Veined rapa whelks: Introduction to the veined rapa whelk
Molluscan Ecology Program
 

Introduction to the veined rapa whelk (continued):

shell markings. The scientific name for this species is Rapana venosa, with the first description being given by Valenciennes in 1846. The species was also described by Crosse in 1861 as Rapana thomasiana with the common name Thomas's rapa whelk being applied. It is now generally agreed that these are the same species and that Rapana venosa, being the earlier description, has precedent. Within the scientific classification it is considered to be a member of the family Muricidae, a family of predatory marine snails.

How large might rapa whelks grow?

Rapa whelks may grow to be quite large. The largest record in the literature for the native range is 18.3 cm shell length from Taiwan. A length of 12.1 cm has been published from the Black Sea. Several specimens in excess of 15 cm shell length have been collected from Hampton Roads, Virginia.

 

 

 

What does a rapa whelk look like?

The Veined rapa whelk (Figure 1 to the right) has a heavy short spired shell with a large inflated body whorl and a deep umbilicus. The color is variable from gray to red brown, with dark brown dashes on the spiral ribs, although older specimens can be quite eroded on the outside. Most specimens have distinctive black veins throughout the shell (see #1 in Figure 1 to the right); some animals have black veins on the opercular lip as well. The columella is broad and smooth (#2) and the siphonal canal is short (#3). The edge of the outer opercular lip has small, elongate teeth (#4). Older examples may have some flare to the outer lip. A very characteristic feature of the species is the deep orange color found on the opercular aperture and columella (also #4).

Figure 1: An adult veined rapa whelk

Figure 2: Home range of the rapa whelk.

 

Where do rapa whelks occur naturally?

Rapa whelks are native to the Sea of Japan. In Chinese waters they occur with two other closely related species, Rapana bezoar and Rapana rapiformis. Rapana venosa is restricted to the Yellow Sea, the East China Sea and the Bohai Sea (Figure 2). Rapana bezoar occurs off the southern provinces bordering the South China Sea and is more widely distributed in the Western Pacific, and the Indian Ocean. Rapana rapiformis occurs in the East and South China Seas. This is a region of wide annual temperature ranges, comparable to that of the Chesapeake Bay. In winter populations may migrate from estuarine waters into deeper water (possibly to avoid freezing water surface water).

What does it eat and how?

Rapa whelks are predatory snails that eat a variety of molluscs. They often attack bivalves (oysters, clams, mussels) around the region where the two valves meet, rather than boring a distinct hole (Figure 3). The related species Rapana bezoar, is also a generalist predator on molluscs, attacks other shallow burrowing molluscs. This is a characteristic that has been noted in collections of clam shells from Hampton Roads.

Figure 3: A rapa whelk eating a hard clam.

A short history of events since the discovery of rapa whelks in Chesapeake Bay

Since the initial report of rapa whelks in Hampton Roads following collection of a specimen by members of the VIMS Trawl Survey Group information has been distributed through the news media and by personal communication with a number of people in the fishing industry and academia. These activities have resulted in a number of calls to VIMS to report records of observation or collection and thereby increased our knowledge of the distribution of Rapana venosa in the lower Chesapeake Bay. Adult specimens as well as egg cases continue to be reported from locations in the lower Chesapeake Bay. Rapa whelk egg masses (Figure 4) or groups of egg cases resemble small mats of yellow shag carpet and are quiet distinctive and noticeably different from the egg cases of native snails.

Figure 4: Rapa whelk egg cases.

 
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Document last modified 09.17.2009
© Molluscan Ecology Program. Virginia Institute of Marine Science.
All rights reserved. All images © Juliana M. Harding.