Themisto abyssorum

(Boeck, 1871)

Description
— Generic. Body laterally compressed. Female with antennule (a1) as long as, or shorter than antenna (a2). Mandible with large molar process, mandibular palp with elongated second segment. Maxillar palp leaf-like and broad. Maxilliped with sharp outer plate. Gnathopods unequal in shape. First gnathopod simple, with broad carpus, but without a process (and not forming a chela together with propodus). Carpus of second gnathopod elongated, together with propodus forming a chela. Pereiopods 3-4 with broad carpus. Pereiopods 5-7 longer than pereiopods 3-4 and with elongated propodus. Uropods relatively slender. Telson small.
— Specific. Head shorter than high. Female antennula (a1) slightly curved and as long as antenna (a2). Antennular flagellum (a1) about three times longer than the peduncle, its distal half as thick as the antennal flagellum (a2).
Carpus and propodus of both gnathopods about equal in length and strongly setose. Carpus of second gnathopod elongated to half the length of the propodus. Dactylus as long as propodus.
Pereiopods 3-4 with carpus hardly enlarged, with almost parallel margins; hind margin with few thin setae.
Pereiopod 5-7 of aequal length in bot sexes, with very slender propodus, about as long as segments 3-5. Frontal margin of propodus of pereiopod 5 beset with a row of fine spines.

Size
Length 17-21 mm in Arctic region, 9 mm near the southern limit of distribution.

Depth range
Surface to deep water.

Possible hosts in the North Sea
Aurelia (Phylum Cnidaria). See for references Harbison et al., 1977.

Distribution in the North Sea
All (?) North Sea.

World distribution

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