Araeosoma thetidis (H.L. Clark, 1909)

Anderson, Owen F., 2013, A review of New Zealand and southeast Australian echinothuriinids (Echinodermata: Echinothuriidae) with descriptions of seven new species, Zootaxa 3609 (6), pp. 521-567 : 553-555

Araeosoma thetidis (H.L. Clark, 1909)

Figures 3 G, 4A, 26–28

Asthenosoma thetidis . H. L. Clark 1909.

Araeosoma thetidis . A. Agassiz & H. L. Clark 1909.

Material examined —Bay of Plenty: 2 specimens (172, 154 mm TD), 37° 28.1' S, 177° 7.0' E, 230–318 m, NIWA29419 & NIWA29420; 1 specimen, 37° 42.0' S, 176° 36.0' E, Te Papa EC744 (dry); 2 specimens, 37° 24.6' S, 177° 12.2' E, Te Papa EC3675 (dry); 1 specimen, 37° 16.7' S, 176° 50.9' E, Te Papa EC3688 (dry); 1 specimen, 37° 16.5' S, 176° 50.7' E, Te Papa EC3690 (dry); 3 specimens (161, 150, 146 mm TD), 37° 32.8' S, 176° 58.9' E, 151– 141 m, NIWA6593; 6 specimens (142, 148, 145, 156, 152, 147 mm TD), 37° 32.6' S, 176° 59.0' E, 166– 155 m, NIWA6595; 2 specimens (frozen), 37° 32.9' S, 176° 59.3' E, 142– 136 m, NIWA6596; 2 specimens (156 mm TD), 37° 28.3' S, 177° 12.9' E, 180– 177 m, NIWA6587; 1 specimen (160 mm TD), 37° 28.6' S, 177° 12.9' E, 180– 179 m, NIWA6592; 1 specimen (discarded), 37° 28.0' S, 176° 54.9' E, 225– 210 m, NIWA6599; 1 specimen (195 mm TD), 37° 15.1' S, 176° 50.1' E, 195 m, NIWA23715; 1 specimen (59 mm TD), 37° 15.8' S, 176° 51.3' E, 188 m, NIWA23721; 2 specimens, 37° 16.0' S, 176° 51.0' E, 190 m, NIWA29422; 1 specimen, 37° 14.6' S, 176° 51.0' E, Te Papa EC3686 (dry); 1 specimen, 37° 16.2' S, 176° 50.6' E, Te Papa EC3687 (dry); 1 specimen (75 mm TD), 37° 32.0' S, 176° 58.8' E, 219– 176 m, NIWA6594; 3 specimens (discarded), 37° 32.1' S, 176° 58.3' E, 217– 169 m, NIWA6597; 1 specimen (discarded), 37° 33.2' S, 176° 58.1' E, 190– 154 m, NIWA6598; 1 specimen (148 mm TD), 37° 33.0' S, 176° 58.2' E, 176– 155 m, NIWA29449; 1 specimen (140 mm TD), 37° 33.8' S, 176° 58.7' E, 370– 176 m, NIWA29454; 1 specimen (130 mm TD), 37° 33.0' S, 176° 58.1' E, 254– 170 m, NIWA29458; 1 specimen, 37° 33.8' S, 176° 59.0' E, Te Papa EC5850 (dry); 4 specimens (155, 158, 161, 162 mm TD), 37° 28.2' S, 177° 13.2' E, 200– 175 m, NIWA6586; 5 specimens (188 mm TD), 37° 28.2' S, 177° 13.4' E, 207–216 m, NIWA6589 (frozen) & NIWA6590; 1 specimen (138 mm TD), 37° 29.1' S, 177° 12.9' E, 400– 225 m, NIWA6591 (dry); 2 specimens (164, 170 mm TD), 37° 28.2' S, 177° 7.0' E, 220–320 m, NIWA29421 & NIWA29423; 2 specimens, 37° 28.5' S, 176° 54.3' E, Te Papa EC3689 (dry); 1 specimen (127 mm TD), 37° 33.0' S, 176° 58.4' E, 280– 155 m, NIWA29456; 1 specimen, 37° 16.5' S, 176° 50.7' E, 69–79 m, USNM 1017071. Southeast Australia / Bass Strait: 4 specimens, 37° 57.5' S, 149° 30.3' E, 132–135 m, MV F168940; 1 specimen, 38° 14.5' S, 149° 9.2' E, 200 m, MV F167683; 1 specimen, 40° 7.0' S, 148° 7.0' E, MV F97193 ; 5 specimens, 38° 6.5' S, 149° 21.2' E, 160 m, SS0404/088. Northland: 1 specimen (172 mm TD), 34° 32.7' S, 173° 30.9' E, NIWA45094; 1 specimen (181 mm TD), 34° 24.6' S, 173° 9.7' E, 203– 169 m, NIWA57059. Colville Ridge: 2 specimens, 29° 0.0' S, 178° 0.0' W, Te Papa EC5130 (dry). Norfolk Ridge: 1 specimen, 29° 41.5' S, 168° 3.5' E, 339–344 m, MV (TAN0308/019); 4 specimens (90, 86, 76, 57 mm TD), 23° 28.0´S, 167° 52.0´E, 305–322 m, MNHN DW1657; 3 specimens, 29° 41.8' S, 168° 2.6' E, 322–337 m, MV F168911. New Caledonia: 4 specimens, 23° 28.0' S, 167° 52.0' E, 305–332 m, IE-2007-230. Unless stated, stored in 80% ethanol.

Size range —The median test diameter of the 34 specimens measured was 142 mm, and the largest specimen was 195 mm TD.

Occurrence —The type material of A. thetidis was collected from Botany Bay (NSW, Australia) in 1898 (Clark 1909), and the species was first found in New Zealand north of East Cape by the Terra Nova Expedition of 1910–1913 (Mortensen 1922). It was later recorded in New Zealand by Fell (1958) from the Bay of Plenty, then by McKnight (1975) from the West Norfolk Ridge ( Figure 27 ). The more southern records from “near Campbell Island” referred to in McKnight (1969) are unlikely to have been A. thetidis , and were most likely A. alternatum (see below). There are now 43 further records of A. thetidis , collected from northern New Zealand and southeast Australia, representing 75 individuals. In addition, four echinoids collected from New Caledonia by the RV Alis in 2001 (on loan to NIWA from the Paris Museum) were confirmed as A. thetidis —the first record of this species from these islands. Apart from this, the material examined does not extend the overall distribution greatly from the published records. By far the greatest number of records has come from the Bay of Plenty, especially on or near Rungapapa Knoll, Rangatira Knoll, Tuatoru Knoll, and Tumokemoke Knoll.

The depth range for the species can be securely determined, as there are 27 records where both start and finish depths were recorded. This gives a conservative depth range of 79–339 m and a potential range of 69– 400 m.

Remarks —This species is most closely related to A. alternatum , with which it agrees in a number of ways. The most significant similarity—one that easily distinguishes these species from other Araeosoma species—is in the tuberculation of the oral interambulacra, in which the adradial series has a primary tubercle on every second plate rather than on every plate. This feature, although visible in Figure 26 , is more obvious in the cleaned specimen shown in plate 69 of Agassiz & Clark 1909. The pedicellariae are similar too, especially the coarsely-serrated rostrate tridentate form—although A. thetidis lacks any involute tridentate pedicellariae. Both species have a stiff, robust test and can grow to quite a large size; A. thetidis to at least 195 mm TD and A. alternatum to over 230 mm TD. The two species are most easily differentiated by examining the continuation of the adradial primary tubercle series onto the aboral side. In A. alternatum this series continues quite regularly on every second or third plate to nearly half way up the column towards the apical system whereas in A. thetidis the series ceases at the ambitus and is replaced by one further interradially which is much less regular, occurring on every second, third, fourth, or fifth plate, with the uppermost tubercle often beyond half way up the column. There is also little depth overlap between the two species, the shallowest record of A. alternatum being 322 m.

In life (in situ) A. thetidis is a striking species, the test a deep red colour but vivid white in the naked regions between adjacent columns of test plates, forming a pattern of 20 radiating stripes ( Figure 28 ). These colours do not persist after capture, however, and alcohol preserved and dried specimens generally are a dark reddish brown fading to a dull fawn colour, the aboral spines usually a light shade of green.

Figures

FIGURE 3. Primary spine sections (left, oral; right, aboral). A, Araeosoma migratum (NIWA 45089); B, A. bakeri (NIWA 6564); C, Hapalosoma amynina (NIWA 6621); D, A. tertii (NIWA 29453); E, A. alternatum (NIWA 53579); F, A. anatirostrum (NIWA 29442); G, A. thetidis (NIWA 29419); H, A. bidentatum (NIWA 23720); I, A. leppienae (NIWA 23724).

FIGURE 26. Araeosoma thetidis, NIWA 6595 (150 mm TD). Left, aboral view; right, oral view.

FIGURE 27. Araeosoma thetidis. Distribution within the New Zealand region, from material examined. Number of records = 43. The dashed line is the 1000 m contour.

FIGURE 28. Araeosoma thetidis. Photograph taken by the NIWA Deep Towed Imaging System (DTIS) from east of North Cape, New Zealand (173.16 ° E, 34.42 ° S, 188 m). The flatfish to the right of the urchin is a witch (Arnoglossus scapha).