Rapana venosa

Species of gastropod

Rapana venosa, common name the veined rapa whelk or Asian rapa whelk, is a species of large predatory sea snail, a marine gastropod mollusc or whelk, in the family Muricidae, the rock shells. This large sea snail has become an invasive species in many different localities around the world.

The shell of Rapana venosa is globose (rounded) and heavy, possessing a very short spire, a large body whorl, a strong columella and a deep umbilicus. The aperture is large and roughly ovate. Ornamentation is present externally as axial ribs, smooth spiral ribs ending in blunt knobs at both the shoulder and body whorl, and internally as small elongated teeth disposed along the outer lip margin. The external color varies from gray to reddish brown, with dark brown dashes on the spiral ribs. Some specimens may have distinctive black/dark blue vein like coloration patterns throughout the inner portions of the shell, usually originating from each individual tooth at the outer lip. A diagnostic feature for this species is the deep orange color found in the aperture and on the columella. The height of the shell can reach up to 180  mm (about 7 in). Rapa whelks were first found in the Black Sea in the 1940s. Within a decade this mollusk had spread along the Caucasian and Crimean coasts and moved into the Sea of Azov. From 1959 to 1972, its range extended into the northwest Black Sea, to the coastlines of Romania, Bulgaria and Turkey. These whelks have become established in the Adriatic and Aegean seas, and have also been found in the Tyrrhenian sea, on the Northern Atlantic coast of France, and the southeast coast of South America, in Uruguay and the Rio de La Plata estuary (including Samborombon Bay), and in Argentina. In the United States the first specimen discovered was in August 1998 by members of the Virginia Institute of Marine Science (VIMS) Trawl Survey Group in Hampton Roads, Virginia. The species is now widely distributed and established in Chesapeake Bay. one of two marine gastropods on the list.

Veined rapa whelks favor compact sandy bottoms, in which they can burrow almost completely. The native habitat of this species is a region of wide annual temperature ranges, comparable to other localities. Fleeing cold waters in the winter, this species may migrate to warmer, deeper waters, thereby evading cool surface waters. This fertile sea snail is extremely versatile, tolerating low salinities, water pollution and oxygen deficient waters. Shell drilling, however, is also not unknown in this species.

Rapana venosa is dioecious, which means each individual organism belonging to this species is distinctly male or female. after which it lays clusters of egg cases that resemble small mats of white to yellow shag carpet, The pelagic veliger larvae (a larval form common to various marine and fresh water gastropod and bivalve mollusks) then hatch, persisting in the water column for 14 to 80 days Imposex is characterized by the development of masculine sexual organs in female individuals as a consequence of exposure to organic tin compounds, such as tributyltin (TBT). Such compounds are biocide and antifouling agents, commonly mixed in paints to prevent marine encrustations on boats and ships. For this reason, it is not uncommon for high concentrations of such compounds to be present in the sea water near shipyards and docking areas, consequently exposing the nearby marine life to its possibly harmful effects. This unnatural development of male reproductive organs, however, has shown no negative effects on populations of this species, and no loss of reproductive capabilities of female R. venosa as a consequence of Imposex has been observed so far.