Bougainvillia muscus ( Allman, 1863 )

Calder, Dale R., 2010, Some anthoathecate hydroids and limnopolyps (Cnidaria, Hydrozoa) from the Hawaiian archipelago 2590, Zootaxa 2590 (1), pp. 1-91 : 21-23

Bougainvillia muscus ( Allman, 1863)

Figs. 9–11

Perigonymus muscus Allman, 1863: 12 [incorrect subsequent spelling of Perigonimus M. Sars, 1846 ].

Bougainvillia sp. — Tusov & Davis, 1971: 52.

Garveia sp. — Cooke, 1977: 84, fig. 12.

Bougainvillia ramosa .— Cooke, 1977: 84, fig. 13.

Garveia humilis .— Grovhoug & Rastetter, 1980: 252.

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

Material examined. Oahu: Honolulu Harbor, 26.vi.1945, several tangled colonies with entoprocts, to 2.5 cm high, with gonophores, BPBM D258.–Oahu: Honolulu Harbor, 2.vii.1945, several tangled colonies, to 5.3 cm high, without hydranths and gonophores, BPBM D261.–Oahu: Pearl Harbor, Dry Dock #2, 29.iii.1948,>100 colony fragments, to 6 cm high, with gonophores, BPBM D288.–Oahu: Honolulu Harbor, Ala Wai Yacht Harbor, 1 m, on stems of Pennaria disticha , no date, one colony, to 1 cm high, with medusa buds, identified as Garveia humilis, BPBM (without collection number).–Oahu: Pearl Harbor, Station 15, 21º22’19” N, 157º56’09” W, 27.xi.2007, one colony, to 1.8 cm high, with medusa buds, coll. S.L. Coles, ROMIZ B3822.– Oahu: Honolulu Harbor, La Mariana Sailing Club dock, 21º19’16.90” N, 157º53’37.95” W, 16.vii.2009, 3 colony fragments, to 4.5 cm high, with medusa buds (and medusae liberated in laboratory), coll. D.R. Calder, ROMIZ B3823.

Description. Hydroid colonies erect, up to 6 cm high, arising from a creeping hydrorhiza. Hydrocaulus monosiphonic, somewhat crooked, irregularly branched, widest at base, narrowest distally; perisarc of hydrocaulus golden-colored, relatively thick basally, thinner elsewhere, with sporadic wrinkles but otherwise essentially smooth; main branches tortuous, more slender than hydrocaulus; perisarc of main branches wrinkled basally, tending to be crinkled elsewhere, not annulated; terminal branchlets slender basally, shorter ones gradually increasing in diameter distally, longer ones tending to be cylindrical beyond base, extreme proximal end wrinkled to spirally twisted; perisarc of branchlets crinkly, extending distally as a cup-shaped pseudohydrotheca over base of contracted hydranth, not extending as a sheath over bases of tentacles or over hypostome. Hydranths cylindrical to fusiform; tentacles filiform, 12–16 in number, amphicoronate, arranged in two close whorls around distal end of hydranth; hypostome conical. Endoderm of hydranths ochre-coloured in life.

Gonophores free medusae. Medusa buds pear-shaped, invested with thin perisarc, arising via short stalks on terminal branchlets below hydranths. Newly liberated medusae thimble-shaped, umbrella 0.6–0.7 mm high, 0.5–0.6 mm wide; mesoglea moderately thick; umbilical canal present at apex; vestige of pedicel attaching medusa bud to hydroid sometimes forming an apical wart or small cone, peduncle lacking; manubrium short, small, tubular, with simple mouth; oral tentacles four, unbranched, inserted on manubrium just above mouth, appearing slightly capitate with a small cluster of nematocysts at distal end; radial canals four; ring canal present; tentacle bulbs four, conical, base rounded; marginal tentacles filiform, eight, with two per tentacle bulb; ocelli eight, conspicuous, dark red, one at base of each tentacle; velum broad; endoderm of manubrium and tentacle bulbs cream to orange-coloured. One-day-old laboratory-raised medusae about 1 mm high and wide; oral tentacles unbranched; marginal tentacles two per tentacle bulb; gonads beginning development interradially on manubrium. Three-day-old medusae about 1.3 mm high and wide; oral tentacles unbranched; marginal tentacles 12, with three per tentacle bulb; ocelli eight; exumbrellar surface dotted with minute batteries of nematocysts; gonads well-developed, one with mature egg bearing an outer envelope armed with numerous heterotrichous microbasic euryteles.

Remarks. Cooke (1977) reported this species from Hawaii, as Bougainvillia ramosa ( Van Beneden, 1844b) . That name was later shown to be invalid ( Calder 1988) and has been replaced by the binomen B. muscus ( Allman, 1863) . Cooke believed that the hydroid reported from the same area by Tusov & Davis (1971) as Bougainvillia sp. was conspecific with his material, and I agree. Hydroids from Ala Wai Yacht Harbor, Oahu, identified by Cooke (1977) as Garveia sp. , are also regarded here as small colonies of B. muscus . So too are the records of Garveia humilis ( Allman, 1877) from Pearl Harbor and Kaneohe Bay by Grovhoug & Rastetter (1980). The complicated taxonomy of Bougainvillia muscus has been reviewed recently by Calder (1988) and Schuchert (2007).

It seems remarkable zoogeographically that a species originally described from southern England might occur in Hawaii and elsewhere in the central and western Pacific. While Bougainvillia muscus is reportedly widespread in coastal waters of the Atlantic, Pacific, and Indian oceans (e.g. Millard 1975; Calder 1988; Schuchert 1996), the probability that such a wide range actually exists is given more credibility in light of 16S sequence data by Schuchert (2007). Divergence values of European and New Zealand populations were found to be quite low, suggesting that they are indeed conspecific.

Hydroids of Bougainvillia muscus were frequent on floating docks in sheltered waters of Honolulu Harbor and Pearl Harbor, Hawaii, during July 2009. Medusae liberated from these colonies were raised to maturity in the laboratory during this study. Specimens were kept at room temperature (21º C) in a covered beaker containing natural seawater, and fed newly hatched Artemia twice a day. Water was changed after each feeding. Development was somewhat slower than described in medusae of this species from Bermuda ( Calder 1988). While gonads began to appear at about the same time (two days after liberation), development of a third marginal tentacle per tentacle bulb was observed in three-day-old medusae, a day later than those from Bermuda. Branching of oral tentacles was also delayed, with most still unbranched even after four days. Differences are attributed to different culture conditions. Specimens from Bermuda were raised at warmer temperatures (28–29º C) and fed several times a day instead of just twice. Medusae of this species are thought to be short-lived; of those raised in Bermuda, none lived longer than 3.5 days. Those raised in Hawaii were preserved at maturity after four days.

Information on ecology and distribution of this species is given by authors including Peña Cantero & García Carrascosa (2002), Vervoort (2006), and Schuchert (2007). Bougainvillia muscus appears to be nearly cosmopolitan in warm and temperate regions.

Reported distribution. Hawaii. Oahu: Kaneohe Bay ( Tusov & Davis 1971); Kaneohe Bay, on stems of Halocordyle [= Pennaria disticha ] ( Cooke 1977, as B. ramosa ); Ala Wai Yacht Harbor ( Cooke 1977, as Garveia sp. ); Pearl Harbor and Kaneohe Bay ( Grovhoug & Rastetter 1980, as Garveia humilis ).

Worldwide. Western and eastern Pacific; western and eastern Atlantic; Indian Ocean; 0–100 m, doubtful to 1193 m ( Calder 1988; Peña Cantero & García Carrascosa 2002; Schuchert 2007; Mills et al. 2007).