Hapalosoma amynina, Anderson, Owen F., 2013

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 : 560-564

Hapalosoma amynina sp. nov.

Figures 3 C, 4B, 32–35

Holotype —From Rungapapa seamount in the Bay of Plenty, northeast New Zealand: 37° 32.6´S, 176° 59.0´E, 166– 155 m (111 mm TD), NIWA6621. Deposited in the NIC, Wellington. Caught on 13 November 2004 by RV Tangaroa . Stored in 80% ethanol.

Paratypes —Bay of Plenty (all on or in the vicinity of Rungapapa and Tuatoru Knoll): 1 specimen (106 mm TD), 37° 32.6´S, 176° 59.0´E, 166– 155 m, NIWA81374; 1 specimen (108 mm TD), 37° 28.6´S, 177° 12.9´E, 180– 179 m, NIWA6619; 1 specimen (99 mm TD), 37° 32.1´S, 176° 58.2´E, 217– 169 m, NIWA45139; 2 specimens (99, 100 mm TD), 37° 32.0´S, 176° 58.8´E, 219– 176 m, NIWA6620; 1 specimen (105 mm TD), 37° 33.0´S, 176° 58.2´E, 176– 155 m, NIWA29416; 1 specimen (108 mm TD), 37° 33.0´S, 176° 58.2´E, 176– 155 m, NIWA81372. All stored in 80% ethanol except NIWA81372, stored dry.

Other material —Bay of Plenty (mostly on or in the vicinity of Rungapapa, Tuatoru, Tumokemoke, and Rangitira Knolls): 1 specimen (99 mm TD), 37° 33.8´S, 176° 58.7´E, 370– 176 m, NIWA29417; 2 specimens (101, 93 mm TD), 37° 33.0´S, 176° 58.2´E, 280– 155 m, NIWA29455; 1 specimen, 37° 30.0´S, 176° 24.0´E, Te Papa EC9363; 1 specimen, 37° 28.3´S, 177° 12.9´E, Te Papa EC9522; 1 specimen (115 mm TD), 37° 28.1´S, 177° 7.0´E, 230 m, NIWA29444; 1 specimen, 37° 16.2´S, 176° 50.6´E, Te Papa EC3678 (dry); 1 specimen, 37° 33.2´S, 176° 58.7´E, Te Papa EC3680 (dry); 1 specimen, 37° 36.8´S, 176° 59.7´E, Te Papa EC3677 (dry); 1 specimen, “Bay of Plenty”, 163–182 m, Te Papa EC1232 (dry). West Norfolk Ridge: 2 specimens (88, 90 mm), 33° 45.3´S, 167° 17.1´E, 254–259 m, MV (TAN0308/99); 1 specimen, 32° 41.3´S, 167° 38.10´E, Te Papa EC3679 (dry). Those not dry stored in 80% ethanol.

Etymology —Named after Amy and Nina Anderson , used as a noun in apposition.

Diagnosis —Adults relatively large for the genus, up to 115 mm TD, test outline sub-pentagonal; test and spines deep red; dactylous pedicellariae with 3 valves. Tridentate pedicellariae of two kinds; a smaller form in a range of sizes with long, narrow blades and a larger form with massively expanded blades. Primary tubercles on every plate in the adradial interambulacral series on the oral side, continuing above the ambitus for 1–2 plates as the only primary tubercles on the aboral side.

Description —Test of holotype ( Figure 32 ) moderate size (100 mm TD), sub-pentagonal, flattened, ambitus not much rounded. Colour of test, spines, and tube-feet brilliant red, owing to the pigment in skin and test plates—the latter dark red underneath the skin. This red colour contrasts strongly with the white of the hoofs, spine bases where the skin has rubbed off, and to a lesser extent the tips (sucking discs) of the oral tube-feet. When cleaned, the membranous spaces between plates are also white. Primary tubercles perforate and non-crenulate. Ratio of interambulacrum to ambulacrum width at the ambitus, 2:1.

The interambulacral columns cleaned for examination have 33 plates, 14 on the oral side and 19 aborally; ambulacral columns have 42 plates, 21 on each side. Interambulacral plates very long and narrow aborally, only slightly angled to each other; although exact plate boundaries partially concealed by thick membranous connective tissue, distinct membranous spaces clearly visible in the median area between successive plates. Wide gaps between columns in the interambulacral midline, becoming narrower towards the ambitus. Interambulacral plates relatively much wider orally, with a much narrower midline gap.

Aboral test plating ( Figures 32 , 33 ): Aboral primary tubercles limited to one or two at the ambitus which mark the end of the main oral interambulacral series. Between 4 and 6 equal-sized and evenly spaced large secondary tubercles on the outermost interambulacral plates, mostly towards the outer end, gradually reducing in number on successive plates adapically so that on the 8 or 9 innermost plates there is only a single tubercle. These tubercles align to form usually four oblique series down each column, becoming less regular and more limited to the outer edge of the plates adapically, the outer two series generally ending about half way up the column. The inner half of these plates bare except for a few smaller secondary tubercles which may form into discernable series parallel to those of the larger tubercles. Secondary tubercles in the aboral ambulacra arranged into two series at the inner end.

One series, adjacent to the inner tube-feet, occurs very regularly on each plate in the column; the other series perradial to the first, occurring in the outer half of the column, less regular. Tube-feet arranged into evenly spaced rows of three, inner accessory plate pore often noticeably larger than outer, main plate pore generally adjacent to outer margin. Smaller secondary and miliary tubercles not obvious on remaining area of plates.

Apical system about 27 mm across; component plates scattered with small spines, their exact number and the plate edges difficult to determine due to the covering of skin and membranous tissue. Madreporite raised, roughly circular. Genital pores small, opening in a membranous space within or beyond the genital plates. Some details of the apical system are clearer in the cleaned and dried paratype (NIWA29416). In this specimen the genital plates are composed of 3–4 separate plates, the whole distinctly elongated so that the genital pore is located down the interradius generally adjacent to about the third interambulacral plate. In one column, however, there are two genital plates which extend down to the 5th or 6th interambulacral plate, in a similar fashion to that frequently observed in Araeosoma migratum . Also in this specimen about 45 small plates can be seen surrounding the anus, the inner ones forming a rough ring.

Oral test plating ( Figure 33 ): A regular adradial series of primary tubercles in the interambulacra, occurring on every plate from the peristome to the ambitus and usually continuing onto the aboral side for one or two plates. An inner series of primary tubercles, occasionally missing a plate, runs from near the interradial suture just beneath the ambitus to about mid-plate in the centre of the column where it ceases or, more noticeably in the dry paratype (NIWA29416) is continued by secondary tubercles down to the peristome. Parts of the aboral series of secondary tubercles continue onto the oral side to form one or two indistinct series down the outer end of the plate, this feature again more obvious in the dried paratype. Ambulacra with a small primary tubercle in a perradial position on a few of the plates in the distal half; plates without these tubercles bear instead secondary tubercles of various sizes which combine to form a rough series down each column. In addition to this each plate has 1–3 secondary tubercles randomly placed; miliary tubercles and granules not obvious over the remaining space on the plates.

Only ambulacral plates on the peristome, about 11 or 12 per column; all but one or two of the smaller distal plates bear a single tube-foot surrounded by 3–4 tubercles spread along the plate. Interambulacral midline cut back deeply away from the peristome to accommodate movement of the jaw, this cut away area replaced by a thin membrane. This feature much more clearly clearly seen in the dried paratype, which otherwise differs slightly from the holotype in that there are fewer (9–11) plates per column. Buccal notches shallow, gills moderately large, lobate, red.

Spines cylindrical, hollow, red; milled ring usually slightly oblique; shafts smooth, with up to about 45 fine, longitudinal striations. These striations simple v-shaped wedges in cross-section in the aboral spines examined, but club-shaped wedges with distal extensions in the oral spines. Oral spine wall moderately thick, with a layer of meshwork; aboral spine wall very thin, with no strengthening meshwork in the spines sectioned ( Figure 3 C). Many oral primary spines remain intact on the holotype; these spines distinctly curved (towards the mouth) and ending in a white hoof of moderate length (up to about 2x spine width) and slightly flared ( Figure 4 B). The largest spine (which lacks a hoof) 30 mm long by 1.2 mm in diameter.

Pedicellariae ( Figure 34 ): Three forms of pedicellariae present in the holotype. A very large, rare, rostrate tridentate form up to about 4 mm head length with simple, large, rounded blades which broaden towards the tip from a narrow base, similar to that of H. peluccidum (Mortensen 1935) ; the neck very short, the stalk long. A smaller rostrate tridentate form, in a range of sizes, similar to the large form but with much narrower blades only slightly expanded distally; neck about half the head length, stalk about 2–2.5 times the head length. Triphyllous pedicellariae of the usual form, about 0.4–0.5 mm head length with a long neck (2–3 times head length) and slightly longer stalk. The blade relatively short, strengthened with light meshwork in some specimens, the involute basal part completely enclosed usually only for a short distance above the base. Dactylous pedicellariae of the usual form for Hapalosoma (see Mortensen 1935, figure 69d), head about 2 mm long with three valves reduced to fine, fragile rods enveloped within large conjoined glands. No obvious neck, stalk about 2–3 times head length. These pedicellariae relatively common on the holotype and other specimens searched, generally found on the aboral side near the ambitus.

Sphaeridia sub-spherical (about 0.4 mm long by 0.3 mm wide) with distinct longitudinal striations, located perradial and slightly adoral to the base of the inner tube foot in each ambulacral plate.

Size range —The average test diameter of the 14 specimens measured was 102 mm, and the largest specimen was 115 mm TD.

Occurrence —All but 3 of the 21 specimens (14 out of 16 records) were collected from a group of seamounts within a small area in the Bay of Plenty, in the northeast of the North Island. The remaining specimens come from two samples trawled from Wanganella Bank on the West Norfolk Ridge, west of the northern tip of North Island ( Figure 35 ). Seven of the Bay of Plenty records (eleven individuals in all, including the holotype) were collected from a single seamount, Rungapapa Knoll.

The conservative depth range for the species is 117–254 m, with a potential range of 106– 370 m.

Remarks —The Te Papa specimen of H. amynina (Te Papa EC1232) was included in Baker’s (1972) account of Araeosoma coriaceum as his specimen No. 2. As explained above, Baker’s other specimen (No. 1) was also incorrectly identified as A. coriaceum and is now the holotype of the new species Araeosoma bakeri sp. nov.

The oral surface of H. amynina is at first glance remarkably similar to that of Araeosoma tertii ; the colour, spines and hoofs being almost indistinguishable. It is not until the tuberculation of the aboral surface is examined that the two species can easily be separated. It is also interesting that the two species have been found in similar locations and at similar depths; H. amynina at 117–254 m and A. tertii at 180– 260 m. Despite this similarity, details of the aboral surface and especially the pedicellariae place them clearly into different genera.

The pedicellariae of H. amynina are very similar to those of H. pellucidum and this, or perhaps H. pulchrum (known from a single specimen from Norfolk Island), may be its closest relative. The aboral surface of H. amynina is similar to that of H. pulchrum in the near absence of primary tubercles and rows of similar size secondary tubercles on the interambulacral plates, but whereas there are up to 13–14 such tubercles on the widest plates near the ambitus in H. pulchrum there are only about 6 in H. amynina . The pedicellariae of H. pulchrum were not described in any detail by Rowe (1989) but the tridentate form observed on his specimen is quite distinct from that of H. amynina , being relatively much shorter and wider. No examples of the large, broad-valved form common to H. amynina and H. pellucidum were seen on H. pulchrum . The red colouration of H. amynina is quite constant among the individuals examined, and differs entirely from that of H. pulchrum (pale green), H. pellucidum (whitish), and the fourth member of this genus H. gemmiferum (light brown).

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 4. Oral spine hoofs. A, Araeosoma thetidis (NIWA 6595); B, Hapalosoma amynina (NIWA 6621); C, A. alternatum (NIWA 53579); D, A. migratum (NIWA 45089); E, A. tertii (NIWA 29453); F, A. bakeri (NIWA 6564); G, A. anatirostrum (NIWA 29442); H, A. bidentatum (NIWA 23720).

FIGURE 32. Hapalosoma amynina sp. nov., holotype, NIWA 6621 (111 mm TD). Left, aboral view; right, oral view.

FIGURE 33. Hapalosoma amynina sp. nov., holotype, NIWA 6621. Details of coronal plates. Top, aboral; bottom, oral; left, ambulacra; right, interambulacra.

FIGURE 34. Hapalosoma amynina sp. nov., holotype, NIWA 6621. SEM images of pedicellariae. A – C, valves of triphyllous pedicellariae; D, G, H, valves of narrow-bladed tridentate pedicellariae; E & I, dactylous pedicellariae (E, base; I, tip); F, valve of large, broad-bladed pedicellaria.

FIGURE 35. Hapalosoma amynina sp. nov. Distribution of confirmed records within the New Zealand region, from material examined. Number of records = 16. The dashed line is the 1000 m depth contour.