Diacavolinia strangulata (Deshayes, 1823)
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 well developed. Shell sculpture consists of faint growth lines and faint transverse striation. The dorsal lip has a notch, a gutter, a pronounced constriction and inner hump. Micro-zooplankton and phytoplankton are its food and it is a mucus feeder. It lives in the Atlantic and probably the Pacific Ocean at shallow depths(Diacavolinia strangulata).
The hyaline shell is triangular; it has a brown colour especially along the centre of the dorsal side. The dorsal lip has a small notch in the broad rostrum, a gutter and a strong constriction. Lateral spines as found in Diacavolinia longirostris. An abrupt lateral constriction in the rostrum gives rise to a tubercle distally, separated from the rest of the dorsal side. The ventral lip is of moderate size and shows a normal median depression. The lateral spines are only slightly bent, sharp and hooked; the gutter corners are small. The 18 ventral ribs are strong, line-shaped and composed of rows of tubercles. The lateral lines are nearly straight, the flanks are well pronounced. The dorsal side is slightly flattened, with well-developed central and weaker latero-dorsal ribs; the lock ribs are small. The lock area, main tubercle and link are well-developed. The lunar tubercle is relatively small and the minor tubercle is strongly reduced. There is an extremely small second lock mechanism is marked by a little curve in the lateral border of the dorsal side. The growth lines are typical and there are ribs on the dorsal side. A moderate hump is present without inner hump; the rostrum projects anteriorly. The protoconch II area does not project far it has a relatively broad caudal joint. In the holotype the caudal joint is 0.64 mm; the moon-shaped caudal fold is 0.72 mm long. There are no lip flaps; moderate lip bellies and well-developed lip shoulders are present. The aperture is rather narrow. In the holotype the lip angle is about 140°, the lock angle is 71°, and the side angle is 76°(Diacavolinia strangulata 2).
The shell length ranges from 4.64 to 3.36 mm and width from 4.16 to 2.76 mm.
A special description for this forma is not available, see Diacavolinia longirostris.
This species is a protandric hermaphrodite.
This species is phytophagous and epipelagic.
Diacavolinia strangulata was originally described from the W-Pacific Ocean; the records described in this paper are from the Atlantic Ocean and the species probably has a wider distribution, see the Diacavolinia strangulata map.
It was hard to select one of the forms in this genus as the "real" strangulata. The one with a clear constriction and a rostrum directed anteriorly was finally seen as agreeing most with the original description giving these as the most typical characters. Representatives of this species are very rare. The closest relatives of this species are Diacavolinia constricta and Diacavolinia ovalis both differ in the position of the lateral spines which are more bent dorsally.
Cavolinia longirostris var. strangulata Hedley, 1907: 285, 299, pl. 54, fig. 13.
Types could not be located.
Type locality: never indicated clearly but it should be the Indo-Pacific Ocean (cf Tesch, 1948). It is incorrect to restrict it to the locality of the present specimens: the Atlantic Ocean.