Balella mirabilis ( Nutting, 1905 )

Calder, Dale R., 2010, Some anthoathecate hydroids and limnopolyps (Cnidaria, Hydrozoa) from the Hawaiian archipelago 2590, Zootaxa 2590 (1), pp. 1-91 : 29-31

Balella mirabilis ( Nutting, 1905)

Fig. 17

Balea mirabilis Nutting, 1905: 940 , pl. 2, fig. 3, pl. 7, figs. 3, 4.

Balella mirabilis .— Calder, 2004: 20.

Type locality. USA: Hawaii, between Molokai and Maui, 232 m ( Nutting 1905) .

Material examined. Maui: Albatross Stn. 4077, off northeast coast, 99 fm (181 m), 21.vii.1902, several colony fragments, largest fragment 2.9 cm high, with poorly preserved hydranths, without gonophores, USNM 22171 [originally identified as Corydendrium corrugatum and labelled “cotype”].–Kauai: Albatross Stn. 4135, 225–294 fm (411–538 m), 01.viii.1902, fragments of at least three colonies, largest fragment 6 cm high, with poorly preserved hydranths, without gonophores, USNM 22172 [originally identified as Corydendrium corrugatum , labelled “cotype,” and in a vial together with USNM 22171].

Description. Hydroid colonies erect, robust, polymorphic, reaching to 6 cm high, arising from a tangled hydrorhizal tuft, apparently anchoring colony on a sedimentary substrate. Hydrocaulus polysiphonic with tubes interconnecting, naked coenosarc occurring in grooves parallel to tubes, stem quite rigid, irregularly branched in one plane, nearly straight, diameter gradually decreasing distally; branches straight to slightly curved, little branched or unbranched, polysiphonic to extreme ends but gradually tapering distally. Hydrocaulus and branches densely armed with small dactylozooids. Perisarc sometimes forming a shallow, thin, cup-shaped collar at base of hydranths; colour dark brown in older and thicker parts of colony, becoming straw-coloured in younger distal parts. Hydranths naked except for small basal collar of perisarc, arising at irregular intervals, most frequent on branches, clavate to pyriform with an elongate and relatively slender aboral stalk; tentacles filiform, in two distinct whorls; proximal whorl of tentacles somewhat smaller, about 12– 16 in number; mid-distal whorl of tentacles tending to be larger, about 8–12; hypostome elongate. Dactylozooids largely or entirely naked, digitate, solid, with outer ectoderm and inner endodermal core.

Gonophores not seen.

Remarks. Balella mirabilis ( Nutting, 1905) was originally described from the Hawaiian Islands. Type material of the species was never received at the NMNH (Geoff Keel, pers. comm., 01 September 2009) and apparently has been lost. A neotype is needed, preferably from the same general locality. While one of the lots listed above might serve the purpose, neither is in good condition and it seems better to defer action in the hope that a better colony will eventually be found.

Although Nutting’s (1905) hydroid was infertile, colonies of the species with medusa buds, arising from gonozooids, were described later from Japan ( Jäderholm 1919) and Indonesia ( Schuchert 2003). Gonozooids described by Jäderholm lacked tentacles, while those studied by Schuchert usually had a single filiform tentacle. The hydroid has not yet been linked to a known medusa, and the life cycle of the species remains obscure.

Balella irregularis ( Fraser, 1938a) from the Galápagos Islands was considered conspecific with B. mirabilis by Calder et al. (2003). Although subsequently treated as valid (Calder et al. 2009) because of apparent differences in development of proximal tentacles on the hydranth, such differences may represent intraspecific variation and a reassessment of the two forms is needed.

As noted earlier by Schuchert (2003), the dense basal tuft of hydrorhizal fibres suggests that this species grows on sedimentary substrates. Balella irregularis was also found on a substrate of sand and coralline red algae (Calder et al. 2009).

Reported distribution. Hawaii. Albatross Stn. 3856, “between Molokai and Maui…, 127 fathoms” (232 m) ( Nutting 1905).

FIGURE 18. Hydrodendrium gorgonoides : habit of 21-cm-high colony, BPBM D522.

FIGURE 19. Hydrodendrium gorgonoides : part of branch with two hydranths, each bearing a gonophore, BPBM D521. Scale equals 0.5 mm.

FIGURE 20. Hydrodendrium gorgonoides : nematocysts, BPBM D521. a, desmoneme. b–c, heterotrichous microbasic euryteles.

Worldwide. Hawaii; Japan; Indonesia; (?)Galápagos Islands, as B. irregularis ; 49–232 m ( Nutting 1905;

Hirohito 1988; Schuchert 2003; Calder et al. 2009).

Figures

FIGURE 17. Balella mirabilis: part of hydrocaulus with hydranths (after Nutting 1905).