Symplectoscyphus paulensis Stechow, 1923

Watson, Jeanette W., 2003, Deep-water hydroids (Hydrozoa: Leptolida) from Macquarie Island, Memoirs of Museum Victoria 60 (2), pp. 151-180 : 170-171

Symplectoscyphus paulensis Stechow

Figures 20A–D

Symplectoscyphus paulensis Stechow, 1923a: 8 .— Stechow, 1923b: 172.— Stechow, 1925: 467, fig. 28.— Millard, 1967: 183, figs 4G, H.— Vervoort, 1972b: 180, figs 60b, 61.— Millard, 1975: 317, figs 102A–C.— Millard, 1977b: 107.— Millard, 1978: 199.—Stepan-jants, 1979: 71, pl. 17 fig. 2.— Hirohito, 1983: 51, fig. 24.— Vervoort, 1993: 263, figs 63a–d, 65a.—Blanco, 1994: 154.— Bouillon et al., 1995: 74.

Material examined. Stn 120, TM K2790, NMV F91329, specimens alcohol-preserved; NMV F91348, malinol-mounted microslide, three complete infertile colonies, the tallest 100 mm high and fragments of others, possibly branches shed from these colonies. Colonies heavily overgrown by Calamphora quadrispinosa .

Description. Colonies irregularly and profusely branched more or less in one plane. Hydrorhiza a tuft of stolons detached from substrate. Stem of tallest colony 3 mm wide above hydrorhiza, heavily fascicled, stolons growing upwards to become polysiphonic tubes of stem. Branches (hydrocladia) to 30 mm long, slender, polysiphonic tubes often extending a short distance along branch. Branches thereafter monosiphonic (hydrocladia), branched subdichotomously several times at c. 120°, a hydrotheca in each dichotomy.

Hydrocladial internodes long, cylindrical, widening a little below hydrotheca, perisarc smooth, sometimes undulated, internode widening distally; nodes distinct, oblique to almost transverse, marked by a narrowing of perisarc, frequently a tumescence above or below node; a node on each side of hydrotheca in dichotomy.

Hydrothecae alternate, distant, given off almost in one plane just below node at an angle of c. 80° to internodal axis, almost cylindrical, narrowing very slightly to margin, walls smooth, adcauline wall gently convex, adnate adcauline wall short, becoming free opposite or just below node, free wall convex to almost straight, but less curved than adnate part, at least twice length of adnate part; abcauline wall slightly concave, curving smoothly outward, contiguous with internode. Hydrotheca widest at junction of adnate and free adcauline wall, narrowing a little to margin, floor narrow, flat, a minor thickening of perisarc at base of adcauline wall, a triangular foramen and thinning of perisarc in internode beneath floor.

Margin with 3 low, equidistant cusps separated by broad, rather shallow embayments; margin often with numerous fine replications, operculum of 3 triangular valves. Perisarc of hydrotheca thin, slightly thicker at marginal replications, operculum thin.

Hydranth with c. 24 tentacles, a strand of tissue attaching hydranth to hydrotheca about one-third distance up adcauline wall.

Colour. Pale yellow-brown.

Measurements (µm)

Hydrocladium length of internode 1000–1440

diameter at node 120–176 Hydrotheca length of free adcauline wall 792–840

length of adnate adcauline wall 328–392

length of abcauline wall 880–960

width at floor 184–280

width at margin 400–480

Distribution. A moderately deep-water species from 680 m in the southern Indian Ocean ( Stechow, 1923b), 440 m in the south-west Indian Ocean, 347 m off Mozambique ( Millard, 1967), 424–428 m on Vema Seamount ( Vervoort, 1972a) and 399–500 m in Antarctica ( Stepanjants, 1979) .

Remarks. Although flexuous, the apical branches are rather brittle and easily broken. The hydrothecae are mostly arranged in one plane, but on some hydrocladia there is a tendency to face frontally. The small, thin marginal replications are slightly everted and are probably remnants of opercular attachments. The hydrothecae in the branch dichotomies do not differ in size or shape from those on the internodes.

The colonies are so heavily overgrown by Calamphora quadrispinosa that it is difficult to distinguish the stolons of that species from the polysiphonic tubes of S. paulensis . The syntype of S. paulensis is strongly polysiphonic ( Vervoort, 1993) while monosiphonic hydrocladia of S. paulensis are similar to S. bathyalis Vervoort, 1972 . S. bathyalis was rejected because of its weakly expanding hydrothecae.

The present specimens are the largest colonies of S. paulensis ever recorded. Previous records are of small polysiphonic colonies or monosiphonic fragments.

Figures

Figures 20A–D. Symplectoscyphus paulensis, stn 120. A, colony. B, distal monosiphonic branches. C, part of distal branch. D, rim of hydrotheca showing obtuse cusps. Scale bar: A, 50 mm; B, 10 mm; C, 1 mm; D, 0.5 mm.