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(G.O. Sars, 1863)

Description
Generic features. General form slender and delicate. Eyes well developed, short, reniform and flattened dorso-ventrally, pigment brilliant red in living specimens. Antennal scale with outer margin entire or coarsely serrate, without setae, terminating in a strong spine beyond, no distal suture. Last four pairs of pleopods of the male well developed and biramous, first pair with endopod reduced to a single segment. Uropod, exopod and endopod undivided, setose alle round; no spines on outr margin of exopod; inner margin of endopod may be minutely serrated. Telson very short, entire, trapeziform, lateral margins naked; apex truncate, armed with 2 pairs of strong spines; no median plumose setae.
— Species. General form somewhat slender and delicate, cephalothorax wider than abdomen. On the mid-ventral surface of each thoracic segment there is in males and immature females a stalked, club-shaped process with a rounded head thickly set with short strong spines. These processes are smaller on the first and last somites.
Carapace very slightly produced between the eyes but not sufficiently to form a rostrum; posterior margin evenly arcuate leaving the last two thoracic somites exposed in dorsal view. Last abdominal somite not quite as long as the two preceding ones together.
Antennal scale longer than the antennular, and half as long again as its own peduncle; outer margin without and but with 8-10 strong serrations of which the most distal is longer than the apex of the scale, no distal suture.
Eyes large, pyriform in dorsal view; flattened dorso-ventrally so that in lateral view they appear to be of a long oval shape with the long sides parallel; cornea. much wider than stalk kidney-shaped in dorsal view; pigment brilliant red.
Thoracic limbs 3-8 with the endopods very long and fragile, becoming progressively longer posteriorly, the eighth extending, when stretched backwards, to the posterior margin of the last abdominal somite; carpus nearly twice as long as the propodus from which it is divided by an oblique suture; propodus divided into two subsegments of which the proximal is the shorter; nail long and very delicate. Pleopods of the male well developed, biramous, natatory appendages except for the first pair in which the endopod is reduced to a single segment bearing the usual setiferous basal expansion. Pleopods of the female reduced to simple linear unsegmented plates, which are progressively longer posteriorly.
Telson short, about half as long as the last abdominal somite, trapeziform, tapering distally, width at base equal to length, lateral margins naked and slightly concave; posterior margin straight, armed with two pairs of strong spines and two median plumose setae. In the female the four spines are almost equal in length but in the male the outer pair are shorter than the inner.
Uropods with exopod long and narrow. margins subparallel, setose all round, apex obliquely truncate, endopod shorter than exopod, tapering distally, outer margin setose with a few delicate plumose submarginal setae in addition to the usual marginal ones; inner margin finely serrulated throughout in females and immature males. Holt and Beaumont (1900, p. 231) pointed out that this serrulation disappears in males as they become mature but in females it persists throughout life. This observation has been confirmed by later workers in E. serrata and noted in E. abyssorum also.

Colour
Clear and transparent with a reddish orange pigment spot on either side of each abdominal somite, a band of orange running across the fourth somite and a delicate longitudinal band of pale yellow running along each side of the cephalothorax; eyes very bright red.

Size
Adult up to 11 mm long.

Depth range
Hyperbenthic, 130-570 m.

Remarks
This species may easily be recognised by the following characters: distal serration on outer margin of antennal scale longer than the apex of scale; endopod of eighth thoracic limb reaching the distal end of the last abdominal somite; posterior margin of telson straight; inner margin of endopod of uropod finely serrulated throughout its whole length in females and immature males; a spined club shaped process present on the ventral surface of each thoracic somite in males and immature females. At one time the serrulations on the outer margin of the antennal scale were regarded as the most useful specific character, but E. abyssorum also shows the same peculiarity. The differences between these two species will be discussed later.

Distribution in the North Sea
Northern and eastern North Sea

World distribution
E North Atlantic: 50-71°N; shelf to upper slope.

[After Tattersall and Tattersall, 1951]

Erythrops serrata