Marine Species Identification Portal : Thysanoessa vicina

Thysanoessa vicina Hansen, 1911

Etymology: Thysanoessa - small tassel; vicina - neighboring

Eye: The eye is bilobed with a transverse constriction. The width of the upper lobe is shorter and somewhat narrower than the width of the lower lobe (T. vicina eye & rostrum).

Peduncle of 1st Antenna: There is no elevated lappet on the 1st segment, but the 1st segment ends dorsally at an acute angle (T. vicina lappet lacking). In the females the 2nd and 3rd segments are slender, the 3rd segment is longer and more slender than the second. In the males the 2nd and 3rd segments are shorter and thicker than in the female (T. vicina,). The upper flagellum is somewhat or considerably longer than the sum of 2nd and 3rd segments.

Rostrum: It is sometimes short, but usually long, reaching to almost the front of the eye, and is an acute triangle (T. vicina eye & rostrum) (T. vicina vs. T.macrura rostrum).

Carapace: There is a well-developed, lateral denticle on the margin. At its post-ocular edges, the frontal plate bends slightly upward and outward as a narrow flange, appearing to shield slightly the upper part of the eye (T. vicina carapace).

Thoracic legs: The 2nd pair of legs is elongate (T. vicina thoracic legs).

Abdomen: There are no keels or spines. The 6th segment is less than or equal to the length of the sum of 4th and 5th segments (T. vicina).

Length: Adults are up to 16 mm.

Petasma: The spine-shaped process is thin and curved. The terminal process is a little expanded on the inner side towards the terminal margin which is convex with fine saw-teeth along the front side. The proximal process has the end somewhat expanded and curved backwards, and the terminal margin is transverse and serrated (T. vicina petasma).

Thelycum: Described by Costanzo and Guglielmo, 1977.

Comments: T. vicina andT. macrura are closely related and difficult to distinguish. T. vicina is the smaller species. The flagella of the 1st antenna and the terminal process of the male petasma are characters used to separate them.

ECOLOGY
T. vicina is a food source for whales.

HORIZONTAL DISTRIBUTION
T. vicina is circumpolar in the Antarctic, south of 50°S or 55°S, but not extending near to the Antarctic continent. Thus, its habitat is generally north of that of T. macrura, but the two species overlap near 60°S, but this region of overlap is poorly known owing to the similarity of the two species (T. vicina distribution). Overlap of the two species is not indicated on the map of their distribution, particularly the immatures.

VERTICAL DISTRIBUTION
T. vicina lives above about 350 m.

LARVAE
Undescribed.

The larvae may be similar to T. macrura but smaller.

Thysanoessa vicina