“Pontocypria helenae new species (text-figs. 3 A-H, 4 A-G, 5 A-D, F, H, pl. I, pl. II figs. 1, 2, 4, 7-10)
Diagnosis – Carapace extremely large and conspicuously dimorphic, females being much larger than males; dorsal margin distinctly angulate with greatest height almost exactly at midlength; tiny normal pore canals abundant but not conspicuous, external setae almost entirely absent. Muscle-scar pattern with one or more scars usually subdivided. Ovaries extremely large, some females with nearly the entire vestibule filled with eggs (pl. II figs. 9, 10).
Exopodite of mandible large, seven rayed. Maxilla retaining segmentation of palp, first two podomeres each with one seta, distal podomere with two setae; masticatory process apparently with 3, 2, and 4 setae each, moderately long but of simple structure; anterodistal seta of third masticatory process thicker than others and more than twice as long. Distal hook of antenna with anterior barb very drastically reduced. Third thoracic leg with very finely pectinate apical seta, shorter bladed seta, others short and simple. Distal claw of furca slightly longer and thicker than proximal claw, both barbed and very finely pectinate. Copulatory organ of male with horizontal ventral margin, concave dorsal margin, swollen and obliquely truncated distally, with short curved hinged piece, other structures obscure.
Material – More than 100 specimens of both males and females, no juveniles, from starfish collected at “Eltanin” stations 410, 415, 439, 445, 469, 514, 534, 625, 695, 722, 997, 1082, 1084, at “East Wind” stations 66-027, 66-028, 66-036, 66-038, and at Antarctic localities USNM Acc. No. 226350. All specimens were living on the asteroids when collected, preserved in alcohol, but subsequently dried. No living or subfossil specimens have been found in the sediments from these and nearby Antarctic stations available in Smithsonian collections.
Holotype: adult male USNM 119792; collected at “East Wind” station 66-028, position 60°48’S 44°13.5’W, depth 105-103 fms, 11 February 1966 with 5-foot Blake Trawl; clinging to tube foot of the large specimen of Psilaster charcoti (Koehler) figured in pl. I. Length of right valve 1.27 mm, height 0.59 mm; length of left valve 1.19mm, height 0.63 mm.
Allotype: adult female USNM 119793, taken from same asteroid as the holotype. Length of right valve 1.43 mm, height 0.75 mm; length of left valve 1.42 mm, height 0.75 mm.
Paratypes: adult male USNM 119794 from “Eltanin” station 1082 on Bathybiaster loripes Sladen; adult female USNM 119806 from “Eltanin” station 410 on Psilaster charcoti (Koehler); adult female USNM 119807 from “East Wind: station 66-028 on Psilaster charcoti (Koehler); eight other dissected specimens USNM 119795 from “Eltanin” station 410 or East Wind 66-028.
Habitat – The new Antarctic species Pontocypria helenae is visibly a commensal on at least three species of the Asteropectinidae (Asteroidea). It has been found clinging to the tube feet, or more rarely to the membrane covering the ambulacral plates, of Psilaster charcoti (Koehler) and, less commonly, of Bathybiaster loripes Sladen and Lonchotaster (?) tartareus Sladen. Typically, an individual is clinging to the base of a tube foot by one antennal hook, this hook piercing a thin fold of host tissue (pl. II fig. 2). They may also occur along the side of the tube foot or on the membrane covering the ambulacral groove. None has been found on the dorsal surface of the starfish.
The ambulacral surfaces of the dry asteroids are presently quite clean with only small amounts of adhering sediment. However, the ostracodes might well withstand considerable washing by currents or after collection. The attachment by the hook is a strong one: specimens pulled off the starfish (in its present dried condition) are always found to be lacking the terminal podomeres of one antenna, still embedded in the starfish. In each of the specimens dissected, only one hook was so engaged, the other antenna retracted within the carapace.
Although these asteroids are known to be predatory, their stomach contents yielding mollusc shells and fragments of crustaceans, it is likely that they supplement their diet to some extent by microscopic food particles entrapped in ciliary mucous currents in the ambulacral area. The food habits of the Pontocyprididae are unknown, but the simple structure of the mandible and maxillae, which are especially weak in Pontocypria, seems to indicate that they are scavengers of soft detrius, for which these food-bearing currents of perhaps even the mucus itself would provide a ready-made solution.
The absence of juveniles of P. helenae in any of the populations and the normal (for Pontocypria) development of locomotive and feeding structure indicate that this is probably not the sole habit of the species. The only peculiarly adaptive feature of this species is the disappearance of the distal barb of the antennal hook, so that it is no longer bifid. There is no evidence that they are in any way damaging to the host asteroid.
Table I
Infestation frequencies for Antarctic asteroids
Ship
Station
Depth in meters
Number of specimens examined
Psilaster
Bathybiaster
Lonchotaster
Eltanin
410
220-420
5 of 11
2 of 3
Eltanin
415
406-465
1 of 1
Eltanin
439
128-165
1 of 1
Eltanin
445
3819-3876
4 of 4
Eltanin
469
3623-3271
1
Eltanin
514
3587-3668
1
Eltanin
534
2540-2580
1 of 1
Eltanin
625
2910-3038
1
Eltanin
695
3138-3144
1
Eltanin
722
3138-3239
1
Eltanin
997
769
1 of 2
Eltanin
1082
298-302
2 of 2
Eltanin
1084
298-403
2 of 2
East Wind 66-027
762-595
1 of 1
East Wind 66-028
188-192
1 of 1
East Wind 66-036
292-294
1 of 4
East Wind 66-038
174-192
5 of 6
USNM 226350, SI-1, 2
440
16 of 21
2 of 5
USNM 226350, TR-19
308
1 of 1
Total
37 of 52
9 of 14
5
Other stations of fig. 1
0 of 22
0 of 206
Data incomplete
Total
37 of 74
9 of 218
5
Distribution – The asteroids examined were all collected in Antarctic waters, mainly at stations of the U.S.N.S. “Eltanin” but also from other recent Antarctic expeditions. Figure 1 shows the locations of these stations. The depths at which Pontocypria helenae was found range from 128 to 3876 meters. The exceptionally large size of this ostracode is a typical feature of abyssal ostracodes generally. See table I for the depth and number of asteroids infested at each station.
Pontocypria helenae has been observed thus far on three Antarctic species of Astropectinidae: Psilaster charcoti (Koehler), Bathybiaster loripes Sladen, and Onchotaster (?) tartareus Sladen. It is absent from Leptychaster flexuosus (Koehler) (five specimens examined) and L. accrescens (Koehler) (nine specimens examined) and has not been observed on representatives of other families.
The infestation frequency is highest for Psilaster, with 37 out of 74 specimens examined yielding at least one ostracode. Many specimens carry 2 to 10 ostracodes; one specimen of Psilaster (pl. I) is inhabited by nearly 100 of these “free-loaders”. They may be found on both juvenile and adult asteroids, ranging from 3 to 10 inches in diameter.
The living and subfossil ostracode assemblages of sediments from about 36 Antarctic localities, including many “Eltanin” station of text-fig. 1, do not include P. helenae or any other species of Ponotcypria.” (Maddocks 1968, p.128-132)
