Plumarella diadema ( Cairns, 2006 ), 2013

TAYLOR, M. L., CAIRNS, S. D., AGNEW, D. J. & ROGERS, A. D., 2013, <strong> A revision of the genus <em> Thouarella </ em> Gray, 1870 (Octocorallia: Primnoidae), including an illustrated dichotomous key, a new species description, and comments on <em> Plumarella </ em> Gray, 1870 and <em> Dasystenella </ em>, Versluys, 1906 </ strong>, Zootaxa 3602 (1), pp. 1-105 : 92-94

Plumarella diadema ( Cairns, 2006)

Fig. 36

Thouarella (Thouarella) diadema Cairns, 2006: 181–184 , figs 10–11; Cairns & Bayer 2009: 28 (listed)

Thouarella sardana Zapata-Guardiola & López-González, 2010b: 136–139 , figs 2c,d, 5, 7

Plumarella diadema Cairns 2011: 8

Material examined: Holotype, USNM 1078187, R/V Calypso , sta. 1776, 241 km SE of Sao Paulo, Brazil, 24˚54’04”S, 44˚26’00”W, 1000 m; Paratype of Thouarella sardana USNM 1123420, Antarktis XIX/5, R/V Polarstern, sample no. PS61/164–01, west of South Georgia Island, sub-Antarctic, 53˚23’48”S, 42˚42’02”W, 312–321 m, 9 Apr 2002 ; Paratype of T. sardana, USNM 1123420; USNM 1130273, USNM 1129185 and USNM 1130274 (from same location), R/ V Eltanin, cruise 22, sta. 1536, west tip of South Georgia Island, sub-Antarctic, 54˚30’S, 39˚20’W, 659–686 m, 8 Feb 1966 .

Other material: USNM 98090, R/ V Eltanin, cruise 6, sta. 339, west of Beauchene Island , south of Falkland Islands, sub-Antarctic, 53˚06’S, 59˚27’W, 512–586 m, 3 Dec 1962 , 2 colonies; USNM 98095 and USNM 98094 (same location), R/ V Eltanin, cruise 9, sta. 740, east of Cape Horn , Drake Passage, Tierra del Fuego, Argentina, 56˚06’S, 66˚24’W, 384–494 m, 18 Sep 1963 ; USNM 98098 and USNM 77396 (from same location), R/ V Eltanin, cruise 22, sta. 1592, Burdwood Bank , Scotia Sea , 54˚44’S, 55˚33’W, 1647–2044 m, 14 Mar 1966 ; USNM 98089, R/ V Eltanin, cruise 5, sta. 283, west of Adelaide Island , Antarctic Peninsula, 66˚26’S, 74˚46’W, 3350–3693 m, 25 Oct 1962 ; USNM 77396, ZMH, R/ V W. Herwig, sta. 226, SW Atlantic , 33˚53’S, 51˚52’W, 460 m, 11 Jun 1966 ; ZMH, R/ V W. Herwig, sta. 191, SW Atlantic , 46˚13’S, 59˚49’W, 805 m, 17 Jan 1971 ; USNM 98101, R/ V Professor Siedlecki, cruise 86–01, sta. 2, Shag Rocks, South Georgia Island, Sub-Antarctic , 53˚20’S, 42˚42’W, 417–514 m, 29 Nov 1986 .

Description

See the holotypic publication for full taxonomic description ( Cairns 2006). We add that that the specimens reported herein, including the holotype of T. diadema (now Plumarella diadema ), usually reveal 2–8 small accessory operculars beneath the operculars.

The polyp arrangement was originally described as “roughly alternating” ( Cairns 2006, p.181), however, with the wider body of material examined here, we conclude that this is not strictly true as usually the polyps originate from all sides of the branchlet. Also, P. diadema can have a pinnate colony structure ( USNM 98089, Fig. 36b,c ) and most colonies appear bilateral, although they have branching in 3 directions and are thus technically bottlebrush.

The marginals of some polyps of USNM 98030 have double spines and operculars that are bifurcate, likely a variation in a single colony ( Fig. 36d,e ).

Distribution

Additional specimens expand the range of P. diadema from São Paulo, Brazil, south to the tip of Argentina and east to South Georgia Island, sub-Antarctic. The depth of occurrence ranges from 278–3693 m.

Remarks

Thouarella sardana was differentiated from T. diadema because it has accessory operculars ( Zapata-Guardiola & López-González 2010b). However, the holotype of T. diadema also has accessory operculars (although they do not occur in every polyp), which were not mentioned specifically in the original description ( Cairns 2006), and thus these species are considered to be conspecific, as was suggested in Cairns (2011). Thouarella diadema has no keel on the inner surface of its marginals and it is thus considered to be a Plumarella , in agreement with Cairns (2011).

A deep-living specimen of P. diadema (USNM 98098, 1647– 2044 m), did not have accessory operculars in any of the polyps studied but was identical in every other respect to this species. The deepest specimen, USNM 98089 (3350–3693 m), is pinnate but the polyps and sclerites are identical to those of P. diadema .

One specimen from SMF (WH 1971, sta. 191) has much smaller polyps, a maximum height of 2 mm (half the size of other specimens) and a very bushy, ramified branching structure. Some marginal scales of this specimen have a wider, winged base and a smoother inner surface. However, in all other respects, this specimen was identical to P. diadema and is thus included here; it may be a juvenile specimen.

Comparisons

Plumarella diadema differs from Plumarella (formerly Thouarella ) bayeri Zapata-Guardiola & López-González 2010b in having more acutely triangular/arrowhead-shaped operculars, and colonies with bushy/bottlebrush rather than dichotomous branching.

Thouarella variabilis is very similar to P. diadema except polyps on colonies of T. variabilis are smaller and the spines of the marginals are keeled, rather than being channelled and circular in cross-section, as in P. diadema . The difference between these two forms of spines, one keeled, one not, differentiate Thouarella and Plumarella . Additionally, operculars on the polyps of T. variabilis tend to be narrower, leaving visible gaps into the subopercular region when viwed from the anterior, whereas the operculars of polyps of P. diadema are wider, and form a more complete covering.

The long spines of the marginals on polyps P. diadema can be mistaken for those of Dasystenella acanthina , but the polyps of the latter occur in whorls, and that genus is defined by having five, rather than eight, marginal scales.

Figures

FIGURE 36. Plumarella diadema. Holotype, USNM 1078187: a) 6 cm colony; d) inner and e) outer surface of bifurcate marginal. USNM 98089: b) close up of polyps; c) pinnate colony form, 10 cm; c) 10 cm pinnate colony form. Photos by SJ.