Recognising variability in the shells of argonauts (Cephalopoda: Argonautidae): the key to resolving the taxonomy of the family

Julian K. Finn

Memoirs of Museum Victoria Vol 77 p. 63–104 (2018)

DOI
https://doi.org/10.24199/j.mmv.2018.77.05

Abstract

Argonauts (Cephalopoda: Argonautidae) are a family of pelagic octopuses that are most commonly recognised by the beautiful white shells of females (known as paper nautiluses), prized by beachcombers the world over. Taxonomic delineation of the group has historically relied exclusively on features of the shells of females and has resulted in more than 50 species names being coined worldwide. This approach has created considerable confusion in the taxonomy of the family because argonaut shells are not true molluscan shells and display considerable variation in form. This study closely examined a large number of argonaut shells from museum collections throughout the world. Two types of shell formation that had been previously attributed to separate argonaut species were recognised within individual shells. It is proposed here that the different shell forms reflect the effects of ecological or biological factors or events, often manifesting as dramatic changes in shell growth and shape within the development of an individual shell. The resulting combinations of shell formation types clearly explain both the extreme variation observed across large numbers of argonaut shells and the high number of nominal species names coined in the past. Researchers coining new fossil argonaut species based solely on shell characters are advised to proceed with caution. This study supports parallel morphological and molecular research recognising the existence of only four extant argonaut species worldwide: Argonauta argo, A. hians, A. nodosus and A. nouryi.

Citation

Finn, J.K. 2018. Recognising variability in the shells of argonauts (Cephalopoda: Argonautidae): the key to resolving the taxonomy of the family. Memoirs of Museum Victoria 77: 63–104.

Publication date: 22 November 2018

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