Bougainvillia muscus ( Allman, 1863 )

Calder, Dale R., 2017, Additions to the hydroids (Cnidaria, Hydrozoa) of the Bay of Fundy, northeastern North America, with a checklist of species reported from the region, Zootaxa 4256 (1), pp. 1-86 : 22-24

Bougainvillia muscus ( Allman, 1863)

Figs. 7 f, g, 10

Perigonymus muscus Allman, 1863: 12 [incorrect subsequent spelling of Perigonimus M. Sars, 1846 ]? Bougainvillia superciliaris .— Verrill 1874: 733 [not Bougainvillia superciliaris ( L. Agassiz, 1850) ].? Bougainvillia carolinensis .— Stafford 1912: 72.— Fraser 1918: 338.— Brinkhurst et al., 1976: 10, unnumbered figure [not

Bougainvillia carolinensis ( McCrady, 1859].

? Bougainivillia superciliaris .— Henry & Kenchington 2004a: 127 [incorrect subsequent spelling of Bougainvillia Lesson, 1830 ] [not Bougainvillia superciliaris ( L. Agassiz, 1850) ].

Type locality. England: Devon, Torquay (Torbay) ( Allman 1863: 12).

Material examined. NS: Annapolis Basin, Annapolis Royal, on mooring line, 19.ix.1984, three polysiphonic colony fragments, up to 2.5 cm high, without hydranths, with tendrils, one fragment with medusa buds, coll. J.S. Bleakney, ROMIZ B511.—NB: St. Andrews, Brandy Cove, on algae on wharf piling, intertidal, 21.viii.1984, two polysiphonic colonies, up to 4.1 cm high, without medusa buds, with tendrils, coll. D. Calder, ROMIZ B605.—NB: Letete, on pontoon slip of wharf, just below surface, 14.viii.1988, 12.5° C, 31.5‰, coll. D. Calder, ROMIZ B4135.—NB: St. Andrews, pontoon slip at public wharf, 45°04’17”N, 67°03’17”W, <1 m, on Ascophyllum nodosum , 32.5‰, 9°C, 27.v.1999, one monosiphonic colony, up to 1.9 cm high, without medusa buds, with tendrils, coll. D. Calder, ROMIZ B3083.—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, colony without medusa buds, coll. D. Calder, ROMIZ B3087.—NB: St. Andrews, pontoon slip of public wharf, 45°04’17”N, 67°03’17”W, just below surface, 16° C, 20.viii.1999, two monosiphonic colonies, up to 3.2 cm high, with medusa buds and tendrils, coll. D. Calder, ROMIZ B3120.—ME: Cobscook Bay, near Estes Head, 44°53’36”N, 66°59’37”W, 07.viii.2005, on aquaculture float, <1 m, several fragments of a polysiphonic colony, up to 2.5 cm high, without medusa buds, with tendrils, coll. D. Calder, ROMIZ B4129.

Description. Hydroid colonies erect, up to 4.1 cm high, arising from a creeping hydrorhiza; distal parts of colony with vermiform tendrils of various lengths. Hydrocaulus monosiphonic or polysiphonic, crooked to nearly straight, at least basally, irregularly to more or less alternately branched, widest at base, narrowest distally; main branches tortuous to nearly straight, usually more slender than hydrocaulus; terminal branchlets slender proximally, short ones gradually increasing in diameter from proximal to distal end, long ones mostly cylindrical above base, proximal end wrinkled; perisarc of hydrocaulus relatively thick basally, thinner elsewhere, mostly wrinkled but with some smooth parts, commonly overgrown with diatoms and protozoans; perisarc of main branches mostly wrinkled, nowhere regularly annulated; perisarc of tendrils very thin, slightly wrinkled; perisarc of branchlets wrinkled, extending distally as a cup-shaped pseudohydrotheca over base of contracted hydranth, not extending as a sheath over bases of tentacles or over hypostome, pseudohydrotheca not so apparent when hydranths extended. Hydranths cylindrical to fusiform to sac-shaped; tentacles solid, filiform but tapering from slender tip to broader base, up to 16 in number, amphicoronate, arranged in two close whorls around distal end of hydranth; hypostome conical.

Gonophores free medusae. Medusa buds subspherical to pyriform, borne at end of stalks arising singly from branchlets below hydranths, stalks often quite long; entire structure invested in thin perisarc.

Cnidome ( Fig. 10 )

desmonemes (n = 10): 4.1–4.4 µm long × 2.5–2.8 µm wide (undischarged)

microbasic euryteles (n = 10): 5.8–6.7 µm long × 2.9–3.2 µm wide (undischarged)

Remarks. Hydroids referable to Bougainvillia Lesson, 1830 were frequent during this study on floating structures in Passamaquoddy Bay , including pontoon slips of wharves ( ROMIZ B3083, ROMIZ B3087, ROMIZ B3120), aquaculture floats ( ROMIZ B4129), and mooring lines ( ROMIZ B511). Although medusae were not raised from any of the colonies, the specimens otherwise conformed with accounts of B. muscus ( Allman, 1863) . As with populations of the species from European waters (Schuchert 2007; Calder 2012), both polysiphonic and monosiphonic colonies were observed, and tendrils (apical or terminal stolons) were frequent on them. Medusa buds on fertile colonies arose singly from ultimate branchlets rather than being grouped on branched stalks, as in the morphologically similar trophosomes of B. pyramidata ( Forbes & Goodsir, 1853) . Medusa production in hydroids of B. muscus from the lower Bay of Fundy appears to occur during late summer. Specimens from Annapolis Royal, NS ( ROMIZ B511), collected on 19 September 1984, bore medusa buds, as did material from St. Andrews, NB ( ROMIZ B3120), collected on 20 August 1999 .

Although this is the first report of B. muscus from the Bay of Fundy, and from Atlantic Canada, at least some earlier reports of hydroids of B. superciliaris ( L. Agassiz, 1850) and B. carolinensis ( McCrady, 1859) from the Fundy region may have been based on misidentifications of this species. While the medusa stage of B. superciliaris has indeed been reported from the Bay of Fundy (e.g., Stimpson 1853, as Hippocrene superciliaris ; Bigelow 1914; Fish & Johnson 1937; Shih et al. 1971; Trott 2004a), its hydroid is now known to occur as stolonal colonies unlike the erect and branched forms mistakenly attributed to the species in older literature on hydrozoans (e.g., L. Agassiz 1862; A. Agassiz 1865; Mayer 1910a; Fraser 1944; Berrill 1949). Reliable accounts of the hydroid of B. superciliaris , described as stolonal and obscure, were provided for the first time in the 1960s ( Uchida & Nagao 1960; Werner 1961; Nagao 1964; Edwards 1966). Of particular note, Werner (1961) followed the complete life cycle of the species from medusa to stolonal hydroid and back to medusa in the laboratory. Hartlaub (1911) had earlier outlined the life cycle of a stolonal species that he thought was B. superciliaris , but his account is now known to have been based instead on B. principis (Steenstrup, in Lütken, 1850) ( Vannucci & Rees, 1961; Edwards 1966; Schuchert 2007).

Misconceptions in the North American literature about the hydroid stage of B. superciliaris having an erect and branched colony of moderate size originate from the works of L. Agassiz (1862) and A. Agassiz (1865), and confusion has persisted until recent times. Clarifying the identity of the species entails going back to its establishment, as Hippocrene superciliaris , based solely on a medusa population from Massachusetts, USA ( L. Agassiz, 1850: 273, pls. 1–3). Years later, a hydroid was subjectively linked to it by L. Agassiz (1862) and A. Agassiz (1865) . No type material exists (medusae and hydroids identified as B. superciliaris at MCZ were all collected after the original description), but there is little uncertainty about the identity of the medusa. However , the hydroid that L. and A. Agassiz linked to the medusa of B. superciliaris had an erect and branched colony form. Life cycle studies noted above ( Uchida & Nagao 1960; Werner 1961; Nagao 1964) clearly demonstrated that hydroids of the species are stolonal. Subsequent identifications of hydroids based on the erroneous early descriptions of B. superciliaris by the Agassizs are therefore unsound. Questions then arise whether the hydroids they described and illustrated can be recognized as those of another known species. Hartlaub 1911: 174) suggested that they might be conspecific with either B. ramosa (sensu Van Beneden, 1844b) (= B. muscus ) or B. carolinensis . Vannucci & Rees (1961: 87) also thought the hydroid and young medusa stages might be identical with B. ramosa (= B. muscus ). Schuchert (2007) considered that identification unlikely because older medusae described in the work of A. Agassiz bore at least seven tentacles per marginal bulb, and adults of B. muscus usually have fewer ( Russell 1953, as B. ramosa ; Kramp 1961, as B. ramosa ; Schuchert 2007). However , it was not made clear in the younger Agassiz’s monograph , or in an earlier paper by him ( A. Agassiz 1862), how development of the medusa was followed, whether from cultures in the laboratory or more likely from specimens captured in the plankton and assumed to be the same species. In any case, the identity of the hydroid in question remains unclear. Taxonomic and life cycle investigations are warranted to better resolve the identity of one or more species of hydroids referable to the genus Bougainvillia occurring along the boreal coast of northeastern North America . Meanwhile, records of B. superciliaris from the Bay of Fundy are included here with question in the synonymy list of B. muscus , a species reported herein. As for B. carolinensis , it is a warm-temperate species ranging from southern Florida and the Gulf of Mexico northwards to Massachusetts ( Mayer 1910a; Bigelow 1914; Kramp 1961; Petersen 1964; Segura- Puertas et al. 2009) and is unlikely to occur in cold waters of the Bay of Fundy . Bougainvillia rugosa S.F. Clarke, 1882 , a species with large hydroid colonies and with medusae that are fertile at liberation, is unreported north of Chesapeake Bay on the east coast of the USA ( Calder 1971).

Detailed taxonomic accounts of B. muscus are given by Vannucci & Rees (1961, as B. ramosa ), Calder (1988), and Schuchert (2007). Of particular note, molecular evidence was provided by Schuchert in support of the supposed wide geographic distribution of the species.

Nomenclaturally, the specific name muscus is a Latin noun meaning “moss.” Originally combined with Perigonimus M. Sars, 1846 (gender: masculine), it remains unchanged when combined with the genus Bougainvillia (gender: feminine) (ICZN Art. 31.2).

Recorded distribution. Bay of Fundy: recorded for the first time as Bougainvillia muscus . Bay of Fundy (? Verrill 1874, as Bougainvillia superciliaris ); St. Andrews, NB (? Stafford 1912, as B. carolinensis ); Katy Cove and Joe’s Point, St. Andrews, NB (? Fraser 1918, as B. carolinensis ); Passamaquoddy Bay (? Brinkhurst et al. 1976, as B. carolinensis ); Bay of Fundy (? Henry & Kenchington 2004a, as Bougainivillia superciliaris ).

Eastern North America: Bay of Fundy to southern New England and Bermuda ( Calder 2010); medusa stage reported southwards to the Carolinas ( Allwein 1967; Calder & Hester 1978).

Elsewhere: believed to be essentially circumglobal (Schuchert 2007; Calder 2010, 2012).

Figures

FIGURE 7. Filiferan hydroids. a, Corydendrium dispar, colony with three hydranths, SNM HYD- 000871. Scale equals 0.5 mm. b, Corydendrium dispar, distal end of hydrocaulus with a hydranth, SNM HYD- 000871. Scale equals 0.25 mm. c, Rhizogeton fusiformis, hydranth and young female gonophores, ROMIZ B 3101. Scale equals 0.5 mm. d, Rhizogeton fusiformis, developing female gonophores, ROMIZ B 3101. Scale equals 0.25 mm. e, Rhizogeton fusiformis, female gonophores, ROMIZ B 3101. Scale equals 0.25 mm. f, Bougainvillia muscus, part of colony with two hydranths, ROMIZ B 3120. Scale equals 0.25 mm. g, Bougainvillia muscus, part of colony with medusa buds and tendrils, ROMIZ B 3120. Scale equals 0.5 mm.

FIGURE 10. Bougainvillia muscus, nematocysts of hydroid, ROMIZ B 3120. a, desmoneme. b, two heterotrichous microbasic euryteles. c, heterotrichous microbasic eurytele, discharged.