species, although based only on small individuals, we are now confident that these large deep-sea squid are magnapinnids, and we include them here. The title photograph shows the thicker regions of the arms and tentacles that are often held at nearly right angles to the body axis and the long, slender portions of the arms and tentacles that trail the squid and are nearly parallel to the body axis. Apparent counterparts for these regions of the arms/tentacles are present in the juveniles. For ease of description we give separate names to these two regions: the proximal-arms/tentacles and the distal-arms/tentacles.
Based on similarity (cladistic analyses have not been made), this family apparently belongs with the "chiroteuthid families" (Vecchione and Young, 1998). These families include the Chiroteuthidae, Mastigoteuthidae, Joubiniteuthidae, Batoteuthidae and Promachoteuthidae. It shares the following characteristics with these families:
- Buccal connectives attach to ventral margins of arms IV.
- Gladius apparently with elongate secondary conus (except in Promachoteuthidae).
- Absence of the "teuthoid" tentacular club.
A few additional characters are shared with the Chiroteuthidae and Mastigoteuthidae:
- Fins terminal (often large) extending well beyond the posterior end of the muscular mantle (this feature is also present in the Lepidoteuthidae).
- Oval funnel-locking cartilage but without protrusions (this feature is also present in the Joubiniteuthidae and Promachoteuthidae).
One of the chiroteuthid families with ...
- narrow, very elongate (vermiform) distal-arms and distal-tentacles.
- very large fins.
- an oval funnel locking-apparatus