Staurotheca undosiparietina

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 : 2705-2707

Staurotheca undosiparietina (Stepan’yants, 1979)

(figure 17)

Thuiaria sp. 1 p.p. Naumov and Stepan’yants, 1962: 92–93.

Thuiaria undosiparietina Stepan’yants, 1979: 94, pl. 18 figure 3, pl. 24, figures G, Z (in part); Blanco, 1994a: 160; 1994b: 196; Peña (Cantero) et al., 1996: 8.

Thuiaria pachyclada : Stepan’yants, 1979: 93–94, pl. 18 figure 2A, B; Blanco, 1984b: 193–196, figures 1–8.

Staurotheca undosiparietina: Peña Cantero et al., 1997: 336 , 370–373, figure 11; 1999: 160.

Selaginopsis pachyclada: Peña Cantero, 1991: 78–82 , pls 8, 42, pl. 64 figure c, d; Peña Cantero and García Carrascosa, 1994: 121, figure 3e–i; 1995: 28–32, figures 7A–L, 8A–F, 61B, C; Peña (Cantero) et al., 1996: 8.

Material examined. 22 / 1535, two fragmented stems (largest fragment ca 140 mm long), with male and female gonothecae ( USNM 1003274; RMNH-Coel. 30319; MNCN 2.03/292); 22 / 1536, one stem ca 100 mm high ( USNM 1003275; RMNH- Coel. 30320); 575 / 085, three fragments up to 20 mm long ( USNM 1003276); 601 / 008, five fragments up to 40 mm long, with female gonothecae ( USNM 1003277); 601 / 012, two stems up to 250 mm high, with female gonothecae ( USNM 1003278; RMNH- Coel. 30321; MNCN 2.03/293); 601 / 018, one stem ca 320 mm high, with female gonothecae ( USNM 1003279); 601 / 023, one stem ca 280 mm high, with female gonothecae ( USNM 1003280); 601 / 077, one stem ca 270 mm high ( USNM 1003281); 601 / 083, one stem ca 170 mm high, with male gonothecae ( USNM 1003282); 601 / 106, one stem ca 260 mm high ( USNM 1003283); 601 / 130, two stems ca 310 and 270 mm high ( USNM 1003284; RMNH-Coel. 30322; MNCN 2.03/294); 9 / 671, one extremely fragmented stem ( USNM 1003285; RMNH-Coel. 30323); 9 / 732, several extremely fragmented stems (largest fragment ca 90 mm long), with male gonothecae ( USNM 1003286; RMNH-Coel. 30324; MNCN 2.03/295).

Description. Stems up to 320 mm high, polysiphonic over a great extension. Main stem distinct, deprived of branches basally. However, when branching becomes frequent, main stem becoming indistinct. Branching scarce, irregular and in several planes.

Hydrothecae present over entire colony, though inconspicuous in polysiphonic parts. Hydrothecae arranged in verticils of three to five hydrothecae (figure 17A) forming 6–10 longitudinal rows. Hydrothecae (figure 17A–F) immersed into the branches for approximately half of their volume and adnate for almost full adcauline length; free adcauline wall inconspicuous. In lateral view hydrotheca cylindrical and slightly abcaudally directed; abcauline wall slightly concave. In frontal view maximum diameter at hydrothecal base, slightly decreasing upwards. Hydrothecal aperture circular and tilted downwards, forming an acute angle with long axis of stem; rim even and sometimes with renovations. Hydrothecal diaphragm mushroom-shaped, though sometimes abcauline projections absent.

Male and female gonothecae present, both originating at the hydrothecal base. Female gonotheca oval (figure 17G), provided with a distal, laterally depressed aperture due to the presence of one adcauline cusp and one, better developed, abcauline cusp. Male gonotheca fusiform (figure 17H), with a small, circular aperture at the end of an inconspicuous neck. Both male and female gonothecae with abcauline keel.

Remarks. Peña Cantero et al. (1997) demonstrated that the holotype and paratype of Staurotheca undosiparietina belong to two different species, the latter being referred to S. polarsterni .

As stated above, after the revision of the type material of Staurotheca pachyclada (Jäderholm, 1904) , the material assigned to Jäderholm’s species by Stepan’yants (1979), Blanco (1984b) and Peña Cantero and García Carrascosa (1995) is now considered conspecific with S. undosiparietina sharing with this species the general shape of the colony, the scarce branching in several planes, the number of longitudinal rows of hydrothecae, and the shape of the hydrothecae and gonothecae, the former having a mushroom-shaped diaphragm.

Ecology and distribution. Staurotheca undosiparietina is a shelf species (Peña Cantero et al., 1997). It has been found at depths from 74 (Peña Cantero and García Carrascosa, 1995 as Selaginopsis pachyclada ) to 700 m (Stepan’yants, 1979 as Thuiaria pachyclada ); our material was collected from 93 to 686 m. It has been taken on bottoms of rocks, gravel and mud (Stepan’yants, 1979 as Thuiaria pachyclada ), mud with stones, stones, and rocks with mud (Peña Cantero and García Carrascosa, 1995 as Selaginopsis pachyclada ). It is used as a substratum by other hydroids (Peña Cantero and García Carrascosa, 1995 as Selaginopsis pachyclada ); we also found colonies of Halecium sp. and Sertularella sp. Stepan’yants (1979, as Thuiaria pachyclada ) reported colonies with gonothecae from December to May and Peña Cantero and García Carrascosa (1995, as Selaginopsis pachyclada ) from November to January. In our material, fertile colonies were collected in February, September, November and December. It therefore seems fertile throughout much of the year, except during the winter months.

Staurotheca undosiparietina appears to be endemic to West Antarctica. It has been reported from off the South Shetland Islands (Stepan’yants, 1979, also as Thuiaria pachyclada ; Peña Cantero and García Carrascosa, 1995, as Selaginopsis pachyclada ), Elephant Island (Peña Cantero and García Carrascosa, 1995, as Selaginopsis pachyclada ; Peña Cantero et al., 1997) and South Georgia (Stepan’yants, 1979, as Thuiaria pachyclada ; Blanco, 1984b, as Thuiaria pachyclada ; Peña Cantero and García Carrascosa, 1995, as Selaginopsis pachyclada ). Our material comes from off Shag Rocks and South Georgia.