Abstract
Treatise Online no. 47: Part M, Chapter 18: Ammonites and Octopuses
Highlights
The unique shell of the female Argonauta, and its external resemblance to some ammonite shells, give rise to questions that have puzzled paleontologists and biologists from time to time, and that have not been satisfactorily resolved
Arms of pair I of the female are expanded into thin flaps of tissue that cover the shell (Fig. 1), which is secreted at the anterior margin by glands along the edge of the arm flap
Solution of the calcite in dilute HCl leaves behind the organic matter, having the form of the shell but no stiffness
Summary
The unique shell of the female Argonauta, and its external resemblance to some ammonite shells, give rise to questions that have puzzled paleontologists and biologists from time to time, and that have not been satisfactorily resolved. Arms of pair I (the dorsal pair) of the female are expanded into thin flaps of tissue that cover the shell (Fig. 1), which is secreted at the anterior margin by glands along the edge of the arm flap. The shell (Fig. 2–3) is made of calcite with a high proportion of organic matter. Solution of the calcite in dilute HCl leaves behind the organic matter, having the form of the shell but no stiffness. Argonauta is the only Recent genus placed in the family Argonautidae. The shell ornament of Argonautinae commonly consists of sinuous, bifurcating ribs on the side, ending in sharp, elongated tubercles flanking a smooth venter. A large number of specific names has been proposed for argonauts on the basis of different forms of the shell (Robson, 1932), the animal being unknown for most of these. A large number of specific names has been proposed for argonauts on the basis of different forms of the shell (Robson, 1932), the animal being unknown for most of these. Norman (2003, p. 190) stated that there are at least five species, of which three are well known
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