Diacavolinia elegans Van der Spoel, Bleeker and Kobayasi, 1993
Overview
This is a medium sized, uncoiled thecosomatous pteropod, 0.6 cm long. It has a flat dorsal side with moderately developed ribs. The ventral side is vaulted. The caudal spine is absent and a caudal spine mark is not left when the ventral and dorsal sides grow together. The lateral spines are well developed. Shell sculpture consists of faint growth lines and a very faint transverse striation. The small dorsal lip has no notch and no constriction. Micro-zooplankton and phytoplankton are its food, it is a mucus feeder. It lives in warm waters of all oceans at shallow depth (Diacavolinia elegans).
Taxonomic Description
The colourless, hyaline shell is light violet and slightly triangular. The dorsal lip has no notch in its rostrum but no constriction; the rostrum is short not broad, it is hollow though a well separated gutter is not developed. The ventral lip is medium sized and shows a moderate median depression. The hooked lateral spines bend, only slightly dorsally and project laterally. The dorsal side is slightly convex, the central dorsal rib is well developed, the latero-dorsal ribs are moderately developed and the lock ribs are small. The ventral ribs, in the type material, are weakly developed, 18 in number and line-shaped; in some non-type specimens from the Banda Sea, these ribs are stronger developed, up to 24 in number. The flanks are not pronounced; the lateral lines are slightly convex. The lock area is visible and the lock mechanism is medium sized. The main tubercle is hooked, the lunar tubercle is small and the minor tubercle is absent. The secondlock system is, though rudimentary, still present. The growth lines are typical. There is no hump. The protoconch II area projects moderately. In the holotype the caudal joint, 1.16 mm long, is clearly visible; the caudal fold, 0.84 mm long, is moon-shaped, the left and right fold form a small angle in ventral view. There are no lip flaps; the lip bellies are weak; the lip shoulders are small. The aperture is wide. In the holotype the lip angle is 161°, the side angle is 74°, and the lock angle is 73°. The dorsal aperture rim is sharp, the ventral rim is thickened slightly.
The shell length ranges form 6.16 to 3.36 mm and width from 5.44 to 2.80Êmm.
Juveniles
A special description for this form is not available, see Diacavolinia longirostris.
Reproduction
This species is a protandric hermaphrodite.
Ecology
This species is phytophagous.
Distribution
Diacavolinia elegans is a wide spread species being recorded from the Indo-Malayan and Banda Sea and the adjacent west and central Pacific Ocean and N-Atlantic Ocean, see the Diacavolinia elegans map.
Others
Diacavolinia elegans resembles Diacavolinia ovalis and Diacavolinia deblainvillei in general shape. The latter species differ, however, in having a notch or a constriction. The present species may be easily confused with juveniles of other species. Presence of a fully developed lock mechanism and thickening of the ventral lip rim should be noted to determine the adult stage of the shell before identification as Diacavolinia elegans.
Types
Diacavolinia elegans Van der Spoel, Bleeker and Kobayasi, 1993: 136, fig. 9.
Holotype (ZMUC. gas.156) in ZMUC and four adult and one juvenile paratypes (ZMA. moll. 3.92.009) in ZMAN.
Type locality: 3°40.5'N 137°53'E, 0-100 m depth, CDAE Stat. 3751iv, 12 July 1929.
Etymology: The elegant shape of the dorsal lip lacking notches and constrictions, was the reason for the species name elegans.