Hygrosoma hoplacantha (Wyville Thomson, 1877)

Anderson, Owen F., 2016, A review of New Zealand and southeast Australian echinothurioids (Echinodermata: Echinothurioida) — excluding the subfamily Echinothuriinae — with a description of a new species of Tromikosoma, Zootaxa 4092 (4), pp. 451-488 : 472-474

Hygrosoma hoplacantha (Wyville Thomson, 1877)

( Figures 18–21 )

Material examined. 288 specimens from 108 records (NIWA, MV, Te Papa).

Lord Howe Rise: 2 specimens, 31° 45.7´S, 159° 20.9´E, 565–960 m, MV F167647; 3 specimens, 34° 59.3´S, 162° 11.2´E, 1573 m, NIWA45045. West Norfolk Ridge: 2 specimens, 32° 35.8´S, 167° 38.6´E, 325–497 m, MV F167633; 3 specimens, 35° 35.8´S, 169° 33.4´E, 1760–1789 m, MV [TAN0308/167]. Louisville Seamount Chain: 1 specimen, 40° 6´S, 165° 10´W, Te Papa EC9365. Northern North Island: 3 specimens, 34° 58.8´S, 169° 29.6´E, 1288–1294 m, MV F168944. Challenger Plateau: 1 specimen, 38° 34.9´S, 167° 8.9´E, 974– 974 m, NIWA33636; 1 specimen, 40° 50.1´S, 168° 14.8´E, 1009 m, NIWA45044; 2 specimens, 37° 30.5´S, 168° 36.4´E, 967 m, NIWA29507; 1 specimen, 37° 16.4´S, 169° 40´E, 1713–1773 m, NIWA33628. Bay of Plenty: 1 specimen, 37° 6.1´S, 176° 34.1´E, 970 m, NIWA29463; 1 specimen, 37° 19.4´S, 177° 7.3´E, 534– 424 m, NIWA6607; 1 specimen, 37° 14.2´S, 177° 16.6´E, 1126–1134 m, NIWA6605; 1 specimen, 36° 57.6´S, 177° 19.9´E, 1396–1462 m, NIWA6601; 2 specimens, 36° 57.6´S, 177° 19.9´E, 1396–1462 m, NIWA6602; 1 specimen, 36° 56.8´S, 177° 20.1´E, 1323–1346 m, NIWA6604; 1 specimen, 36° 47.7´S, 177° 25.5´E, 1530– 1515 m, NIWA58636. East coast North Island: 1 specimen, 41° 2.3´S, 176° 37.5´E, 940 m, NIWA29467; 1 specimen, 39° 50.3´S, 177° 51.8´E, 1264 m, NIWA76744; 2 specimens, 41° 23.6´S, 176° 21.7´E, Te Papa J 061384 (dry). Cook Strait: 12 specimen, 41° 54´S, 174° 56´E, 1323– 1153 m, NIWA64303; 16 specimens, 41° 41.5´S, 175° 38.1´E, 1324–1362 m, NIWA63054; 2 specimens, 41° 41.9´S, 175° 39´E, 1040–1080 m, NIWA63030; 4 specimens, 41° 43.3´S, 175° 39.8´E, 1486– 1473 m, NIWA63096; 1 specimen, 41° 38.2´S, 175° 52.3´E, 1580– 1580 m, NIWA63154; 3 specimens, 41° 38.2´S, 175° 52.3´E, 1580– 1580 m, NIWA63160; 4 specimens, 41° 38.2´S, 175° 52.3´E, 1580– 1580 m, NIWA63169; 1 specimen, 41° 21.8´S, 176° 12´E, 998– 987 m, NIWA63749. Chatham Rise: 1 specimen, 44° 15´S, 175° 26´E, 594 m, NIWA45123; 1 specimen, 42° 37.4´S, 175° 55.3´E, 1202–1215 m, NIWA33618; 1 specimen, 42° 37.4´S, 175° 55.7´E, 1183–1203 m, NIWA33614; 1 specimen, 44° 4.7´S, 178° 15.3´E, 935 m, NIWA29495; 2 specimens, 44° 13.8´S, 178° 26.4´E, 1090 m, NIWA29465; 1 specimen, 44° 16.5´S, 178° 31.6´E, 1148–1165 m, NIWA33544; 2 specimens, 44° 41.1´S, 179° 1.2´E, 1610–1688 m, NIWA45028; 4 specimens, 44° 12.4´S, 179° 3.6´E, 959 m, NIWA29497; 2 specimens, 42° 21.9´S, 179° 24.4´E, 1832–1835 m, NIWA76452; 1 specimen, 42° 42.6´S, 179° 59.8´E, 1265– 1236 m, NIWA45109; 5 specimens, 42° 44.6´S, 179° 50.5´W, 1098– 1099 m, NIWA58242; 2 specimens, 44° 31´S, 179° 31.5´W, 1130 m, NIWA29489; 2 specimens, 42° 42.7´S, 178° 59.8´W, 1022 m, NIWA45047; 12 specimens, 42° 37.1´S, 178° 20.4´W, 1193–1208 m, NIWA33596; 2 specimens, 42° 37.1´S, 178° 20.4´W, 1193–1208 m, NIWA33597; 2 specimens, 42° 39.3´S, 177° 12.8´W, 1377– 1402 m, NIWA33598; 1 specimen, 42° 47.2´S, 176° 43.3´W, 996–1009 m, NIWA33575; 2 specimens, 44° 42.7´S, 176° 33.2´W, 1016 m, NIWA29491; 1 specimen, 44° 42.7´S, 176° 33.2´W, 1016 m, NIWA29496; 1 specimen, 44° 40.1´S, 176° 4.6´W, 1003 m, NIWA29466; 2 specimens, 42° 45´S, 175° 4.5´W, 1482 m, NIWA45050; 2 specimens, 42° 59.7´S, 175° 0.6´W, 968 m, NIWA45046; 1 specimen, 42° 45.9´S, 179° 40.3´E, Te Papa EC9371. East coast South Island: 2 specimens, 44° 47´S, 172° 48´E, 1130 m, NIWA29431; 1 specimen, 45° 21.1´S, 173° 35.8´E, 1386 m, NIWA45036; 3 specimens, 45° 52.3´S, 174° 4.9´E, 1676 m, NIWA45082; 1 specimen, 44° 41´S, 174° 20.9´E, 859 m, NIWA29425; 2 specimens, 44° 41´S, 174° 20.9´E, 859 m, NIWA29441; 3 specimens, 45° 25´S, 174° 30´E, 1233 m, NIWA29459; 2 specimens, 45° 45.8´S, 174° 30.5´E, 1586 m, NIWA45080; 1 specimen, 42° 7.3´S, 174° 34.5´E, 1499– 1452 m, NIWA63768; 20 specimens, 42° 7.3´S, 174° 34.5´E, 1499– 1452 m, NIWA63792; 5 specimens, 42° 6.3´S, 174° 34.6´E, 1058– 1006 m, NIWA63986; 13 specimens, 42° 7.5´S, 174° 34.7´E, 1280– 1246 m, NIWA63950; 3 specimens, 42° 7.5´S, 174° 34.7´E, 1280– 1246 m, NIWA63964; 1 specimen, 42° 2.8´S, 174° 41.8´E, 1391– 1327 m, NIWA64071; 1 specimen, 42° 2.6´S, 174° 42.3´E, 1310– 1250 m, NIWA64090; 1 specimen, 44° 37.1´S, 174° 52´E, 791 m, NIWA29499; 1 specimen, 45° 0.9´S, 174° 53.9´E, 1058–1114 m, NIWA58644; 1 specimen, 45° 45.3´S, 171° 22.4´E, Te Papa EC9364; 3 specimens, 44° 42´S, 173° 11´E, Te Papa EC3674 (dry). Southern South Island: 1 specimen, 47° 20´S, 169° 55´E, 1004 m, NIWA29462; 21 specimens, 47° 27.2´S, 169° 58.9´E, 941–951 m, NIWA61624; 1 specimen, 47° 27.2´S, 169° 58.9´E, 941–951 m, NIWA66713; 1 specimen, 46° 38.5´S, 170° 59´E, 1275 m, NIWA45119; 6 specimens, 46° 0´S, 171° 33´E, 1222 m, NIWA29427; 5 specimens, 45° 57.9´S, 171° 45.7´E, 1235–1268 m, NIWA45049 (1 dry); 3 specimens, 45° 57.9´S, 171° 45.7´E, 1235–1268 m, NIWA45113. West coast South Island: 1 specimen, 42° 41.1´S, 169° 31.2´E, 925 m, NIWA45034; 2 specimens, 42° 39.3´S, 170° 0.7´E, 420 m, NIWA29498. Bounty Plateau: 1 specimen, 49° 9´S, 177° 18´E, 978 m, NIWA29433; 1 specimen, 49° 42´S, 178° 56.1´E, 980 m, NIWA29461. Campbell Plateau: 4 specimen, 48° 19´S, 171° 59´E, 1108 m, NIWA29432; 1 specimen, 50° 24.4´S, 173° 44´E, 755 m, NIWA29439; 1 specimen, 48° 7´S, 174° 2´E, 1167 m, NIWA45110; 1 specimen, 50° 15.1´S, 174° 5.5´E, 772–776 m, NIWA66702; 3 specimens, 50° 29´S, 174° 10´E, 965 m, NIWA45075; 1 specimen, 50° 6.5´S, 174° 18.2´E, 765– 751 m, NIWA66709; 3 specimens, 50° 31´S, 174° 19´E, 1026 m, NIWA45105; 1 specimen, 48° 24.2´S, 174° 20.6´E, 872–920 m, NIWA45136; 2 specimens, 45° 23´S, 175° 29´E, 1277 m, NIWA29464; 1 specimen, 48° 31.1´S, 175° 29.2´E, 938– 896 m, NIWA66701; 1 specimen, 48° 8´S, 175° 56´E, 1427 m, NIWA45071; 4 specimens, 49° 48´S, 176° 1´E, 1256 m, NIWA29452; 4 specimens, 49° 48´S, 176° 1´E, 1256 m, NIWA45125; 1 specimen, 49° 19.6´S, 176°° 33.1´E, 1522–1552 m, NIWA58974; 1 specimen, 48° 15.5´S, 174° 59´E, Te Papa EC9370; 2 specimens, 48° 12´S, 174° 54´E, 1038– 1006 m, Te Papa EC9655; 5 specimens, 48° 18.1´S, 174° 56.5´E, 982–996 m, Te Papa EC9711. Southeast Australia: 2 specimen, 40 40.2´S, 145 15´E, 33 m, MV [80-Sa-1 stn115]; 2 specimens, 41° 13.1´S, 148° 49.1´E, 1330 m, MV [SS0399/97]; 3 specimens, 39° 48.3´S, 149° 6´E, 1923–1962 m, MV [SS01/00/260]; 4 specimens, 38° 31.3´S, 149° 21.1´E, 1986– 1360 m, MV F168939; 1 specimen, 38° 11.4´S, 149° 32.1´E, 593 m, MV [SS0404/094]; 4 specimens, 38° 14.5´S, 149° 41.4´E, 660– 660 m, MV [S01/85/49]; 1 specimen, 34° 57.4´S, 151° 16.1´E, 1402–1420 m, MV [STN11SLOPE]; 1 specimen, 34° 51.2´S, 151° 21.2´E, 1725– 1701 m, MV [STN13SLOPE]; 1 specimen, 34° 41.6´S, 151° 22.3´E, 1896– 1642 m, MV F168943; 1 specimen, 34° 43.1´S, 151° 23´E, 2250 m, MV F84954 ; 1 specimen, 34° 34.3´S, 151° 40.5´E, 2800– 2700 m, MV [STN60SLOPE]. Unless stated, all stored in 80% ethanol.

Size range. Maximum size up to at least 214 mm TD.

Occurrence. Previously, the only records of this species in the region were from northwestern Australia (Rowe & Gates 1995). These new records now show that it is one of the most commonly caught species of echinothurioid in the region, particularly around New Zealand, where it has frequently been observed in seafloor camera surveys living on sandy or muddy substrates ( Figure 19 ). The extensive list of records covers all of the main offshore bathymetric features of the region except for the Kermadec Ridge, the Macquarie Ridge, and regions south of Campbell Island ( Figure 20 ).

A conservative depth range for the New Zealand specimens is 497–1923 m, similar to the 360–2068 m reported by Mortensen (1935) for specimens taken from the Indo-West Pacific region, including Japan, Malaysia, and the central Indian Ocean.

Remarks. This species was first recognized in New Zealand as H. luculentum by McKnight (1974) from specimens (including NIWA29459) collected from off the east coast of the South Island. McKnight (1974) provided no comparison with other Hygrosoma species, mentioning only that it differs from other New Zealand echinothurioids (especially Araeosoma thetidis ) “in having the curved peristomial and adjacent primary spines lacking a conspicuous white hoof and the single series of pores and tube-feet orally”. An examination of the tridentate pedicellariae and the orientation of the aboral ambulacral pores would have been necessary to distinguish this species from H. hoplacantha and H. petersii . After examining pedicellariae on specimens from one of McKnight’s records (the other apparently lost) along with numerous other records collected over the following 40 years it is now clear that the species found in the New Zealand region is H. hoplacantha . The main distinguishing feature, the large, broad-bladed tridentate pedicellariae, display the strongly involuted blade with serrated edge of this species rather than the wide mid-section and straight-edged blade of H. luculentum ( Figure 21 ). Although distinctive, these pedicellariae were not common in the specimens examined, and not found at all in McKnight’s original specimens. Ophicephalous pedicellariae, known from H. petersii and H. hoplacantha , were not found in any specimens. In addition, the primary spines of oral plates near the peristome are not so strongly bent as in H. luculentum . There was much variability in the curvature of these spines in the several specimens examined, with many quite straight—but none could be described as ‘hockey-stick’ (Mortensen 1935).

The three known species of Hygrosoma are very closely related (Mortensen 1935), with the Atlantic H. petersii differing from the two Indo-Pacific species in the compression of the aboral pore series into two series rather than three and the lack of the short, broad-bladed tridentate pedicellariae. All Hygrosoma species are relatively large, with the maximum size of H. hoplacantha in New Zealand at least 214 mm.

Figures

FIGURE 18. Hygrosoma hoplacantha, NIWA 45049. (130 mm TD). Left, aboral view; right, oral view.

FIGURE 19. Hygrosoma hoplacantha. In situ image taken by a deep towed-camera system (DTIS) from R. V. Tangaroa, in 1556 m at 41 ° 42.9´S, 175 ° 40.7´E (Cook Strait). Note the large white hoofs.

FIGURE 20. Hygrosoma hoplacantha. Distribution of confirmed records in New Zealand and southeast Australia, from material examined. Number of records = 108.

FIGURE 21. Hygrosoma hoplacantha (NIWA 33597, 214 mm TD). A, head of large tridentate pedicellaria, B – D, head and valves of small tridentate pedicellariae; E – F, valves of triphyllous pedicellariae.