Corydendrium dispar Kramp 1935

Corydendrium dispar Kramp, 1935

Figs. 7 a, b, 8

Corydendrium dispar Kramp, 1935: 3, figs. 1a, b, 2a–d, 3, unnumbered plate, figs. 1a, b, 2–8.

Type locality. Sweden: Kattegat, Kungsbackafjord, 26 m (Kramp 1935).

Material examined. NS: Petit Passage, south of East Ferry, datum + 5 cm, 14.x.1970, on a mussel shell (Mytilus edulis) with other hydroids, one colony, without gonophores, coll. K.W. Petersen, SNM HYD- 000871.

Description. Hydroid colony minute, up to 4 mm high, with both stolonal and erect parts, arising from a creeping hydrorhiza; growth monopodial with terminal hydranths. Hydrocaulus when present monosiphonic, curved and twisted, slender basally, very gradually expanding distally, giving off a few irregular branchlets or a branch. Branches and branchlets adnate to axis for a short distance at proximal end before diverging, with branches similar in form to main axis; ultimate branchlets mostly short, slender basally, expanding distally, about 0.15–0.20 mm in diameter terminally. Perisarc thin, double-layered, this especially noticeable towards base of hydrocaulus or pedicel, with inner layer thicker, outer layer filmy, more or less wrinkled throughout. Hydranths terminal, clavate, up to 0.5 mm long, 0.15 mm wide, partially surrounded basally by perisarc; hypostome dome-shaped. Tentacles filiform, scattered, about 10-14 in number.

Gonophores not seen.

Cnidome (Fig. 8)

Hydranths—

desmonemes (n = 10): 4.5–5.2 µm long × 2.7–3.1 µm wide (undischarged)

microbasic euryteles (n = 10): 8.0–9.9 µm long × 4.0–4.9 µm wide (undischarged)

Remarks. Kramp (1935) discovered this boreal species during an examination of hydroids collected in the Skagerrak and Kattegat by L.A. Jägerskiöld of the Göteborgs Naturhistoriska Museum, Sweden. He recognized that it was similar to but specifically distinct from Corydendrium parasiticum (Linnaeus, 1767), a warm water species, and established the binomen C. dispar for it. Specimens from Norway, identified earlier by Bonnevie (1899b) as C. parasiticum, were examined by Kramp and found to be C. dispar. Gonophores arise as oval to nearly spherical external outgrowths of the stem, branches, and branchlets, and are not contained within perisarcal tubes of stem and branches during development as in C. parasiticum (Kramp 1935). Males of the species are much more highly reduced in structure than females.

An infrequently encountered hydroid, Corydendrium dispar has been reported most often from the Kattegat, in both Swedish (Kramp 1935; Jägerskiöld 1971; Schuchert 2004) and Danish (Dahl et al. 2009) waters. Elsewhere, it has been found along the west coast of Norway as far north as the Trondheimfjord (Kramp 1935), and from the Faroes (Jensen & Frederiksen 1992; Schuchert 2004). This is the first record of the species from the Atlantic coast of North America.

Specimens of Corydendrium dispar examined here were collected by K.W. Petersen (SNM HYD- 000871) on a mussel shell in Petit Passage, Nova Scotia. The location is characterized by powerful tidal currents that flow through a narrow channel connecting St. Mary’s Bay and the Bay of Fundy. With a vertical tidal range in the region of about 7 m, maximum surface currents exceed 3 m /second during an average spring tide (Durand et al. 2008). The colony, or colonies, were small, inconspicuous, and partially obscured by the growth of other hydroid species. Discovery of the species near low water at this unusual site is noteworthy in that previous records of C. dispar (Kramp 1935; Jägerskiöld 1971; Jensen & Frederiksen 1992; Schuchert 2004) are from greater depths (26–260 m).

Recorded distribution. Bay of Fundy: recorded for the first time.

Eastern North America: recorded for the first time.

Worldwide: Scandinavia, from the Trondheimfjord to the Kattegat (Kramp 1935); Faroe Islands (Jensen & Frederiksen 1992; Schuchert 2004); Atlantic Canada (this study).