Note on Caledoniella montrouzieri Souverbie, a Gastropod Mollusc living commensally on Stomatopod Crustacea

When studying the collections of indo-westpacific Stomatopod Crustacea of the Rijksmuseum van Natuurlijke Historie at Leiden and the Zoological Museum at Amsterdam, I found three specimens of Gonodactylus chiragra (Fabr.) that on the ventral surface of the body were provided with commensal Gastropods. These Gastropods were kindly identified for me by Dr. C. G. F. H. BAYER, curator of Molluscs of the Rijksmuseum van Natuurlijke Historie. In a report on the Stomatopoda collected by the Snellius Expedition (HOLTHUIS, 1941, p. 280) I made already mention of the presence of this Gastropod Mollusc on two of the examined Stomatopod specimens. A female of Gonodactylus chiragra (Fabr.) collected by the Snellius Expedition at Amboina, Moluccas (September 11-17, 1930) had a specimen of Caledoniella montrouzieri Souv. placed on the ventral surface of the eighth thoracic segment between the bases of the third pereiopods, while a second specimen of this Gastropod species was attached to the ventral surface of the last abdominal segment of the Stomatopod. A female of Gonodactylus chiragra (Fabr.) belonging to the collection of the Amsterdam Museum and collected at Amboina (1913, leg. M.M. WILLEMSZ GEEROOMS) had a juvenile Gastropod attached to the ventral surface of the eighth thoracic segment between the bases of the pereiopods. This mollusc also belongs in the genus Caledoniella and probably is C. montrouzieri Souv., but because it is not yet adult, its identity could not be made out with certainty. The specimen of Gonodactylus chiragra collected by the Snellius Expedition showed between the pleopods egg masses of a Gastropod Mollusc species (see HOLTHUIS 1941, fig. 7a). It seems highly probable that these egg masses are those of Caledoniella montrouzieri Souv. The eggs in these masses were in different stages of development, in some of them the young larvae were already visible.