Staurotheca Allman, 1888

Watson, Jeanette W., 2003, Deep-water hydroids (Hydrozoa: Leptolida) from Macquarie Island, Memoirs of Museum Victoria 60 (2), pp. 151-180 : 169-170

Staurotheca Allman, 1888

Staurotheca vanhoeffeni (Peña Cantero, García Carrascosa and Vervoort)

Figures 19A–E

Staurotheca vanhoeffeni Peña Cantero et. al., 1996: 1–10, figs 1–3.—Peña Cantero et al., 1997: 373, fig. 12. Dictyocladium affine . — Vanhöffen, 1910: 331, figures 44a–c. Thuiaria affinis . — Stepanjants, 1979: 95, pl. 18 figs 1A, B, pl. 24 figs D–F. Selaginopsis vanhoeffeni . —Peña Cantero and García Carrascosa, 1994: 121, figs 3j–n.

Material examined. Stn 44, NMV F91322, several sparingly fertile branch fragments, specimen alcohol-preserved. Stn 122, TM K2781, specimen alcohol-preserved, NMV F91347, malinol mounted microslide from infertile colony detached from substrate

Description. Colony stiff and woody, stem 2 mm thick at base, detached from hydrorhiza. Stem sparsely branched in one plane, primary branches rather geniculate, pointing upwards, straight or curved, a few second order branches present. Stem and lower branches fascicled, tubes consisting of a sheath of more or less concentric layers of perisarc surrounding stem; sheath thick proximally, layers becoming fewer but lumpy along branches, completely enclosing branches but branches visible through transparent outer perisarc. Hydrocladia (branches) long, straight, internodes variable in length, 1–10 groups of hydrothecae on internode, nodes oblique to transverse, deeply constricted.

Hydrothecae flask-shaped, immersed in internode, walls not in contact, typically 3 but sometimes 4 (on older hydrocladia) arranged in a verticil around internode, base of each slightly upwardly displaced with respect to others; a proximal athecate section of internode below basal-most hydrotheca. Adcauline hydrothecal wall straight to weakly convexly curved proximally, curvature more convex in distal third, abcauline wall almost straight to faintly concave with outward flexure below marginal rim; base of hydrotheca flat to weakly concave, a thick knot of perisarc at base of adcauline wall. Margin of hydrotheca circular, a tilted slightly upwards, edentulate, not everted, protruding just clear of internode, rim often ragged and produced into a short collar by numerous fine replications; operculum a thin, low dome.

Female gonothecae given off branch above a hydrotheca; pedicel short, wide, slightly bent, merging into gonotheca; body of gonotheca heart-shaped, widening from base to rounded shoulder, walls smooth to faintly undulated, distal end a platform with central wide orifice surrounded by a low collar and a pair of wing-shaped lobes, side of collar slightly outwardly turned and facing adcaudally. Perisarc very thick. No male gonothecae found.

Colour. Colony uniformly dark brown

Measurements (µm)

Branch (hydrocladium)

length of internode 1360–6000

width at node 320–400

length of infrathecal internode 360–840

width across hydrothecal pair, margin to margin 840–1100

Hydrotheca length (diagonal) across adcauline wall 900–1000 length of abcauline wall 780–1000 maximum width 312–384 width across floor 344–400 diameter at margin 280–336

Gonotheca length, base (excluding pedicel) to shoulder 1360–1460 width across shoulder 1360–1420 length of pedicel 140–200 width of pedicel at base 200–300 height of apertural collar 360–480 diameter of collar 700–900

Distribution. Circumantarctic (Peña Cantero et al., 1997).

Remarks. The stiff woody colony of the most intact specimen matches previous descriptions of Staurotheca vanhoeffeni . Dimensions of the two undamaged female gonothecae from stn 44 fit those given by Vanhöffen (1910). Stepanjants (1979) and Peña Cantero et al., (1997) described and figured male gonothecae: none are present in the Macquarie Island material. None of these authors mention the distinct knot of perisarc at the base of the adcauline hydrothecal wall. The fascicular tubes envelop the proximal part of the stem in contorted, more or less concentric layers of thickened, tough perisarc.

Figures

Figures 19A–E. Staurotheca affinis stn 44. A, part of colony. B, branch internode. C, D, replicated hydrothecal margins. E, female gonotheca. Scale bar: A, 50 mm; B, E, 1 mm; C, D, 0.5 mm.