Octocorallia, Haeckel, 1866

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 : 20-22

Subclass Octocorallia

Order Alcyonacea

Suborder Calcaxonia Grasshoff, 1999 1

Family Primnoidae Milne-Edwards, 1857

Thouarella Gray, 1870

Primnoa Valenciennes, 1846 : pl. 12, figs 2, 2a (only images); Milne-Edwards 1857: 140; Gray 1857: 286; 1859: 483; Kölliker 1865: 135

Thouarella Gray, 1870: 45 ; 1872: 746; Studer 1878: 649; 1887: 50; (in part), Wright & Studer 1889: 59–61 pl. 11, 14; Versluys 1906: 22–24; Thomson & Henderson 1906: 38–41 (comparison table); Kükenthal 1907: 202–208; 1908: 10–11; 1912: 292; (in part) Bayer 1961: 294 (key to genus); 1981: 936 (key to genus); Broch 1965: 24; Stibane 1987: 17–26, pl. 1(4), 2(4); Williams 1992: 277

Rhopalonella Roule, 1908: 2–3 , pl. 1, figs 5–8

? Hookerella Gray, 1870: 45

Thouarella (Diplocalyptra) Kinoshita 1908b: 454 , 457 (key to subgenus), pl. 17, fig. 2 (in Japanese, English translation at USNM); 1908c: 517–519 (in Japanese, English translation at USNM); 1908d: 52 (key to subgenus, in German)

Not Primnodendron Nutting 1912: 71–72 , pl. 9, fig. 2, 2a; pl. 19, fig. 4

Thouarella (Epithouarella) Kükenthal 1915: 150–151 (key to subgenus and species); 1919: 435 (key to subgenus and species); 1924: 299 (key to subgenus and species); Bayer 1956: F220

Thouarella (Euthouarella) Kükenthal 1915: 149–150 (key to subgenus and species); 1919: 414–415 (key to subgenus and species); 1924: 292 (key to species); Bayer 1956: F220; Bayer & Stefani 1989: 455 (key to subgenus); Cairns 2006: 176, 187–188

Thouarella (Parathouarella) Kükenthal 1915: 150 (key to species); 1919: 425–426 (key to species); 1924: 296–297 (key to subgenus and species)

Thouarella (Thouarella) : Bayer 1956: F220; Bayer & Stefani 1989: 455 (key to subgenus); Cairns 2006: 176

Definition

The colony consists of a main stem, generally simple with rare divisions. Branching is either pinnate, dichotomous, or in a bottlebrush manner (where it is branched in at least 3 directions). Polyps are isolated, paired, or in whorls, generally upwardly inclined at 45–90˚ from the branchlet. Polyp heads are wider than the base and completely protected by 5-8 rows of longitudinally arranged scales each of 5–15 (generally 5–8) scales. Adaxial body-wall scales are often reduced in size and number.

A well-developed, conical operculum consists of 8 operculars; on rare occasions accessory operculars are found beneath the operculum. Opercular scales are lanceolate, arrowhead-shaped, or tongue-shaped, often with a keel. The operculum is surrounded by 8 marginals, often in 2 alternating rings of 4 because the operculum circumference is not large enough to accommodate 8 adjacent marginals. Marginals are keeled on their inner surface; keels are simple, channelled, or a complex multi-keel. Marginals often fold over the operculum, with the keel fitting into the concave outer opercular surface. Opercular scales are lanceolate, arrowhead-shaped, or tongueshaped, often with a keel.

Distribution

A wide global distribution: South Africa, Chile, western Atlantic from Burdwood Bank to northern Florida, Japan, Aleutian Islands, Australia, Tasman Sea, New Zealand, especially common around Antarctica /sub-Antarctic. Found from 60–2100 m depth.

1. Calcaxonia are not monophyletic in recent phylogenetic studies ( McFadden et al. 2006; Taylor et al., in prep), however a taxonomic revision has not been completed.

Comparisons

Thouarella was placed close to three genera within the most recent phylogenetic morphological analysis of Primnoidae ( Cairns & Bayer 2009) : Pyrogorgia Cairns and Bayer, 2009 ; Amphilaphis Studer and Wright , in Studer, 1887; and Convexella Bayer, 1996 . The bottlebrush form of Thouarella can also be easily mistaken for several other genera with similar branching morphologies.

Species of Convexella have marginal scales with a smooth inner surface whereas those of Thouarella have a keel.

The only species of Thouarella that may be described as having the distinctive “radiating spinose ridges” ( Cairns & Bayer 2009) found on the outer surface of body-wall scales of Pyrogorgia , is T. striata . However, the polyps of the latter are isolated and the colonies bushy, which is very unlike the uniplanar, dichotomous colony shape and polyp whorls of Pyrogorgia species , making Thouarella and Pyrogorgia clearly distinct.

According to Cairns and Bayer (2009) Amphilaphis differs from Thouarella in having polyps with eight ‘complete’ rows of body-wall scales, whereas the two adaxial rows of body-wall scales in Thouarella are relatively reduced in size. This scale size reduction is a particularly difficult character to quantify. Amphilaphis species are not considered within this revision as it was written prior to the recent revision of the genus Amphilaphis (Zapata- Guardiola & López-González, 2012).

Thouarella is most closely related, in terms of polyp morphology, to Plumarella and Amphilaphis . Species of Plumarella are uniplanar, often plumose, whereas only six species of Thouarella are truly uniplanar, although some bottlebrush arrangements are compressed giving a uniplanar appearance (e.g. T. brucei ). The polyps of Plumarella species are usually placed in an alternately biserial manner (there are a few species with isolated polyps), whereas within Thouarella only T. bipinnata Cairns, 2006 , T. minuta , and T. koellikeri have polyps that are approximately biserial. Marginal scales of Plumarella species are fixed, i.e. do not fold over the operculars (although this is a difficult character to judge, especially in species with long marginals, e.g. T. variabilis ). Species of Plumarella have eight rows of body-wall scales; the number of scales in a row can be reduced adaxially, which is very similar to Thouarella . Polyps of Plumarella often stand at 90° to the branchlet, whereas those of Thouarella are mostly at 45–80°. All of these characters are not exclusive to either Thouarella or Plumarella . The only diagnostic character to separate the two genera is the presence or absence of keeled marginals; a keeled marginal is considered a character of Thouarella , unkeeled is Plumarella ( Cairns 2010) .

As already mentioned, there are a number of genera with bottlebrush colonies that are often mistaken for Thouarella . The similarities and differences between these genera and Thouarella are listed below:

Colonies of Dasystenella Versluys, 1906 have a bottlebrush formation and are often misidentified as Thouarella . Dasystenella primarily differs from Thouarella in having polyps with just five marginal scales, compared to eight in the latter. Only one species of Dasystenella has been described ( D. acanthina ) yet much variation was observed amongst specimens seen throughout this study. Dasystenella requires further investigation as there is likely more than one species ( Cairns 2006).

Although it has a bottlebrush colony shape, the newly described genus Tauroprimnoa Zapata-Guardiola & López-González, 2010 differs from Thouarella in having polyps with only four marginals.

The recently described bottlebrush genus Digitogorgia Zapata-Guardiola & López-González, 2010 has marginals with a smooth inner surface and numerous irregular longitudinal rows of body-wall sclerites and is thus distinct from Thouarella .

Fannyella (Scyphogorgia) Cairns and Bayer, 2009 also has a bottlebrush form and is separated from Fannyella (Cyathogorgia) Cairns and Bayer, 2009 only by branching morphology (the latter being dichotomously branched, verging on pinnate). Fannyella Gray, 1872 has ascus-type body-wall scales, which have a distinct boundary separating their exposed distal area from the covered proximal area, whereas Thouarella has even, unsectioned, non-ascus body-wall scales.

Colonies of Parastenella Versluys, 1906 are mostly uniplanar, however, they can be bushy with isolated, paired, or whorled polyps and could be easily mistaken for Thouarella . The most distinctive difference between these two genera is the morphology of the distal border of the marginal scales of the polyps; marginal scales of Parastenella polyps have a fluted hollow structure whereas those of Thouarella are unfluted.

Species Group 1—isolated polyps