Radicipes stonei Sp., sp.

Radicipes stonei sp. nov.

Figs. 2 C, 6

Radicipes verrilli.— Stone & ShotWell, 2007: p. 107, Appendix 2.1 (table). Radicipes Sp. — Watling et al., 2011: p. 47, fig. 2.2G–H, p. 70, fig. 2.5.

Types. Holotype: J 2105-4-1 (USNM 1418007). Paratypes: J 2096-6-1, 52°23’34.2"N, 174°53’3.24"W, 2153 m (USNM 1418006, one specimen); JD-092, 53°27’12”N 163°23’22”W, 3580 m (Derickson Seamount, Aleutian Islands) (USNM 1081191, one specimen); JD-093 53°00’53”N 161°14’35”W, 3179 m ( Derickson Seamount, Aleutian Islands) (USNM 1081144, one specimen).

Type Locality. 51°53’12.18"N, 178°21’27.18"W (northwest of Tanaga Island, Aleutian Islands), 2107 m.

Description. Colonies white, delicate, golden-iridescent aspect and coiled both clockwise or counterclockwise in ascendant direction. AXis 2.9 mm maXimum diameter. First one-third of colonies (up to 12 cm) usually without polyps. Polyps 1.0–3.0 mm long, inclined 45° to 90° in relation to aXis, linearly disposed on only one side of colony, in a frequency of about three polyps per centimeter, spaced 2.0–5.0 mm from each other, but ranging from one to five polyps per centimeter. Density of polyps decreasing toward branch tip and distance between polyps increasing in the same direction. Body wall of polyps with rods, longitudinally arranged, some with a flat end and (rarely) completely flattened (scale-like), 0.13–0.86 mm long and 0.03–0.10 mm wide (Figs. 2 C, 6A). AdaXial side with large supporting curved rods, with slightly flattened and rounded tips. Outer lateral side with flattened rods, half the length of abaXial supporting rods. Size of rods decreasing toward the oral portion of tentacles. Inner lateral and adaXial side with sparse flattened scales with almost blunt tips, sometimes naked. Coenenchymal scales longitudinally grooved and with at least one flattened tip, longitudinally arranged, uniformly surrounding aXis from base to polypar portion (eXcept in juvenile colonies), gradually changing in length and form in the same direction. Basal coenenchymal scales larger, more deformed and more tuberculate than those from polypar portion, 0.15–0.68 mm long and 0.05–0.12 mm wide (Fig. 6 C). Juvenile specimens with four to eight longitudinal sclerite rows along the coenenchyme. In basal sterile portion, short scales and rods present, oval or waisted (8-shaped) in shape. In polypar portion scales are as long as the rods from the body wall. In polypar line, rods from the body wall frequently connect coenenchyme between two adjacent polyps. Tentacular rods smaller with slightly flattened ends, 0.14–0.3 mm long and 0.02–0.06 mm in width (Fig. 6 B). Pinnular rods completely flat, with ridges and serrate margins, 0.06–0.14 mm long and 0.01–0.04 mm wide (Fig. 6 D).

Comparisons. Along with R. pleurocristatus and R. aureus, this species shares the longest polyps and body wall sclerites in the genus. Colonies of R. stonei sp. nov. are quite delicate, but their polyps are similar to those of R. pleurocristatus in general aspect (especially in comparison with the holotype of R. verrilli). The ratio between the maXimum length of the polypar and coenenchymal sclerites is another distinctive feature. In R. pleurocristatus, the length of the coenenchymal sclerites never reaches more than half that of those from the body wall, whereas in R. stonei sp. nov. they are nearly the same size. Radicipes pleurocristatus can also have slightly flattened short rods close to the base, transversely or irregularly arranged, whereas R. stonei sp. nov. has only scales longitudinally disposed. The latter has less sculptured coenenchymal scales with more regular margins and with at least one much flattened tip. Furthermore, the two species colonize different bathymetric ranges (Table 1).

Etymology. Named in honor of Robert P. Stone, coral and sponge authority of the Alaskan region.

Remarks. This species was probably photographed during NOAA cruises in the Aleutian Ridge, forming dense meadows in muddy bottoms, and this record is already mapped and available in the literature (see Watling et al., 2011, p. 47, fig. 2.2G. and p. 70, fig. 2.5). The species was first recorded at the location as R. verrilli by Stone & Shotwell (2007).

DNA sequences obtained from the holotype (USNM 1418007) for COI+igr+msh1 are similar to the specimen sequenced by McFadden et al. (2011) and Pante et al. (2012) from station J209661 (Alaska: uncorrected p -distance = 0.07%) (see GenBank accessions KY748360 and KY748361, unpublished data). Analyses made by the authors mentioned above show an isolation of the Alaskan lineage, supporting the establishment of the new species. Genetic distances (uncorrected- p) of R. stonei sp. nov. to other non-Alaskan Radicipes sequences range from 0.21% to 0.92% (unpublished data).

The morphological similarity as well as the closeness with the geographical range of R. pleurocristatus indicate that these two species may have a common origin. In fact, the analyses by Pante et al. (2012) (e.g. NIWA 28821, NIWA 45304 and NORF47/2-NIWA) show a common origin of Radicipes species from Alaska (R. stonei sp. nov.), Solomon Islands, Western Australia, New Caledonia and New Zealand.

If we consider one of the specimens sequenced by Pante et al. (2012) as being R. pleurocristatus, there is at least one more undescribed species inhabiting the Indo-Pacific.

Distribution. Gulf of Alaska (Derickson Seamount) and Aleutian Islands, 1207–3580 m.