Diacavolinia vanutrechti Van der Spoel, Bleeker and Kobayasi, 1993 forma vanutrechti Van der Spoel, Bleeker and Kobayasi, 1993
This is a medium sized, uncoiled thecosomatous pteropod, 0.5 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 as the ventral and dorsal sides grow together. The lateral spines are small but pronounced usually hook-shaped. Shell sculpture consists of growth lines and faint transverse striation. The dorsal lip does not have a notch, a constriction, or an inner hump but a gutter is present. Micro-zooplankton and phytoplankton are its food and it is a mucus feeder. It lives in the Indian and W-Pacific Ocean at shallow depths (Diacavolinia v. vanutrechti 2).
The hyaline brown shell is slightly triangular. The dorsal lip usually does not have a notch in the slender rostrum; there is no constriction, a gutter is present. In a few specimens and in one paratype, a notch is found (Diacavolinia v. vanutrechti). The ventral lip is moderately sized and has a clear median depression. The lateral spines are strongly bent, the spines are hook-shaped; the gutter corners are small. The 14 thin ventral ribs are slightly comb-shaped. The lateral lines are convex and the flanks are well developed. The dorsal side is convex, with a weak central rib, latero-dorsal ribs and lock ribs. The lock area is small, showing a small main tubercle and link, the lunar and minor tubercle are of equal size. A second lock mechanism is present midway between the lateral spine and the normal lock area. The growth lines are typical. A hump is absent. The protoconch II area projects moderately. In the holotype the small caudal joint is 1.08 mm; the caudal fold, 1.00 mm long, is straight or even convex in some specimens and the left and right fold form an angle. There are no lip flaps; weak lip bellies and very small lip shoulders are present. The aperture is wide. In the holotype the lip angle is 150°, the lock angle is 76°, and the side angle is 73° (Diacavolinia v. vanutrechti 1). The holotype has a shell length of 4.36 mm, the width is 3.64 mm.
The shell length ranges from 4.88 to 3.76 mm and width from 3.64 to 2.40 mm.
A special description for this forma is not available, see Diacavolinia longirostris.
This species is a protandric hermaphrodite.
This species is phytophagous.
Diacavolinia vanutrechti forma vanutrechti is an Indo-West Pacific taxon found in the W-Pacific and N-Indian Oceans, see the Diacavolinia v. vanutrechti map.
Representatives of this taxon without a notch resemble Diacavolinia elegans, but the present species differs in having larger lip shoulder and a prominent second lock.
Diacavolinia vanutrechti forma vanutrechti Van der Spoel, Bleeker and Kobayasi, 1993; 135, fig. 7.
Holotype (ZMUC. gas 153) and 5 paratypes (ZMUC. gas 154) in ZMUC, 3 paratypes (ZMA. moll. 3.92.008) in ZMAN.
Type locality: 14°37'N 119°52'W, 0-100 m depth, CDAE. Stat. 3731 iv.
Etymology: The name is given in honour to our friend and colleague Dr. W. L. van Utrecht, who kindly assisted the first author during many expeditions and research projects.