Tubularia acadiae Petersen 1990

Tubularia acadiae Petersen, 1990

Figs. 1, 2, 4 a

Tubularia acadiae Petersen, 1990: 198, figs. 39, 40.

Tubularia couthouyi.— Bleakney, 1972: 933.– Bromley & Bleakney, 1985: 11, unnumbered figure [not Tubularia couthouyi L. Agassiz, 1860].

Type locality. USA: Massachusetts, Vineyard Haven (Petersen 1990: 198).

Material examined. NS: Minas Basin, 26.iv.1967, 4°C, two solitary hydroids, up to 7 cm high, one with female and one with male gonophores, coll. J.S. Bleakney, ROMIZ B629.

Description. Examined hydroids solitary, comprising fragments of three hydrocauli with hydranths. Hydrocauli unbranched, 5 cm and 7 cm long, maximum diameter 2 mm, mostly straight with a few irregular bends, incised by a few nodes marking points of growth and regeneration, gradually increasing in diameter from proximal part to distal end, each bearing a terminal hydranth above a bulbous neck; longitudinal peripheral canals about 7 in number, with one being wider than others, these canals sometimes branched and anastomosing. Perisarc on hydrorhiza thick except at distal end, extending over and appearing filmy around neck region, terminating at base of hydranth, smooth except for irregularly located nodes, golden- to amber-coloured in thick areas, thin and clear over neck region. Hydranths pear-shaped with slender hypostome, separated from bulbous neck region by a prominent circumferential groove, reaching 1.2 cm high from groove to tip of hypostome, maximum diameter 1.0 cm; tentacles occurring in aboral and oral whorls. Aboral tentacles about 55 in number, crowded, slightly staggered, laterally flattened at base, gradually tapering from proximal end to tip, about 1.3 mm long in preserved material, merging with ridges extending down over basal region of hydranth. Oral tentacles about 60 in number, tapering from proximal end to tip, to 5 mm long in preserved specimens, scattered within a narrow band around hypostome, bases adnate to hypostome and forming longitudinal ridges on it.

Gonophores fixed sporosacs, borne on 10-12 thick blastostyles arising from hydranth just above aboral tentacles; blastostyles with unbranched main stem approximately as long as hydranth when fully developed, each one with several short, slender side branches bearing gonophores; sporosacs of both sexes borne on long pedicels. Female sporosacs oval; distal end with orifice surrounded by 4-5 laterally flattened, fin-shaped crests extending from one-third to half-way or more down outer wall of sporosac, commonly with 2-3 developing embryos or actinulae that do not entirely fill sporosac cavity; spadix long, sausage-shaped. Male sporosacs subspherical, lacking lateral crests, terminal appendages, and radial canals; spermatic tissue nearly filling sporosac cavity.

Cnidome (Fig. 2)

desmonemes (n = 10): 6.0–6.3 µm long × 3.6–4.0 µm wide (undischarged)

large haplonemes (n = 5): 10.4–11.1 µm long × 6.5–7.3 µm wide (undischarged)

small haplonemes (n = 3): 6.8–7.5 µm long × 4.0–4.3 µm wide (undischarged)

large stenoteles (n = 6): 12.5–13.2 µm long × 10.3–11.8 µm wide (undischarged) small stenoteles (n = 10): 9.7–10.8 µm long × 7.0–7.9 µm wide (undischarged) heteronemes (n = 10): 11.2–13.2 µm long × 3.8–4.3 µm wide (undischarged) Remarks. Tubularia acadiae Petersen, 1990 was originally described from material collected at several locations near Woods Hole, Massachusetts, during the winter and early spring of 1964 (Petersen 1990). That account provides the only published record of the species, and only female colonies were mentioned. Petersen found the species again in 1970 while undertaking field work in Minas Basin, NS, during a visit to Acadia University (recorded as “ Tubularia acadiae n.sp. ” in a letter to Prof. J.S. Bleakney, received 24 January 1977). However, the latter record was never published, and it was not mentioned in his original description of the species. While no etymology of the specific name was given, it could refer either to Acadia University or to the geographic region known as Acadia (“Acadie” in French) that was once a colony of France in northeastern North America. Both of these possibilities suggest a link to the Bay of Fundy region.

Hydroids of T. acadiae are decidedly robust, and hydrocauli of the species are marked by nodes. These “joints” appear to be sites marking extension points of the hydrocaulus, and at least some likely represent locations where hydranths once existed. In Fraser’s (1944) key to species of Tubularia Linnaeus, 1758 from the Atlantic coast of North America, possession of a “jointed stem” was a prime character leading to identification of T. couthouyi L. Agassiz, 1860. In that regard, and in its large size as well, T. acadiae might easily be confounded for T. couthouyi. Indeed, records of T. couthouyi from Minas Basin (Bleakney 1972; Bromley & Bleakney 1985), the same location as material examined here, are taken to have been based on the morphologically similar T. acadiae. As for Tubularia couthouyi, it is close to and possibly conspecific with T. indivisa Linnaeus, 1758 (Petersen, 1990; Schuchert 2010).

Tubularia acadiae differs from both T. couthouyi and T. indivisa in the morphology of its female gonophores. Those of T. acadiae have 4-5 fin-shaped crests at the distal end of the sporosac wall, while such crests are lacking in the other two species. Female sporosacs of T. regalis Boeck, 1860 have similar crests, but that species differs from T. acadiae in having blastostyles that lack side branches, sporosacs that either lack pedicels or occur on very short ones, and hydroids that grow as entwined clusters rather than as single polyps (Petersen 1990). The basal disc of T. regalis is also broadly lobed and dome-shaped rather than circular with a crenulated margin. Meanwhile, T. couthouyi has been distinguished from T. indivisa largely on the basis of its “jointed” stem. Such nodes and regular annulations are rare in T. indivisa (Schuchert 2010). It is unclear whether joints in the hydrocaulus of that species are formed as typical nodes or as points of hydranth regeneration. Hydroids assigned to T. couthouyi are also said to be more robust than those of the better-known Linnean species. According to Fraser (1944), hydrocauli of the species reach 15 cm high, while the diameter across hydranths and extended tentacles sometimes attains 3–4 cm. He reported that hydranths of T. couthouyi bore as many as 30-40 aboral tentacles and 50 oral tentacles. Yet these measurements and tentacle numbers scarcely if at all exceed those reported in T. indivisa (see Schuchert, 2010). Another difference, according to Fraser (1947a: 147), is the existence in T. couthouyi of a series of deep annulations on the hydrocaulus immediately beneath the hydranth. However, these structures are not mentioned or illustrated in the original description of the species (L. Agassiz 1862). Finally, Agassiz believed that his species differed from T. indivisa in being an inhabitant of brackish waters, although T. indivisa has been found in salinities as low as 18‰ (Schönborn et al. 1993).

Male gonophores of T. acadiae, previously undescribed, were observed in examined material (ROMIZ B629) and have been described herein. They are much as in T. indivisa and T. regalis, although perhaps somewhat more nearly round in shape than in those species (Fig. 1). Also previously undescribed is the cnidome of the species, illustrated here (Fig. 2).

Phylogenetic studies by Nawrocki et al. (2013) support the hypothesis that Tubulariidae Fleming, 1828 is monophyletic. Three lineages were recognized within the family, with one of them including the genera Tubularia and Hybocodon L. Agassiz, 1862, another including Ectopleura L. Agassiz, 1862, and a third comprising Ralpharia Watson, 1980 and Zyzzyzus Stechow, 1921a. Hydroids assigned to Tubularia, Hybocodon, and Ectopleura are quite similar in morphology. All three genera have been reported in the Bay of Fundy, although the sole representative of Hybocodon (H. prolifer L. Agassiz, 1860) is known there only from its medusa stage (Fish & Johnson 1937). Several characters distinguish these three genera (Table 1).

Species of Tubularia and Hybocodon are held to differ from those of Ectopleura in being solitary rather than colonial. Cornelius (1995a) noted that current definitions of the term “colony” do not adequately differentiate the various types of colonies that are now known to exist in hydrozoans. Within the group, a colony is usually understood to constitute an assemblage of interconnected polypoid and/or medusoid individuals derived asexually from a single larval stage (Cornelius 1995a; Bouillon et al. 2006; Nawrocki & Cartwright 2012; Brinckmann-Voss & Calder 2013). However, colony formation of a distinctly different kind is known to occur in Ectopleura larynx (Ellis & Solander, 1786). Nawrocki & Cartwright (2012) discovered that colonies in that species were formed through the fusion of sexually generated polyps rather than by asexual propagation.

Tubularia acadiae has been reported at depths from extreme low water spring (Bleakney 1972, as T. couthouyi) to 30 m (Petersen 1990). Type material, comprising 31 specimens reaching a maximum of 8 cm high, was collected on stones and shells in the area around Woods Hole, Massachusetts. It is a species of boreal waters, having been found during winter and spring both at its type locality and in Minas Basin.

Recorded distribution. Bay of Fundy: recorded for the first time as Tubularia acadiae. Kingsport, Minas Basin, NS (Bleakney 1972, as Tubularia couthouyi L. Agassiz, 1860); Minas Basin, NS (Bromley & Bleakney 1985, as T. couthouyi).

Eastern North America: Minas Basin, NS (reported herein) to the Woods Hole area, Massachusetts (Petersen 1990).

Elsewhere: as above.