Halecium lankesterii ( Bourne, 1890 )

Schuchert, Peter, 2005, Taxonomic revision and systematic notes on some Halecium species (Cnidaria, Hydrozoa), Journal of Natural History 39 (8), pp. 607-639 : 618-620

Halecium lankesterii ( Bourne, 1890)

( Figure 7 )

Halecium robustum Pieper 1884, p 166 ; Broch 1912, p 14, Figure 1 ; Babić 1913, p 470, Figures 4–6 ; Bedot 1914, p 82, Plate 5 Figure 6 .

[Not Halecium robustum Verrill 18745 Zygophylax pinnata (G. O. Sars 1874) .]

Haloikema lankesterii Bourne 1890, p 396 , Plate 26 Figures 1 , 2 .

Halecium sessile var. Billard 1904, p 160.

Halecium ophioides: Babić 1910 , Plate 1 Figure 1b ; Babić 1913, p 469, footnote.

? Not Halecium lankesterii: Hamond 1957, p 302 , Figures 9 , 10 ; Vervoort 1959, p 221, Figures 3–5 ; Millard 1975, p 153, Figure 50B–E; Cornelius 1995, p 285, Figure 65.

Halecium lankesteri: Bedot 1911, p 213 , Plate 11, Figures 1–5 ; Peña Cantero and García Carrascosa 2002, p 66, Figure 13 a–c.

Material examined

MHNG INVE 33471 , as Halecium lankesteri , France, Brittany, Roscoff , coll. 6 July 1912 by M. Bedot, mentioned in Bedot (1914), with female gonothecae. MHNG INVE 33478 , as Halecium robustum, Roscoff , 1 June 1910, leg. M. Bedot. MHNG INVE 33479 Halecium robustum, Roscoff , May 1910, leg. M. Bedot. MHNG INVE 33480 , as Halecium robustum, Roscoff , 6 May 1910, leg. M. Bedot.

Description

Colonies erect, stems unbranched or sparingly branched, up to 8 mm high and with up to 40 hydranths. Stems arise from creeping hydrorhiza. Stems always monosiphonic, irregularly segmented, regularly with intercalated segments without hydrotheca, these internodes short and with two marked bulges at their ends ( Figure 7C ). Internodes generally short and stout, sides often undulated. Hydrotheca sitting at the end of segment like a prolongation of it, rim perpendicular to segment axis. One or two side-branches, if present, arising immediately below hydrotheca, angles quite acute ( Figure 7D ). Hydrotheca with slightly diverging wall, these quite straight, not curved; diameter at level of diaphragm 0.15–0.17 mm, depth 30–45 mm. Secondary hydrothecae present, with hydrophore. Hydranths with 20–24 tentacles, body and tentacles containing zooxanthellae. Gonothecae arising from within primary hydrothecae. Female gonotheca pear-shaped, about 0.8–0.9 mm long, slightly compressed, opening on side, formed by a short, vertical, completely adnate tube with a median septum, opening without distinct hydrotheca, but rim with some desmocytes; opening plane perpendicular to long axis of gonotheca; two protruding hydranths present; about three eggs per gonotheca. Male gonotheca not observed; according to Babić (1913) oblong ellipsoid, 0.68–0.85 mm long, smooth, without hydranths.

Distribution

Mediterranean, tropical and subtropical eastern Atlantic, English Channel , North Sea , South Africa, Moçambique. Type localities: near Plymouth, England (details in Cornelius 1975) .

Remarks

The type material of Bourne (1890) did not include gonothecae, a character usually indispensible for a correct identification of Halecium species. Two other traits, however, allow recognition of the species. This is for one the presence of zooxanthellae, for the other the segmentation pattern with its short, ahydrothecate segments with bulging ends (or segments constricted in the middle). Bourne’s material had both characteristics. Babić (1913) and Bedot (1914) described fertile material. Later authors, like Vervoort (1959), Millard (1975) and Cornelius (1995), also included material lacking zooxanthellae and with smooth perisarc. The female gonothecae depicted by Hamond (1957), Vervoort (1959) and Cornelius (1975, 1995) differ from the one depicted in Figure 7E and they appear identical to that of H. beanii ( Figure 5G ). The egg number is also higher than usually found in H. lankesterii . These differences prompted Peña Cantero and García Carrascosa (2002) to postulate that the mentioned material of Cornelius and Vervoort actually belonged to a different, so far unnamed species. I concur with Peña Cantero and García Carrascosa (2002). The occurrence of fertile, monosiphonic stems of Halecium beanii (see under this species) led me to suspect that the material of Hamond (1957), Vervoort (1959) and Cornelius (1975, 1995) was actually composed of monosiphonic colonies of H. beanii . Hamond (1957) acknowledged that H. beanii and H. lankesterii resemble each other very closely, but he insisted that they are distinct. He kept them apart on account of the sharply curved side-branches. His colony in Figure 9 resembles more H. lankesterii and it thus appears that his material contained indeed some H. lankesterii besides monosiphonic H. beanii .

Halecium lankesterii also occurs in the Mediterranean and can be confounded with H. petrosum if no female gonothecae are present. The presence of zooxanthellae, the wider hydrothecae and the characteristic ahydrothecate segments of H. lankesterii help to distinguish them (compare Figures 7 and 8 ).

Halecium nanum Alder, 1859 resembles closely H. lankesterii as described above. Both have zooxanthellae in their tissue. The female gonotheca of H. nanum has two hydrothecae that reach to the distal end ( Calder 1991), while they end roughly in the middle in H. lankesterii . Their different ecology additionally suggests that they are likely separate species. Halecium nanum is usually epiphytic, mostly occurring on pelagic Sargassum sp. in warmer waters of the Atlantic. Cornelius (1995) thought that it might be wider spread and occur on a wider range of substrata.

Figures

Figure 1. Halecium scutum Clark, 1877; colony silhouettes of material from The Faroes. (A) MHNG INVE 33550; (B) BIOFAR station 699; (C) BIOFAR station 459. Scale bar: 2 cm.

Figure 2. Halecium scutum Clark, 1877. (A) From BIOFAR 699; (B) BIOFAR 556; (C–E) Holsteinsborg, Greenland; (F, G) Augpilagtoq, Greenland. (A–C, F) Segments from monosiphonic parts with primary and sometimes secondary hydrothecae (scale bar: 0.2 mm); (D) female gonotheca in side view, eggs stippled (scale bar: 0.2 mm); (E) higher magnification of gonothecal opening, side view (scale bar: 0.1 mm); (G) male gonotheca (same scale bar as D).

Figure 3. Halecium halecinum (Linnaeus, 1758); colony silhouettes, note variation of shapes. (A) Canary Islands; (B) The Faroes (BIOFAR station 111); (C) The Faroes (BIOFAR station 554). Scale bar: 2 cm.

Figure 4. Halecium halecinum (Linnaeus, 1758). (A–C) Segments of monosiphonic parts, with secondary hydrothecae, note length variation of internodes, BIOFAR station 350, 205 and 351; (D) BIOFAR 351, female gonotheca in side view; (E) as in (D), but seen from anterior side, note bipartite hydrotheca; (F) BIOFAR 597, male gonotheca. Scale bar: 0.2 mm.

Figure 5. Halecium beanii (Johnston, 1838). (A, D) From Roscoff; (B, C, E–H) from The Faroes. (A–C) Colony silhouettes (scale bar: 1 cm); (D–F) subterminal portions of branches (scale bar: 0.2 mm); (G) female gonotheca, middle one seen from side of hydrothecae, right one shown with developing embryos (scale bar: 0.2 mm); (H) male gonotheca (same scale bar as G).

Figure 6. Halecium beanii (Johnston, 1838). (A–D) After material from South Africa; (E–F) after material from New Zealand. (A) Two internodes (scale bar: 0.2 mm); (B) female gonotheca in oblique view (scale bar: 0.2 mm); (C) cross-section of female gonothecae in about the middle of its height, note polygonal outline (same scale bar as B); (D) three male gonothecae, note variability (same scale bar as B); (E) two internodes (same scale bar as A); (F) female gonotheca (same scale bar as B).

Figure 7. Halecium lankesterii (Bourne, 1890); after material from Brittany. (A) Colony silhouette (scale bar: 5 mm); (B) part of stem (scale bar: 0.2 mm); (C) lower part of stem with characteristic ahydrothecate segments with constriction in middle (scale bar: 0.1 mm); (D) hydrothecate segment (same scale bar as C); (E) female gonotheca in oblique view, shown without hydranths (scale bar: 0.2 mm); (F) female gonotheca seen from anterior side (same scale bar as E); (G) lateral view of female gonotheca, higher magnification of opening (scale bar: 0.1 mm).

Figure 8. Halecium petrosum Stechow, 1919; after material from Banyuls-sur-Mer. (A) Colony silhouette (scale bar: 5 mm); (B) two internodes (scale bar 0.2 mm); (C) branching point (same scale bar as B); (D) hydrophore, primary and secondary hydrothecae (scale bar: 0.1 mm); (E) hydrotheca with straight walls (same scale bar as D); (F) female gonotheca in side view (same scale bar as B); (G) hydrotheca of female gonotheca in anterior view (anterior side in F is directed towards left) (same scale bar as D); (H) part of male colony, sperm masses stippled, note that this sample shows signs of multiple re-growth and regeneration, its identity is not entirely secure (scale bar: 0.2 mm).

Figure 9. Halecium labrosum Alder, 1859. (A, B) From Roscoff; (C, D) from The Faroes, MHNG INVE 33524 and 33581; (E) MHNG INVE 25337, Iceland; (F) MHNG INVE 26684, Iceland; (G) MHNG INVE 28451, Greenland. (A) Silhouette of infertile colony (scale bar: 1 cm); (B–D) internodes and secondary hydrothecae (scale bar: 0.2 mm); (E) female gonotheca (scale bar: 0.5 mm); (F) distal opening of female gonotheca (scale bar 0.1 mm); (G) male gonotheca (same scale as E).

Figure 10. Halecium labrosum Alder, 1859. (A–D) MHNG INVE 33563, Iceland; (E–G) MHNG 33583, The Faroes. (A) Colony silhouette (scale bar: 1 cm); (B) segments of distal branch, note short internodes (scale bar: 0.2 mm); (C) gonotheca (scale bar: 0.5 mm); (D) distal opening of gonotheca (scale bar: 0.2 mm); (E) colony silhouette (scale bar: 1 cm); (F) segments of distal branches, note variability of internode length; (G) gonotheca (scale bar: 0.5 mm).

Figure 13. Halecium textum Kramp, 1911; after MHNG INVE 33592, Iceland. (A, B) Hydrothecae and internodes, note strong corrugation (scale bar: 0.1 mm); (C) part of colony with three female gonothecae, eggs stippled (scale bar: 0.5 mm).