Staurotheca multifurcata Peña Cantero, García Carrascosa and Vervoort, 1999

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 : 2693-2696

Staurotheca multifurcata Peña Cantero, García Carrascosa and Vervoort, 1999

(figure 12)

Staurotheca multifurcata Peña Cantero et al., 1999: 159–161 , figures 2, 3B.

Selaginopsis sp. 1 Peña Cantero, 1991: 87–90, pls 10, 44, pl. 65 figure b; Peña Cantero and García Carrascosa, 1994: 121, figure 3o–s; 1995: 35-38, figures 11A–J, 12A–E, 62A.

Selaginopsis sp. 2 Peña Cantero, 1991: 90–93, pls 11, 45, pl. 66 figure a; Peña Cantero and García Carrascosa, 1994: 121, figure 4a–e; 1995: 38–42, figures 13A–J, 14A–F, 62B.

Material examined. 575 / 020, one fragmented stem (largest fragment ca 150 mm long), with female gonothecae (USNM 1003241; RMNH-Coel. 30304); 575 / 032, three fragments up to 50 mm long, with female gonothecae (USNM 1003242); 575 / 083, one fragmented stem (up to 140 mm long), with female gonothecae (USNM 1003243; RMNH-Coel. 30305); 575 / 094, one extremely fragmented stem, at least 180 mm high (USNM 1003244; RMNH-Coel. 30306; MNCN 2.03/284); 575 / 095, several fragmented stems up to 220 mm long, with male and female gonothecae (USNM 1003245; RMNH-Coel. 30307; MNCN 2.03/285); 575 / 097, several fragmented stems up to 190 mm long, with female gonothecae (USNM 1003246; RMNH- Coel. 30308; MNCN 2.03/286); 575 / 098, two stems up to 200 mm high, with male and female gonothecae (USNM 1003247; RMNH-Coel. 30309; MNCN 2.03/287); 601 / 011, one stem ca 105 mm high (USNM 1003248); 601 / 040, one stem ca 350 mm high, with male gonothecae (USNM 1003249); 601 / 076, one stem ca 480 mm high, with male gonothecae (USNM 1003250; RMNH-Coel. 30310; MNCN 2.03/288); 601 / 077, one stem ca 340 mm high, with male gonothecae (USNM 1003251); 601 / 081, one stem ca 270 mm high, with male gonothecae (USNM 1003252).

Description. Stems up to 480 mm high, of dark brown colour and polysiphonic over a great part of their length. Main stem slightly geniculate. Branching starting at basal part of colony, frequent, in one plane, and approximately alternate. Branches distinctly constricted at their origin, originating at an angle of ca 45°, curving and running more or less parallel to the original branch. Branches with irregularly arranged perisarc constrictions.

Hydrothecae present all over the colony, although invisible in polysiphonic parts. Hydrothecae usually arranged in decussate verticils of three to six hydrothecae, forming 6–12 longitudinal rows (figure 12A); however, decussate pairs of hydrothecae may be present in youngest, distal branches. Hydrothecae (figure 12A–F) sunken into the branches and stems for approximately half of their volume, adcauline wall adnate for almost full length. In lateral view hydrotheca cylindrical, slightly curved abcaudally. In frontal view maximum diameter at hydrothecal base and then slowly decreasing in diameter towards the aperture. Hydrothecal aperture either even and approximately circular, or uneven with a more or less distinct prolongation of the abcauline hydrothecal wall, making the aperture laterally depressed. Hydrothecal aperture either tilted downwards, forming an acute angle with the longitudinal axis of stem, or tilted upwards, being more or less perpendicular to long axis of branches. Rim of hydrothecal aperture sometimes with a few shallow renovations. Diaphragm mushroom-shaped.

Male and female gonothecae present, inserted directly at hydrothecal base. Female gonotheca (figure 12G) with a basal, cone-shaped portion and a distal, eccentric neck, placed near adcauline wall of gonotheca. Neck with two lips of varied development, one abcauline and one adcauline. Abcauline lip usually better developed, forming distal part of gonotheca, whereas adcauline lip is either absent or scarcely developed in which case the gonothecal aperture is lateral and closed by a thin membrane of perisarc. However, other gonothecae have a much less-developed abcauline lip, and then the gonothecal aperture is distal and lacks the operculum. This variability in the structure of the female gonothecae is probably due to development, which is supported by the fact that in the situation described first, there is an ovum in each gonotheca (gonothecal aperture closed by a membrane), whereas in the second the gonothecae are empty (open apertures). Male gonotheca fusiform (figure 12H), without distinct peduncle, and provided with a distal and usually eccentrically placed, cone-shaped neck provided with a small circular aperture.

Cnidome composed of microbasic mastigophores in two size groups: a larger (19.6–23.8×4.9–5.6 Mm) and a smaller group (8.4–9.8×2.1–2.8 Mm).

Remarks. The variability in the hydrothecal shape, especially with regards to the abcauline elevation of the aperture, is observed even in the same colony. Usually, the hydrothecae with abcauline elevation occur in the distal part of the colony.

Peña Cantero and García Carrascosa (1994, 1995) described as Selaginopsis sp. 2 material of a species of Staurotheca which is here considered conspecific with S. multifurcata , since it agrees with this species in colony structure and in shape and size of hydrothecae and gonothecae.

In the material from Stn 575/98 a male colony also gives rise to female gonothecae. This phenomenon was already noted by Peña Cantero and García Carrascosa (1995) in the material described as Selaginopsis sp. 2 from Station ANT 154, though in this case it was a female colony which also gave rise to male gonothecae. In both colonies some branches arise from the gonothecae. This phenomenon seems to result from the use of the gonothecal structure to form a new branch which may also carry gonothecae. New branches apparently develop from fenestrae normally used for the formation of gonothecae or develop from female gonothecae after a period of inactivity of the colony or because of reconstruction of the colonial skeleton after the death of the former colony. The fact that either branches with male gonothecae spring from branches with female gonothecae (as in Peña Cantero and García Carrascosa’s material) or branches with female gonothecae spring from branches with male gonothecae (as in our material) seems to indicate either a change of sex or may indicate development of a new colony, of different sex, from a planula (re-utilizing the colonial structure). The alternate branching of the colony is only interrupted by such ‘reconstructed’ branches.

Staurotheca multifurcata is close to S. affinis (Jäderholm, 1904) in colony structure (cf. table 6), with polysiphonic and erect, fan-shaped stems, alternately branched in one plane, and with hydrothecae provided with a mushroom-shaped diaphragm. They clearly differ, however, in the number of hydrothecae per verticil, as in S. multifurcata there are usually three to six hydrothecae per verticil, forming 6–12 longitudinal rows, whereas in S. affinis there are normally three hydrothecae per verticil throughout the colony, forming six longitudinal rows [in the material studied by Peña Cantero and García Carrascosa (1995) there are four hydrothecae per verticil throughout the colony]. In both species, however, decussate pairs of hydrothecae may be also found in the youngest branches.

Ecology and distribution. Staurotheca multifurcata is a shelf species. It was found at depths from 279 to 330 m on rocky bottoms (Peña Cantero et al., 1999), whereas Peña Cantero and García Carrascosa (1995) reported it from 100 to 254 m (as Selaginopsis sp. 2 ) and we found it from 57 to 346 m. Staurotheca multifurcata has been collected on rocky (Peña Cantero et al., 1999) and stony bottoms (Peña Cantero and García Carrascosa, 1995 as Selaginopsis sp. 2 ). It is used as substratum by other hydroids ( Billardia sp. , Lafoea sp. , Halecium sp. , Sertularella sp. , Symplectoscyphus sp. ). It was found with gonothecae in December (Peña Cantero and García Carrascosa, 1995 as Selaginopsis sp. 2 ; Peña Cantero et al., 1999). In our material, fertile colonies were collected in May, June and December.

Staurotheca multifurcata appears to be endemic to the Scotia Ridge islands. It has been found off Clerke Rocks (Peña Cantero and García Carrascosa, 1995 as Selaginopsis sp. 2 ; Peña Cantero et al., 1999), South Georgia (Peña Cantero and García Carrascosa, 1995 as Selaginopsis sp. 2 ; present material), Shag Rocks (present material) and from off Bristol Island, in the South Shetland Islands (Peña Cantero and García Carrascosa, 1995 as Selaginopsis sp. 2 ).