Antarctoscyphus biformis ( Jäderholm, 1905 )

Peña Cantero, Álvaro L., Roig Ferrer, Estela & Miranda, Thais P., 2017, Species of Antarctoscyphus Peña Cantero, García Carrascosa and Vervoort, 1997 (Cnidaria: Hydrozoa: Symplectoscyphidae) collected by US Antarctic expeditions: biogeographic implications, Journal of Natural History (J. Nat. Hist.) 51 (25 - 26), pp. 1437-1477 : 1448-1453

Antarctoscyphus biformis ( Jäderholm, 1905)

( Figures 4 , 5 (a–d), 6)

Sertularella biformis Jäderholm, 1905, p. 28 , pl. 11, figs 1–3. not Sertularella biformis – Totton, 1930, p. 199, fig. 45, pl. 2, fig. 8; Naumov and

Stepanjants, 1972, p. 47, fig. 9; Stepanjants, 1979, p. 66, pl. 11, fig. 5 [=

Antarctoscyphus grandis ( Blanco, 1977) ]. Antarctoscyphus biformis – Peña Cantero et al., 1997, p. 25.

Material examined

Eltanin: 12/1002, three stems c. 10, 18 and 20 mm high, on stone.

Holotype of Sertularella biformis ( Swedish Museum of Natural History , SMNH register no. 2986), Stn 8, 11–02– 1902, 360 m, 64°3’ S, 56°37 ʹ W ( Erebus and Terror Gulf, Graham Region), one stem, c. 17 mm high.

Diagnosis

Stems monosiphonic, unbranched, up to 20 mm high. Cauline internodes long and arranged in a slight zigzag fashion. Cauline apophyses very short, not overpassing distal node, and strongly directed upwards. Paired branches strongly directed upwards, short and weakly branched; each branching at second and fourth internode, giving rise to a second-order branch. Paired branches divided into short internodes distinctly shortening distally. Hydrothecae arranged unilaterally, although alternately directed outwards, forming two longitudinal rows on same side of branch. Hydrothecae distinctly overlapping; packaging increasing distally. Hydrotheca mostly laying on internode; roughly cylindrical. Adcauline wall convex, particularly at distal part; adnate along about one-fifth of its length. Abcauline wall basally straight, becoming concave distally. Adcauline wall distinctly longer. Hydrotheca wider basally, distinctly narrowing distally. Adcauline cusp much more developed than abcauline ones. Internal abcauline cusp present. Gonothecae unknown.

Description

Monosiphonic, unbranched stems, up to 20 mm high. Stem internodes arranged in a slight zigzag fashion. Cauline internodes provided with an apophysis at distal part, giving rise to two paired branches and a hydrotheca at axil in between ( Figure 4 (b)). Cauline apophyses very short, not overpassing distal node of cauline internode, and strongly directed upwards. Paired branches strongly directed upwards, short and weakly branched. Each paired branch branching first at second internode, giving rise to a second-order branch, and again at fourth internode, giving rise to another secondary branch ( Figure 4 (a)). Paired branches divided into internodes. Length of branch internodes decreasing distally; nodes disappearing at distal part. Each branch internode provided with a hydrotheca.

Hydrothecae with unilateral arrangement ( Figures 4 (a,c,d) and 5(a—c)), alternately leaning outwards, particularly at distal part ( Figures 4 (c,d) and 5(a–c)). Hydrothecae closely packed. Packaging increasing along branches: at basal part, hydrothecae not reaching following ones ( Figure 4 (a)); more distally, overpassing basal part of alternate ones ( Figures 4 (d) and 5(a)); at distal part, hydrothecae overpassing half of alternate ones and even reaching basal part of following hydrothecae on the same side ( Figures 4 (c) and 5(b,c)). Hydrotheca laying on internode for most of its length, adnate in about one-fifth of its adcauline length and more or less straight, except for its distal third ( Figures 4 (c,d) and 5(a–c)). Adcauline wall convex, particularly at distal part. Abcauline wall basally straight, becoming concave distally. Adcauline wall distinctly longer. Hydrotheca wider basally, distinctly narrowing distally ( Figures 4 (c,d) and 5(a–c)). Hydrothecal aperture abcaudally directed ( Figures 4 (c) and 5(a–d)), with three marginal cusps ( Figure 4 (d–f)); adcauline cusp much more developed. An internal abcauline cusp present ( Figure 5 (d)).

Gonothecae unknown.

Measurements (in µm)

Cauline internodes: length 4.0– 6.5 mm, diameter 800–1100 µm. Hydrotheca: free adcauline length, range 300–375, mean 345 ± 35 (n = 9); adnate adcauline length, range 575–625, mean 600 ± 20 (n = 9); abcauline length, range 725–900, mean 800 ± 77 (n = 9); diameter at aperture, range 200–225, mean 210 ± 13 (n = 9). Cnidome: larger size group, range 10.4–11.9 × 3.3–4.3, mean 11.2 ± 0.6 × 3.8 ± 0.4 (n = 6).

Description of holotype

Stem c. 17 mm high. First 6 mm with accompanying stolon arising from aperture of first hydrotheca and running up and down. First 2.5 mm of stem without hydrothecae; the remainder with hydrothecae alternately arranged in one plane ( Figure 6 (a)). First 13 cauline hydrothecae simple ( Figure 6 (a)); 14th with remnants of one paired hydrotheca; 15th without any paired hydrothecae; all succeeding stem hydrothecae with paired hydrothecae ( Figure 6 (b)).

First cauline node appearing after 20th hydrotheca. Second node present after 23rd hydrotheca; after it, stem broken. Consequently, stem provided with a single internode with three cauline hydrothecae and their corresponding paired hydrothecae.

Only paired hydrothecae present ( Figure 6 (b)); with no sign of further branch development.

Hydrothecae tubular, curved outwards ( Figure 6 ). Adcauline wall convex. Abcauline wall straight basally, becoming concave distally. Adcauline wall distinctly longer ( Figure 6 (a)). Hydrothecal diameter distinctly smaller at distal part ( Figure 6 (a,b)). Rim of hydrothecal aperture with three marginal cusps ( Figure 6 ); adcauline one much more developed.

Measurements (in µm)

Cnidome: larger size group, range 9.5–10.5 × 3.0–3.5, mean 10.2 ± 0.3 × 3.3 ± 0.3 (n = 10).

Remarks

Antarctoscyphus biformis had never been reported since the original description, based on an unbranched stem of 20 mm height. Due to the absence of branching in Jäderholm’ s material there was uncertainty about whether this species belongs to the genus Antarctoscyphus (cf. Peña Cantero et al. 1997). The USARP material described above undoubtedly belongs to Jäderholm’ s species, coinciding in both the shape and size of the hydrotheca, which allowed us to improve knowledge about this uncommon species and confirm that we are dealing with a species of Antarctoscyphus .

Bathymetric and geographic distribution

Antarctoscyphus biformis has a much-restricted known distribution. It had only been recorded from Erebus and Terror Gulf (Graham Land, Antarctic Peninsula), where it was collected at a depth of 360 m ( Jäderholm 1905). Our material comes from the nearby Elephant Island, where it was collected at a depth of 265 m, on a stone.

Figures

Figure 4. Antarctoscyphus biformis (Jäderholm, 1905): (a) paired branch showing branching and hydrothecal arrangement; (b) distal part of cauline internode showing axillary hydrotheca and basal part of paired branches; (c) fragment of distal part of a branch showing shape and arrangement of hydrothecae; (d, e) hydrothecae; (f) detail of hydrothecal distal part, showing cusps. Scale bars: 1 mm (a), 500 µm (c), 250 µm (b, d), 50 µm (f).

Figure 5. Antarctoscyphus biformis (Jäderholm, 1905): (a–c) hydrothecal shape and arrangement; (d) distal part of hydrotheca showing abcauline internal cusp (arrow). Antarctoscyphus fragilis Peña Cantero, Svoboda and Vervoort, 1999: (e, f) hydrothecae. Scale bar: 200 µm (a–c, e, f), 100 µm (d).

Figure 6. Antarctoscyphus biformis (Jäderholm, 1905) (Holotype): (a), cauline hydrothecae showing alternate arrangement; (b) cauline hydrotheca with paired hydrothecae; (c) hydrotheca (frontal view). Scale bars: 250 µm.