Narella gilchristi, (THOMSON, 1911)

Taylor, M. L. & Rogers, A. D., 2017, Primnoidae (Cnidaria: Octocorallia) of the SW Indian Ocean: new species, genus revisions and systematics, Zoological Journal of the Linnean Society 181, pp. 70-97 : 73-79

NARELLA GILCHRISTI ( THOMSON, 1911)

( FIGS 4, 5)

Stachyodes gilchristi Thomson, 1911: 885 , pl. 44, fig. 1, pl. 45, fig. 2a,b; – Stiasny, 1940: 34, text-fig. H, pl. 1, fig. 8.

Stachyodes gilberti Kükenthal, 1919: 468 (?misspelling of S. gilchristi ); – 1924: 316.

Stachyodes capensis Thomson, 1917: 25 , text-fig. 5, pl. 3.

Narella gilchristi – Williams, 1992: 272–276, figs. 1G, 63–65.

Material examined: NHMUK 2016.19 ( JC066-3824 ) , RRS JamesCook,sta.7,ev.10,SapmerBank, 36°47.798′S, 052°6.315′E, 300–700 m, 7 December 2011; NHMUK 2016.20 ( JC066-216 ) , NHMUK 2016.21 ( JC066-217 ) , NHMUK 2016.22 ( JC066-212 ) , RRS James Cook, sta. 4., ev. 2, Coral Seamount, 41°20.708′S, 42°55.2922′E, 1365 m, 12 November 2011; NHMUK 2016.23 ( JC066- 640 ) , NHMUK 2016.24 ( JC066-641 ) , NHMUK 2016.25 ( JC066-643 ) , NHMUK 2016.26 ( JC066-644 ) , NHMUK 2016.27 ( JC066-645 ) , NHMUK 2016.28 ( JC066-647 ) , sta. 4, ev. 4, 41°22′48.780′S, 42°51′09.109′E, 1332 m, 13 November 2011; NHMUK 2016.29 ( JC066-716 ) , NHMUK 2016.30 ( JC066-717 ) , NHMUK 2016.31 ( JC066-718 ) , NHMUK 2016.32 ( JC066-719 ) , sta. 4, ev. 4, Coral seamount, 41°22′48.780′S, 42°51′09.109′E, 800–1332 m, 13 November 2011. SEM stubs – T146-148 .

Description: Largest colony ( NHMUK 2016.19, JC066- 3824) 40 cm tall, ~ 14 cm wide, lyrate branching (remainder are mostly fragments), some secondary dichotomous branching ( Fig. 4h). Branching sometimes in more than one plane with different planes interconnected by thin branchlets. Branches thick, up to 8.0 mm diameter, rigid. Axis smooth, gold. No holdfast.

Calyces mostly in whorls of 6–7 ( Fig. 4a, g), whorls modestly spaced, ~7 whorls per 3 cm of branchlet, rarely 8 ( Fig. 4b, c). Whorl diameter ~5.0–6.0 mm. Calyces 2.5–3.0 mm tall ( Fig. 4e), each with three pairs of abaxial ( Fig. 4a, e) and one pair of square adaxial body-wall scales.

Basal scales ( Fig. 5d, e) tall, 2.5–3.0 mm, slender, 1.0– 1.5 mm wide, standing almost perpendicular to branchlet, forming a closed ring, distal quarter to third is a projecting lobe ( Figs 4e, f, 5d, e). One pair of adaxial body-wall scales. Two to three small, thick, irregular sclerites ( Fig. 5h) at base of basal scales, could be described as infrabasal. Medial scales ( Fig. 5i, j) slightly shorter than buccal scales, 1.3–1.4 mm long, 1.1–1.3 mm wide, squarish in shape. Buccal scales ( Fig. 5f, g) 1.5–1.6 mm long, 1.3–1.4 mm wide, flared distally, with fine ridging along inner distal edge; lateral edges curve around side of polyp, extending to form cowl around operculum; distal inner edges also finely ridged. Distal edge of medial and buccal scales thin, therefore sometimes broken and jagged.

In lateral view operculum mostly hidden by cowl ( Fig. 4b, c, e). Opercular scales (330–400 μm tall, 150– 325 μm wide) with large keel (side view – Fig. 5a). Like congenerics, opercular size decreases progressively from ab- to adaxial. Opercular scale shape ranges from lanceolate ( Fig. 5b) to ones bearing one wide lobe laterally ( Fig. 5c). Opercular scale outer surface often deeply concave, mirroring inner, keeled surface. No tentacular scales observed.

Outer surface of all above scales smooth; close-up with fine, low granular lines ( Fig. 5m). Inner surfaces vary, tending to be covered with dense granular markings basally ( Fig. 5n), with a smooth or finely ridged distal area.

Coenenchymal scales (300–400 μm) irregular in shape with upturned edges, forming thick mosaic of cover over axis ( Fig. 5k). Secondary inner layer of small irregular coenenchymal scales present ( Fig. 5l).

Known distribution: SW Indian Ocean, 90–1365 m depth.

Remarks: Four gall-forming mesoparasites from the Infraclass Ascothoracida, Subphylum Crustacea, were found on specimen NHMUK 2016.19, JC066-3824. Colony, or many polyps of the colony, is brooding. Basal scales can be modified and attached to adjacent sclerites to form tubes for commensal polychaete worms.

Comparisons: The sclerites of N. gilchristi presented here are near identical to those of holotype material held at the Smithsonian National Museum of Natural History ( NMNH, S. Cairns, personal communication). Specimens examined here appear to have thinner scales than those described in Williams (1992). They have sparser whorl placement and the basal scales are taller. However, polyp structure and other sclerite sizes and shapes are very similar to those described in Williams (1992). Taking both these sources into account we thus consider these specimens to be N. gilchristi .

Lyrate colony shape is confirmed only in four species of Narella : N. gilchristi , N. valentine sp. nov., N. compressa and N. bellissima .

On first glance N. bellissima is very similar to N. gilchristi , with smooth outer surfaces on scales and basal scales departing branchlets at 90°; however, the former has smaller polyps, whorls much more densely placed than the latter, and tentacular scales. Calyces of N. valentine sp. nov. are far smaller than those of N. gilchristi . Polyps of the former have a peaked basal cowl whereas those of the latter have two basal scales with rounded lobate projections. The species also differ in number of polyps per whorl and whorl density. The holotype of N. compressa would appear to be half of what may well be a lyrate colony ( Kinoshita, 1908; plate 3, image 25). Polyps also have a tall basal scale rising perpendicular from the branchlet, similar to N. gilchristi . The polyps of N. compressa are smaller and there are 11–12 whorls per 3 cm of branchlet; far more than are found in N. gilchristi presented here. A fresh assessment of Kinoshita’s material is required to confirm that N. compressa is not conspecific with N. gilchristi .

Thick mosaic-like coenenchymal scales are found on N. clavata , N. mosaica , N. compressa and N. gilchristi . Although basal scales of N. gilchristi can be as tall as N. clavata , they are not laterally fused and the coenenchymal layer is not as thick in N. gilchristi . Narella mosaica has shorter basal scales than those found in N. gilchristi and thus does not have the large cowl formed by the basal scales (seen in Fig. 4f).

There are three species where branching pattern is unknown: N. ornata , N. hawaiinensis and N. ambigua . Narella gilchristi differs from N. ornata in having more polyps per whorl and taller basal body-wall scales that are rounded and lacking ridges. There is little detail in the original description of N. ambigua ; the few details of polyp size and number of calyces per whorl are similar to N. gilchristi ; however, until examined these species should remain separate and valid. Narella hawaiiensis has fewer calyces per whorl than N. gilchristi , shorter, less robust basal scales that have ridges (something lacking in the latter), sclerites that are thinner, and more brittle, and ridged coenenchymal scales; very different characters to that found in the latter.