Halisiphonia arctica Kramp, 1932

Marques, Antonio Carlos, Cantero, Alvaro Luis Peña & Migotto, Alvaro Esteves, 2006, Revision of Halisiphonia Allman, 1888 (Cnidaria, Hydrozoa, Hebellidae), with comments on its taxonomic position, Journal of Natural History 40 (17 - 18), pp. 1047-1062 : 1049-1052

Halisiphonia arctica Kramp, 1932

( Figure 1 ; Table I)

Halisiphonia arctica Kramp 1932, p 37 , Figures 17–20, 31; Kramp 1963, p 53, 106 (incorrectly assigned as ‘‘n. sp.’’); Schuchert 2001, p 61, Figure 47.

Material examined

Holotype: Halisiphonia arctica Kramp, 1932 , colony with gonothecae in alcohol ( ZMUC no number).

Type locality

Baffin Bay ( Greenland), 74 ° 419N, 70 ° 309E, 1200 m, 23 August 1928, on Eudendrium planum Bonnevie, 1898 , ‘‘Godthaab’’ Expedition Sta. 135 .

Description of holotype

Colony stolonal, creeping on hydrocaulus of Eudendrium planum . Stolonal hydrorhiza—a network of branching and anastomosing tubes of thin perisarc—giving rise to numerous pedicellate hydrothecae and five gonothecae. Pedicels smooth, with three to six complete basal annuli, 0.36–4.85 mm long, almost cylindrical throughout (0.10–0.13 mm wide where walls are parallel), slightly and progressively widening to base of hydrothecae, merging into it almost imperceptibly. Hydrothecae deep conical to almost cylindrical, 0.67–1.13 mm high (from diaphragm up to distal renovation), 0.11–0.23 mm wide at diaphragm, 0.19–0.38 mm wide at aperture, with straight and smooth walls (sometimes with inconspicuous undulations) and thin perisarc; margin entire, slightly flaring, with up to 13 renovations; aperture perpendicular to long axis of hydrotheca. Diaphragm membranous, transversal; desmocytes small (ca 4 Mm in diameter) and inconspicuous, irregularly distributed or forming one or two transversal rows above diaphragm. Hydranths 0.15–0.25 mm high, 0.16–0.22 mm wide at base of tentacles, with 12–16 tentacles, hypostome conical. Retracted hydranths lying over diaphragm. Hydranth regenerations leaving marks outside (margin renovations) and inside the hydrotheca; new diaphragm formed above the preceding one resulting in a fine thickened line around inner side of hydrotheca and corresponding cycles of desmocytes (not always seen); previous diaphragm may disappear. Hydranth base may be marked with several slight constrictions at the place of older diaphragms.

Gonothecae spatulate, rounded basally, truncated apically, a narrow transverse slit as superior aperture, arising singly from hydrorhiza on short, annulated pedicels (two to three rings). Pedicel 0.10–0.13 mm high, 0.10–0.13 mm wide. Gonotheca 2.50–3.42 mm high, 1.45–1.73 mm wide at aperture, 0.40–0.53 mm wide at base. Two gonothecae containing medusa buds, clearly seen through the fine and transparent gonothecal perisarc. Each gonotheca with two buds in a row, occupying only a fraction of gonothecal inner space; distal bud larger and more developed, with recognizable tentacles, manubrium, and umbrella. Umbrella twice as high as wide, mesoglea thin; manubrium tubular, reaching about halfway to bell margin. In both gonothecae, buds enclosed by a mantle. Peduncle uniting blastostyle to stem coenosarc broken in both cases. Apparently four tentacles with large bulbs. No nematocysts on the exumbrella or on the mantle. Neither radial canal (at higher magnification, 400X) nor sensorial structures (ocelli, statocysts) seen. Absence of gonads indicating that buds possibly represent immature medusae.

Nematocysts of two categories. Heterotrichous microbasic mastigophores (seen discharged), 7.0–8.0X2.0–3.0 Mm, rice grain-shaped, common, ratio shaft/capsule51:1. Heterotrichous?macrobasic euryteles (not seen discharged), 10.0–12.5X4.0–5.5 Mm, bean-shaped, common.

Remarks

Halisiphonia arctica has not been recorded again since its original description from Greenland. The species was considered similar to H. megalotheca by Schuchert (2001), who notes that the only difference between them is the more elongate hydrotheca of H. arctica .

However, concerning gross morphology, H. arctica is distinguished from its congeners by the combination of two characters: everted margin and annulated pedicels. Halisiphonia megalotheca and H. nana have everted margins but both lack annuli in their pedicels. Halisiphonia arctica differs from H. galatheae , with which it shares the presence of annuli in the pedicel, by having everted hydrothecal margin. Halisiphonia arctica also shows twice (up to 13) as many renovations as H. galatheae (up to six) and H. nana (up to six), although this may be a variable character. The process of hydranth regeneration of H. arctica leaves the scars of the old diaphragms, as described and illustrated by Kramp (1932, p 39, Figures 18– 20), a unique feature among the species of the genus.

The medusa of H. arctica was previously reported by Schuchert (2001, p 61) from the holotype, the same material being described here. Besides the presence of medusae suggesting affinities with Hebella ( Schuchert 2001) , the morphology of the medusa buds of H. arctica , in some aspects (umbrella tall, four tentacles with large bulbs, manubrium cylindrical) comparable to the newly liberated medusae of Hebella scandens ( Bale, 1888) and Hebella furax Millard, 1957 (see Andrade and Migotto 1997; Migotto and Andrade 2000, respectively), indicates affinities between Halisiphonia and Hebella . Moreover, once this stage becomes better known, there could be a drastic modification on the classification of Halisiphonia , and the genus might even fall into synonymy with a medusa-based genus.

Distribution

The species is only known for Greenland, at the depth of 1200 m.

Figures

Figure 1. Halisiphonia arctica Kramp, 1932. (A) Hydrotheca, lateral view; (B) portion of a colony; (C) hydrothecal diaphragm; (D) base of hydrotheca showing desmocytes; (E) gonothecae, lateral view. Scale bars: 200 Mm (A); 1.0 mm (B); 25 Mm (C); 100 Mm (D); 500 Mm (E).