Tiaropsis multicirrata M. Sars 1835

Tiaropsis multicirrata (M. Sars, 1835)

Figs. 17 a, b

Thaumantias multicirrata M. Sars, 1835: 26, pl. 5, figs. 12 a–c [medusa].

Type locality. Norway: near Bergen (M. Sars 1835).

Material examined. NB: Richardson, Deer Island, 44°59’42”N, 66°56’45”W, on pontoon slip of wharf, <1 m, on Mytilus edulis, 34‰, 9° C, 22.v.1999, one colony, without gonophores, coll. D. Calder, ROMIZ B3089.

Description. Colony stolonal, with hydrorhiza entangled in filamentous algae growing on a mussel. Hydrorhiza mostly smooth, 0.1 mm in diameter, lacking internal septa, bearing pedicellate hydrothecae. Hydrothecal pedicels very short, less than 0.15 mm high, appearing irregularly annulated, supporting a hydrotheca at distal end. Hydrothecae erect, slender, deep, subcylindrical with smooth walls, without a distinct diaphragm basally, infrequently renovated, capped by a long cone-shaped operculum, hydrothecal walls typically widening very gradually from proximal to distal end, total length of hydrothecae from base to tip of operculum 0.4–0.8 mm, width at base of operculum about 0.15 mm and at insertion with pedicel 0.10 mm. Operculum a folded continuation of hydrothecal wall having about 10 pleats when closed, not distinctly demarcated from hydrothecal wall. Perisarc everywhere moderately thin but not flimsy. Nematothecae absent.

Gonothecae not seen.

Remarks. Tiaropsis multicirrata (M. Sars, 1835) was originally described from a medusa discovered in Norway. Knowledge of its hydroid remained obscure until a colony was linked to T. multicirrata in studies by Rees (1941) at Millport, Scotland. Rees found the hydroid on an old Buccinum shell, and based his identification on a medusa liberated from it in the laboratory. Later, Korsakova (1949) and Naumov (1951) raised similar hydroids from planulae released by medusae of the species. Based on the morphology of its trophosome, Naumov (1960) concluded that the hydroid was identical with one described earlier as Cuspidella mollis Spasskii, 1929 from the Russian coast of the Barents Sea. The species differs from Cuspidella Hincks, 1866, as defined by its type species C. humilis Hincks, 1866, in having pedicellate instead of sessile hydrothecae. As noted by Rees (1941), L. Agassiz (1850: 296) reported raising a “campanularioid polypidom” from planulae liberated by a medusa of Tiaropsis diademata L. Agassiz, 1850, but he did not describe or illustrate it. The medusa T. diademata, from the east coast of North America, was shown by Kramp (1919) to be conspecific with the European T. multicirrata.

While the inconspicuous hydroid of Tiaropsis multicirrata has not been reported before from the Bay of Fundy, its medusa stage has long been known from the area (e.g., Whiteaves 1901; Bigelow 1914; Fish & Johnson 1937; Shih et al. 1971; Shih 1977; Linkletter et al. 1977). Elsewhere on the east coast of North America, medusae of the species have been reported from Rhode Island (Mayer 1910b, caption to fig. 11, pl. 31, as T. diademata) to the Canadian Arctic, including Baffin Island (Dunbar 1942; Barry 1974) and Foxe Basin (Grainger 1959, 1962). On the west coast, it is known to occur from southern British Columbia (Arai & Brinckmann-Voss 1980) to the Bering Sea (Bigelow 1913, as T. diademata) and on into the Beaufort Sea (Grainger 1975). Although hydroids of this species have been reported infrequently and are poorly known, Arai & Brinckmann-Voss reported them to be “very common” on wharves at Departure Bay and French Creek, British Columbia, Canada. Based on knowledge of its medusa, T. multicirrata has been described as a northern boreal species (Russell 1953) and as a subarcticboreal species (Barry 1974).

In terms of seasonality, Mayer (1910b) reported that medusae of the species (as Tiaropsis diademata) appear in great numbers on the coast of New England during March. By mid-May, numbers there decline significantly, and medusae disappear during summer. More recently, the species was observed from February to April in the Eel Pond at Woods Hole, Massachusetts (Costello & Mathieu 1995). To the north, medusae are described as being frequent to abundant, at least seasonally, along the east coast of Newfoundland (Kramp 1920; Pinhey 1927, as T. diademata). Observed seasonality is similar in British Columbia (Arai & Brinckmann-Voss 1980), with young medusae appearing in March and adults being present until early June. In Britain, medusae first appear in late winter or early spring and are mature by July (Russell 1953).

Other aspects of the biology of Tiaropsis multicirrata have been reviewed by authors including Russell (1953), Naumov (1960), Arai & Brinckmann-Voss (1980), and Cornelius (1995a). An exhaustive account of the morphology and development of the medusa is given by Russell. According to Naumov, fertilized eggs are retained in the gonad of the female medusa and are released into the water as planula larvae. Some of the diverse food items known to be ingested by medusae were listed by Arai & Brinckmann-Voss. For the most part, both hydroid and medusa stages are inhabitants of shallow waters, although Barry (1974) reported medusae over a depth range of 0– 150 m in waters of northern Canada.

As might be expected, molecular data summarized by Maronna et al. (2016) confirm a close relationship between Tiaropsis multicirrata and several so-called “campanulinoids.” In their phylograms, the species appears particularly close to Tiaropsidium kelseyi Torrey, 1909 (family Tiaropsidae Boero et al., 1987), Opercularella pumila S.F. Clark 1875 and Phialella quadrata (Forbes, 1848) (family Phialellidae Russell, 1953), Racemoramus panicula (G.O. Sars, 1874) (questionably to family Phialellidae), Mitrocomella brownei (Kramp, 1930) and M. niwai Bouillon & Barnett, 1999 (family Mitrocomidae Haeckel, 1879), and Calycella syringa (Linnaeus, 1767) (family Calycellidae Kramp, 1913).

Detailed synonymy lists of the medusa stage of Tiaropsis multicirrata are given in Russell (1953), Kramp (1961), and Arai & Brinckmann-Voss (1980).

Recorded distribution. Bay of Fundy: hydroid recorded for the first time. Medusa recorded from Bay of Fundy (Whiteaves 1901; Fish & Johnson 1937); Eastport, ME (Bigelow 1914).

Eastern North America: western Greenland to New England (Cornelius 1995a; Shih et al. 1971).

Elsewhere: circumpolar in cool waters (Cornelius 1995a), including the eastern North Atlantic (Brittany to the White Sea) and North Pacific (British Columbia to the Bering Sea, and the Yellow Sea and northern Japan to the eastern and northern seas of the Russian Federation) (Naumov 1960; Arai & Brinckmann-Voss 1980; Yamada & Hirano 1983; Antsulevich 2015).