Halisiphonia megalotheca Allman, 1888

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 : 1055-1057

Halisiphonia megalotheca Allman, 1888

( Figure 2 A–C)

Halisiphonia megalotheca Allman 1888, p 31 , Plate 16, Figure 1, 1a ; Murray 1896, p 357; Kramp 1932, p 40; Kramp 1951, p 123; Vervoort 1966, p 122–123, Figure 24; Vervoort 1972, p 60, Figure 17a; Stepanjants 1979, p 55–56, Plate 9, Figure 11; Rees and Vervoort 1987, p 31; Dawson 1992, p 15.

? Halisiphonia megalotheca: Stechow 1925, p 452 .

Laföea (Halisiphonia) megalotheca: Levinsen 1893, p 165 ; Broch 1917, p 14.

Laföea megalotheca: Marktanner-Turnerestcher 1895, p 404 ; Billard 1910, p 5–6.

Material examined

Holotype: single slide, BMNH 1888.11 .13.20, two empty hydrothecae and one empty gonotheca.

Additional material

Single slide, five hydrothecae and one young gonotheca rising from a stolon creeping on a Hexactinellid, Vema Expedition, Sta. 14–29, 30 March 1958, South Africa, 41 ° 039S, 07 ° 499E, 4961 m (deposited in the collection of the NNM 5 RMNH—coel. 7406) .

Type locality South of Australia, 42 ° 429S, 134 ° 109E, 2600 fathom (54755 m), ‘‘Challenger’’ Expedition

Sta. 160.

Description of holotype

Colony stolonal, with two empty hydrothecae (remains of tissue are present inside pedicels and base of hydrothecae) and one empty gonotheca arising from hydrorhiza ca 0.12 mm wide. Pedicel smooth, without annulations or constrictions, 1.25–1.90 mm long, almost cylindrical (0.14–0.15 mm wide at base; 0.16–0.18 mm wide distally) except near hydrotheca, where it expands, merging into base of hydrotheca. Walls of pedicel uniformly thick (25–30 Mm); annular thickening of perisarc suggesting a feeble diaphragm; several rows of desmocytes (ca 5 Mm in diameter) above annular thickening (more conspicuous in one hydrothecae). Hydrothecae campanulate, 2.10–2.60 mm high, 0.22–0.24 mm wide at base, 0.65–0.67 mm wide at aperture. Margin of hydrotheca entire, without renovation; aperture round, inconspicuously everted, perpendicular to long axis of hydrotheca. Hydrothecal wall smooth, with thick perisarc, though thinning distally (20 Mm at base; 10– 12 Mm at middle; 7–10 Mm near aperture). Hydranths not present.

Gonothecae spatulate, laterally compressed, rounded basally, truncated apically, with a narrow transverse slit as superior aperture, arising singly from hydrorhiza on short, smooth pedicels. Pedicel ca 0.20 mm long and 0.18 mm wide at base. Gonotheca 2.38 mm total height (including pedicel), 1.16 mm maximal width, ca 0.90 mm wide at apex, 0.61 mm wide at base.

Only one category of nematocysts observed, heterotrichous?microbasic mastigophores (not seen discharged), 15–17X2–4 Mm (15.75¡0.76X2.94¡0.78, n 58), rice grainshaped common.

Additional data

Vervoort (1972, p 60) described specimens from the South Atlantic (4961 m), noting the presence of ‘‘spatulate, very compressed body that might represent young gonotheca’’. Rees and Vervoort (1987, p 34) described deep-water material from off Oman, in the Arabian Sea, with ‘‘one well preserved hydranth found, attached deep inside hydrotheca, just above ‘diaphragm’; 14 tentacles’’.

Remarks

Halisiphonia megalotheca has the largest hydrothecae so far described for the genus (at least twice as long; see Table IV). The two hydrothecae present in the holotype are similar in dimensions with the values given by Allman (1888, p 31; ‘‘hydrothecae measure about one-tenth of an inch in length’’; see Table I), but his illustration ( Allman 1888, Plate 16, Figure 1 ) depicts hydrothecae with a greater length/width ratio than those presently found in the holotype. Stechow (1925, p 452) reports the species for the Indian Ocean (38 ° 409S, 77 ° 38.69E, 672 m deep) creeping on Symplectoscyphus paulensis Stechow, 1923 and Sertularella υaldiυiae Stechow, 1923, remarking on its somewhat thinner pedicels and absence of diaphragm, although the place where the hydranth base was attached to the hydrotheca could be determined. The material described by Stechow (1925) presents characteristics intermediate between H. galatheae and H. megalotheca , with hydrothecal length closer to the former and pedicel length closer to the latter. This possibly led Rees and Vervoort (1987, p 31–34, reporting H. megalotheca ) to consider H. megalotheca conspecific with H. galatheae . Previous authors (e.g. Vervoort 1966, 1972), primarily on the basis of the much longer pedicels of the former, recognized both as separate species. Rees and Vervoort (1987, p 34) justified their decision based on the apparent existence of intermediate specimens, varying from the ‘‘short stalked H. megalotheca ’’ to the ‘‘long stalked H. galatheae ’’. Yet, the margin of the hydrotheca of H. galatheae is straight while that of H. megalotheca is everted, although only slightly. Also, we could confirm that Kramp (1956) did not notice that the pedicels of H. galatheae are annulated basally (see above), contrasting with those of H. megalotheca that are completely smooth. As the specimens studied by Vervoort (1972) and Rees and Vervoort (1987) include hydrothecae with both straight and everted margins, but without annulated pedicels, we do not regard them as conspecific with H. galatheae , although some of them could be assigned to H. megalotheca . This species was originally described based on few hydrothecae only, certainly not representing the range of variation of morphometrical characters possibly exhibited by the species. The material identified by Vervoort (1966) as H. galatheae , but later considered conspecific with H. megalotheca by Rees and Vervoort (1987), has straight walls and long pedicels (up to 15 mm long) with ‘‘some indistinct rings or wrinkles’’ ( Vervoort 1966, p 121). Vervoort’s (1966, Figure 22) illustration and description of the gonotheca of H. galatheae appear to be similar in shape and size to those we found in the holotype of the species, suggesting his identification was possibly correct (see above).

Distribution

The species is known from the south of Australia ( Allman 1888), South Africa ( Vervoort 1972), off Oman ( Rees and Vervoort 1987) at depths varying from 692 ( Stechow 1925) to 4961 m (Vervoort 1962). We consider the record from St Paul ( Stechow 1925) as doubtful.

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).

Figure 2. (A–C) Halisiphonia megalotheca Allman, 1888: (A) gonotheca (left) and hydrotheca, lateral view; (B) base of hydrotheca; (C) base of hydrotheca showing desmocytes; (D) Halisiphonia galatheae Kramp, 1956: gonotheca, lateral view. Scale bars: 800 Mm (A); 500 Mm (B); 25 Mm (C); 450 Mm (D).