Chitonaster johannae Koehler 1908

Chitonaster johannae Koehler, 1908

(Figures 6 A–G)

Koehler, 1907: 144; 1908: 542; A.M. Clark, 1993: 250; (as C. johannae Koehler, 1907 )

Distribution. South of South Orkney, South Georgia Islands, and Elephant Islands, 2856–4204 m.

Distinctions from other species. Chitonaster johannae is herein restricted to those Chitonaster with valvate pedicellariae, abactinal arm plates in transverse series, with clustered spines on abactinal and superomarginal spines with relatively small abactinal plates, and lacking papulae. All C. johannae examined with these characters, including Koehler’s (1908) original description are apparently restricted to abyssal depths (> 2856 m). Shallowwater specimens, including those referred to C. johannae by Mein (1992) and Stampanato and Jangoux (1993), are referred to C. trangae n. sp.

Comments on type material. MNHN EcAh 3511 is herein designated as the lectotype from Koehler’s (1908) syntype series. It corresponds in nearly ever regard to one specimen, with R=23.0 mm, indicated in Koehler’s (1908) full description and designation of this species. This lot included a tag reading “ Scotia ”, the collecting vessel. Other members of Koehler’s syntype series could not be located in the Paris collections and it is unclear how many of the syntypes remain extant. EcAh 3511 is the functional holotype for this species.

Material examined. MNHN EcAh 3511, 62º10’S, 41º20’W, 3246 m (=1775 fms). Coll. Scotia 18 March 1903 (1 wet spec. R= 2.3 cm, r= 1.1); USNM 1086359 66˚ 23 S, 45˚ 49 W to 66˚ 20 S, 45˚ 52W, 4200–4204 m. Coll. U. Southern California. (1 dry spec. R=2.5, r=1.1); USNM 1018953 South of South Orkney Islands, Weddell Sea. 63˚21’S, 44˚51’W to 63˚28’S, 44˚57’W, 3587–3660 m. coll. US Antarctic Research Program. (1 dry spec. R=2.3, r=1.1); USNM E13501. South of South Georgia, South Atlantic Ocean. 56˚53’ S, 37˚33’W, 3138–3144.0 m. Coll. R/V Eltanin (2 dry specs.R=2.9, r=1.2; R=3.3, r=1.3). E 13502, SE of South Orkney Islands, Antarctica. 62˚05 S, 40˚44’W. 3250–3285.0 m. Coll. R/V Eltanin (1 dry spec. R=2.6, r=1.1). CASIZ 162495. Near Livingston Island, 61.00˚43.70” S 60.00˚42.62”W, 2856– 2852.9 m. Coll. R. Mooi & S. Lockhart, 19 Feb 2002. (31 wet specs., R=0.9, r=0.4; R=0.9, r=0.4; R=1.0, r=0.5; R=1.3, r=0.5; R=1.4, r=0.6; R=1.5, r=0.6; R=1.6, r=0.6; R=1.6, r=0.7; R=1.7, r=0.6; R=1.7, r=0.7; R=1.7, r=1.0; R=1.8, r=0.7; R=1.8, r=0.7; R=1.9, r=0.7; R=1.9, r=0.8; R=2.0, r=0.8; R=2.0, r=0.8; R=2.0, r=0.8; R=2.0, r=0.8; R=2.1, r=1.0; R=2.3, r=1.0; R=2.4, r=0.9; R=2.4, r=1.1; R=2.5, r=1.0, R=2.6, r=1.0, R=2.6, r=1.1, R=2.6, r=1.1; R=2.7, r=1.0; R=2.7, r=1.1; R=3.0, r=1.3; R=3.2, r=14); CASIZ 163080. Elephant Island, 60.00˚38.79”S, 53˚57.42’W 2896– 2895 m.(1 wet spec. R=1.2, r=0.6); CASIZ 163081. Near Elephant Island, 60.00˚38.35”S, 53˚57.36’W, 2893.2–2893.6 m. (1 wet spec. R=1.0, r=0.4)

Description. Body form stellate (R/r=2.0–2.6) with arms elongate. Disk swollen, convex. Interradial arcs rounded.

Abactinal plates scalar, flattened, overlapping over one another forming mosaic-like pattern if viewed from coelomic side (Fig. 6 A). Fasciolar grooves weakly present. Abactinal body wall thin. Abactinal plates polygonal to irregularly shaped, relatively small, with six to nine plates extending from superomarginal to superomarginal at base of each arm. Carinal series of abactinal plates relatively conspicuous, forming two to three discrete transverse rows on arms, which are aligned with spine rows on adjacent superomarginal plate series (Fig. 6 B, D). Each plate with spines, one to three, short, blunt, cylindrical and densely clustered on each abactinal plate (Fig. 6 B, C). Peripheral accessories absent. Other than short spines, bivalve pedicellariae are the only primary structures present on abactinal surface, usually only on disk rather then arms (Fig. 6 C). Madreporite round with deep sulci, flanked by five plates. Papulae absent.

Superomarginal and inferomarginal series are aligned 1:1, each with approximately 24–36.

plates per interradus (from armtip to armtip) (Fig. 6 F). Plates are rectangular with L>W. Superomarginals and inferomarginals each have two to four blunt, cylindrical spines in a linear series across the surface of the marginal plate, which is aligned in series with those plates on the abactinal arm plates (Figs 6 D, F). Aside from the spines, pedicellariae and other accessories, such as granules or spinelets are absent from the marginal plate surface. Terminal plates round and bare, lacking spines or other accessories.

Actinal interradial regions are large with one to three (usually two) chevron series present with relatively few plates, between the inferomarginals and the adambulacrals (Fig. 6 E). Plate boundaries are obscured by membrane (Fig. 6 G). Each plate bears one to two, usually one large cylindrical blunt spine per plate. Spinelets, small, thorny, irregularly distributed on actinal intermediate surface (Fig. 6 G). Bivalve pedicellariae, similar to those on the abactinal surface are also irregularly present on the actinal surface. These pedicellariae are typically bivalve but can be trivalved and often irregularly shaped (Fig. 6 G). Sometimes these are as large as the other actinal plates and are present on the center of each interradius, but there was no regular pattern observed in every specimen. Oral region is deeply concave in some specimens

Adambulacral plate boundaries obscured by membrane, rectangular to quadrate in outline. Furrow spines, two, relatively slender, cylindrical, circular in cross-section (Fig. 6 G). Single subambulacral spine present, approximately twice the thickness, circular in cross-section separated from furrow spines by discrete space. Small thorny spinelet present at base of subambulacral spine adjacent to actinal interradial region. Oral plates with three furrow spines and one oral spine projecting into the mouth per plate. Suboral spines each with one large and two smaller sized spines.