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.
Shell description
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).
Distribution
This species is native to the marine and estuarine waters of the western Pacific, from the Sea of Japan, Yellow Sea, East China Sea and the Bohai Sea.
Rapana venosa is included in Russia's Red Book as threatened with extinction. The original known habitat for this species was the Far East, but since 1947 it has been found in the Black Sea, and its shell became a popular souvenir in Crimea. Recently this species has been found as an exotic in the Chesapeake Bay, on the eastern coast of the United States.
Nonindigenous distribution
According to some authors, it appears to be the case that the spreading of this species outside its natural range has been made possible by the planktonic larval stage being transported along with ballast water in the hulls of ships, or that egg masses may have been transported with products of marine farming.
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.
Rapana venosa is considered among the 100 worst alien species in Europe in the DAISIE European Invasive Alien Species Gateway, one of two marine gastropods on the list. It is considered as about the 52nd the worst alien species in Europe.
Ecology
Habitat
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.
Feeding habits
Veined rapa whelks are carnivorous selective predatory gastropods whose main diet consists of a variety of other mollusk species, mainly epifaunal bivalves such as oysters (Crassostrea virginica) and mussels (Mytilus galloprovincialis, Modiolus and Geukensia), but also clams (Anadara inaequivalvis, Chamelea gallina, Tapes philippinarum, Venus verrucosa, and the northern quahog Mercenaria mercenaria). Prey are chosen by the whelk according to their species and size. Most snails feed by drilling a hole into their bivalve prey, but rapa whelks usually smother their prey by wrapping around the hinged region of the shell and feed by introducing their proboscis between the opened valves. The whelk can also secrete a thick mucus that may or may not contain biotoxins to weaken the prey. Shell drilling, however, is also not unknown in this species.