Fig 1.
Geographical position of the sample sites in the New Caledonia and Vanuatu regions.
(A) Sampling sites (New Caledonia and Vanuatu) of the Nautilus specimens east of Australia. (B) Sampling site of Nautilus macromphalus specimens near New Caledonia marked with a cross. (C) Sampling site of Nautilus pompilius near Vanuatu marked with a cross.
Fig 2.
Shell fragments of the Nautilus pompilius specimen from Vanuatu (AMNH 310431) and the three Nautilus macromphalus specimens from New Caledonia.
(A) N. pompilius. (A3-A4) Exemplary fragments of the shell. (A5) Dentritic structures on the shell surface produced by boring ‘naked’ foraminiferans (producing morphotype 3). (B) Specimen AMNH 93431, N. macromphalus. (C) Specimen AMNH 93432, N. macromphalus. (D) Specimen AMNH 93433, N. macromphalus. Scale bar for the shells is 1 cm unless indicated otherwise.
Table 1.
Sample specifications of the four studied Nautilus specimens.
Fig 3.
Attachment scars on the shells of Nautilus macromphalus from New Caledonia.
(A) Cluster of Rosalina bradyi attached to the shell of specimen AMNH 93433. (B) Attachment scar of R. bradyi (Morphotype 1) (Rb) on the shell of specimen AMNH 93431; remains of the fringe of pseudopodia indicated with 'p'. (C) SEM image of R. bradyi (Rb) attached to the Nautilus shell and overgrown by the black layer (bl). (D) SEM image of epoxy resin casts showing an attachment scar (Morphotype 2) of a foraminifer specimen with affinity to Gypsina vesicularis; the center displays a spiral morphology that is surrounded by a circular depression (arrow) (specimen AMNH 93431).
Fig 4.
Ontogeny of Morphotype 3 in Nautilus macromphalus from New Caledonia as seen in SEM images of epoxy-resin casts.
(A) Initial boring. (B) An initial tunnel is bored into the substrate. (C) The termination of the stalk forms the first swelling (①). (D) The trace continues to extend into the substrate and begins to form incremental lateral swellings (①–③). (E) The number of increments arranged as a spiral increases (①–⑥). (F) Mature morphology with a spiral of numerous increments, a large chamber, and connections to the substrate via radiating rhizoidal galleries (arrows).
Fig 5.
Morphotype 3 in Nautilus macromphalus from New Caledonia as seen in SEM images of epoxy-resin casts.
(A) Cluster of traces in an epoxy-resin cast. (B) Photograph of shell surface, showing the entrance pit produced by the foraminifer. (C) Shell surface featuring the mature stage with large main chamber and pronounced rhizoids. (D) Broken shell allowing insight of the cavity produced by the 'naked' foraminifer with organic remains and two chambers (arrows).
Fig 6.
Morphotype 4 in Nautilus macromphalus from New Caledonia.
(A) SEM image of initial borings of the foraminifer in an epoxy-resin cast. (B) Mature morphology with numerous irregularly branching galleries forming a hemispherical plexus. (C) Close-up of galleries displaying their irregular surface texture. (D) SEM-photograph of shell surface illustrating the entrance of the foraminiferan trace.