Lafoea annulata, Watson, 2003

Watson, Jeanette W., 2003, Deep-water hydroids (Hydrozoa: Leptolida) from Macquarie Island, Memoirs of Museum Victoria 60 (2), pp. 151-180 : 158-159

Lafoea annulata sp. nov.

Figures 8A–E

Material examined. Stn 44, NMV F91315 , holotype, specimen alcohol-preserved, NMV F91341 malinol-mounted microslide from holotype colony; infertile colony on a fragment of primnoid gorgonian, hydrorhiza intergrown with those of other hydroids .

Description (of holotype). Colony 70 mm high and 40 mm wide; hydrorhiza a broken tangled mass of tubular stolons coalescing to form polysiphonic tubes of stem; colony branched almost from base in disorderly flabellate fashion, base of stem and lowest branch 1 mm thick, both heavily fascicled, polysiphonic tubes almost linear, sometimes a little twisted in lower stem region then running up branches; distal region of some branches with 2 or more tubes, a few branches monosiphonic. Branches bent at various angles, becoming more or less straight distally; walls of ultimate branches smooth without nodes. Apical stolonisation occurring on several branches where a tube becomes free of branch, walls of free tubes contorted and undulated, sometimes rejoining branch.

Hydrothecae given off without apophyses from monosiphonic branches or from peripheral tubes of polysiphonic branches; hydrothecae in opposite pairs or in groups of three, one arising from each tube of branch, if three, the third arising close to opposite pair, forming an incipient whorl of 3, groups well separated at variable distances along branch. Hydrothecal pedicels tubular, length variable but mostly long, straight to bent, widening distally and merging smoothly into base of hydrotheca below puncta line; pedicels usually deeply annulated to almost smooth, frequently one side more deeply annulated than other.

Hydrothecae rather fragile, long, tubular, slightly asymmetrically bent with one wall slightly convex in basal third, opposite wall weakly concave to straight; diaphragm very thin, transverse to slightly oblique, saucer-shaped with central hydropore marked by an indefinite double ring of small scattered punctae; a slight thickening of hydrothecal wall at puncta line. Margin of hydrotheca circular, transverse to hydrothecal axis, rim smooth, noticeably everted, many hydrothecae with up to 5 everted marginal replications, usually well separated, some well below rim.

Perisarc in polysiphonic stem region and branches quite thick, thinning in monosiphonic parts; in branches with fewer tubes, perisarc of youngest tube markedly thinner than others; perisarc of hydrothecae thin, transparent and shining. Hydranths too poorly preserved for description; remnants emerging from many hydrothecae as a long strand of tissue.

Nematocysts large, bean-shaped, probably isorhizas, 21–22 X 8.5–9 µm, none discharged, but containing a long, probably isometric, closely coiled tubule; abundant in coenosarc of polysiphonic tubes of branches.

Colour. Colony translucent pale honey-yellow, monosiphonic branches and hydrothecae almost colourless.

Measurements (µm)

Branch diameter of monosiphonic branch 56–88

distance between groups of pedicels 900–2000

length of pedicel to puncta line 1720–4000

proximal diameter of pedicel 80–144 Hydrotheca diameter at puncta line 128–160

length, puncta line to margin (including regenerations) 520–704

diameter of margin (including eversion) 200–240

Remarks. An empty conical structure at the broken distal end of a branch may be a damaged gonotheca; the structure is transparent, adpressed to the branch with the wider end facing distally and is overgrown by several polysiphonic tubes; it could be an empty corophiid tube. The diaphragm at the puncta line of the hydrotheca may have a downwardly directed hydropore but because of its delicacy the actual structure could not be ascertained. The free stolons at the ends of several branches seem to have developed from hydrothecal pedicels which have reverted to polysiphonic tubes, growth then proceeding onward without development of a hydrotheca. The thin strands of tissue issuing from many hydrothecae may be collapsed protective sheaths of hydranths. Several hydrothecae have remnants of tissue adhering to the rim which could easily be mistaken for opercular fragments.

Similar species considered were Lafoea fruticosa (M. Sars, 1850) , L. gracillima Alder, 1856 , L. capillaris G. O. Sars, 1874 , L. elegantula ( Broch, 1903) , L. dumosa Fleming, 1828 and L. benthophila Ritchie, 1909 . While L. annulata has a hydrotheca with everted margin similar to L. benthophila that species has an upwardly directed pedicel so that the hydrothecae are held close to the branch. Similarly to L. annulata , hydrothecae of L. dumosa from western Europe are arranged in groups of two or three ( Cornelius, 1995) but lack an everted margin. Vervoort (1972a) described the range of variation of South Atlantic L. fruticosa from latitudes 42° to 60° S. However, it is much smaller in critical dimensions of hydrotheca and pedicel and the hydrothecae have less everted margins than those of L. annulata . A small colony from the Ross Sea recognised as L. gracillima by Totton, 1930 approaches the dimensions of the present specimen but his figures do not show the annulated pedicels characteristic of L. annulata .

Figures

Figures 8A–E. Lafoea annulata sp. nov., stn 44. A, colony. B, distal stolonisation at end of branch. C, hydrotheca with twisted and partially annulated pedicel. D, hydrotheca with almost smooth pedicel. E, undischarged nematocyst from coenosarc of branch. Scale bar: A, 25 mm; B, 1 mm; C, D, 0.5 mm; E, 20 µm.