Staurocladia charcoti Bedot 1908

Staurocladia charcoti (Bedot, 1908)

(Pl. 1F–L)

Wandelia charcoti Bedot, 1908: 1, pl. 1.

Eleutheria charcoti — Browne, 1910: 27. — Gilchrist, 1919: 519, 520.

Staurocladia charcoti — Browne & Kramp, 1939: 278. — Kramp, 1959: 98, fig. 60; 1961: 61; 1968: 24, fig. 57A. — O'Sullivan, 1982: 25.

Eleutheria hodgsoni Browne, 1910: 28, pl. 3, figs 1–4 (syn. nov.). — Gilchrist, 1919: 519, 520. — Kramp, 1948: 2. — Mann & Zapfe, 1950: 7, figs.

PLATE 1. A–E: Hydractinia angusta (Hartlaub, 1904) — colony on worm tube, in life (A); preserved material, details showing gastro- and gonozooids (B), spines protruding from the superficial sheet of naked coenosarc (C), some being contiguous with each other (D), and having their surface provided with low ridges (E). F–L: Staurocladia charcoti (Bedot, 1908) — female (F) and male (G) medusae, the latter showing the ornamentation due to the pigment granules in the endoderm; medusae foraging (H, I); exumbrellar view of a medusa stained in toto and seen with transmitted (J) and incident (K) light, demonstrating that radial canals are unbranched; basal pad of nematocysts clasping around for a certain distance of the circumference of a tentacle (L, arrows), seen in aboral view. M–Q: Candelabrum penola (Manton, 1940) — specimen in life (M); preserved material, basal part showing blastostyle region (below) and lower portion of the tentacle region above (N); detail of the blastostyle region (O) and three isolated blastostyles showing gonophores and tentaculate lobes (P); transverse section through the tentacle region (Q) showing capitate tentacles (left) and endodermal folds (right). R: Sertularella gaudichaudi (Lamouroux, 1824) — colony in life and female gonotheca (insert); the reddish tinge in some parts of the colony is due to biofilm on surface. S: Symplectoscyphus cumberlandicus (Jäderholm, 1905) — living colony. T: Orthopyxis norvegiae (Broch, 1948) — preserved male (left) and female (right) gonothecae showing gonophores (scale bar equals 500 µm).

Staurocladia hodgsoni — Browne & Kramp, 1939: 278. — Kramp, 1959: 98, fig. 61; 1961: 61; 1968: 24, figs 56, 57B. — O'Sullivan, 1982: 25, fig. 9.

Eleutheria vallentini — Vanhöffen, 1911: 201, fig. 5, pl. 22 figs 1, 2; 1913: 357 [not Staurocladia vallentini (Browne, 1902)]. Eleutheria kerguelensis Gilchrist, 1919: 521 (syn. nov.). — O'Sullivan, 1982: 29, fig. 10. not Staurocladia kerguelensis — Kramp, 1957: 155.

Material examined. Stn. SUF — 30.i.2011, Ant.19/2011 (9 m): two medusae, umbrella diameter 5 and 6 mm, respectively, both with 10 radial canals, and ca. 56 and 65 tentacles1, respectively, former female, latter male (MHNG-INVE-79805). Stn. PRZ — 17.ii.2011, Ant.17/2011 (15 m): a medusa, umbrella diameter 7 mm, 9 radial canals, ca. 55 tentacles, female (MHNG-INVE-79801); Ant.20/2011 (15 m): two medusae, umbrella diameter 4 and 3 mm, 12 and 11 radial canals, ca. 55 and 37 tentacles, female and male, respectively; Ant.21/2011 (15 m): two medusae, umbrella diameter 5.5 and 6.0 mm, both with 10 radial canals, ca. 48 and 47 tentacles, respectively, former male, latter female (MHNG-INVE-79802). Stn. ESC — 01.ii.2011, Ant.18/2011 (19 m): two medusae, umbrella diameter 3 and 4 mm, 10 and 9 radial canals, ca. 27 and 34 tentacles, respectively, both male (largest medusa as MHNG-INVE-79804); 05.ii.2011, Ant.22/2011 (9 m): four medusae, umbrella diameter 3, 3, 5 and 8 mm, with 10, 9, 7 and 10 radial canals, and ca. 36, 31, 40 and 62 tentacles, sexes male, male, female and male, respectively (MHNG-INVE-79803).

Description. Umbrella watch glass shaped in young individuals (Pl. 1 F, G), to nearly hemispherical in somewhat contracted, older specimens (Pl. 1I); diameter up to 8 mm; mesoglea rather thin and transparent. Manubrium conical, partly projecting through the aperture of the broad velum; surface of manubrium with a number of longitudinal creases, more obvious in older specimens; terminally crowded with nematocysts. Radial canals varied in number (up to 12), ending in circular canal; number increasing with age. Endoderm above middle part of radial canals containing dark-pigmented bodies organized so as to take the shape of lateral, often divided, anastomozing "branches" (Pl. 1G). Tentacles, up to at least 65 in fixed specimens, closely packed together around margin of the umbrella; divided immediately above origin into a upper and lower branches; upper branch with an apical nematocyst knob and additional clusters placed alternately on the lateral sides; up to 16 on each side; lower branch without nematocyst clusters, ending in adhesive, flattened disk. On the proximal most, oral side of the main stem of the tentacles, conspicuous pads of nematocysts clasping around for a certain distance of the circumference of the tentacles, not fused laterally so as to form a continuous ring; an ocellus at each tentacle base on aboral side. Gonads around the manubrium, never topping the radial canals; eggs randomly arranged; male gonads lobate, perradiar in position (Pl. 1J, K).

Remarks. The taxonomy of S. charcoti has been unresolved for decades, with several questions about its relationships to S. hodgsoni (Browne, 1910) and S. kerguelensis (Gilchrist, 1919) unanswered.

When Bedot (1908) described Wandelia charcoti, the fragmentary condition of the specimens upon which his new species was based, prevented him from allocating it to a known genus or family. In spite of this, the description and illustrations he provided were of great accuracy and, upon a careful reading of his account, some important information could be gathered. His species is mainly characterized by the upper branches of the tentacles2 carrying lateral, alternately-placed clusters of nematocysts. The radial canals were said to be provided with slender, lateral "branches", with a tendency towards anastomosis. Astonishingly, an important observation was overlooked by some authors (e.g. Kramp 1959, 1968), although it is rather clearly stated by Bedot: "There are no nematocyst clusters on the sides of these tentacles3 but, near their insertion point4, one can always notice a nematocyst cluster5". In other words, this means that an interrupted band of nematocysts occurs as isolated pads on the basal portion of the main stems of the tentacles.

1. Tentacle number could not be ascertained with certainty in fixed material, due to their partial loss after fixation and the general contracted condition of the specimens, with the tentacles often interwoven.

2. Bedot could not figure out that the tentacles were actually divided into lower and upper branches. Instead, he thought that two types of tentacles were present ("Ces tentacules sont de deux sortes").

3. Bedot refers to the lower branch of the marginal tentacles.

4. The main stem of the tentacles is very short in S. charcoti, so that the lower branches appear as inserted directly on the margin of umbrella.

5. " Il n'y a pas de boutons urticants sur les côtés de ces tentacules, mais, près de leur point d'insertion, on remarque toujours une accumulation de nématocystes".

Browne (1910) recognized a second Antarctic species of cladonematid medusa, S. hodgsoni, with a tentacular structure similar to that of S. charcoti, but distinguished from it by its "very short" radial canals, devoid of lateral "branches". Browne was able to examine Bedot's specimens of S. charcoti, but we do not know whether he was able to confirm the structure and position of the nematocyst pads, although it was expressly stated for his S. hodgsoni: "On the under side of the basal portion of the tentacles is situated a thick pad of nematocysts".

Numerous specimens of a crawling medusa obtained at Kerguelen were studied by Vanhöffen (1911), who merged both Bedot's and Browne's species into the synonymy of S. vallentini (Browne, 1902), arguing that the sole medusa obtained by the latter author could have the upper branch of the tentacles rotated by 90 degrees6, thus giving the impression that the nematocysts clusters were arranged above and below, not laterally.

Moreover, upon examination of living specimens, Vanhöffen noticed the same apparent ramifications and anastomoses of the radial canals7 as in S. charcoti, but was unable to confirm their presence in fixed specimens or in histological sections8. We also note that medusae stained with Grenacher's borax carmine and mounted in toto indeed show that the radial canals are unbranched, the pigment granules having been dissolved in the ethanol used to dehydrate the specimens (Pl. 1J, K).

Additionally, owing to the very crowded position of the tentacles, Vanhöffen doubted that the ring of nematocysts at the tentacle bases was segmented into isolated pads9 as in S. hodgsoni, although his specimens perfectly matched the description given by Browne (1910) 10. This difference lead Gilchrist (1919) to introduce a new species, Eleutheria kerguelensis, for Vanhöffen's material.

Additional subantarctic (from South Georgia) specimens assigned to S. hodgsoni were studied by Kramp (1948), who was able to settle this question: "as a matter of fact, there is an isolated pad of nematocysts on the adaxial side of each tentacular base and no continuous ring".

Subsequent authors (e.g. Kramp 1959, 1968) kept provisionally distinct the three species of Staurocladia, though evidences exist now in favor of including both S. hodgsoni and S. kerguelensis in the synonymy of Bedot's species. On one hand, the differences concerning the supposed ramification of the radial canals noted by Browne (1910) are simply related to the growth of the medusa, as illustrated by the present material from King George Is., in which only the largest specimens display this feature (type material of S. hodgsoni comprised very young medu-

6. " As a difference for E. vallentini, Browne states that the nettle warts are differently placed on the sides of the upper [branches of the] tentacles compared to the other species, so that these tentacle branches seem rotated by 90°. Because only a single individual was examined by him and a misinterpretation is not excluded, I cannot figure out the importance of this feature" [translated from German].

7. "I have also seen these anastomosed structures, which seem to interrupt the radial canals in their middle, in living animals from Kerguelen, and I have sketched them" [translated from German].

8. "Whether there are really ramified canals, as I also assumed at first, has become doubtful to me, because I did not find again these structures in preserved animals or even in sections" [translated from German].

9. "Because the tentacles are closely-set together, often scarcely leaving gaps between them, I think that this circumstance is not suitable to separate the species" [translated from German].

10. "Moreover, the detailed description given by Browne for E. hodgsoni is equally applicable to the Kerguelen specimens and, consequently, I avoid to repeat it here" [translated from German].

sae with the bell diameter of 1–2 mm, while Bedot's specimens of S. charcoti attained a size of ca. 4 mm across the umbrella).

On the other hand, Vanhöffen was only dubious and did not expressly state that his medusae were characterized by a continuous ring of nematocysts below the tentacle bases. Our material demonstrates that the nematocyst pads are often difficult to observe individually, especially in fixed material but, upon adequate conditions (angle of view, lighting and magnification), their presence is indisputable (Pl. 1L, arrows). In our opinion, there is little doubt that S. kerguelensis represents no more than a junior synonym of S. charcoti.

Kramp (1957) provisionally assigned to S. kerguelensis two young, somewhat mutilated, specimens of a medusa from Kerguelen, characterized by the presence of a nematocyst ring below the umbrella margin, and of about 20 tentacles, of which only three retained their nematocyst clusters (besides the terminal one, only one or two clusters occurred), whose position was uncertain. Inspection of our in situ photographs of S. charcoti show, for example, a medusa with 12 tentacles, each of these already carrying 6 pairs of lateral clusters of nematocysts. We conclude that Kramp's material belongs to another species of Staurocladia, possibly S. vallentini (Browne, 1902) (for a recent redescription of the latter, see Galea & Schories 2012)

Geographical distribution. In the Antarctic, the species was found in the Wilhelm Archipelago (Bedot 1908), McMurdo Sound (Browne 1910), Graham Land (Mann & Zapfe 1950), and the South Shetland Islands (present study). The species also occurs at some subantarctic localities, such as South Georgia (Kramp 1948) and Kerguelen (Vanhöffen 1911, 1913).