Antennella singulata, Watson, Jeanette E., 2011

Watson, Jeanette E., 2011, New species, new records and redescriptions of Thecate hydroids (Cnidaria: Hydrozoa: Leptothecata) from Southern Australia, Zootaxa 3122, pp. 1-36 : 15-18

Antennella singulata sp. nov.

Fig. 8 A–H

Material examined. Holotype, NMV F171361, microslide, male colony, on reef, North Arm Channel, Western Port, depth 8 m, coll: J. Watson, 9/01/1997. Paratype, NMV F171362, microslide and remaining preserved material, infertile colony, St Leonards pier, on sponge, depth 3 m, coll: J. Watson, 20/01/2010. Paratype, NMV F171363, microslide and remaining preserved material, St Leonards pier, on sponge, depth 2 m, coll: J. Watson, 8/ 03/2010. Paratype NMV F171374, microslide, female colony, Port Welshpool, Victoria, on Caulerpa , depth 2 m, coll: J. Watson, 25/02/1978. Material in author’s collection: Western Port, Victoria, on wharf piling, coll: J. Watson, depth 3 m, 3/12/1994. Port Welshpool jetty, on the green alga Caulerpa , depth 2 m, coll: J. Watson, 25/2/1978. Gabo Island, eastern Victoria, on red alga and sponge, depth 17 m, coll: J. Watson, 15/2/1972. Coniston Bay, Port Kembla, New South Wales, depth 11 m, on mussels coll: J. Watson, 12/9/1975.

Description from holotype and paratypes. Colony arising from a ramified hydrorhiza; stolons tubular, surface moderately smooth, poorly adherent to substrate. Stems erect, monosiphonic, to 5 mm long, typically unbranched, but sometimes with a single short side branch, basal segment of hydrocladium of same diameter as stolon, beginning with one, sometimes two athecate internodes of variable length with a strong transverse node followed by a longer internode with long oblique distal joint, two or three nematothecae in a line along internode.

Hydrocladium comprising alternate long, slender hydrothecate and ahydrothecate internodes; ahydrothecate internode usually the longer, ahydrothecate internode with a transverse to weakly oblique proximal node, sometimes marked only by an indentation in perisarc, distal node long, oblique, ending just below floor of hydrotheca.

Hydrotheca cup-shaped, set at an angle of 40–45° to hydrocladial axis, walls straight to slightly expanding, abcauline wall thicker than adcauline, margin transverse to hydrothecal axis, weakly everted, perisarc thinning distally to margin, rim entire, floor of hydrotheca concave, a foramen connecting with internode at base of abcauline wall.

Ahydrothecate internode with one median nematotheca almost central on internode, nematotheca bithalamic, base stout, almost adnate to internode, cup reduced to a triangle; three nematothecae on hydrothecate internode, one inferior median, bithalamic, base stout, closely adnate to internode, cup similar to median; twin lateral nematothecae not reaching hydrothecal margin, basal chamber cylindrical, about same length as nematotheca, basal chamber of nematotheca elongate conical, cup wide and shallow, reduced on side facing hydrotheca; median superior nematotheca bithalamic, beak-shaped with stout base, tucked below hydrotheca. Hydrorhiza with scattered nematothecae similar to laterals, but with longer bases.

Male gonotheca facing forward along hydrocladium, borne on a pedicel of two or three short segments beside median inferior nematotheca; kidney-shaped to ovoid, walls smooth, perisarc thin; one long conical nematotheca above base, basal chamber of nematotheca long, narrow, cup shallow saucer-shaped. Aperture of gonotheca terminal, circular, slightly oblique to gonothecal axis, operculum a sheet of tissue. Female similar to male, but with two large nematothecae near base, gonophores developing into a single large planula at maturity.

Cnidome comprising two categories of nematocysts:

i) microbasic mastigophore (?p-mastigophore), capsule bean-shaped, 16– 17 x 10–12 µm, shaft 10–12 µm, inflated about mid length to distal third with two rows of spines, thread thick, moderately long, abundant, site unknown.

ii)?isorhiza, capsule small, pyriform, 4– 6 x 2–3 µm, thread thick, moderately long, site unknown.

Colour of colonies pale creamy yellow.

Hydrocladium

basal length of athecate internode 120–320 basal length of nematothecate internode 360–624 diameter of internode 56–64 basal length of nematothecate internode 240–312 basal length of hydrothecate internode 200–224 width at transverse node 48–52 length of abcauline wall 152–160 length of free adcauline wall 112–120 diameter at rim 176–192

Nematotheca

median, athecate segment, length base 30–40 median, abcauline depth of cup 20–26 median inferior, length base 40–58 median inferior, abcauline depth of cup 28–30 lateral, length of pedicel 50–58 lateral, length of base to cup 24–36 width cup, lateral view 50–51 median superior, length 24–36 gonothecal, length of base 64–88 gonothecal, length of base 80–82 gonothecal, depth of cup 32–40

Gonotheca

female, length of pedicel 56– 72 female, length 432– 456 female, maximum width 240– 280 male, length of pedicel 80– 11 male, length, excluding pedicel 448– 560 male, maximum width 256–280

Remarks. Six species of Antennella are reported from Australia: A. secundaria ( Gmelin, 1791) , A. tubulosa ( Bale, 1894) , A. campanulaformis ( Mulder & Trebilcock, 1909) and A. microscopica ( Mulder & Trebilcock, 1909) , A. dubia Stechow, 1923b and A. siliquosa Stechow, 1923b .

In a review of the family Halopterididae Schuchert (1997) examined the type specimen of A. microscopica but found it too fragmentary for confident recognition. No more material of A. microscopica has been found; it is likely to be a poorly preserved specimen of another species of Antennella . A. tubulosa is a rare species which has been recorded only twice, once from the type locality of Port Phillip ( Bale 1894) and from Pearson Island in the eastern Great Australian Bight ( Watson 1973). Schuchert (1997) redescribed A. campanulaformis from Mulder & Trebilcock’s type material and included A. dubia and A. siliquosa from Western Australia in its synonymy.

A. secundaria is a widely distributed species in southern Australia ( Stechow 1923b; Watson (1973, 1997, 2000, 2002, 2003), Queensland ( Pennycuik 1959) and northern Australia ( Watson 2000). Schuchert (1997) considered A. secundaria to be a very variable species with one to three median nematothecae on the ahydrothecate internode, suggesting it may prove to be a group of species.

The finding of the present material led to re-examination of the author’s extensive collection of Antennella from southeastern Australia. While many specimens bear two to three median inferior nematothecae on the ahydrothecate internode, some from various localities consistently bore only one on a long, slender internode; it is here recognised as a new species, Antennella singulata . A. singulata is closely related to but is distinguished from A. secundaria by the single median nematotheca on the ahydrothecate internode.

Antennella singulata occurs on a variety of substrates including soft sponges, mussel shells and algae.

Etymology. Named for the single nematotheca on the ahydrothecate internode.

Distribution. Western Port, Port Phillip and south-eastern Australian coast to Port Kembla, New South Wales.

Figures

FIGURE 8. Antennella singulata sp. nov. A, Paratype colony from St Leonards. B, hydrocladium from paratype. C, female gonotheca, one nematotheca hidden. D, lateral nematotheca. E, median inferior nematotheca from hydrothecate internode. F, nematotheca from ahydrothecate internode. G, micobasic mastigophore, H,? isorhiza Scale bar: A, 1 mm, B, C, 0.5 mm, D – F 0.2 mm, G, H, 10 µm.