(fig. 5 Q, R)
Sertularia (gracilis) filiformis Allman, 1888: 51, pl. 24 figs 1, 1A.
Sertularella filiformis — Hartlaub, 1905: 636, fig. B 4.
Sertularella filiformis var. reticulata — Ritchie, 1907: 77.
Symplectoscyphus filiformis — Totton, 1930: 194, fig. 42, pl. 3 fig. 9. — Blanco, 1982: 159, figs 10–15. — Galea, 2007: 68, fig. 16 A–I.
Sertularella subdichotoma — Hartlaub, 1901 (pro parte): 33, pl. 1 figs 3, 4, 6 –9, 11– 16, pl. 2 figs 10 –12, 14–17, 51, 52, pl. 3 figs 4, 14 [not pl. 2 fig 13, pl. 3 figs 3, 13 = S. subdichotomus (Kirchenpauer, 1884)]. — Jäderholm, 1903: 278. — Hartlaub, 1904: 6. — Jäderholm, 1904 b: 3. — Hartlaub, 1905: 629, figs V 3, W 3. — Jäderholm, 1905: 25, pl. 9, fig. 8. — Jäderholm, 1910: 4. — Jäderholm, 1926: 6.
Symplectoscyphus subdichotomus — Blanco, 1967 a: 273, pl. 3 figs 6 –8, 10, 11, pl. 4 figs 1, 2. — Blanco, 1967 b: 118, pl. 4 figs 5–10. — Vervoort, 1972: 140, figs 44 B–D, 45. — Leloup, 1974: 42, fig. 40. — Blanco, 1976: 49, pl. 6 figs 1, 2. — Milstein, 1976: 83, figs 7, 10, 12, 31. — Millard, 1977 (pro parte): 37, fig. 11 D, E. — Blanco, 1984: 34, pl. 29 figs 64–66. — El Beshbeeshy, 1991: 232, fig. 59. — Branch & Williams, 1993: 13, fig. — Galea, 2007: 71, fig. 17 A–G. — El Beshbeeshy, 2011: 178, fig. 59.
Simplectoscyphus subdichotomus (incorrect subsequent spelling) — Blanco, 1969: 49, figs 1–18.
not S. subdichotomus Kirchenpauer, 1884: 46, pl. 16 figs 1, 1A, 1 B.
Sertularella johnstoni — Ridley, 1881: 104. — Naumov & Stepanjants, 1962 (pro parte): 83.
Material examined. Stn. GNZ — 25.v. 2007, S06 (10 m): a luxuriant colony, with mostly immature male gonothecae, a few only having developed the characteristic terminal tube. Stn. AMI — 26.v. 2010, S07 (5 m): a luxuriant, infertile colony. Stn. YBU — 01.xii. 2009, S 23 (20 m): a colony with some rare female gonothecae, mostly spent; S 25 (10 m): a fragmentary, sterile colony; 20.vi. 2010, S02 (20 m): a sterile colony; 26.iv. 2011, S 16 (20 m): a rather fragmentary colony with rare female gonothecae, these already spent. Stn. FSI — 01.iii. 2010, PTA019 (20 m): a fragmentary colony with numerous female gonothecae, mostly spent; 03.i. 2011, S08 (20 m): an infertile colony; S09 (20 m): a luxuriant colony with male immature gonothecae, a few with the terminal tube already formed; 04.i. 2011, S 18 (20 m): a luxuriant colony with numerous spent female gonothecae; S 25 (40 m): a rather small, though fertile colony, bearing numerous male gonothecae (MHNG-INVE- 79631); S 33 (30 m): a large colony with a few immature gonothecae whose sex could not be ascertained; S 38 (25 m): a sterile colony; 06.i. 2011, S01 (30 m): a luxuriant colony with partly immature and partly mature male gonothecae; S 13 (30 m): a couple of stems epizoic on Synthecium protectum; S 16 (30 m): a luxuriant colony with numerous female gonothecae, some containing eggs, others already spent (MHNG-INVE- 79632); S 29 (30 m): several sterile stems epizoic on Halecium pallens; 07.i. 2011, S03 (40 m): a sterile colony on worm tube.
Remarks. In a situation possibly unprecedented amongst hydroids, taxonomic confusion prevailed over the identity of S. filiformis for more than a century. The species was often misidentified as S. subdichotomus (Kirchenpauer, 1884), and the origin of this confusion comes, most curiously, from its own author. Kirchenpauer listed two very remote localities for material on which he based his species, viz. Bass Strait, Australia, and the Strait of Magellan, South America. All of this material was treated as a single taxon, hydrothecae and gonothecae (except for the terminal tube of the latter, which was said to be missing) of which were found to come close to those of the northern S. tricuspidatus (Alder, 1856) and the Australian S. johnstoni (Gray, 1843). Kirchenpauer also added the following: "I previously named this form S. Johnstoni var subdichotoma, but it represents a specifically different form 10 ".
Although the description of S. subdichotomus given by Kirchenpauer was brief and vague, he indicated, however, a key character which could make subsequent authors suspicious: the absence of a terminal tube on the gonotheca.
In his revision of the genus Sertularella, Hartlaub (1901) stated the following: "For the time being, I cannot decide whether the material from the Straits of Magellan is identical [to the Australian one]. The description I am giving of the species refers only to the South American material; in addition to the original material of Kirchenpauer from the Expedition of the Gazelle housed in the Museum of Berlin, I examined material collected by the expeditions of Michaelsen and Plate 11."
Further on in his account, Hartlaub provided a description and three figures (pl. 1 fig. 6, pl. 2 figs 51, 52) representing gonothecae from South American specimens: "Gonothecae borne on stem and branches, leaning on them, often crowded, egg-shaped, with more or less pronounced annular ridges which become less conspicuous where in contact with adjacent structures, with a rather long tube widening at aperture 12 ". He also gave a figure of a gonotheca (pl. 3 fig. 13) from Australian material, and it becomes obvious that reliable morphological differences, such as the absence of both frills and the terminal tube, occur between the two species. Hartlaub likely did not realize the importance, in particular, of the terminal tube in discriminating between the South American and the Australian specimens. Additionally, he neither tackled, nor made any remark concerning Symplectoscyphus filiformis (Allman, 1888), a sympatric species originally described from Port Famine (Puerto del Hambre), Chile. In a later account (Hartlaub 1905), he only copied the original description of this species given by Allman.
Afterwards, almost all subsequent authors (see synonymy above) who dealt with South American hydroids scrupulously followed Hartlaub's (1905) interpretation and invariably reported the occurrence of S. subdichotomus from the area, totally ignoring S. filiformis. A misleading concept of Kirchenpauer's (1884) species was thereby spread and perpetuated.
In an earlier publication, one of us (Galea 2007) reported the occurrence of both S. filiformis and S. subdichotomus in southern Chile. The discrimination between them was made exclusively on accounts of the shape of the terminal tube of the gonothecae (i.e. filiform in Allman's species, and funnel-shaped in Kirchenpauer's). No significant distinctive character in their trophosomes could be noted. At that time, several essential bibliographical references (viz. Kirchenpauer 1884, Hartlaub 1901, Totton 1930, Blanco 1969) were unavailable to the first author of this study, and the present taxonomic correction was found necessary.
In the account by Totton (1930), some relevant information is given, as follows: 1) the specimen illustrated by Kirchenpauer (1884) was drawn after Australian material, and was selected by Totton as the holotype of S. subdichotomus; 2) its gonotheca is devoid of free frills and the aperture "is on a very short and wide tube"; 3) the gonothecae of S. filiformis are "sexually dimorphic, female longer, broader, usually with one or two more annulations, with a longer and wider distal tube".
The sexual dimorphism of the gonothecae is also illustrated in the figures given by Hartlaub (1901): two are obviously female (pl. 1 fig. 6, pl. 2 fig. 52) and one male (pl. 2 fig. 51).
10. Ich habe diese Form früher S. Johnstoni var subdichotoma benannt, sie ist aber doch eine spezifisch verschiedene Form. 11. Ob es identisch ist mit dem Material der Magalhaens-Strasse, lasse ich einstweilen unentschieden. Meine Schilderung der Art bezieht sich ausschliesslich auf südamerikanisches Material, und zwar standen mir zur Verfügung ausser dem Original Kirchenpauer's Material der Gazelle-Expedition aus dem Berliner Museum, und solches von den Expeditionen Michaelsen und Plate.
12. Gonotheken, an Stamm und Zweigen sitzend, sich an diese anlehnend, oft gedrängt stehend, eiförmig, mit mehr oder minder hohen Ringleisten, die auf der anliegenden eingesenkten Fläche verstreichen, mit ziemlich langem, gegen die Mündung erweitertem Ausführungsrohr.
Later, Blanco (1969) discussed at length the variation of the gonothecal shape in " S. subdichotomus ", and distinguished two types of gonothecae, suggesting a possible sexual dimorphism, without being able to confirm her assumption. Indeed, the gonothecal content in her material seemed similar in both types of gonothecae, and she supposed that it was male ("el contenido gonangial es, no obstante, similar; al parecer masculino").
In the substantial hydroid material examined by one of us (H.R.G.) over an interval of several years, and in material examined here, a large number of spent gonothecae were often found. When gonophores were present within gonothecae, they appeared as compact, ovoid masses surrounding the blastostyles. In rare instances, however, fixation was successful, as illustrated by female specimens from Stn. FSI, S 16 (06.i. 2011) whose gonothecae contain 4–5 rounded eggs; the terminal tube is funnel-shaped. Specimens from Stn. FSI, S 25 (04.i. 2011) bear male gonothecae, comparatively shorter and narrower, and containing an ovoid, homogenous mass of sperm cells. Totton's (1930) earlier observation (see above) is thus confirmed, documenting sexual dimorphism in this species. For comparative measurements of the gonothecae, see Galea (2007).
Additionally, more recent data became available on the gonotheca of S. subdichotomus, confirming Totton's observations, viz. "apical part of gonotheca with large terminal plateau with a wide, short central or slightly displaced funnel. Spiral fold around gonotheca with 10–13 twists, and carina as in Symplectoscyphus j. johnstoni; no flange or frill observed" (Vervoort & Watson 2003).
Our observations clearly show that S. filiformis and S. subdichotomus are distinct, readily distinguished species on both morphological and biogeographical grounds.
Distribution in Chile. The northernmost record is from Tocopilla (Leloup 1974); from there the species ranges uniformly southwards to Tierra del Fuego (Jäderholm 1903).
World records. This species is mainly restricted to the subantarctic. Its northernmost records along the Pacific coast of South America are from Rio de la Plata (Milstein 1976) and off Mar del Plata (El Beshbeeshy 2011). The species spreads soutwards to Tierra del Fuego, and occurs around the Falkland Islands (Jäderholm 1905, Totton 1930), the Burdwood Bank (Jäderholm 1905), the Kerguelen and Crozet shelves (Millard 1977), Marion and Prince Edward Islands (Branch & Williams 1993). There are also rare records from the Weddell Sea (Blanco 1967 a).