Caulophacus (Caulophacus) adakensis Reiswig & Stone 2013, n. sp.

Caulophacus (Caulophacus) adakensis n. sp.

(Figs. 19 & 20, Table 10)

Synonymy. Caulophacus (Caulophacus) sp. nov. Stone et al., 2011: 35.

Material examined. Holotype: USNM# 1196557, ROV ' Jason II' from RV ' Roger Revelle', dive J2100, 01 August 2004, Adak Canyon, 13 km SE of Cape Yakak, Adak Island, Aleutian Islands, Alaska, 51º31.531'N, 177º05.417'W, 1806 m, dry & ethanol.

Other material. C. (C.) aff. adakensis, USNM # 1196558, ROV 'Jason II' from RV ' Roger Revelle', dive J2096, 28 Jul 2004, North Aleutian Slope, 32.8 km N of Atka Island, Aleutian Islands, Alaska, 52º23.570'N, 174º53.077'W, 2180 m, long dead, dry.

Description. The truly magnificent holotype (Figs. 19A, B), an extremely large mushroom-shaped body borne on a long rigid stalk, was collected intact but the stalk was intentionally broken for storage and shipping. Total length of the dried specimen, with body canted unnaturally on stem during drying, is 90.3 cm; in natural state the length was 75 cm. The body disc (dry) is 31 x 40 cm in diameter and up to 38.5 mm in thickness. Both lower (= inhalant or dermal) (Fig. 19C) and upper (= exhalant or atrial) (Fig. 19D) surfaces are smooth, lacking prostalia, with loose spicule lattices covering the subsurface canal entrances, 3–5 mm in diameter in the lower surface and 5–8 mm in diameter in the upper surface, easily visible through the covers. A horizontally extensive subsurface space underlies the covering lattice in the inhalant area, but this is lacking in the exhalant area; there the exhalant canals run directly to the covering lattice without an intervening subsurface cavity. The 68 cm long stalk tapers from its insertion on the lower body surface to a diameter of 2.1 cm at midpoint and 1.8 cm at its minimum just above the large foliate attachment disc. It is hollow with three longitudinal canals evident at the point of section (Fig. 19E) but a single 7 mm diameter canal in the lower stalk. The margin at the junction of inhalant and exhalant surfaces is sharp and lacking obvious large marginal spicules (Fig. 19F). Spicules are entirely loose in the body, dominated by bundles of long diactins oriented in all directions (Fig. 19G). In the stalk the main diactins do not occur in bundles but are individually oriented obliquely; they are all fused by spot junctions at contact points and short synapticula between spicules not in direct contact.

The second specimen (Fig. 19B smaller) is a dead, hollow, cylindrical stalk with a foliose basal disc similar to that of the holotype; it is 35.4 cm long and tapers in diameter from 2.8 cm at top to 1.5 cm at its narrowest point. It contains a single axial canal 1.1 cm in diameter at the top. It has been dead for some time and is entirely washed out. Attribution of this specimen to the same taxon as the live spicule-bearing specimen is based upon similarity in size and form of the two stalks, their geographic proximity, 178 km between collection sites, and lack of an alternate appropriate Caulophacus species in the area.

Megascleres are hypodermal and hypoatrial pentactins, parenchymal macrohexactins, dermal and atrial pinular hexactins, and parenchymal diactins; all share the same ray end pattern: roughened subterminal area ending in a bare rounded cap (spicule dimensions are given in Table 10). Hypodermal spicules are mainly pentactins (85%, Fig. 20A) but some (15%) have one tangential ray undeveloped and are irregular tetractins. The pentactins have strong, tapering rays, usually without proximal spines but 20% of tangential rays and 64% of proximal rays have strong spines adjacent to the spicule center. Ray ends have fine subterminal spined areas but the tips are smooth and rounded. Hypoatrial spicules (Fig. 20B) are all pentactins similar to those of the dermal side, but slightly smaller and thinner. They more commonly have proximal spines (Fig. 20B 1) on 64% of the tangential rays and 80% of the proximal rays. Parenchymal macrohexactins (Fig. 20C) are larger than the surface pentactins, but ray form is similar. Proximal spination occurs on at least one ray in 80% of these but spination on all six rays is uncommon (20%, Fig. 20C 1). Parenchymal stauractins occur occasionally. Dermalia (Fig. 20D), atrialia (Fig. 20E), and marginalia are similar pinular hexactins with bushy distal rays and vertically spined tangential and basal rays. Great variation of pinular ray form occurs in spicules of both surfaces but the dermal pinular rays are shorter and thicker than those of the atrial side. Pinular spicules are uncommonly pentactine (3%), and most pinular rays have blunt tips that are overgrown by scales—terminal spines occur in only 25% of the pinules. Parenchymal diactins (Fig. 20F) have inflated roughened ends with a small smooth rounded cap. Thinner spicules have four well-developed central knobs but they are insignificant or undetectable in thicker spicules.

Microscleres are all variations on a basic form—coarsely-thorned terminal rays ending in hemispheric discs with 3–6 large marginal teeth (Fig. 20G). Discohexatins (Fig. 20H) are the largest but least common (15%) of the microscleres. Hemidiscohexasters (Fig. 20I) with 1–3 terminals are the most common (60%) and intermediate in size. Discohexasters (Fig. 20J) with 2–4 terminals per primary ray are smallest and intermediate in abundance (25%). The latter two forms have very short terminal rays and some may be considered discasters.

Loose spicules in the stalk are hypodermal pentactins and dermal pinules. The hypodermal pentactins are similar to those of the body proper but all lack proximal spines. The pinules consist of approximately equal numbers of hexactine and pentactine forms. A few have very long pinular rays. No microscleres were found in the stalk.

Etymology. The species name, adakensis, refers to the location of collection, Adak Canyon.

Remarks. The new Aleutian Islands spicule-bearing Caulophacus clearly belongs to subgenus Caulophacus, presently with 18 valid species, by virtue of its possession of only discoid microscleres. Using the simple character of microsclere form, the new specimen is distinguished from 11 species of C. (Caulophacus) by having hemidiscohexasters as its most common microsclere (absent or rare in those 11 species). It is distinguished from 5 additional species by having only spherical discohexasters (stellate or lophoid forms occur in those 5 species). It is most similar to C. discohexaster Tabachnick and Lévi, 2004 but differs in having much larger spherical discohexasters, the mean diameter of the Aleutian Islands specimen (82–121–165 µm) being outside the entire size range of the New Caledonian form (72–108 µm). Comparison of the new form with C. antarctica Schulze and Kirkpatrick, 1910 is not considered possible since very sparse spicules described from the latter (washed-out stalks) are very likely to be extrinsic in origin, or at least not convincingly proper. The Aleutian Islands Caulophacus is thus considered an easily distinguishable new species, designated here as Caulophacus (Caulophacus) adakensis.

Review of all video footage collected with the ROV 'Jason II' indicates that this is an uncommon species, occurring singly on bedrock and large boulders at depths between 1326 and 2680 m. The lithodid crab Paralomis verrilli was using the holotype as an elevated perch. Other associated fauna include the demosponge Abestopluma ramosa and the large brittle star Gorgonocephalus eucnemis.