Boreonymphon abyssorum (Norman, 1873),

Phylum:Arthropoda Siebold, 1848
Class:Pycnogonida Latreille, 1810
Order:Pantopoda Gerstaecker, 1863
Family:Nymphonidae Wilson, 1878
Genus:Boreonymphon Sars, 1888
Synonyms:Boreonymphon robustum sensu Hansen, 1887, Sars, 1891, Schimkewitsch, 1930 & Appellof, 1912

Hltpe: male with eggs. Porcupine St. 56, 1869, 60°02'N, 6°04'W, 480 fm. (878 m), — 0.7°C. British Museum (Nat. Hist.), London.

Present description and drawings based on a male of 9 mm with young of 1.5 to 3 mm. Michael Sars, 26 June 1902, 62°52'N, 4°14'E, 880 m, Ad. S. Jensen leg. Zoological Museum, University of Copenhagen.

Body: slender, width of body equalling length of first two body segments together; lateral processes not touching each other. Ocular segment as long as three last segments together. Bristles present dorsally on front and hind edges of ocular segment, and on hind edge of segments 2 and 3. Segment 4 without node or conspicuous bristles in front of the abdomen. Lateral processes with one row of bristles on dorsal surface. The entire animal is covered very sparsely with tiny hairs.

Abdomen : straight, narrowly ovoid, maximum breadth in the middle. Sparsely but evenly covered with small bristles.

Eye tubercle: prominent; narrowly pointed in lateral view.
Proboscis : slightly tapering distally. As long as ocular segment. Sparsely covered with minute hairs. Width at base about twice that of scapus base.

Chelifores: scapi diverging, slender, as long as ocular segment, with scattered and rather coarse bristles. Base and apex of equal width but scapi narrowing somewhat in proximal third, especially in dorsal view.

Chelae slender. Movable finger evenly curved, almost twice as long as palm. Fixed finger of same strength and curvature as movable, and longer than palm. Movable finger bears a few bristles ventrally in proximal third. Palm not much inflated, with scattered coarse bristles, which are especially long at the base of the fixed finger.

Palps: when stretched out the third joint of the palp reaches well beyond the tip of the proboscis. Ratio between joints 2 and 3 is 4:3. Joint 4 two thirds the length of 5, and together they are slightly longer than joint 3. Joints 2 and 3
bear scattered bristles of varying length, the bristles being longer and more numerous in distal half of the joints. Joints 4 and 5 more evenly covered with bristles.

vigers: joints 4 and 5 very nearly of equal length, both beset with a mixture of backward curving bristles and more or less straight ones pointing in various directions. Joint 4 with parallel sides, 5 somewhat widening distally. Joint 6 half as long as 5, with straight bristles, especially ventro-distally.

Legs: first leg has femur and both tibiae of equal length. Last three legs have 2nd tibia distinctly longer than the two preceding joints, which are of equal length. Ratio between femur and the three coxae together is 3:2. Femur strongly widening distally. Second tibia 2 2/3 the length of tarsus and propodus together. Ratio between tarsus and propodus is 3:5 (Fig. 2). Claws slender, about half as long as propodus. Auxiliary claws present in pairs but minute. Legs (except tarsus and propodus) with scattered, distally pointing bristles of varying length, increasing in number from coxae to 2nd tibia. Tarsus and propodus have naked sides. Tarsus has an even cover of bristles on dorsal and ventral surfaces, while on propodus the dorsal bristles run in two parallel rows.

Variations

 Hairs and bristles: bristles on dorsal surface of lateral processes may be scattered rather than in one row. The parallel rows of bristles on the dorsal surface of propodus may be confluent in the first pair of legs.

Shape: a few specimens have the proboscis subcylindrical or slightly bulging in the middle.

Proportions: scapi normally equalling the length of the ocular segment, but small variations in both directions can be found.

Others: the scapi normally are strongly diverging, but specimens with almost parallel scapi (fixation artefact?) are present in the material. In a few specimens the auxiliary claws are absent in one or more legs.

Females: generally as males, but joints 4 and 5 of oviger somewhat shorter and less densely covered with bristles.

Literature

  • Just J. (1972). Revision of the genus Boreonymphon G.O. Sars (Pycnogonida) with a description of two new species, B. Ossiansarsi Knaben and B. compactum Just. Sarsia, 49, 1-28.

Author: Zakharov Denis V. / 22.02.2017
Last edit: Zakharov Denis V. / 14.03.2017

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