The Elegant Lavender Interior of the Gastropod Drupa forum

The gastropod Drupa Röding, 1798 is a Pleistocene to Recent genus, with about eight species and several possible subspecies. The type species [the original species used to define this genus] is Drupa morum Röding, 1798, commonly known as the “Purple Drupa, the Purple Pacific Drupa, or the Mulberry drupe snail.” The word “drupa” is Latin for ripen, in the sense of ripening of fruit. The Drupa shell does resemble a small berry (e.g., Mulberry).

 

Drupa morum Röding, 1798 from the Indo-Pacific area. The first image above is of the dorsal (back) side of the shell. The second image is of the ventral (front) side of the shell. The characteristic lavender color of this species is on present on one side of the aperture. The number "2" at the top refers to a later slide, which shows this same specimen in a series of other specimens.

Genus Drupa belongs to family Muricidae, and some specialists place the genus in the subfamily Thaidinae. Drupa is a predatory gastropod that prefers to eat worms, as well as some gastropods. The modern-day geographic distribution of Drupa is essentially restricted to between 35°N and 35°S (the area in "red," shown in the map below), in the Indo-Pacific (tropical) shallow-marine waters among coral reefs or rocky areas. Many of the species of Drupa are widespread within this region.

The species of Drupa are determined by several main morphologic features: the number of spiral rows of knobs on the last whorl (largest whorl), the shape of the knobs, the number and position of the labral teeth on the outer lip, the number and position of the columellar teeth along one side of the aperture (the main opening of the shell), and the color of the aperture. The labral teeth and the columellar teeth (both the oblique and straight ones) are labelled on the immediately following image.

The next two "strip images" show a growth series of six specimens of D. morum. The first one shows the dorsal side of each shell (numbered in increasing size), and the following strip shows the corresponding ventral side of each shell.

 Height range is 27.3 to 35 mm.

If you look carefully, you will see that the number of labral teeth and the number of columellar teeth, as well as their spacing, are not all the same on every specimen, even though the sizes of the specimens are similar. Nevertheless, all six specimens are Drupa morum. If the identification were based on only two specimens (numbers 1 and 6---see image below), however, it would seem that there are two species. That is why one needs to study as many specimens as possible. The outer lip of D. morum is especially prone to reabsorption of the calcium carbonate making up the shell, thus the details of the outer lip are not constant.

In the following image, specimen no.1 had reabsorbed some of the shell material making up its labral teeth along the outer lip of its shell. Specimen no. 6, which has all of its labral teeth, is shown for comparison.