(Forskål, 1775)
Description
— Aggregate form with very thin and flabby, fusiform test. Body oval to cylindrical. Typical aggregate form with two rows of pigment spots at each side from the endostyle over almost the entire ventral surface of the body. Six muscle bands that are continuous dorsally but interrupted ventrally. M1-M2 unite mid-dorsally, this muscle pair is very closely joined by M3 and M4, making a group of four muscle bands. M5 and M6 are also united mid-dorsally. The muscle bands display asymmetry at the ventral side of the animal. There are distinct dextral and sinistral individuals which are mirror images. The intestine is coiled into a nucleus. The ovary and embryo are situated metween M5 and M6 at the right side.
— Solitary form with very thin and flabby test (closely adhering but loosely attached to the body wall, as it is often lost in preserved specimens). Nine very wide body muscles that cover almost the whole body. A variable number of body muscles touch or fuse in the mid-dorsal region. All muscles except M8 are completely continuous around the body. The intestine is coiled into a nucleus. The dorsal tubercle is a short straight stick. The stolon is tightly coiled underneath the nucleus.
Size
Length of aggregate form: up to 23 mm; length of solitary form: up to 71 mm.
Depth range
Epipelagic, living between the surface and ca. 150 m. Does not migrate vertically.
Distribution in the North Sea
Possible occurrence in the northern North Sea; intruding from the Northeast Atlantic, where it frequently has been found up to 70°N.
World distribution
Cosmopolitan, eurythermic species in temperate and tropical waters, absent from the Red Sea and the subtropical South Pacific Ocean. Although I. punctata has a wide distribution, it is one of the less common salpids.
Remark
The number of muscle fibres in the solitary forms is subject to distinct clinal variation, increasing from lower to higher latitudes, i.e. from warmer to colder waters (see Van Soest, 1975a).