Actinernus antarcticus ( Carlgren, 1914 )

Rodríguez, Estefanía & López-González, Pablo J., 2013, <strong> New records of Antarctic and Sub-Antarctic sea anemones (Cnidaria, Anthozoa, Actiniaria and Corallimorpharia) from the Weddell Sea, Antarctic Peninsula, and Scotia Arc </ strong>, Zootaxa 3624 (1), pp. 1-100 : 5-10

Actinernus antarcticus ( Carlgren, 1914)

( Figs. 1–3 ; Table 1; Appx. 1, 2)

Porponia antarctica Carlgren, 1914 .

Actinernus antarcticus: Carlgren 1918 ; Carlgren 1949.

non Actinernus elongatus (Hertwig, 1882) ; Dunn 1983; Fautin 1984.

MATERIAL EXAMINED

Polarstern ANT XXII/3 : stn. PS67/154-7 ( BEIM: ANT-3506, 1 specimen; BEIM: ANT-3507, 1 specimen) .

COMPARATIVE MATERIAL EXAMINED

Porponia antarctica Carlgren, 1914 . NMSZ 1921.143.1756. Syntypes. “ Scotia Collection, off Coats Land, 71º22’S, 16º34’W, 1,410 fm, 16/3/1904 ” (2 specimens). Labelled as Actinernus antarcticus ( Carlgren, 1914) .

Porponia antarctica Carlgren, 1914 . NMSZ 1921.143.1756. Syntype. “ Scotia Collection, off Coats Land, 71º22’S, 16º34’W, 1,410 fm, 16/3/1904 ” (1 specimen). Labelled as Actinernus antarcticus ( Carlgren, 1914) .

Porponia elongata Hertwig, 1882 . NHM 1889.11.25.29. Syntypes. “ Challenger (Coll.), stn. 160; 2,600 fm, 13 Mar 1874, genotype” (2 specimens). Labelled as Actinernus elongatus (Hertwig, 1882) .

DIAGNOSIS

Actinernus specimens with thick, cylindrical, cartilaginous column, to 30 mm diameter and 58 mm height in preserved specimens; column whitish to pink in living specimens, white in preserved specimens. Column distally expanded, irregularly lobate. Oral disc wide, to 43 mm diameter. No marginal sphincter. Tentacles about 60, long (to 36 mm) and pointed, tapering distally. Aboral base of tentacles with thickened mesoglea, to 4 mm in diameter, tapering distally gradually; thickened region of tentacle extend into column margin. More mesenteries proximally than distally. Mesenteries thin, to 28 at actinopharynx level; after first six pairs, mesenteries grow in lateral endocoels with retractor muscles oriented as directives toward exocoels. Cnidom: spirocysts, basitrichs, and microbasic b - and p -mastigophores. For a complete description of A. antarcticus , see Carlgren (1914).

GEOGRAPHIC AND BATHYMETRIC DISTRIBUTION

Actinernus antarcticus was only known from East Antarctica (type locality) and this material represents the first citation of new specimens since the original description in 1914. Although the type locality is described as “off Coats Land waters” ( Carlgren 1914: 50), the coordinates (71º22’S 16º34’W) do not correspond with that locality: Coats Land is located in the Weddell Sea whereas the type locality coordinates correspond to Hakkon VII Sea, located in the eastern Weddell Sea. Actinernus antarcticus was described at 2,566 m (1,410 fathoms) depth ( Carlgren 1914).

This new record expands both the geographic and bathymetric distribution of Actinernus antarcticus . This species is distributed north of Peninsula Antarctica, off the South Shetland Islands (62°31.36’S 64°40.23’W); the depth range of the species is extended to 2,566–3,800 m .

We consider this species an Antarctic endemic distributed in bathyal depths ( Fig. 3b ).

REMARKS

Dunn (1983) synonymized Actinernus antarcticus and A. elongatus based on i) the lack on internal data of A. elongatus and the poor state of the specimens she studied, ii) similarity of cnida data of A. elongatus , A. antarcticus , and her material, iii) similar structure of the mesogleal aboral thickenings of the tentacles in A. elongatus and A. antarcticus , and iv) relative proximity of the type locality of A. elongatus (42°42’S 134°10’E, south of Australia) and the specimens that she studied (south of New Zealand). However, according to Hertwig (1882), A. elongatus has more mesenteries distally than proximally whereas in A. antarcticus , mesenteries are more numerous proximally. The structure of the mesogleal thickenings of the aboral base of the tentacles is different: in A. antarcticus , tentacles are stout, tapering uniformly toward the tip whereas in A. elongatus , the aboral thickness of the tentacle changes abruptly so an aboral thickened base is clearly distinct from a filament-like tip (see Hertwig 1882: Pl. I figs. 1, 2; Carlgren 1914: 51, fig. 1a; Fig. 1 ). After the revision of the type material of both species, we confirm that the shape of the mesogleal aboral thickenings of the tentacles is different at the species level in Actinernus . However, cnida measurements are very similar among species (data not shown).

TABLE 1. Size ranges of the cnidae of Actinernus antarcticus ( Carlgren, 1914) ; for comparative cnidae data of the species see Carlgren (1914, 1940). S: ratio of number of specimens in which each cnidae was found to number of specimens examined. N: total number of capsules measured. F: Frequency, +++ = very common, ++ = common, + = rather common, --- = sporadic. Abbreviations: Mc, Microbasic. Mean (Χ) and standard deviation (SD) no calculated because are based on fewer than 40 capsules.

We do not consider the material studied by Dunn (1983; Fautin 1984) to belong to Actinernus elongatus . The description and figures of the distal column and aboral tentacle thickenings provided by Dunn (1983: 5, fig. 5) do not correspond to the type material of A. elongatus . Further revision is necessary to confirm the identity of the material studied by Dunn (1983; Fautin 1984).

Suborder NYNANTHEAE Carlgren, 1899

ENDOMYARIA Stephenson, 1921

Family ACTINIIDAE Rafinesque, 1815

Figures

FIGURE 1. External anatomy of Actinernus antarcticus (Carlgren, 1914) [BEIM(ANT-3507)]. a) Lateral view of living specimen. b) Detail of the column margin showing the mesogleal thickenings in the outer base of the tentacles in living specimen. Scale bars: a, 60 mm; b, 10 mm.

FIGURE 2. Cnidae of Actinernus antarcticus (Carlgren, 1914). a, e, i, m;) Spirocysts. b, d, f, g, j, n) Basitrichs. c, h, l, p) Microbasic b-mastigophore. k, o) Microbasic p-mastigophores.

FIGURE 3. Distribution map of species. a) Overview. b) Actinernus antarcticus (Carlgren, 1914). c) Aulactinia sulcata (Clubb, 1902). d) Bolocera kerguelensis Studer, 1879. e) Epiactis georgiana Carlgren, 1927. f) Glyphoperidium bursa Roule, 1909. Green triangles, type locality; green circles, previous localities; red circles, localities from this study; dark line, Subtropical Front; light line, Polar Front. AP, Antarctic Peninsula; DP, Drake Passage; RS, Ross Sea; SS, Scotia Sea; WD, Weddell Sea.