Sperosoma cf. nudum Shigei, 1978

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 : 460-463

Sperosoma cf. nudum Shigei, 1978

( Figures 6–9 )

Material examined. 39 specimens from 21 records (NIWA, AM, MV).

Southeast Australia: 3 specimens (108, 119, 136 mm TD), 34° 51.2´S, 151° 21.2´E, 1725 – 1701 m, MV (STN13SLOPE); 5 specimens, 34° 55.8´S, 151° 15.0´E, 1115–1152 m, AM J24887 ; 2 specimens, 38° 22.7´S, 149° 18.4´E, 1073– 1069 m, MV F84963 ; 1 specimen, 39° 52.5´S, 149° 1.1´E, 1538– 1501 m, MV F168902; 3 specimens, 41° 54.3´S, 148° 45.1´E, 1273– 1190 m, MV (STN83SLOPE); 5 specimens, 41° 13.1´S, 148° 49.1´E, 1330 m, MV (SS0399/97). West Norfolk Ridge: 1 specimen (175 mm TD), 34° 58.8´S, 169° 29.6´E, 1288–1294 m, MV (TAN0308/160); 1 specimen (160 mm TD), 35° 17.9´S, 168° 58.8´E, 1890 m, NIWA46079. Bay of Plenty: 1 specimen (167 mm TD), 36° 47.7´S, 177° 25.5´E, 1530– 1515 m, NIWA6608. East Coast North Island: 1 specimen (170 mm TD), 39° 27.5´S, 179° 55.5´E, 2127–2130 m, NIWA6613; Challenger Plateau: 1 specimen (190 mm TD), 41° 22.7´S, 166° 44.4´E, 2092 m, NIWA45073; 3 specimens (112, 117, 190 mm TD), 41° 22.7´S, 166° 44.4´E, 2092 m, NIWA45074; 1 specimen (dry, 116 mm TD), 41° 22.7´S, 166° 44.4´E, 2092 m, NIWA46082; 2 specimens (131, 142 mm TD), 41° 15.2´S, 167° 7.2´E, 1463 m, NIWA45077. Chatham Rise: 1 specimen (97 mm TD), 42° 41.8´S, 175° 32.3´W, 1482 m, NIWA45032; 1 specimen (115 mm TD), 42° 45.0´S, 175° 4.5´W, 1482 m, NIWA45051; 1 specimen (48 mm TD), 42° 38.3´S, 178° 59.9´E, 2039– 1687 m, NIWA45061; 1 specimen (145 mm TD), 44° 41.1´S, 179° 1.2´E, 1610–1688 m, NIWA45029; 1 specimen (59 mm TD), 44° 40.9´S, 179° 1.2´E, 1600–1706 m, NIWA45114. East Coast South Island: 2 specimens (204, 214 mm TD), 45° 57.9´S, 171° 45.7´E, 1400–1415 m, NIWA29451. Campbell Plateau: 1 specimen (dry, 200 mm TD), 48° 7.0´S, 174° 2.0´E, 1167 m, NIWA45111. Unless stated, all stored in 80% ethanol.

Size range. The 22 measured specimens range in size from 48 mm to 214 mm TD, with a mean of 141 mm TD.

Occurrence. Widespread around New Zealand, from the north of North Island and Challenger Plateau in the west, the Chatham Rise in the east, and the Campbell Plateau in the south; as well as southeast Australia ( Figure 7 ). The conservative depth range for the species is 1073–1701 m, with a potential maximum range of 1029–2092 m.

The six type specimens of Sperosoma nudum were collected from around the Izu Islands, central Japan, in depths of 1410–2080 m. The species has not subsequently been reported.

Remarks. The New Zealand and Australian material resembles Sperosoma nudum in several ways. All types of pedicellariae ( Figure 8 ) match very closely; the small narrow and large wide tridentate forms and the distally rounded, moderately enclosed triphyllous forms figured by Shigei (1978) all being present. The arrangement of the aboral ambulacral plating also matches closely, with the main plate generally extending from the midline to the adradial border, and the pores forming an irregular double-series ( Figure 9 ). In the new material the pores of the main plate and outer secondary plate are typically distinctly reduced in size and difficult to locate. There are some differences in the number of plates on each surface (being generally more numerous in the New Zealand specimens, Table 3 ) but this was variable, with plate numbers in a smaller specimen (118 mm TD) more similar to the type material for which the counts were only approximate in any case (Shigei 1978). The plates of the oral ambulacra are typical for Sperosoma , with the non-poriferous central plates clearly discernable in the specimens examined ( Figure 9 ).

The number of spines on the buccal plates also differs somewhat, 8–10 in the specimens examined compared with 13–14 in the type material. A striking similarity is the madreporite ( Figure 6 ), distinctive in many specimens examined for the paw-shape formed by its split into one large and several smaller plates (although Shigei 1978 states that the madreporite is undivided, his Figure 5 seems to show the condition described here quite clearly). The Japanese species is named for the lack of secondary tubercles on the aboral side. This feature is variable in the New Zealand species, with some quite naked but others (e.g. Figure 6 ) less so.

Examination of numerous specimens of the two species found in New Zealand and southeast Australia has shown much variation in some of the characters used to distinguish species. For example, the pores in the aboral ambulacra are close to each other, laterally, so that small variations in placement within and between specimens make it difficult to say whether they form a single ragged row as described for S. durum , two rows ( S. crassispinum ), no discernible pattern ( S. biseriatum ) or quincunx (the remaining species), and placements resembling each of these types can be seen in both species. Also, the exclusion of the main ambulacral plate from the adradial boundary is noticeable in some specimens of Sperosoma cf. nudum (e.g., NIWA29451 and NIWA45029) but not in others. The use of such variable characters to establish several distinct species based on extremely limited material casts some doubt on their validity. For this reason the exact identity of this species cannot be determined with certainty, particularly as it has not been possible to examine any of the type material of S. nudum , but its strong similarity to this species is acknowledged here.

Figures

FIGURE 5. Sperosoma obscurum, NIWA 58244. Transition of ambulacral plate arrangement between aboral and oral surfaces. The approximate position of the ambitus is shown by the dark horizontal line, with aboral plates above and oral plates below; the perradial suture is to the left. Inner secondary plates are shown in white, outer secondary plates in light grey, and main plates in dark grey.

FIGURE 6. Sperosoma cf. nudum, NIWA 46079. (170 mm TD). Left, aboral view; right, oral view; insert, close-up of madreporite.

FIGURE 7. Sperosoma cf. nudum. Distribution of confirmed records in New Zealand and south-eastern Australia, from material examined. Number of records = 21.

FIGURE 8. Sperosoma cf. nudum, NIWA 46079 (160 mm TD). A – B, valves of large, broad tridentate pedicellariae; C – G, valves and head of small, narrow tridentate pedicellariae; H – I, valves of triphyllous pedicellariae.

FIGURE 9. Sperosoma cf. nudum, NIWA 45073 (190 mm TD). Details of ambulacral plates: left, aboral; right, oral.

Tables

TABLE 3. Coronal plate counts for Sperosoma cf. nudum. –, not counted.

		Number of plates
		oral aboral
Specimen	TD (mm)	A IA A IA
NIWA46082	118	14 10 15 16
NIWA45073	190	15 10–11 18 19–20
NIWA46079	160	15–16 10–11 17–18 17–18
Shigei (1978)	155–170	10–12 10–12 13–15 13–15