Halecium marsupiale Bergh 1887

Halecium marsupiale Bergh, 1887

Figs. 17 e, f

Halecium marsupiale Bergh, 1887: 334, pl. 28, figs. 2a, b.

Type locality. Russian Federation: Kara Sea, 20 fm (37 m) (Bergh 1887: 334).

Material examined. NB: Passamaquoddy Bay, off the northwestern side of Deer Island, on Hydrallmania falcata in a lobster trap, 19.vi.1985, three colonies, up to 1 cm high, without gonophores, coll. D. Calder, ROMIZ B4132.

Description. Hydroid colonies erect, up to about 1 cm high, arising from a creeping, smooth to somewhat wrinkled hydrorhiza. Hydrocaulus monosiphonic, unbranched or sparingly branched, annulated at insertion with hydrorhiza, divided into internodes of varying length by distinct nodes, older hydrocauli of larger plumes straight basally, with 1-4 internodes bearing neither branches nor hydrothecal pedicels, geniculate beyond basal region, with internodes annulated basally or throughout, annulations strongest over proximal end, each internode widening at distal end in form of a Y and bearing two apophyses, with one apophysis supporting internode above and the other supporting a hydrophore or a branch, branches or hydrophores given off alternately from opposite sides of hydrocaulus. Perisarc mostly quite thin and glassy. Branches, when present, resembling distal parts of hydrocaulus. Young hydrophores with a swelling or an annulation or two above a basal node separating them from apophysis of hydrocaulus, occasionally with a deep constriction proximally, slightly wrinkled or smooth and gradually widening distally, bearing a terminal hydrotheca or primary hydrotheca; a pseudodiaphragm sometimes evident on hydrophore just below hydrotheca, with its development greater on the adcauline side; primary hydrophores commonly supporting shorter secondary or tertiary ones arising from diaphragm of hydrotheca below. All hydrothecae borne on hydrophores clearly set off from internodes of hydrocaulus, with none being sessile; hydrothecae quite deep for the genus, with a diaphragm below a ring of distinct desmocytes, hydrothecal cavity widening distally; margin flaring, often everted; hydrothecal wall more distinctly concave on adcauline side, hydrothecal depth to 0.07 mm from diaphragm to margin, diameter at diaphragm to 0.12 mm, at margin to 0.2 mm. Hydranths relatively large, some strongly constricted in mid-region, with a distal whorl of about 16-20 filiform tentacles; basal web not observed in preserved specimens; proboscis prominent, dome-shaped.

Gonophores and gonothecae not seen.

Remarks. Halecium marsupiale Bergh, 1887, previously known only from waters of the Russian Federation, is described as “rather rare” (Naumov 1960) or “rare” (Antsulevich 2015). Russian authors have recorded it from the Barents Sea in the west to the Bering Sea in the east. It was originally described from the Kara Sea by Bergh (1887) in collections from the Danish Dijmphna (Dymphna) Expedition.

Halecium marsupiale is easily distinguished from its congeners even in the absence of gonophores. No hydrothecae occur at the distal ends of its cauline internodes, as in most species of the genus Halecium Oken, 1815. Instead, they are borne at the tips of well-developed hydrophores that are separated from cauline internodal apophyses by distinct nodes. That morphology is similar in several other species of the genus, including H. muricatum (Ellis & Solander, 1786) from boreal and Arctic waters, H. muricatum forma abyssale Broch, 1918 from bathyal waters north of Iceland, and H. filicula Allman, 1877 from the Straits of Florida. All three differ from H. marsupiale in lacking pronounced annulations on the cauline internodes, and in having much larger trophosomes with polysiphonic stems and branches. Another is H. groenlandicum Kramp 1911, a robust, polysiphonic species from boreal and Arctic regions of the northern hemisphere. Unlike in H. marsupiale, its colonies have long, straight, smooth internodes, each with several apophyses, and its hydrothecae are shallow and only slightly flaring. Halecium sp., described from the Mid-Atlantic Ridge by Calder & Vervoort (1998), differs in having long and mostly smooth cauline internodes.

According to Naumov (1960), hydroids of Halecium marsupiale occur predominantly at depths between 50– 100 m, although they have been found over a bathymetric range of 11–245 m. Biogeographically, the species extends from Arctic regions into the boreal zone. Its discovery in the boreal Bay of Fundy expands its known geographic range to waters of northeastern North America. Literature on the species is given in the synonymy list of Antsulevich (2015).

Gonophores were lacking in specimens examined from the Bay of Fundy. As described by Naumov (1960) and Antsulevich (2015), gonothecae of the species are sac-shaped, laterally flattened, and smooth, with a short stalk and a small terminal aperture. When ripe, gonophores are extruded though the aperture into a spherical marsupium.

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

Eastern North America: recorded for the first time.

Elsewhere: Barents Sea, White Sea, Kara Sea, Laptev Sea, Chukchi Sea, Bering Sea, Sea of Okhotsk, Sea of Japan (Naumov 1960; Antsulevich 2015).