Thouarella crenelata Kükenthal, 1907

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 : 48-52

8. Thouarella crenelata Kükenthal, 1907

Figs 18 , 19

Thouarella crenelata Kükenthal, 1907: 205 ; 1912: 302

Thouarella (Epithouarella) crenelata Kükenthal 1915: 151 (key); 1919: 436–438, text figs 216–219, pl. 43, fig. 70; 1924: 300–301; Cairns & Bayer 2009: 28 (listed), fig. 7i–m

Material unavailable: The holotype is held in ZMB however material was too fragile to send from ZMB or MNHWU (where fragments are held). The type locality is eastern Bouvet Island, southern Atlantic Ocean, 457 m depth .

Material examined: USNM 98086 ( SEM stubs T53 & T68, stored at NMNH), R/V Hero , cruise 824, sta. 26–1, Lecointe Island, Brabant Island, Palmer Archipelago , Antarctic Peninsula , 64˚14’03”S, 61˚57’57”W, 238–285 m, 24 Mar 1982; USNM 99148, R/V Marion Dufresne, cruise 42, sta. 22, Mac Robertson Land, Lars Christensen Coast, north of Cape Darnley, Antarctica, 66˚58’S, 72˚52’E, 525 m, 26 Jan 1958; USNM 98160, R/V Hero , cruise 731, sta. 1947, Flandres Bay, Danco Coast, Antarctic Peninsula, 65˚00’31”S, 63˚28’06”W, 204–250 m, 11 Mar 1973; USNM 1128900, R/V Hero , cruise 731, sta. 1939, Wednesday Island, Butler Passage, Palmer Archipelago, Antarctic Peninsula, 64˚58’39”S, 63˚45’46”W, 75–120 m, 9 Mar 1973; USNM 1071563, R/V Hero , cruise 731, sta. 1812, Bismarck Strait, Anvers Island, Palmer Archipelago, Antarctic Peninsula, 64˚51’54”S, 63˚39’45”W, 280–300 m, 19 Feb 1973 ; USNM 80154, R/V Professor Siedlecki , cruise 601, sta. 29, South Georgia Island, sub-Antarctic, 54˚32’S, 39˚05’W, 201–210 m, 3 Dec 1986 ; USNM 98028, R/V Eltanin , cruise 22, sta. 1536, west tip of South Georgia Island, sub-Antarctic, 54˚29’S, 39˚22’W, 659–686 m, 8 Feb 1966 ; USNM 97996, R/V Eltanin, cruise 7, sta. 499, south of Coronation Island, South Orkney Islands, sub-Antarctic, 62˚06’S 45˚08’W to 62˚06’S 45˚10’W, 485 m, 20 Feb 1963 ; USNM 58162, R/V Eastwind, sta. 006C, west of Brabant Island, South Shetland Islands, Antarctic Pensinsula , 64˚50’S, 63˚12’W, 283.5 m, 29 Jan 1966 ; USNM 76900, R/ V Edisto, Deep Freeze IV, sta. 31, Nansen Island, Biscoe Islands, Antarctic Peninsula , 66˚20’S, 67˚47’W, 25 Mar 1959 ; USNM 98030, R/V Eltanin , cruise 22, sta. 1536, 54˚30’S, 39˚20’W, west tip of South Georgia Island, sub-Antarctic, 659–686 m, 8 Feb 1966 ; USNM 84342, R/V Eltanin , cruise 9, sta. 732, South Georgia Island, sub-Antarctic, 53˚36’S, 36˚51’W, 220–265 m, 12 Sep 1963 ; USNM 84343, 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 ; USNM 98102, R/V Professor Siedlecki, cruise 86–01, sta. 3, Shag Rocks, South Georgia Island, sub-Antarctic Ocean , 53˚26’S, 42˚29’W, 294–329 m, 29 Nov 1986 ; USNM 98099, R/V Hero , cruise 702, sta. 510, Antarctic , 64˚48’S, 63˚31”18’W, 219 m, 18 Mar 1970; USNM 1129152, R/V Hero , cruise 721, sta. 1143, Wauwermans Island, Bismarck Strait, Palmer Archipelago, Antarctic Peninsula, 64˚57’11”S, 63˚43’W, 230–260 m, 14 Mar 1972; USNM 1129153, R/V Eastwind, cruise 66, sta. 006C, haul 3, 64˚50’24”S, 63˚12’54”W, 283 m, 29 Jan 1966; USNM 1129151, R/V Hero , cruise 731, sta. 1945, Paradise Harbor, Gerlache Strait, Palmer Archipelago, Antarctic Peninsula, 64˚48’27”S, 63˚05’24”W, 260 m, 11 Mar 1973 ; SMF, EPO5 , 3 , sta. 291, GSN 14, 19 Feb 1989 .

Although no material was located in the Smithsonian collection, or elsewhere from the type locality, many specimens that match descriptions of T. crenelata and a photograph of the holotype ( Fig. 18d ) were located, all from the sub-Antarctic.

Description

The colonies are sparsely branched with the longest specimen ( USNM 98086) measuring 35 cm ( Fig. 18a ). The branchlets are in a bottlebrush arrangement on branches although some colonies appear uniplanar where the branchlets curve in 2 directions. The branchlets are mostly simple with some secondary branching and branchlets are up to 30 mm long, arising in all directions (although most are only in 3–4 directions) at an angle of between 60–90˚. Colonies tend to be dark to light yellow.

The polyps are isolated, clavate ( Fig. 18b–d ), 2.3–3.0 mm high (average 2.1 mm), upwardly inclined at 60–90˚, at a density of 5–11 per cm at the branchlet base, reaching 8–19 at tip. Each polyp has 8 longitudinal rows of scales, 6–10 (average 8) in the abaxial row ( Fig. 18c ) reducing to 6–7 per row adaxially. Sclerites get shorter and wider from polyp tip to base.

The operculars are lanceolate ( Fig. 19c ) to arrow-head shaped ( Fig. 19a,b,d ), 530–710 µm high (average 610 µm), 270–380 µm wide (average 325 µm), with a H:W of 1.7–2.4 (average 1.9). The inner surface has a single large keel (keel side view Fig. 19e ) and there are many lateral projections adjacent to the keel. These multiple sharp lateral ridges lead to an irregular distal edge. Lateral areas above the tuberculate base on the inner surface are relatively smooth with a finely serrate edge. The outer surface has many sharp radial ridges or striations from the central proximal area extending towards the distal edge. However, the centre of the scale is smooth with a deep longitudinal valley ( Fig. 19d ), and there are granules proximally and some tubercles showing at the proximal edge.

The marginals are fan-shaped with a curved to pointed, dentate distal edge ( Fig. 19f,g ). They are 380–510 µm high (average 438 µm), 340–480 µm wide (average 420 µm), with a H:W of 1 (average 0.9–1.2). They bear a large keel on the inner surface with multiple dentate projections ( Fig. 19f ) whilst there are smooth areas adjacent to the keel and sparse tubercules across the proximal half. The outer surface has sparse, large granules, some stretching into radial ridges from the central proximal area and tubercles are also visible at the proximal edge ( Fig. 19g ). The marginals have a serrate lateral edge. The adaxial marginals have a reduced keel with tubercles covering the majority of the inner surface of the scales.

The submarginals are elliptical in shape ( Fig. 19h–l ), 410–450 µm high (average 430 µm), 600–610 µm wide (average 600 µm), with a H:W of 0.7–0.75 (average 0.7). The proximal two-thirds of the inner surface is tuberculate with a smooth band across the distal third. There are 3 or 4 small keels and ridges perpendicular to the distal edge ( Fig. 19j–l ). From a side view the keel and ridges have large serrations. The outer surface is smooth with sparse granules centrally ( Fig. 19h,i ) and rare radial ridges and tubercles proximally. The distal edge has wide serrations and the proximal edge is coarsely lobate.

The body-wall scales are relatively wide, short and elliptical ( Fig. 19m –o ), 600–620 µm (average 610 µm) wide, 290–400 µm high (average 345 µm), with a H:W of 0.5–0.7 (average 0.6). The inner surface is tuberculate with a smooth band along the distal edge ( Fig. 19m ). Radial striations along the distal edge of the outer surface result in a serrated distal edge whilst the lateral areas are relatively smooth. There are granules across the proximal area with some tubercles visible at the proximal edge ( Fig. 19n,o ).

The coenenchymal scales are smaller than the body-wall scales, with a circular to irregular shape ( Fig. 19p ), 150 µm diameter, with an irregularly serrate distal edge. The outer surface has granules and radial striations whilst the inner surface is tuberculate.

Distribution

This species has a circum sub-Antarctic distribution, found from depths of 75–686 m.

Remarks

Some branches appear uniplanar, as in the holotype ( Kükenthal, 1907), as the branchlets curve in 2 directions. Kükenthal (1912) referred to this structure as ‘biradial’. It is likely that this is the result of a commensal annelid inducing the branchlets to form around its body.

Comparisons

For a number of characters, Thouarella crenelata , T. chilensis , and T. parachilensis are morphologically similar and are probably closely related (see Table 3). The polyp shapes of these species are similar, although those of T. parachilensis are more bulbous distally than the more modestly clavate polyps of T. crenelata and the polyps of T. chilensis are more flared. Although there are differences in the number of abaxial scales the range of abaxial scale counts in all 3 species overlap making this a poor defining character: T. crenelata 6–11, T. parachilensis 8–15 and T. chilensis 6–8. As well as the varying sclerite shapes and sizes, the most prominent difference among these species is the density of polyp placement at the tip of a branchlet: Thouarella crenelata has 9–19 polyps per cm (average 11), T. parachilensis 18–48 (average 32) and T. chilensis 21–28 (average 22). Although there is moderate overlap in these ranges the branchlet tip of T. parachilensis specimens are ‘barrel-shaped’ with tight polyp placement and thus is distinguishable from T. crenelata . The marginal scales of T. crenelata also have a more pronounced dentate distal edge and the opercular scale surface is much more deeply and distinctly ridged than that found on the polyps of T. chilensis or T. parachilensis .

Thouarella crenelata and T. viridis are very similar species. They were described as different species based on the number of scales in the abaxial row and the surface ornamentation of the mariginal scales ( Zapata-Guardiola & López-González 2010a). Our study reports an expansion in the range of the number of scales in the abaxial row of the polyps of T. crenelata from the 9–10 of Kükenthal (1915; 1924) to 6–11 (average of 8), which overlaps that of T. viridis (6–7). The scales of polyps of T. crenelata have a dentate distal edge whereas those of polyps of T. viridis lack this character.

The colony form of Thouarella crenelata was originally described as similar to that of T. koellikeri ( Kükenthal 1907) , which has nearly pinnate branching, leaving one side of the stem without branchlets (described as “biradial” by Kükenthal 1919). Specimens identified here as T. crenelata are bottlebrush but can have a bilateral appearance when the branchlets curve in two directions. There are a similar number of scales in the abaxial row of the polyps of both T. crenelata and T. koellikeri and both have polyps that are clavate, however those of the latter have operculars with a simpler keel.

Polyps of T. crenelata have a comparable number of scales in the abaxial row, and a similar number of polyps per cm as colonies of T. clavata . But the former has more densely placed polyps at the tip of the branchlets, longer polyps, and polyps with marginals with larger serrations on the distal edge in comparison to the smooth to finely serrate edge of the latter.

Figures

FIGURE 18. Thouarella crenelata. USNM 98086: a) colony, 35 cm; b) polyps; c) abaxial polyp view, e) stereo opercular view of polyp. Holotype, ZMB: d) close up of polyps. Photo d) by Carsten Lueter, ZMB.

FIGURE 19. Thouarella crenelata, USNM 98086: a–c) inner, d) outer and e) lateral view of operculars; f) inner and g) outer surface of marginal scales; h,i) outer and j–l) inner surface of submarginal scales; m) inner and n,o) outer surface of body-wall scales; p) outer surface of coenenchymal scale.