Spirula spirula ( Linnaeus, 1758 )

Klug, Christian, Hoffmann, René, Tischlinger, Helmut, Fuchs, Dirk, Pohle, Alexander, Rowe, Alison, Rouget, Isabelle & Kruta, Isabelle, 2023, ‘ Arm brains’ (axial nerves) of Jurassic coleoids and the evolution of coleoid neuroanatomy, Swiss Journal of Palaeontology (22) 142 (1), pp. 1-22 : 7-9

Spirula spirula ( Linnaeus, 1758)

( Fig. 7 )

Description Te entire specimen is about 40 mm long. For CT-scanning, the extant specimen was stained with tungsten. Due to a subsequent staining with iodine, the specimen was unfortunately destroyed. Te complete arm crown was preserved and composed of eight arms and two tentacles. All of these appendages curved inwards. Te visible part of the arm crown is 6 mm long. It shows small biserial suckers that extend from the base to the middle section of the arms, before merging into a single row at the distal tips. Like the hooks in other species, the suckers decrease in diameter towards the arm tips but have their largest diameter at the first third of the arm. An orthoslice view cutting through the arm bases

( Fig. 7 ) shows the central axial nerve cords surrounded by the arms musculature or slightly moved inwards as darker spots of 0.19–0.27 mm diameter (arm diameter/nerve diameter = ratio). For a list of measurements, see Table 1. Te shell has a diameter of 14 mm and 26 chambers.

spirula

Figures

Fig. 7 Orthoslice made from a CT-data volume (left) and histological section (right) cutting through the arm bases and buccal mass of Spirula spirula (Linnaeus,1758). The arm bases encircle the buccal mass.Each arm has longitudinal muscle fibres surrounding an indistinctive grey mass. The darker spot in the central or subcentral position represents the axial nerves.The ratio between arm diameter and nerve diameter varies between 6:1 in dorsal arms and 4:1 in ventral arms