Themisto abyssorum

Themisto abyssorum, Boeck, 1970

Languages: English

Description

Diagnostic Description

The head is equal in length to the first two somites of the pereon. In antennae I the peduncle is three segmented and short; the flagellum in females is just barely longer than the head, narrowly conical, and not distinctly divided into segments; in sexually mature males the flagellum consists of 13-15 segments and extends to the end of the pereon. The mandibles have a narrow denticulate cutting edge and an accessory plate is present in the left mandible; the dentate process is strong and broad; the 2nd segment of the thin palp is approximately twice longer than the 1st and 1.5 times the 3rd segment. The outer lobe of maxillae I bears a row of setae in addition to two strong apical spines and the palp is broader than long. The outer lobe of maxillae II is narrow and apically armed with two spines; the much broader inner lobe bears only only apical spine. The outer lobes of the maxillipeds are narrow, sickle-shaped, and unarmed along the convex outer margin; the inner lobes form a plate with a straight or concave distal margin; the basal plate is unarmed. The 6th segment of pereopods I is shorter than the 5th and its posterior margin very finely denticulate with a few submarginal short setae; the claw bears a group of short setae in the proximal part of the inner margin. Pereopods II are somewhat longer than pereopods I; the 5th segment has a spoon-shaped process extending to 2/3 the length of the 6th segment and apically bearing a few long setae; the 6th segment has a finely denticulate posterior margin; the claw is straight and smooth. In pereopods III and IV the 4th segment is identical in structure and slightly broadens distally; it is 1/2-2/3 the length of the narrowly oval, almost linear 5th segment; the 6th segment of pereopods III is 1.2-1.5 times longer than the 5th but in pereopods IV almost equal to the 5th segment; the claws are long and smooth. Pereopods V-VII are similar in structure and almost equal in length; the 4th segment is approximately half the length of the linear 5th segment, which in turn is about 2/3 the length of the much thinner 6th segment; the claws are thin, almost straight and smooth, and 2/7-2/5 the length of the 6th segment. The anterior margin of the 5th and 6th segments of pereopods V is smooth while in pereopods VI and VII it is pubescent with short and tender setae. The basipodites of all the uropods are considerably longer than the rami; the outer margin of the rami is smooth and the inner margin finely denticulate. The oval-triangular telson has an acute apex, is 1/3 the length of the basipodite of uropods III, and slightly longer than its own width at the base. The life cycle covers two years; the crustacean dies after reproduction. The period of reproduction is protracted and probably stretches from February to August. [Boeck, 1870]
Author(s): Dunn , Adam
Rights holder(s): Dunn , Adam

Ecology and Distribution

Dispersal

It mainly lives in the upper 100 m layer. [Boeck, 1870]
Author(s): Dunn , Adam
Rights holder(s): Dunn , Adam

Distribution

Arctic Seas and Central Polar Basin. In the western part of the Atlantic Ocean it moves with cold waters south up to the Gulf of Maine, while in the eastern part individuals were found in the Bay of Biscay but only at a depth of a few hundred meters. It does not penetrate farther south than the Bering Strait and is not found in the Pacific Ocean. [Boeck, 1870]
Author(s): Dunn , Adam
Rights holder(s): Dunn , Adam