Halecium labrosum Alder, 1859

Schuchert, Peter, 2005, Taxonomic revision and systematic notes on some Halecium species (Cnidaria, Hydrozoa), Journal of Natural History 39 (8), pp. 607-639 : 623-625

Halecium labrosum Alder, 1859

( Figures 9 , 10 )

Halecium labrosum Alder 1859, p 354 , Plate 13; Hincks 1868, p 225, Figure 27, Plate 44 Figure 1 ; Levinsen 1893, p 204, Plate 8 Figures 8 , 9 ; Broch 1910, p 148, Figures 7 , 8 , Plate 2 Figure 4 ; Broch 1918, p 45, Figure 19; Naumov 1969, p 489, Figures 16B, 343, Plate 16 Figure 2 ; Calder 1970, p 1506, Plate 1 Figures 6–8 ; Cornelius 1975, p 396, Figure 7 ; Cornelius and Garfath 1980, p 282; Cornelius 1995, p 282, Figure 64; Schuchert 2001, p 79, Figure 65A–D.

Halecium crenulatum Hincks 1874, p 150 , Plate 8 Figures 21–23; Levinsen 1893, p 204, synonym.

? Not Halecium reflexum Stechow 1919, p 37 , Figures G, H.

Halecium schneideri: Leloup 1952, p 144 , Figure 78A1–A3.

Material examined (see also Schuchert 2001)

MHNG INVE 28451 , Greenland, Holsteinsborg , 19 July 1953 . MHNG INVE 34235 , France, Brittany, Roscoff, between Islands of Astan et Ty Saozon , depth 5–10 m according to map, 21 April 1910,? leg. M. Bedot , juveniles up to 2 cm, no gonothecae. MHNG INVE 33581 ( BIOFAR 350 ), The Faroes , 62.26 ° N, 7.99 ° W, 107 m, 22 July 1988 . MHNG INVE 33583 ( BIOFAR 553 ), The Faroes , 61.83 ° N, 6.32 ° W, 92 m, 22 September 1989 . MHNG INVE 33524 ( BIOFAR 106 ), The Faroes , 62.28 ° N, 6.8 ° W, 70 m, 24 July 1987 . MHNG INVE 33563 ( BIOICE collection), Iceland, 65.78 ° N, 14.22 ° W, 28–60 m, 24 July 1991 . MHNG INVE 26684 ( BIOICE station 2099), Iceland, 66.62 ° N, 18.24 ° W, 112 m, 4 July 1988 .

Description

Colonies up to 10 cm, arborescent, irregularly branched, predominantly in one plane, stem and some branches polysiphonic. Internodes of unequal length within and between colonies, perisarc corrugated or smooth. Nodes alternately oblique. Hydrotheca on short hydrophore at distal end of internode like a prolongation it, hydrophore not delimited by node, rim of hydrotheca reaching just to level of distal node of segment, sometimes overtopping it. Hydrotheca short, wall distinctly recurved. Renovations frequent, secondary hydrotheca on hydrophore that is several times as long as depth of hydrotheca, walls usually corrugated. Primary hydrophore often with adcauline semi-circular perisarc thickening (pseudodiaphragm), sometimes at adcauline base of hydrophore a projecting perisarc fold ( Figure 9 B–D). Hydranths with 20–24 tentacles. Gonothecae without hydranths, females ovoid, compressed by about a factor of two, with short pedicel, distal end with oval opening that may be on a shallow neck-like process. Male gonothecae similar but smaller.

Typical dimensions

Internode lengths 0.35–1.05 mm, diameter of internodes 0.16–0.26 mm, diameter of diaphragm of primary hydrotheca 0.14–0.21 mm, depth of hydrotheca 40–90 mm. Female gonotheca 1.5–2.1 mm long and 0.8–1 mm broad, male gonotheca 1–1.2 mm long.

Distribution

Arctic-boreal species, in the North Atlantic reaching south at least to Brittany and North Sea, perhaps even Spain and Azores ( Cornelius 1995). Also Northern Pacific and Japan. Type localities: Northumberland coast, Shetland, Moray Firth, UK ( Cornelius and Garfath 1980).

Remarks

Halecium labrosum has very variable internode lengths, so much so that this variability itself becomes a diagnostic character. The lengths are variable within and between colonies. In his key to the British thecate hydroids, Cornelius (1995) characterizes H. labrosum as having a wrinkled or corrugated perisarc. While some colonies indeed have such a corrugated perisarc, especially the secondary hydrophores, there were also regularly colonies with smooth perisarc among the examined material from the North Atlantic (compare Figures 9B, C and 10B ).

Broch (1918) considered Halecium labrosum to be an Arctic or northern Atlantic species. Likewise, Cornelius (1975) considered the English Channel as its probable southern limit. As already mentioned by Broch (1918), it is likely that at least some Mediterranean records of H. labrosum are due to a confusion with other Halecium species, notably H. mediterraneum . Halecium mediterraneum (see below) is by no means easily separable from H. labrosum and in fact might represent a southern form of the latter. The differences between the two forms are only gradual. It differs from H. labrosum in forming smaller, mostly monosiphonic shoots (but some are weakly polysiphonic!), the long hydrophore which makes the hydrotheca always overtop the distal node of the segment, the smaller diameter of the hydrotheca, and the smaller diameter of the segments (internodes). The growth forms are also different, with H. mediterraneum tending to form bushy, tangled masses, while H. labrosum is always arborescent (compare Figures 10A, E and 11A ).

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 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 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 11. Halecium mediterraneum Weismann, 1883; after preserved Mediterranean material. (A) Silhouettes of three fertile colonies showing variability of growth (scale bar: 1 cm); (B) branching pattern of stem (scale bar: 0.2 mm); (C) distal part with geniculate segments (same scale bar as B); (D) primary and secondary hydrotheca (scale bar: 0.1 mm); (E–G) female gonothecae (same scale bar as B), (E) in frontal view and with broad opening, (F) in side view, (G) most commonly found opening size; (H–K) male gonothecae (same scale bar as B), (H) with soft tissue, (I) empty, (K) in side view; (L) empty female gonotheca cut apart to demonstrate secondary capsule within outer capsule (scale bar: 0.1 mm); (M) range of variation of distal openings of female gonothecae (same scale bar as L).