Reevaluation of coleoid cephalopod relationships based on modified arms inthe Jurassic coleoid Mastigophora

Mastigophora brevipinnis Owen, 1856, is a 'fossil teuthid' presently consid ered to be a member of the coleoid cephalopod Suborder Loligosepiina Jeletz ky, which in turn has been placed by various authors in or near the Vampyro morpha Grimpe. Recent morphological and biochemical analyses indicate that vampyromorphs are more closely related to the Octopoda than to the Decapodi formes. Fossils of Mastigophora from the Oxford Clay (Jurassic: Callovian) show soft-tissue preservation and evidence of arm crown specialization. Som e of these fossils have up to eight short, thick arms with circular sucker- like structures and filiform distal extensions, plus what appear to be the bases of two thinner ventrolateral arms. The latter lack proximal suckers : and curve medially to insert into the arm crown, similar to the tentacles that are the modified ventrolateral arms of living squids and cuttlefishes. This suggests that the thinner structures were decapod-like tentacles. If Mastigophora had tentacles homologous with those of modern decapods, then i t was a decapod, because this synapomorphy defines the Decapodiformes. This indication of decapod affinities for Mastigophora brings into question the relationships of the other 'fossil teuthids'. The inferred relationship of the Loligosepiina, including Mastigophora, with the Vampyromorpha, based l argely on similarities of gladius morphology with that of living Vampyroteu this, may reflect shared plesiomorphic characters.