Staurotheca pachyclada (Jäderholm, 1904)

Cantero, A. L. Peña & Vervoort, W., 2003, Species of Staurotheca Allman, 1888 (Cnidaria: Hydrozoa: Sertulariidae) from US Antarctic expeditions, with the description of three new species, Journal of Natural History 37 (22), pp. 2653-2722 : 2698-2702

Staurotheca pachyclada (Jäderholm, 1904)

(figures 14, 15; table 4)

Selaginopsis pachyclada Jäderholm, 1904a : x; 1905: 33, pl. 13 figures 2, 3; Peña (Cantero) et al., 1996: 8.

Staurotheca pachyclada: Stechow, 1923b: 152 ; Peña Cantero et al., 1997: 336.

Staurotheca pachyclada: Peña Cantero and García Carrascosa, 1999: 212 et seq.; Peña Cantero et al., 1999: 160 (in part).

Not Selaginopsis pachyclada: Briggs, 1938: 37 .

Not Selaginopsis pachyclada: Peña Cantero, 1991: 78–82 , pls 8, 42, pl. 64 figures c, d; Peña Cantero and García Carrascosa, 1994: 121, figure 3e–i; 1995: 28–32, figures 7A–L, 8A–F, 61B, C [= Staurotheca undosiparietina (Stepan’yants, 1979)]

Not Thuiaria pachyclada : Stepan’yants, 1979: 93–94, pl. 18 figure 2A, B; Blanco, 1984b: 193–196, figures 1–8 [= Staurotheca undosiparietina (Stepan’yants, 1979)].

Thuiaria affinis : Stepan’yants, 1972: 72.

Thuiaria juncea : Stepan’yants, 1979: 94, pl. 18 figure 4, pl. 24 figures A, V.

Staurotheca juncea: Peña Cantero et al., 1997: 357–359 , figure 6.

Staurotheca juncea p.p. Peña Cantero and García Carrascosa, 1999: 212 et seq.; Peña Cantero et al., 1999: 160.

Selaginopsis sp. 4 Peña Cantero, 1991: 97, pls 13, 47, 66 figure c; Peña Cantero and García Carrascosa, 1994: 122, figure 4k–o; 1995: 45–48, figures 17a–j, 18a–f, 62d.

Thuiaria pachyclada: Blanco, 1994a: 160 ; 1994b: 196.

Hydrotheca

Length of abcauline wall 770–850 Length of free adcauline wall 20–30 Length of adnate adcauline wall 900–1020 Length of adcauline wall 950–1040 Diameter at rim 280–300 Maximum diameter 450–530 Diameter at diaphragm 410–490

Material examined. 12 / 1002, five fragments up to 43 mm long (USNM 1003262); 12 / 1003, seven fragments up to 55 mm long (USNM 1003263); 27 / 1925, one extremely fragmented stem (largest fragment ca 55 mm long) (USNM 1003264; RMNH-Coel. 30316); 32 / 1995, two fragments up to 8 mm long (USNM 1003265); 32 / 1996, two fragments up to 12 mm long and one incipient stem ca 12 mm high (USNM 1003266); 32 / 1997, eight fragments up to 17 mm long (USNM 1003267); 32 / 2095, one stem fragment ca 35 mm long and one branch fragment ca 14 mm long (USNM 1003268); 32 / 2125, numerous fragments up to 45 mm long, with female gonothecae (USNM 1003269; RMNH-Coel. 30317);? 32 / 2128, two fragments up to 28 mm long (USNM 1003270);? 575 / 069, one stem ca 100 mm high (USNM 1003271); 691 / 26, several stems and fragments up to 200 mm high, with female gonothecae (USNM 1003272; RMNH-Coel. 30318; MNCN 2.03/291).

Description. Stems erect, polysiphonic, up to 160 mm high, usually deprived of branches basally. Branching scarce, irregularly pinnate, usually simple and in various planes. Stem and branches sometimes with a few perisarc constrictions. Branches strongly narrowed basally. Perisarc frequently striated.

Hydrothecae present over entire length of colony, though only visible in monosiphonic parts. Hydrothecae arranged in decussate verticils of three to six hydrothecae, forming 6–12 longitudinal rows (figure 14A), cylindrical in lateral view, immersed into the branches for ca two-thirds of their volume and adcaudally almost fully adnate (figure 14A, D). In frontal view hydrotheca cylindrical at upper half, but distinctly widening basally (figure 14A–C, E–H); frequently constricted at about half its length. Hydrothecal aperture circular and tilted downwards, forming an acute angle with long axis of branches. Rim even, usually with a shallow renovation. Hydrothecae lacking mushroom-shaped diaphragm.

Female gonothecae present, originating at hydrothecal base. Gonotheca oval (figure 14I), slightly constricted apically to form a short neck. Gonothecal aperture laterally depressed as the uneven rim is provided with two lobes, an adcauline and a much larger abcauline lobe. Gonothecal wall provided with a series of striae.

Remarks. We had the opportunity to examine the holotype of Selaginopsis pachyclada Jäderholm, 1904 . It is composed of 12 fragments (largest ca 38 mm long, remaining less than 15 mm long). There is a single fragment with a lateral branch, distinctly thinned at its origin. A description follows.

Hydrothecae in type material arranged in decussate verticils of four to six hydrothecae, forming 8–12 longitudinal rows (figure 15A). Hydrothecae sunken into the branches for approximately two-thirds of their volume and adcauline wall adnate to branch for almost its full length (figure 15A). In frontal view hydrotheca more or less cylindrical in upper half and then gradually widening towards basal part (figure 15A–E); sometimes with a constriction at half its length. Hydrothecal aperture circular, tilted downwards, forming an acute angle with long axis of stem and branches. Rim even; usually lacking renovations or only provided with a single one. Hydrotheca without mushroom-shaped diaphragm.

The type has no gonothecae.

Cnidome composed of microbasic mastigophores in two size groups: a larger (21–23.5×4.9–5.6 Mm) and a smaller group (9.8–10.5×2.5–2.8 Mm).

After studying the type material of Selaginopsis pachyclada Jäderholm, 1904 we failed to find differences with all the material previously assigned to Selaginopsis juncea Vanhöffen, 1910 (cf. Stepan’yants, 1979; Peña Cantero et al., 1997), with the exception of that described by Vanhöffen himself. In all that material the stems are erect and strong, and give rise to pinnae in several planes that usually do not rebranch and are strongly narrowed basally. The shape of the hydrothecae is similar to that of the type material described above and there is no mushroomshaped diaphragm. For this reason we consider all that material conspecific with S. pachyclada .

On the other hand, most of the material previously assigned to S. pachyclada by several authors (Stepan’yants, 1979; Blanco, 1984b; Peña Cantero and García Carrascosa, 1994, 1995) is considered now to belong to S. undosiparietina (Stepan’yants, 1979). It agrees with S. pachyclada in the branching in several planes, but it differs in the shape of the hydrothecae which are, moreover, provided with a mushroom-shaped diaphragm.

The material referred to S. pachyclada by Briggs (1938) does not belong here and neither to S. undosiparietina . It may constitute a new species.

Ecology and distribution. Staurotheca pachyclada is a eurybathic species, having been found at depths from 42 (Stepan’yants, 1979 as Thuiaria juncea ) to 470 m (Peña Cantero et al., 1997 as Staurotheca juncea ) on bottoms of mud, stones (Peña Cantero et al., 1997), rock (Stepan’yants, 1979) and stones with mud (Peña Cantero and García Carrascosa, 1994); our material comes from 119–1405 m. It is used as a substratum by other hydroids ( Billardia sp. , Filellum sp. ). Fertile colonies were collected in January (Jäderholm, 1904a; Peña Cantero and García Carrascosa, 1994; Peña Cantero et al., 1997) and from December to February (Stepan’yants, 1979); in our material colonies with gonothecae were found in February.

Staurotheca pachyclada has a circum-Antarctic distribution, being known from both East and West Antarctica. In the former, it has been reported from the Davis Sea (Stepan’yants, 1979 as Thuiaria juncea ). In West Antarctica it is known from off Seymour Island, Graham Land (Jäderholm, 1904a), the South Shetland Islands (Stepan’yants, 1979 as Thuiaria juncea ; Peña Cantero and García Carrascosa, 1994 as Selaginopsis sp. 4 ), Elephant Island (Peña Cantero and García Carrascosa, 1994 as Selaginopsis sp. 4 ) and the east coast of the Weddell Sea (Peña Cantero et al., 1997 as Staurotheca juncea ). Our material comes from the Ross Sea and the Antarctic Peninsula. In the former, it was collected off Victoria Land (off Cape Adare, east of Pennell Bank, east of Cape Hallett, and the central basin). At the Antarctic Peninsula it was found off Elephant Island, north-east of Joinville Island (Antarctic Peninsula), and south of Low Island.

Staurotheca plana Peña Cantero, Svoboda and Vervoort, 1997 Staurotheca plana Peña Cantero et al., 1997: 362–364 , figures 8, 13C; 1999: 160; Peña Cantero and García Carrascosa, 1999: 215.

Remarks. Staurotheca plana is well characterized by the erect and polysiphonic stems, scarcely branched in one plane, by the presence of two to three hydrothecae per verticil, and by the absence of both anastomoses and mushroom-shaped diaphragm (cf. table 6).

Ecology and distribution. Staurotheca plana has been found from depths of 672– 830 m off the eastern coast of the Weddell Sea (Peña Cantero et al., 1997). It was found with gonothecae in February (Peña Cantero et al., 1997).