Halecium scutum Clark, 1877

Schuchert, Peter, 2005, Taxonomic revision and systematic notes on some Halecium species (Cnidaria, Hydrozoa), Journal of Natural History 39 (8), pp. 607-639 : 608-612

Halecium scutum Clark, 1877

( Figures 1 , 2 ) Halecium scutum Clark 1877, p 14 , Plate 4 Figures 13 , 14 ; Broch 1918, p 39, Figures 14 ; Calder 1970, p 1509, Plate 2 Figures 2 , 3 .

Halecium boreale Lorenz 1886, p 26 , Plate 1 Figures 1 , 2 .

Halecium halecinum : in part Broch 1910, p 144, Figure 4 I–VIII (not others).

Halecium beringi Naumov 1960, p 449 , Figures 337, 338; Naumov 1969, p 484, Figures 337, 338; Antsulevich 1987, p 107.

Halecium beanii: Naumov 1969, p 483 , Figure 336; in part Schuchert 2001, p 73, Figure 59A–D.

[not Halecium beanii ( Johnston 1838) .]

Material examined

MHNG INVE 28450 , Greenland, Holsteinsborg , 66.93 ° N, 53.68 ° W, 165 m, 8 July 1971 , with female gonothecae. MHNG INVE 28731 , Greenland, Augpilagtoq , 60.14 ° N, 44.31 ° W, 50–60 m, 30 July 1970 , on rock, with male gonothecae. MHNG INVE 33550 , BIOFAR station 111, The Faroes , 62.11 ° N, 6.5 ° W, 50 m, 25 July 1987 . BIOFAR collection station 556, The Faroes , 61.97 ° N, 6.54 ° W, 41 m, 22 September 1989 , on barnacles. BIOFAR collection station 699, The Faroes , 62.12 ° N, 6.83 ° W, 72 m, 10 May 1990 , on Tubularia indiυisa, with gonothecae. BIOICE collection, Iceland, 65.78 ° N, 14.22 ° W, 28–60 m, 24 July 1991 . BIOFAR station 459, The Faroes , 63.00 ° N, 6.96 ° W, 910 m, 4 June 1989 .

Description

Colonies erect, up to 10 cm (reportedly up to 30 cm), imperfectly pinnate to shrubby, some colonies perfectly planar. Stem sometimes covered by bark-like overgrowth of anastomosed stolons. Main stem and branches polysiphonic, thinning out to monosiphonic ends. Internodes roughly equal in length; nodes oblique, sometimes indistinct. Hydrotheca sitting at the end of segment like a prolongation of it, not or only slightly inclined, slightly overtopping distal node of segment. Hydrotheca very shallow, walls straight, diameter at base 0.18–0.25 mm, depth 20–40 mm, with desmocytes, without pseudodiaphragms, rim of hydrotheca often damaged. Secondary hydrothecae on short hydrophore, the latter usually shorter than 1.5 times the diameter. Male gonotheca club- to oblong sac-shaped, 1.4 mm long. Female gonotheca club-shaped, up to 2 mm long and 0.8 mm broad, straight, somewhat flattened, distal end rounded, opening at side at approximately middle of gonotheca on a distinct shoulder; opening partially covered by a characteristic hood-like process, two protruding polyps, 10– 20 eggs per gonotheca. Nematocysts: two types of capsules, type I (9–10)X(3.5–4) mm; type II (5.5–7)X(1.5–2.5) mm.

Distribution

Circumpolar in the Arctic Sea , in the North Atlantic south to Cape Farewell in Greenland, Iceland and Faroe Islands. Type locality: Clark (1877) gives several localities in Alaska .

Remarks

The trophosome and male gonothecae of Halecium scutum , H. halecinum and H. beanii can resemble each other closely and it is difficult to identify immature or male specimens. In contrast, their female gonothecae are quite distinct and allow a relatively secure identification (compare Figures 2D , 4D and 5G ). The female gonotheca of H. scutum has a characteristic lip or hood above the hydrothecae on its side wall ( Figure 2E ). Unfortunately, the shape of the female gonotheca of H. scutum can occasionally be so variable as to make it resemble that of H. halecinum ( Broch 1918, Figure 14 ). It is therefore not surprising that Broch (1910, as H. halecinum forma gigantea) considered H. scutum as an arctic form of H. halecinum . Later, Broch (1918) revised his opinion and kept both species distinct. Calder (1970) likewise regarded H. scutum as valid and distinct from H. halecinum . Naumov (1969) synonymized H. scutum and H. beanii , a view later hesitatingly adopted by, for example, Cornelius (1975) and myself ( Schuchert 2001).

Examination of material from the Faroes and Greenland, however, convinced me that H. scutum is clearly distinct from both H. beanii and H. halecinum . Although my material from the Faroes did not contain female gonothecae, there were many large infertile and male colonies that agreed well with female colonies from Greenland and with the description of Broch (1918).

Mature colonies of H. scutum are larger and considerably more robust than those of H. halecinum and especially H. beanii (compare Figures 1 A–C, 3A–C and 5A–C). The best character, to distinguish H. scutum from H. halecinum and H. beanii , apart from the female gonothecae, is the relative shortness of the secondary hydrophores ( Figure 2 A–C). These secondary hydrophores are maximally as long as 1.5 times their diameter, but normally much shorter. In H. halecinum and H. beanii , they are longer, the ratio of length to diameter being in the range of 2 and more (compare Figures 2 A–C, 4A–C and 5D, F). Halecium scutum also lacks the characteristic pinnate growth often found in H. halecinum and its hydrophores are in line with the main axis of the internode. In H. halecinum the hydrophores are inclined ( Figure 4A, B ). In H. beanii , the diameter of the hydrotheca is distinctly smaller (0.12–0.16 versus 0.18–0.25 mm), the hydrotheca is usually held oblique relative to the internode axis, and the size of the type I nematocyst capsule is larger.

In the material from the Faroe Islands, one large colony of H. scutum was overgrown with several other hydroids, among them were female and male shoots identified as H. beanii . The differences in the microscopic structure were quite evident. This syntopic occurrence is further evidence for them being separate species. For further details see below under H. beanii .

Another peculiarity of most large colonies of H. scutum is a bark-like covering of the stem by a layer of tightly anastomosed stolons. A similar, but less anastomosed formation may occur in some larger colonies of H. halecinum .

Another European species that can be confused with the species discussed above is Halecium sessile Norman, 1867 . According to Cornelius (1995), this species has very short secondary hydrothecae without distinct hydrophores. This trait may allow a reliable distinction.

Halecium boreale Lorenz, 1886 is likely a synonym of H. scutum . Lorenz (1886) described H. boreale as devoid of female gonothecae and the eggs are reported to develop in the gastric cavity of the feeding zooids (sic!). The males have normal gonothecae. Lorenz depicts a male colony that is indistinguishable from H. scutum . The feeding zooid of this colony contains spherical bodies. It seems to me that Lorenz misinterpreted food items, perhaps even eggs of another animal, as the eggs of his Halecium boreale . Although it is thinkable that there exist Halecium species without gonothecae, I am not aware of any other such species. Moreover, the presence of normal male gonothecae and the position of the eggs within the gastric cavity make Lorenz’s assertion improbable.

Halecium beringi Naumov, 1960 was synonymized with H. scutum by Antsulevich (1987).

Clark’s publication with the original description of H. scutum was apparently published in 1877 and not 1876 ( Cornelius 1982, p 129).

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 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).

Figure 14. Halecium banyulense Motz-Kossowska, 1911, after MHNG INVE 34237. (A) Colony silhouette (scale bar: 1 cm); (B) internode from monosiphonic part (scale bar: 0.2 mm); (C) hydrothecae with regenerated hydrothecae of second and higher degree (scale bar: 0.1 mm); (D) female gonotheca, drawn opaque to visualize radiating depressions (same scale bar as B).