Functional morphology and morphological variability of the operculum of Rapana venosa (Gastropoda, Muricidae)

Abstract

The gastropod Rapana venosa has spread from the Western Pacific to the Black Sea, Mediterranean Sea and coastal regions on both sides of the Atlantic Ocean, largely due to its ecological and morphological plasticity. Numerous works have been devoted to the study of the variability of the Rapa-whelk shell.The functional morphology and morphological variability of the R. venosa operculum have been insufficiently studied, the description of this exosomatic organ is given only schematically. Based on the analysis of a sample of 190 R. venosa specimens collected in two regions of the Black Sea, detailed description given and trends in the morphological variability of the operculum are shown depending on the age and size of the specimens. The characteristics that determine the normal and aberrant development of the operculum were evaluated. It was shown at the first time that R. venosa has regenerative capabilities up to the restoration of lost operculum and morphogenetic adaptive potential. A manifestation of this potential is the formation of a hypertrophied large operculum, the shape of which is not characteristic of any other Muricidae species and gastropod in general. The abnormal size and shape of the operculum is likely a defensive response to pressure from predators, especially crabs. The previously unknown ability to regenerate the operculum broadens the understanding of the physiological capabilities of the Rapa-whelk. The phenomenon of operculum formation with a unique shape among gastropods is another manifestation of morphological plasticity, which made R. venosa one of the most successful invasive species in the recent marine environment.

Keywords: variability, operculum, morphology, regeneration, Rapana venosa