Chitonaster trangae, Mah, Christopher L., 2011

Mah, Christopher L., 2011, Taxonomy of high-latitude Goniasteridae (Subantarctic & Antarctic): one new genus, and three new species with an overview and key to taxa, Zootaxa 2759, pp. 1-48 : 17-19

Chitonaster trangae n. sp.

( Figure 7 A–F)

Mein, 1992: 245; Stampanato & Jangoux, 1993: 181. (as C. johannae )

Diagnosis. Papulae present between abactinal plates. Blunt, cylindrical spines on abactinal and marginal plates. Granules coarse and well-spaced. Abactinal plates larger than in other known Chitonaster species ( C. cataphractus , C. felli , and C. johannae ).

Etymology. This species is named for Trang Ngyuen, US Antarctic Research Program for her enthusiasm and diligent contributions to the study of Antarctic marine invertebrates.

Distribution. Palmer Archipelago, Antarctic Peninsula, Vahsel Bay, Weddell Sea, South Orkney Islands, Scotia Sea , South Shetland Islands, Bransfield Strait, Off Enderby Land. 104–412 m depth.

Distinctions from other species. Chitonaster trangae n. sp. occurs primarily in shallow-water settings (100– 400 m). It is distinguished primarily by the presence of papulae on the disk (papulae are absent in the deep-water taxa), the larger, coarser, and more widely-spaced surface granules and/or blunt cylindrical spines.

Material examined. HOLOTYPE USNM E13585 Vahsel Bay, Coats Land, Weddell Sea, Southern Ocean. 77˚44’S, 35˚30’W, 412 m. Coll. J. Tyler (1 dry spec. R=3. 6, r=1.3).

PARATYPES: USNM E50555 . South of Laurie Bay, South Orkney Islands. Scotia Sea. 61˚18’06”S, 44˚ 23’24”W, 289– 291 m. Coll. US Antarctic Research Program. (1 dry spec. R=5.6, r=2.3); USNM 1101456 Elephant Island, South Shetland Islands, 61˚03’22S, 54˚42’43W, 402 m. coll. S. Kim & Moss Landing Marine Labs (2 wet specs. R=6.5, r=2.7; R=4.1, r=2.0); USNM 1121466 South of Anvers Island. 64˚50’30”S, 63˚ 15’W”W, 104– 146 m. Coll. D. Pawson and D.F. Squires. (1 dry spec. R=4.1, r=2.1); CASIZ 174667 Bransfield Strait, 62° 23' 59.9”S, 54° 28' 11.9” W, 388 m. Coll. S. Lockhart aboard RV Yuzhmorgeologiya, 1 March 2006. (1 wet spec. R=4.7, r=1.9). CASIZ 175987 Bransfield Strait 62° 38' 59” S, 55° 36' 35”W, 177– 165 m. Coll. S. Lockhart and V. Smith aboard R/V Yuzhmorgeologiya 20 Dec 2007. (2 wet specs. R=3.1, r=1.7; R=3.7, r=2.3).

Material examined (non-types). USNM E13503. NW of Brabant Island, Palmer Archipelago, Antarctic Peninsula.63˚51’S, 62˚38’W, 128–165.0 m. Coll. R/V Eltanin, USARP 9 Jan 1963 (11 dry specs. R=4.4, r=1.9; R=3.4, r=1.4; R=3.0, r=1.2; R=3.9, r=1.4; R=4.0, r=1.2; R=3.3, r=1.1; R=1.6, r=0.7; R=4.8, r=1.8; R=2.3, r=1.8; R=0.9, r=0.6; R=0.9, r=0.5); USNM 1081975 Low Island, South Shetland Islands, Southern Ocean. 63˚26’S, 62˚15’W to 63˚25’S, 62˚14’W. 119– 124 m. Coll. US Antarctic Research Program. (3 dry specs. R=5.3, r=3.0; R=3.2, r=1.6; R=4.0, r=1.8); USNM 1082741 Southeast of South Orkney Islands, Scotia Ridge, Scotia Sea. 61˚26’S, 41˚55’W to 61˚24’S, 41˚55’W, 593– 598 m. Coll. U.S. Antarctic Research Program/U. Southern California. (1 dry spec. R=2.5, r=1.1); USNM 1082877 Elephant Island, South Shetland Islands 61˚18’S, 56˚9’W to 61˚20’S, 56˚10’W˚. 220– 240 m. Coll. Univ. Southern California (1 dry damaged specimen); USNM 1101454 Elephant Island, South Shetland Islands, 60˚34’26S, 55˚05’23W, 258 m. coll. S. Kim & Moss Landing Marine Labs (1 wet spec. R= 4.2, r=1.6). USNM 1101461 Elephant Island, South Shetland Islands, 61˚09’35S, 54˚32’57W, 331 m. coll. S. Kim & Moss Landing Marine Labs (1 wet spec. R=5.1, r=2.2). USNM 1101462 Elephant Island, South Shetland Islands, 61˚09’35S, 54˚32’57W, 331 m. coll. S. Kim & Moss Landing Marine Labs (2 wet specs. R=4.0, r=2.1; R=3.3, r=1.5); USNM 1131425. Southern Ocean. 62˚41’S, 54˚43’W, 210–220 m, Coll. R/V Eltanin, US Ant. Res. Program. (1 wet spec. R=2.2, r=1.0); USNM 1136769 Dallmann Bay, Southern Ocean, 64˚00’S, 62˚00W, 120 m. Coll. R/V. Polar Duke. (1 dry spec. R=2.9, r=1.3).

Not examined. MV F 122614, Off Enderby Land, 65º56’24” S, 50º 52 06W, 386– 400 m. Coll. M/S Nella Dan 15 Nov. 1985.

Description. Body strongly stellate (R/r=1.8–2.7) with elongate arms, inflated disk ( Fig. 7 A).

Abactinal plates, flattened, scalar, with overlapping edges ( Fig. 7 D). Plates irregular to jagged with blunt edges in outline, relatively large (approximately 3–4 across arm base). Abactinal plates are thicker relative to other species, which results in relatively shallow fasciolar grooves between plates, especially on disk. Each plate covered by two to twelve spines, varying from blunt cylindrical, appearing almost granular to pointed conical ( Fig. 7 A, F). Spine size varies on some individuals with some showing two sizes, a larger, thicker 1.2–2.0 mm spine and a smaller 0.5 to 1.0 mm spine ( Fig. 7 F). Granular, blunt spines are also present on some individuals ( Fig. 7 C). Spines/granules distributions vary with some specimes showing spines closely clustered, others evenly spaced from one another, with some spines sometimes absent from plate surface. Large bivalved pedicellariae with elongate smooth-edged blades also present on abactinal surface, approximately equal in size to plates on which they sit ( Fig. 7 B). Aside from spines and pedicellariae, other secondary smaller accessories such as smaller peripheral granules are absent. Papulae present on disk and arms, four to six present between jagged edges of each plate ( Fig. 7 D). Madreporite convex, flanked by four to six plates, with moderately developed sulci.

Marginal plate series interradially facing more laterally, whereas those on distal arm face more dorsally ( Fig. 7 E). Superomarginal and inferomarginal plate series correspond 1: 1 in smaller specimens (~R=1.0 cm) but become offset in larger individuals (~R>2.0 cm) with larger superomarginals and smaller inferomarginals. Superomarginals number 16 (in R=1.0)–32 (in R=5.3) whereas inferomarginals number 24 to 46 (for R=1.0 and R= 5.3 cm respectively). Both superomarginals and inferomarginals are more quadrate interradially becoming more rectangular distally. Similar to the grooves on the abactinal plates, marginal series show shallow fasciolar grooves between superomarginal and inferomarginal plate contacts. Each plate with spinelets, one to nine, blunt and/or conical similar in size and shape to those present on the abactinal plates. Some spines larger with smaller spines <10% of larger spine size. Spine morphology varies across individuals showing more spiny, conical tips versus others with evenly distributed thickened, blunt, cylindrical shaped spines. Spines with conical, pointed tips often clustered together not as widely distributed as blunt spines. Larger spines on inferomarginal often arranged in a distinct linear series facing ventrolaterally with superomarginal spines in a more scattered pattern. Marginal plates are bare with no other secondary accessories, such as granules or spinelets present forming peripheral borders or covering plate surface. Pedicellariae absent on marginal plates.

Actinal intermediate regions, relatively well developed compared to other Chitonaster species, typically with two or even a partial third actinal “chevron” series, each composed of approximately six or seven individual plates limited to disk ( Fig. 7 B). Actinal plates absent from arms. Actinal plates quadrate, flattened, scalar, similar to those on abactinal surface. Plate boundaries obscured by fleshy membrane. Each plate with spines, two to six, cylindrical and blunt or conical and spiny tipped, sometimes clustered or in short series but other times discretely spaced from one another. Some spine series with individual spines enlarged, distal spines smaller. Actinal surface spination is similar to those on inferomarginal plates and spination appears confluent. Large bivalve or trivalve pedicellariae, 9 to 28 in number, with smooth valves, each pedicellariae is the size of the actinal plate on which it sits and evenly distributed across the actinal surface (Fib. 7B). Pedicellariae are flanked by six to seven sharp thorny spinelets on each side similar in appearance to spinelets described below.

Furrow spines two, exceptionally three, in transverse series, enlarged, cylindrical, thickened with blunt tip ( Fig. 7 B). A shorter subambulacral spine, usually about 50–60% of the length of the furrow spine, variably with blunt or spiny tip sits adjacent to the transverse furrow spine series. Often scattered among the actinal surface at the base of the furrow and subambulacral spines are short, thorny spinelets but otherwise surface accessories, such as those which make up surface granulation are absent. Furrow spines, blunt, elongate on oral plates, two, with a third spine projecting into the mouth. Two spines, blunt tipped, elongate present on oral plate surface.

Figures

FIGURE 7. Chitonaster trangae nov. sp.. Holotype USNM E 13585. A. Abactinal Surface .. B. Actinal surface. USNM 1121466 C. Granules on abactinal arm surface. USNM E 13503. D. Coelomic view of abactinal plates showing papular pores .. USNM E 50555 - E. Lateral view of marginal plates and abactinal spines. F. Abactinal spines and plate variation. Scale Bar = 0.5 cm.