Thouarella pendulina ( Roule, 1908 )

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 : 56-60

10. Thouarella pendulina ( Roule, 1908)

Figs 22 , 23

Rhopalonella pendulina Roule, 1908: 4 , pl.1, fig. 5–8; Gravier 1914: 70–77, text figs 86–98, pl. 5, figs 21–15; Kükenthal 1912: 290

Thouarella pendulina Kükenthal 1915: 151 ; 1919: 440; 1924: 302

Thouarella (Thouarella) pendulina Cairns & Bayer 2009: 27 (listed); Zapata-Guardiola & López-González 2010a: 179

Thouarella antarctica Broch 1965: 24–26 , pl. 2, figs 5–7

Material examined: Holotype, MNHN –Octo.0000–0232 and paratype, MNHN –Octo.0000–0211, Expedition Antarctique Francaise (1903–1905), no. 640 collected, Booth (Wandel) Island.

Other material: USNM 98341, R/V Islas Orcadas, cruise 876, sta. 111, Coronation Island, South Orkney Islands, sub-Antarctic, 60˚25’36”S, 46˚25’18”W, 97–128 m, 16 Feb 1976, 2 colonies; USNM 98359, R/V Hero , cruise 721, sta. 1075, Arthur Harbour, Anvers Island, Palmer Archipelago, Antarctic Peninsula, 64˚47’24”S, 64˚7’36”W, 91–104 m, 23 Feb 1972, 3 colonies; USNM 1130339, R/V Eltanin, cruise 27, sta. 1896, Franklin Island, Victoria Land, Antarctica, 76˚10’S, 168˚17’E, 70–81 m, 18 Jan 1967; USNM 1130348, south end of Balleny Islands, Buckle Island, Antarctica, 66˚53’S, 163˚19’E, 55–164 m, 10 Feb 1974, 15 colonies; USNM 1130344, R/V Hero , cruise 731, sta. 1756, Arthur Harbour, Anvers Island, Palmer Archipelago, Antarctic Peninsula, 64˚47’14”S, 64˚06’43”W, 91 m, 17 Feb 1973; USNM 85314, R/V Hero , cruise 721, sta. 1073, Arthur Harbor, Anvers Island, Palmer Archipelago, Antarctic Peninsula, 64˚47’30”S, 64˚07’36”W, 64–100 m, 23 Feb 1972; USNM 98149, R/V Hero , cruise 691, sta. 33, Arthur Harbor, Anvers Island, Palmer Archipelago, Antarctic Peninsula, 63˚46’30”S, 61˚47’51”W, 73–91 m, 13 Feb 1969; USNM 98150, R/V Hero , cruise 702, sta. 507, Port Lockroy, Wiencke Island, Palmer Archipelago, Antarctic Peninsula, 64˚49’18”S, 63˚31’21”W, 64–128 m, 17 Mar 1970; USNM 98158, R/V Hero , cruise 731, sta. 1944, Neumayer Channel, Anvers Island, Palmer Archipelago, Antarctic Peninsula, 64˚46’40”S, 63˚25’33”W, 100–150 m, 11 Mar 1973; USNM 98170, R/V Eltanin, cruise 6, sta. 435, Astrolabe Island, Bransfield Strait, Antarctic Peninsula, 63˚14’S, 58˚42’W, 73 m, 8 Jan 1963; USNM 98171, R/V Eltanin, cruise 6, sta. 436, Astrolabe Island, Bransfield Strait, Antarctic Peninsula, 63˚13’S, 58˚47’W, 73 m, 8 Jan 1963; USNM 98228, R/V Islas Orcadas, cruise 876, sta. 107, Coronation Island, South Orkney Islands, sub- Antarctic, 60˚26’30”S, 46˚22’48”W, 102–108 m, 16 Feb 1976; USNM 98335, off south end of Buckle Island, Balleny Islands, Antarctic, 66˚53’S, 163˚19’E, 55–164 m, 10 Feb 1974; USNM 98343, USAP, SOSC–L46, Antarctic, 63˚17’S, 62˚09’W, 12 Jan 1973; USNM 98360, R/V Hero , cruise 721, sta. 5438, Arthur Harbor, Anvers Island, Palmer Archipelago, Antarctic Peninsula, 64˚47’27”S, 64˚07’W, 32–90 m, 27 Mar 1972; USNM 98363 and 98390 (same location), R/V Islas Orcadas, cruise 876, sta. 112, Coronation Island, South Orkney Islands, sub- Antarctic, 60˚27’48”S, 46˚23’06”W, 93–102 m, 16 Feb 1976; USNM 1120943, R/V Hero , cruise 691, sta. 28, south of Low Island, South Shetland Islands, sub-Antarctic, 63˚25’30”S, 62˚09’30”W, 91 m, 10 Feb 1969; USNM 1129159, R/V Eltanin, cruise 32, sta. 2059, south of Pennall Bank, Ross Sea, Antarctica, 77˚58’30”S, 178˚4’58”E, 655 m, 25 Jan 1968; USNM 1130330, R/V Hero , cruise 691, sta. 33, Hoseason Island, Bransfield Strait, Antarctic Peninsula, 63˚36’30”S, 61˚47’51”W, 73–91 m, 13 Feb 1969; USNM 1130342, R/V Eltanin, cruise 27, sta. 1896, Victoria Land, Franklin Island, Ross Sea, Antarctic, 76˚10’01”S, 168˚16’58”E, 70–81 m, 18 Jan 1967; USNM 1130344, R/V Hero , cruise 731, sta. 1756, Arthur Harbor, Anvers Island, Palmer Archipelago, Antarctic Peninsula, 64˚47’13”S, 64˚6’42”W, 91 m, 17 Feb 1973; USNM 1130345, R/V Eltanin, cruise 51, sta. 5762, Moubray Pennell Bank, Victoria Land, Ross Sea, Antarctic, 76˚2’6”S, 179˚57’W, 347–358 m, 9 Feb 1972; USNM 1130347, R/V Hero , cruise 731, sta. 1915, west of Bonaparte Point, Arthur Harbor, Anvers Island, Palmer Archipelago, Antarctic Peninsula, 64˚47’S, 64˚4’32”W, 35–60 m, 6 Mar 1973; USNM 1130349, R/V Hero , cruise 731, sta. 1823, Arthur Harbor, Anvers Island, Palmer Archipelago, Antarctic Peninsula, 64˚47’20”S, 64˚6’58”W, 90–110 m, 20 Feb 1973; SMF, EPOS 03, sta. 212, GSN 2, Weddell Sea, 60˚50’S, 55˚38.9’W, 414 m, 15 Jan 1989; SMF, Terre Adélie, Antarctica, D114, Patrick Arnaud leg, no precise location or depth information; SMF, R/V Hero , sta. 90, South Janus Island, Palmer Archipelago, Antarctica, 73–100 m, 23 Mar 1972, no precise location information; SMF, R/V Hero , sta. 90, South Janus Island, Palmer Archipelago, Antarctica, 62–90 m, 23 Mar 1972, no precise location information.

Description

The description of the holotype is of a 34.5 cm long colony, 60 mm at its widest point. Colonies of this species are generally of an unbranched bottlebrush arrangement ( Fig. 22a,b ), although a few have been seen to have limited branching with 2 or more stems. The branchlets leave the main stem in at least 4 directions, extend horizontally, then droop, most having secondary and tertiary branching which can appear simple as divisions are very close to the stem. The branchlets are 1–3 mm apart, and up to 40–42 mm long. The axis is woody with fine longitudinal striations, flexible (except at colony base which is thickened into a calcified holdfast) and is 5–6 mm diameter base.

The polyps are crowded ( Fig. 22c,d ), with a density of 27–41 per cm (average 34). They are 0.9–1.2 mm high (average of 1 mm), appressed against the branchlets, 2–3 times longer than their diameter, and irregularly arranged. There are fewer polyps at the branchlet base, and they are more clustered at the centre and tip of the branchlets whilst there are no polyps on the main stem. The polyps are cylindrical at their base, thicker towards the operculum, with a slightly rounded shape and pointed summit. There are 4–5 scales in the abaxial row ( Fig. 22d ) but fewer in the adaxial row.

Eight operculars create a tall cone rising above the marginals with the 2 adaxial operculars being reduced in size. The operculars are in 2 alternate circles, one inner, one outer, however this is not strict as the adaxial operculars are often inside the inner opercular circle. There are 6–7 isosceles triangle to lanceolate-shaped operculars, each having an acutely pointed distal edge ( Fig. 23b–e ). Opercular scale sizes range from 260–490 µm high (average 357 µm), 150–320 µm wide (average 240 µm), with an average H:W of 1.5. There are 1 or 2 adaxially placed, smaller, diamond-shaped operculars ( Fig. 23a ). The outer opercular surface is moderately concave longitudinally and there are granules sparsely covering the proximal area, sometimes these are aligned radially. The inner surface has a simple keel, which may be half the opercular length ( Fig. 23c,d ), and is sometimes channelled and flat-faced whilst the proximal half of the inner surface is tuberculate.

The marginals are in inner and outer alternate circles of 4, although the adaxial marginals are reduced and do not conform to this pattern ( Fig. 22e ). Six of the 8 marginals are diamond to triangular shaped ( Fig. 23f–j ), higher, wider, and rounder than the operculars, 330–650 µm high (average 460 µm), 250–430 µm wide (average 330 µm), with an average H:W of 1.4. Generally the inner lateral marginals have a pointed distal edge that is angled to the right or left ( Fig. 23g,h ). The remaining 2 adaxial marginals are reduced in size and more circular. This reduction can be extreme such that these scales are sometimes not visible from an anterior view. The outer surface of marginals has granules sparsely covering the proximal area and some tubercles at the proximal margin. The inner surface has a modest simple keel and is tuberculate proximally with a narrow smooth band along the distal edge. Some abaxial submarginals have a pointed distal edge ( Fig. 23k ).

Large angular, circular and elliptical body-wall scales ( Fig. 23l–o ) of variable number cover the polyp in rows. These scales are 210–600 µm high (average 350 µm), 230–510 µm wide (average 340 µm), with an average H:W of 1, and are larger towards the polyp anterior. The outer surface is smooth with a few granules at the base whilst the inner surface is tuberculate. All the sclerites of this species have a finely serrate distal edge and roughly lobate proximal edge.

The coenenchymal scales are small, 150–280 µm high (average 220 µm), 120–200 µm wide (average 165 µm), and irregularly circular ( Fig. 23p–t ), with an average H:W of 1.34. The inner surface is tuberculate and granules sparsely placed across the outer surface.

Distribution

This species has a circum-Antarctic distribution and is found from 32–655 m depth.

Remarks

Thouarella pendulina was originally described within Rhopalonella Roule, 1908 , a genus purportedly differentiated from Thouarella in having densely arranged polyps ( Roule 1908). This tight clustering remains one of the distinguishing characteristics of this species although it is now considered to be within the range of variation of Thouarella .

The polyps of this species have two alternating rings of marginals, however the adaxial marginals are usually not synchronised with the alternating pattern and are reduced and thus not visible from the anterior ( Fig. 22e ). The polyps of Thouarella pendulina can in fact be compressed against the stem, reducing the number of adaxial bodywall scales per row to one or two. This is an oddity within Thouarella whose polyps generally depart the branchlets at 45–60˚ and have at least 3–4 adaxial body-wall scales per row.

Thouarella pendulina has a variable gross morphology. Some colonies have tightly packed simple branchlets, which are densely covered in polyps. Other colonies have sparser branching (1–2 per cm) with fewer polyps per cm on branchlets. Some colonies have branching between these extremes.

Comparisons

There are several species that have a similar number of abaxial scales (4–5) as T. pendulina and should thus be compared ( Table 3).

Thouarella pendulina could most easily be mistaken for T. hicksoni , whose colony form is bottlebrush and polyps similar in size (with 4–5 scales in the abaxial row), shape, and are also clustered (although in T. pendulina they are more clustered). However, the operculars of the polyps of T. hicksoni are tongue-shaped, whereas those of T. pendulina are lanceolate with a pointed distal edge. Also, the inner surfaces of the operculars of T. hicksoni do not have a well-defined keel, instead tending to have an area of longitudinal striations.

Although the polyps of T. brucei have a similar number of abaxial body-wall scales as those of T. pendulina , the latter has an almost bilateral colony appearance (although it is technically bottlebrush), polyps that are larger and more flared, and larger operculars than the former.

Thouarella andeep also has 4–5 scales in the abaxial rows, however its polyps are flared and larger, making the operculars and marginals larger than those in the polyps of T. pendulina . The polyps of T. andeep are also less clustered, and more splayed than those of T. pendulina .

The gross morphology of some ramified colonies of T. pendulina is very similar to that of T. variabilis . However, colonies of T. variabilis have longer polyps that are less clustered and elongated marginals that are absent in the former.

Thouarella striata has larger polyps than those found on T. pendulina and distinctive striations on the inner surface of sclerites (lateral to the keel on the marginals and perpendicular to the distal edge on other sclerites) that are absent in T. pendulina .

Thouarella pendulina has a similar shaped polyp to T. longispinosa (= Dasystenella acanthina ). However, the former has eight marginals (not five as in Dasystenella ) and polyps of T. pendulina do not occur in whorls.

Figures

FIGURE 22. Thouarella pendulina: a,d,e) Paratype, MNHN, Oct.0000-0211: a) broken colony; d) abaxial and lateral view of polyps on branchlet; e) stereo opercular view of polyps. USNM 98359: b) colony, 22 cm; c) close up of polyps.

FIGURE 23. Thouarella pendulina, paratype, MNHN, Oct.0000-0211: a,c,d) inner and b,e) outer surface of opercular scales; f,g,h) inner and h,i) outer surface of marginal scales; k) inner surface of submarginal; l) outer and m–o) inner surface of bodywall scales; p–r) outer and s,t) inner surface of coenenchymal scales.