Boreonymphon compactum Just, 1972,

Phylum:Arthropoda Siebold, 1848
Class:Pycnogonida Latreille, 1810
Order:Pantopoda Gerstaecker, 1863
Family:Nymphonidae Wilson, 1878
Genus:Boreonymphon Sars, 1888

Holotype: male of 15 mm with eggs. Bylot Sund, 76°26.8'N, 69°42.3'W, 15 August 1968, 260 m, clay and large stones. Thule Exped. 1968, Just et Vibe St. 35. Zoological Museum, University of Copenhagen.

Body: short and broad; width of body equalling length of first three body segments together. Lateral processes in contact with each other. Ocular segment hardly as long as the two following segments together. Entire body covered dorProboscis : slightly bulging in the middle and gently tapering towards base and apex. Distinctly longer than ocular segment. Surface covered by tufts of tiny hairs about 50 microns long. Width at base equalling that of scapus base.

Chelifores: scapi parallel, almost completely cylindrical in dorsal view, as long as ocular and first half of 2nd segments together. Densely covered by small bristles.

Chelae strong. Movable finger as long as palm, forming an even curve. Fixed finger distinctly weaker than movable and far less curved. Movable finger bears a cluster of bristles ventrally in the middle of proximal half. Palm much inflated, densely covered with small bristles, and with a cluster of longer bristles at the dorsal root of the fixed finger.

Palps: when stretched out the third joint of the palp reaches to the tip of the proboscis. Ratio between joints 2 and 3 is 7:8. Joint 4 slightly longer than 5; joints 4 and 5 together as long as 3. Surface of the palp covered by clusters of tiny hairs; the four terminal joints with an even cover of rather long straight bristles.

vigers: joints 4 and 5 of equal length, both densely covered with a mixture of backward-bent and straight bristles, the bent ones being more numerous on joint 4. Ratio between joints 5 and 6 is 5:3. Joint 6 densely covered with straight bristles. Joints 4-6 all distally widening.

Legs: all legs have femur and both tibiae broad and of equal length. Femur cylindrical. Ratio between femur and the three coxae together is 1 (+) :1. Second tibia twice as long as tarsus and propodus together. Ratio between tarsus and propodus is 3:4 (Fig. 7B). Claws slender, about half as long as propodus. Auxiliary claws absent.

All joints of legs densely covered by small bristles.

Variations

The two adult specimens from Thule (one male and one female) do not show any variations, except that the ovigers of the female are weaker and less densely covered with bristles.

The single specimen (an egg-bearing male) from Tobin differs from the Thule specimens by having the body slightly longer in proportion to the width.sally by small bristles except in the middle of the ocular segment and at the base of the lateral processes. A sparse felt of tiny hairs is present. Segment 4 with a very conspicuous bristle-covered node in front of the abdomen.

Abdomen: long, cylindrical, and bent strongly downwards; barely extending beyond lateral processes of segment 4 in dorsal and lateral views. Bristle covering as on body.

Eye tubercle: low, apically rounded.
Proboscis : slightly bulging in the middle and gently tapering towards base and apex. Distinctly longer than ocular segment. Surface covered by tufts of tiny hairs about 50 microns long. Width at base equalling that of scapus base.

Chelifores : scapi parallel, almost completely cylindrical in dorsal view, as long as ocular and first half of 2nd segments together. Densely covered by small bristles.

Chelae strong. Movable finger as long as palm, forming an even curve. Fixed finger distinctly weaker than movable and far less curved. Movable finger bears a cluster of bristles ventrally in the middle of proximal half. Palm much inflated, densely covered with small bristles, and with a cluster of longer bristles at the dorsal root of the fixed finger.

Palps : when stretched out the third joint of the palp reaches to the tip of the proboscis. Ratio between joints 2 and 3 is 7:8. Joint 4 slightly longer than 5; joints 4 and 5 together as long as 3. Surface of the palp covered by clusters of tiny hairs; the four terminal joints with an even cover of rather long straight bristles.

vigers: joints 4 and 5 of equal length, both densely covered with a mixture of backward-bent and straight bristles, the bent ones being more numerous on joint 4. Ratio between joints 5 and 6 is 5:3. Joint 6 densely covered with straight bristles. Joints 4-6 all distally widening.

Legs: all legs have femur and both tibiae broad and of equal length. Femur cylindrical. Ratio between femur and the three coxae together is 1 (+) :1. Second tibia twice as long as tarsus and propodus together. Ratio between tarsus and propodus is 3:4 (Fig. 7B). Claws slender, about half as long as propodus. Auxiliary claws absent.

All joints of legs densely covered by small bristles.

Variations

The two adult specimens from Thule (one male and one female) do not show any variations, except that the ovigers of the female are weaker and less densely covered with bristles.

The single specimen (an egg-bearing male) from Tobin differs from the Thule specimens by having the body slightly longer in proportion to the width.

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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