Sertularella antarctica Hartlaub, 1901

Galea, Horia R., Häussermann, Verena & Försterra, Günter, 2009, New additions to the hydroids (Cnidaria: Hydrozoa) from the fjords region of southern Chile, Zootaxa 2019, pp. 1-28 : 7-12

Sertularella antarctica Hartlaub, 1901 a

(figs 2J–N, 3A–B, tables 1–2)

Sertularella unilateralis Allman, 1876: 114 . – Allman, 1879: 282, pl. 18 figs 10–11.

not Sertularia unilateralis Lamouroux, 1824: 615 , pl. 90 figs 1–3 [= Symplectoscyphus unilateralis ( Lamouroux, 1824) ].

Sertularella antarctica Hartlaub, 1901a: 82 , pl. 6 figs 27–28. – Jäderholm, 1903: 283. – Hartlaub, 1905: 650, fig. P4. – Jäderholm, 1905: 32, pl. 13 fig.1. – Blanco, 1963: 170, figs 5–6. – Vervoort, 1972b: 105, figs 32–33. – Stepanjants, 1979: 84, pl. 15 fig. 3. – El Beshbeeshy, 1991: 147, figs 35–36.

Sertularia ( unilateralis ) secunda Allman, 1888: 53 , pl. 25 figs 2, 2A, 2B.

not Sertularella secunda Kirchenpauer, 1884: 50 , pl. 17 figs 7–7A [= Symplectoscyphus secundus ( Kirchenpauer, 1884) ].

Sertularella allmani Hartlaub, 1901a: 81 , pl. 5 figs 12–13, pl. 6 figs 1, 8. – Jäderholm, 1903: 283. – Nutting, 1904: 84, pl. 18 figs 3–6. – Hartlaub, 1905: 649, fig. Q4. – Jäderholm, 1905: 32, pl. 12 fig. 11.

Sertularella picta – Millard, 1971: 405, fig. 6A–B [not Sertularella picta ( Meyen, 1834) ].

Material examined. Stn. 10 – 24.02.2008, 8 m, A521 ( MHNG INVE 62835): a single colony composed of several fertile stems, on weed.

Type locality. Swain’s Bay, Kerguelen Islands.

Description. Stems up to 2 cm high, arising from creeping, branching, and anastomozing stolon; the latter strongly flattened, firmly adhering to substrate (not shown). Perisarc yellowish-brown basally, grading to nearly transparent distally; thick throughout, though imperceptibly thinning out towards distal parts of colonies. Stems monosiphonic, nearly isodiametric; divided into internodes by weak, alternately sloping constrictions of perisarc, giving the stem a slight zigzag appearance. Basalmost internode hydrothecate, arising directly from hydrorhiza; provided with 2–5 annuli proximally. Reminder of caulus composed of rather short, fairly regular internodes, each bearing a hydrotheca distally and occasionally a short apophysis for the insertion of cladia below its base; internodes with slight bulges at both ends; hydrothecae alternate, in two parallel rows. Stems pinnately branched in roughly alternate manner. Primary branches borne on their corresponding stem apophyses; often with 2nd - and 3rd -order branching. Branches with similar structure as stem, but straighter and with more pronounced nodes; first internode longer than later ones and provided with 1–2 basal twists. Both hydrothecae and side-branches shifted towards one side of the colony, forming variable angle (70°–150°) between them; each colony with distinct “anterior” and “posterior” sides. Hydrothecae flask-shaped, distinctly swollen in lower halves, narrowing distally, with relatively thick, smooth perisarc; adnate for about 1/3rd to 1/2 their adcauline length; free adcauline wall distinctly convex proximally, concave distally; abcauline wall more or less straight. Hydrothecal margin with four strong cusps, separated by shallow, rounded embayments; rim distinctly thickened. Abcauline cusp generally larger than other three, margin tilted towards adaxial side. Three internal, perisarc projections (one abcauline and two lateroadcauline) always present below the hydrothecal aperture; projections triangular in shape, with rounded tips; hydrothecal aperture quadrate to rhomboidal. Operculum composed of four triangular flaps forming a shallow, conical roof. Hydranths with dome-shaped hypostome, ca. 24 filiform tentacles and abcauline caecum. Gonothecae borne on side branches, in front of colony; each with a minute pedicel, arising from below bases of hydrothecae (not shown); elongated-oval with 6–8 transverse ridges over distal 3/4th of body; distally a short, wide neck provided with 2–5 blunt, shallow projections of perisarc around aperture. Nematocysts: microbasic mastigophores (5.8–6.3) × (1.8–2.0) µm (undischarged).

Remarks. Allman (1876) first described, then redescribed and figured ( Allman 1879) Sertularella unilateralis from Swain’s Bay, Kerguelen. Because of nomenclatural priority, the species was renamed Sertularella antarctica by Hartlaub (1901a) to avoid confusion with Sertularia (= Sertularella ) unilateralis Lamouroux, 1824 , the latter being presently included in the genus Symplectoscyphus Marktanner- Turneretscher, 1890.

sources.

Later, Allman (1888) described Sertularia ( unilateralis ) secunda from Accessible Bay, Kerguelen. When Hartlaub (1901a) revised the genus Sertularella Gray, 1848 , Allman’s (1888) species had to be transferred to that genus but, for priority reasons, was renamed Sertularella allmani , to avoid confusion with Sertularella secunda Kirchenpauer, 1884 , the latter presently belonging to Symplectoscyphus .

Allman (1888) did not note similarities or differences between his two species, though both are characterized by the typical orientation of the hydrothecae and side branches towards one side of the colony.

As underscored by Nutting (1904), the exceptional thickness of the perisarc described by Hartlaub (1901a) in his type of S. antarctica was neither mentioned nor figured by Allman (1876, 1879) in S. unilateralis . Nutting therefore thought that two different species could be involved. Additionally, the type material of Allman’s (1876) species could not be traced ( Vervoort 1972b) for a new examination.

According to Hartlaub (1901a), the degree of thickening of the perisarc is not a solid discriminating factor between species, and he did not exclude the possibility that both S. antarctica and S. allmani could be conspecific. However, he provisionally maintained them as separate species.

El Beshbeeshy (1991) compared Hartlaub’s original specimens of both S. antarctica (sample C.4161) and S. allmani (sample C.4177). Following his view, though very similar in appearance, only minor differences allow their separation. Sertularella antarctica is distinguished from S. allmani by: 1) the larger size of its colonies and side branches; 2) the narrower hydrothecae; 3) the smaller hydrothecal aperture; 4) the presence of basal annuli on the first stem internode; 5) the exceptional thickening of the perisarc.

According to El Beshbeeshy (1991), the specimens of S. antarctica studied by Nutting (1904), Blanco (1963), Vervoort (1972b), and Stepanjants (1979), as well as those assigned to S. picta ( Meyen, 1834) by Millard (1971), belong to S. allmani .

In spite of El Beshbeeshy’s (1991) opinion, we have followed Vervoort (1972b) and have synonymized both S. antarctica and S. allmani , the former having priority over the latter. In doing so, we have compared several distinctive features (table 1) and the measurements (table 2) of the specimens studied by the abovementioned authors.

It therefore becomes obvious that the specific characters listed by El Beshbeeshy are inconstant and may be found in either species. For example, quite large colonies (up to 6 cm high) were observed by Hartlaub (1901a, 1905) in S. allmani . The first stem internode was annulated basally in the specimens studied by Nutting (1904), Millard (1971), Vervoort (1972b), as well as in the present material. Additionally, the dimensions of the hydrothecae in both S. antarctica and S. allmani are highly variable (see table 2). The degree of thickening of the perisarc in the former species seems to be also variable, as illustrated by the material examined by Jäderholm (1905).

The sample C.4206 attributable by El Beshbeeshy (1991) to a distinct, probably new species, due to the larger size of its hydrothecae, is here included in the synonymy of S. antarctica . Its dimensions are indeed very similar to those given by Vervoort (1972b) for the type material of S. secunda Allman, 1888 .

The presence of internal, submarginal cusps of the hydrotheca were scantly reported in the various accounts, as for instance those mentioned by Hartlaub (1901a, 1905), Millard (1971), and the present study.

Taken together, the available data prove that S. antarctica is a very variable species, an opinion also shared with Nutting (1904), who examined numerous samples of this species.

Vervoort’s (1972b) specimens are quite peculiar in possessing an athecate internode between the stem apophyses and the proximal ends of the side branches. Our specimens have colonies identical to that depicted (fig. 10) by Allman (1879) for his S. unilateralis .

Although superficially similar, S. picta is mainly distinguished from S. antarctica by the following features (according to Hartlaub 1901a and El Beshbeeshy 1991): 1) it generally forms large (15–20 cm high), profusely branched colonies, with stems occasionally polysiphonic basally; 2) both the two rows of hydrothecae and the side branches form a very wide angle between them; 3) the internodes of both stems and branches are very long and have a zigzag appearance; 4) the side branches are often given off from nearly every stem internode, the 1st order branches branching again in a similar manner, giving the colony a masslike appearance; 5) the side branches are distinctly annulated basally; 6) the hydrothecal cusps are unequally developed; 7) the apical projections of the gonotheca are not always distinct.

Some authors ( Stepanjants 1979) recognized only minor differences between the above-mentioned species, and suggested that they could be possibly conspecific, pending additional studies to confirm their hypothesis.

TABLE 2: Comparative measurements of Sertularella antarctica Hartlaub, 1901 a, in µm. (1)The length of hydrotheca is

here considered nearly the same as its abcauline side.

Present study El Beshbeeshy (1991), Vervoort (1972), type of El Beshbeeshy El Beshbeeshy type of Hartlaub’s Allman’s (1888) S. (1991), as S. (1991), as (1901a) S. allmani secunda , antarctica Sertularella sp. C.4177 Challenger Stn. 149 nov. C.4206

Colony

– height 2.0 cm 6.0 cm 2.5 cm 5.0 cm 4.0 cm

Internodes

– length 340–640 450–550 600–950 498–845 533–765 World distribution. Kerguelen Island ( Allman 1888, Hartlaub 1901a), South Georgia ( Jäderholm 1905, El Beshbeeshy 1991), Falkland Islands ( Jäderholm 1905), off the eastern side of the Strait of Magellan ( Vervoort 1972b, El Beshbeeshy 1991), Strait of Magellan ( Hartlaub 1901a, Nutting 1904), Marion Island ( Millard 1971), San Juliáni ( Argentina) ( Blanco 1963).

Records from Chile. Nueva and Lennox Islands, Borgin Bay, Martha Bank ( Jäderholm 1903), Puerto Pantalon ( Hartlaub 1901a), South of Chiloé Island (present study).