Symplectoscyphus frondosus, Peña, Álvaro L., 2010

Peña, Álvaro L., 2010, On a new Antarctic species of Symplectoscyphus Marktanner-Turneretscher, 1890 (Cnidaria, Hydrozoa, Sertulariidae), with an annotated checklist of the Antarctic species of the genus, Zootaxa 2494, pp. 29-44 : 30-34

publication ID	https://doi.org/ 10.5281/zenodo.195709
DOI	https://doi.org/10.5281/zenodo.5622799
persistent identifier	https://treatment.plazi.org/id/247AF616-FF8F-FFBC-FF16-FDB0FB06F81B
treatment provided by	Plazi
scientific name	Symplectoscyphus frondosus
status	sp. nov.

Treatment

Symplectoscyphus frondosus sp. nov.

( Figures 1 View FIGURE 1 A–C, 2, Table 2 View TABLE 2 )

Material examined. Stn 82, two complete stems 165 ( NIWA 60488) and 65 mm high ( MNCN 2.03/437), the latter with immature male gonothecae; Stn 102 VV, one fragment c. 6 mm long, with immature female gonothecae ( NIWA 60489); Stn 103, three stems 85, 40 ( NIWA 60490) and 30 mm high ( MNCN 2.03/438); Stn 108, one branched stem c. 300 mm high, with male gonothecae (holotype, NIWA 60491), 16S sequence FN424151 View Materials ; Stn 171, two stems 100 ( NIWA 60492) and 95 mm high ( MNCN 2.03/439), with male gonothecae, on mollusc shell.

Other material. Symplectoscyphus liouvillei ( Billard, 1914) : Spanish Antarctic Expedition Bentart 95, Stn 5A, 23–01–95, 62º41.6855' S 60º31.8195' W (south of Livingston Island, the South Shetland Islands), 256 m, twelve stems up to 185 mm high.

Description (Holotype): Erect, main stem strongly sinuous, giving rise to primary branches spirally arranged, with a complete whorl every five branches. Roughly all branches of similar development, which gives the colony a bottlebrush appearance ( Fig. 1 View FIGURE 1 A). Stem completely and strongly polysiphonic. Branches also with well-developed polysiphony, but becoming monosiphonic distally. Usually only most distal part of branches monosiphonic.

Stem branched ( Fig. 1 View FIGURE 1 A), giving rise to two secondary stems at c. 80 and 110 mm high, 80 and 150 mm long, respectively. The latter, in turn, forming a third-order stem c. 80 mm long. Lower-order stems originating from much developed primary branches.

Rhizoidal hydrorhiza composed of relatively thin stolons, some attached to gravel ( Fig. 1 View FIGURE 1 A). Basalmost part of stem, however, forms a disc-shaped hydrorhiza, clearly indicating original settlement on hard substrate (e.g. pebbles, gravel). First 60 mm of main stem were clearly buried in sediment, as there are numerous rhizoidal stolons, some attached to gravel, and there are either no branches at all basally or just the proximal part of them at distal part ( Fig. 1 View FIGURE 1 A).

Branching much developed ( Fig. 1 View FIGURE 1 A, B), though all branches of similar development, resulting in a bottlebrush-shaped habit. Branching alternate in two planes, occurring always on the upper side of branches and taking place every 4–7 hydrothecae. Primary branches with distinct unbranched proximal part.

Primary branch giving rise to four secondary branches alternately arranged in two planes. They all originate at the upper side of primary branch, at the base of alternating hydrothecae.

First secondary branch forming four third-order branches. Of these, the first branch forms three fourthorder branches; the first of these originates in turn two fifth-order branches; finally, the first fifth-order branch gives rise to one sixth-order one. Second third-order branch giving rise to two fourth-order branches; of these, the first forms one fifth-order branch. Third third-order branch giving rise to one fourth-order one.

The second secondary branch gives rise to three third-order branches. Of these, the first one originates three fourth-order branches. The first of these form two fifth-order branches and, in turn, the first of these gives rise to one sixth-order branch. The second fourth-order branch also gives rise to one fifth-order branch.

Finally, the third and fourth secondary branches give rise to two and one third-order branches, respectively. All this branching occurs in just 17 mm long ( Fig. 1 View FIGURE 1 B).

Branches and stems divided into short internodes by alternating oblique nodes ( Fig. 2 View FIGURE 2 A–E). Diameter of internodes and perisarc development decreasing distally along the branch. One hydrotheca per internode. Hydrothecae alternately arranged in approximately one plane ( Fig. 2 View FIGURE 2 C, D). Hydrotheca straight or just slightly abcaudally directed ( Fig. 2 View FIGURE 2 A–E). Adcauline wall adnate to internode in approximately half its length; free part of adcauline wall approximately straight ( Fig. 2 View FIGURE 2 A–E). Abcauline wall roughly straight. Hydrotheca with an oblique ring of desmocytes ( Fig. 2 View FIGURE 2 B, D). Hydrothecal diameter at aperture provided with three cusps separated by deep embayments ( Fig. 2 View FIGURE 2 A–E). Rim of hydrothecal aperture sometimes with a few renovations.

Gonothecae partially resting on branches, very long and with completely and strongly transversally striated walls. Male gonothecae ( Fig. 2 View FIGURE 2 F) complete, long and thin, roughly of similar diameter throughout, except for the tapering most basal part. Diameter at distal end sharply reduced, ending with a short and wide distal neck ( Fig. 2 View FIGURE 2 F). Female gonothecae ( Fig. 2 View FIGURE 2 G) incomplete, also fusiform, basally tapering, and abruptly ending distally. Diameter much greater than that of male gonothecae.

Remarks. Although the stem is branched in the holotype, stems are unbranched in the remaining colonies available for study (e.g. Fig. 1 View FIGURE 1 C).

The branching pattern described for the holotype is similar to that found in the colonies from the remaining material (e.g. Fig. 1 View FIGURE 1 C). The general structure of branching calls to mind that of Antarctoscyphus grandis (fig. 7C in Peña Cantero et al., 1999).

Symplectoscyphus frondosus sp. nov. appears to be allied to S. liouvillei ( Billard, 1914) , as they both possess erect, polysiphonic stems giving rise to spirally arranged primary branches. They also agree in the general shape of the hydrothecae. However, they are clearly distinguishable by a series of characteristics.

First, they differ in the general habit of the colonies. Even though they both have erect, polysiphonic stems with spirally arranged primary branches, the appearance is completely different ( Fig. 1 View FIGURE 1 ). As indicated above, S. frondosus sp. nov. has strongly rigid, very densely branched, bottlebrush stems with all branches of similar development ( Fig. 1 View FIGURE 1 A, C). By contrast, in S. liouvillei the stems are droopy ( Fig. 1 View FIGURE 1 D and Fig. 14 in Billard 1914), they are decidedly less branched and with branches of an uneven development, in particular becoming more developed distally.

The degree of polysiphonic development is also different. In S. frondosus sp. nov. the polysiphony practically extends all over the colony ( Fig. 1 View FIGURE 1 A, C), whereas in S. liouvillei it distinctly decreases distally, with an important monosiphonic distal part ( Fig. 1 View FIGURE 1 D and fig. 14 in Billard 1914). In S. frondosus sp. nov. the branch polysiphony is similar throughout the colony ( Fig. 1 View FIGURE 1 A, C), whereas in S. liouvillei there are many monosiphonic unbranched primary branches, whereas the most-developed branches have greater polysiphony.

As indicated above, both species have the primary branches arranged in a spiral pattern, but the branches are much more densely packed in S. frondosus sp. nov. than in S. liouvillei . In the former a whorl is complete in ca. 5 mm ( Fig. 1 View FIGURE 1 A, C), whereas in the latter in ca. 17 mm ( Fig. 1 View FIGURE 1 D).

Both species also agree in frequent branching, but differ in branching structure. The branches giving rise to lower-order ones are straight in S. frondosus sp. nov. ( Fig. 1 View FIGURE 1 B), but distinctly sinuous in S. liouvillei . In Billard’s species, those branches strongly arch to the opposite direction of the lower-order ones (fig. 9B in Peña Cantero et al. 2002), giving them the twisting aspect. In addition, in S. liouvillei there is a variable development of the branches, some of them becoming much more developed, particularly distally, whereas they are of similar development in S. frondosus sp. nov.

Although the general shape of the hydrotheca seems similar in both species, detailed comparison shows that the hydrothecae are smaller in S. frondosus sp. nov., particularly in relation to the adcauline length, the adnate part of which is clearly smaller (table 9 in Peña Cantero et al. 2002). The diameter at aperture is also smaller. In S. liouvillei the adnate proportion of the adcauline hydrothecal wall is distinctly larger (table 9 in Peña Cantero et al. 2002).

The hydrothecal internodes in S. frondosus sp. nov. invariably lack the basal constriction at the side of the hydrotheca described in S. liouvillei (Billard’s “bourrelet).

Finally, there are also important differences in the structure of the gonothecae, particularly the male ones, which have completely striated walls in S. frondosus sp. nov. but smooth ones in S. liouvillei . Moreover, in the latter the male gonothecae are much longer. On the other hand, though the structure of the female gonothecae is insufficiently known in S. frondosus sp. nov., because so far only incomplete gonothecae have been found, they also have strongly striated walls, whereas the female gonothecae in S. liouvillei have smooth or inconspicuously striated walls (barely visible when stained).

Amongst the other Antarctic species of the genus only Symplectoscyphus cumberlandicus ( Jäderholm, 1904) and S. sofiae Peña Cantero et al., 2002 are also characterized by forming polysiphonic, erect stems. Nevertheless, they both are clearly different from S. frondosus sp. nov. in colony form, because in those species branching occurs in one plane, usually following an alternate pattern, and typically at every third hydrotheca in S. cumberlandicus . They also differ in the shape and size of the hydrothecae and markedly in the shape of the gonothecae, which are provided with rings in S. cumberlandicus and S. sofiae .

Ecology and distribution. Our material, which includes colonies with gonothecae, was collected in February, at depths between 400 and 564 m off Cape Adare and Cape Hallet.

Etymology. The specific name frondosus refers to the extremely abundant branches.

	Range	Mean ± SD (n=10)
Hydrothecae
length abcauline wall length free part of adcauline wall	380–425 185–245	402.5±14.7 220±23.2
length adnate part of adcauline wall	220–260	240.5±14.2
ratio adnate/free part length adcauline wall	0.90–1.32 425–495	1.1±0.15 461.5±22.3
maximal diameter	170–220	183±16.0
diameter at aperture diameter at diaphragm	140–155 100–150	149±5.2 123.5±11.2
Gonothecae
Male gonothecae length	1800–2250
maximal diameter	300–375
length of neck diameter at aperture	70 110–140
Female gonothecae
length maximal diameter	Up to 1500 400–520