Hydroids of Australia

Stems to 10 mm high, proximal half of stems and lower branch lightly fascicled, becoming monosiphonic in upper region, apophysis of branch with transverse distal node, branch ahydrocladiate proximally, internodes thereafter with strongly oblique nodes, each internode with three alternate, equidistant hydrocladia, one proximal, one in middle and one distal on internode. Perisarc of stem and branches thick and smooth.

Hydrocladia frontal on stem and branches, internodes slender, first internode athecate, distal node oblique, internode with one mesial nematotheca, internodes thereafter alternately thecate and athecate; thecate internode with oblique proximal and trans verse distal node, transverse node sometimes indistinct; no intranodal septa.

Hydrothecae seated on upper side of internode, tubular, deep, occupying almost entire internode, tilted forward at an angle of c. 55° to internode , adnate adcauline wall convex, short, free adcauline wall straight, abcauline wall weakly convex, margin perpendicular to hydrothecal axis, subcircular to oval, rim slightly everted.

Nematothecae bithalamic, mesial hydrothecate inferior seated on a small prominence, a perisarc infilled notch between basal chamber and proximal node, basal chamber short, robust, cup foreshortened on adcauline side, just reaching base of hydrotheca; basal chamber of lateral nematotheca long, conical, movable, cup broad and shallow, reaching hydrothecal margin, excavated on adcauline side. Athecate internode with one mesial nematotheca similar to mesial inferior, proximal on internode, bent forward. Cauline nematothecae similar to mesials, a row of five on internode, one near base of apophysis, one above and one in axil.

Colour: Colourless to white (preserved material). less ↑

Hydrorhiza tubular, creeping on stems and branches of host. Hydrothecal pedicel short, tubular, perisarc smooth, widening a little distally and merging into base of hydrotheca.

Hydrotheca long, tubular, perisarc thick, inclined to one side in distal third so that one wall convex and other concave, body with 8 - 11 deep entire annulations these becoming indistinct proximally, in some hydrothecae annulations reduced to undulations. Margin circular, with up to four replications, inclined to hydrothecal axis, rim distinctly everted, perisarc fairly thin. Diaphragm saucer-shaped, thin , indistinct, without thickening along hydrothecal wall, in empty hydrothecae line of attachment of hydranth marked by a row of internal upward-facing, thorn- like desmocytes. less ↑

Stolon tubular, rugose; stems to 5 mm high, unbranched, lower stem of same diameter as stolon, proximal internode athecate, stem thereafter thecate, internodes with 2 alternate hydrothecae, nodes distinct, oblique, sloping alternately left and right, usually a small tumescence above and below node.

Hydrothecae on both stolon and caulus, all of same shape. Stolonal hydrothecae widely spaced, on a short pedicel, cauline hydrothecae sessile, displaced slightly towards front of stem; hydrotheca tubular, narrowing slightly to margin, adcauline wall convex, about half free of internode, abcauline wall contiguous with border of internode, almost straight to weakly concave; floor of hydrotheca transverse to internodal axis; margin quadrangular (anterior view), rim with 4 cusps, lateral cusps sharp with deep semicircular embayment between, operculum of four fragile triangular valves.

Hydranth with 10–12 tentacles; no evidence of an abcauline caecum in contracted or extended hydranths.

Gonotheca irregularly obovoid, usually widening distally, body deeply crumpled, some gonothecae with 1 or 2 deep flanges, body narrowing into a rather wide, smooth pedicel, some arising from within stolonal hydrothecae, apex of gonotheca a short inverted funnel, orifice circular. Perisarc rather thin, fragile at hydrothecal margin, operculum and gonotheca.

Colour: colony pale yellowish-white. less ↑

Hydrorhiza reptant on substrate, stolons tubular.

Stems monosiphonic, to 4 mm high, straight to slightly zig-zag, simple or sparsely branched near base. Stem internodes widening distally to hydrophore, nodes transverse, deep.

Hydrophore short, primary hydrotheca very shallow, sessile or very closely adpressed to internode at level of node, shallow dish-shaped, sloping gently downwards away from internode, diaphragm distinct with a row of desmocytes above. Margin circular, not everted. Secondary hydrophores rare, on lower parts of stems, issuing from diaphragm of preceding hydrotheca, adcauline wall deeply indented at level of diaphragm. Perisarc smooth throughout, thick on proximal parts of stems, becoming very thin on hydrotheca.

Hydranths robust, very extensible with about 24 stubby tentacles.

Colour yellowish-brown. less ↑

Hydrorhiza reticulating, stolons tubular with very wide flange, moderately adherent to substrate. Pedicels of same width as stolon, arising at intervals from hydrorhiza, variable in length, smooth, sometimes a transverse joint along length resulting from interruption to growth; pedicel terminating in a wide rounded shoulder supporting a subglobular spherule.

Hydrotheca externally broadly conical, basal chamber above spherule deep, narrow, hydrotheca internally deeply campanulate, internal floor (diaphragm) flat, fairly narrow; hydrotheca laterally compressed, wall markedly thickened in plane of compression, thickening ending in a shoulder at or slightly below margin. Margin weakly scalloped and slightly everted.

Gonothecae large, inserted in hydrorhiza on a very short, smooth pedicel; mature gonotheca sub-ovate, recumbent to substrate, compressed, oval in section; young gonotheca triangular. Walls of gonotheca smooth, some broadly undulated, walls contracted below apex in plane of compression into a pair of blunt lateral lobes, apex truncate, slightly concave. Mature male gonophore eumedusoid, almost filling body cavity, a developing gonophore at base; base of each gonad with a pair of vestigal tentacles.

Hydranth with 24—28 tentacles.

Perisarc of pedicels and gonothecae very thick, thinner on hydrotheca.

Colour: Hydrorhiza, pedicels and hydranth white, gonophores pale cream to white. less ↑

Holotype: NMV F157465, 1 fertile stem, alcohol preserved. Depth 2 m, attached to old bivalve shell buried in sand. Blairgowrie jetty, Port Phillip, Victoria, Australia.

Paratype: NMV F157466, 12 fertile stems, alcohol preserved. Depth 2 m, Blairgowrie jetty, Port Phillip, Victoria, Australia; NMV F157467, two fertile stems, alcohol preserved. Depth 2m, Rye, Port Phillip, Victoria, Australia. less ↑

Mature colonies large, up to 15 cm in height and 15 cm in width in a spreading plumose canopy complexly branched with up to 10 orders of branching.

Hydrorhiza a bundle of tough rugose stolons firmly attached to rocky substrate.

Stems strongly fascicled, lower stem ahydrocladiate, in large colonies ahydrocladiate stems up to 10 cm long and 2.5 mm wide, the polysiphonic tubes gradually reducing in number distally, typically a single tube near the end of each branch. Branching from main stem regularly subdichotomous, branch internodes short, nodes oblique, indistinct.

Hydrocladia alternate, frontal, one proximal on each branch internode, moderately long, slightly recurved, length shortening distally along branch; hydrocladial internodes moderately wide, nodes transverse to weakly oblique, faint, a thick entire transverse intranodal septum at one third the distance from proximal end and a thinner, slightly oblique partial septum passing forward into the internode from the base of the lateral nematotheca.

Hydrotheca elongate, base lying along internode, posterior end pointed, anterior end facing upward at c. 40° from internode, a complete intrathecal septum passing almost vertically up through hydrotheca from intranodal septum. Margin with a prominent curved anterior rostrum and a long lozenge-shaped foramen behind rostrum; margin dentate with three pairs of lobate cusps, the anterior pair sharpest, the next pair rounded, the posterior pair shallowest and hidden behind the lateral nematothecae.

Median nematotheca tubular, narrow, following axial line of hydrotheca, orifice circular, level with hydrothecal margin, a small secondary orifice just above junction with anterior rostrum. Lateral nematothecae long, pointing forward, tubular, with a circular terminal orifice slightly ahead of hydrothecal margin, a small notch at base of nematotheca connecting with intranodal septum. Branch nematothecae similar to laterals, one at base of hydrocladium, usually one in fork of branch.

Gonotheca lenticular, without pedicel, large, several borne sparingly on a phylactocarp replacing a hydrocladium on higher branches, one hydrotheca on proximal internode of phylactocarp; usually one or two but sometimes up to five in various stages of development along primary phylactocarp; a short, straight secondary phylactocarp given off internode of primary at base of each gonotheca and closely adpressed to gonotheca, a single or a pair of nematothecae similar to laterals on each phylactocarpal internode, each with a circular terminal orifice and an inwardly facing orifice. Perisarc of gonotheca thick, rim conspicuously thickened, female containing several large ova.

Colour of live colonies silvery white, perisarc of stems brown, gonotheca grey with white scribbly lines, ova cream to mauve. less ↑

Holotype: NMV F147479, microslide (malinol mounted), fertile colony from leaves of the seagrass Amphibolis antarctica, 200 m offshore from Queenscliff, Victoria, depth 2 m; NMV F147481, remainder of holotype colony, alcohol preserved.

Paratype: NMV F147480, microslide (malinol mounted), fertile colony on leaves of the seagrass Amphibolis antarctica, 200 m offshore from Queenscliff, Victoria, depth 2 m. less ↑

Umbrella tall, with thick walls. Has 8 bulbs, of which the perradial ones carry 3-5 tentacles and the interradial ones - no more than 3. Tentacles very flexible, in live specimens several times longer than the umbrella. Ocelli absent. Manubrium is short, the gastric stem is well developed. From the corners of the mouth opening originate 4 branching tentacles, which are ornamented with 3 or 4 projections with nematocysts. The gonad enwraps the manubrium like a ring. Manubrium and bulbs vary in color from brownish-yellow to dark brown to black. Very often carry budding jellyfish on the manubrium, of which the most mature are located near the base, and the youngest near the mouth lobes. Sometimes secondary buds are found on the budding jellyfish. less ↑

Hydrorhiza creeping on host; no true stems present. Hydrocauli up to 35 mm long, monosiphonic, flaccid, sparingly branched, one or two branches given off subdichotomously, a hydrotheca in fork. Internodes long and slender, perisarc smooth, expanding a little distally, one hydrotheca distal on internode, node an indentation in perisarc.

Hydrothecae on front of stem, large, almost tubular; adcauline wall smooth, flatly convex, adnate part very short, convex, floor perpendicular to hydrothecal axis; abcauline wall variable in shape, faintly sinuous, concave or straight; margin of hydrotheca quadrate with four sharp cusps, separated by wide, flat embayments, rim replicated many times with fine, closely packed striae; operculum of four thick triangular valves.

Gonotheca borne beside base of hydrotheca, large, tumid, pedicel merging into body; when mature, irregularly barrel-shaped, expanding to mid-region, body with five to eight smooth annular ridges, these becoming deeper distally; apex with four equidistant cusps similar to hydrotheca, operculum of four finely striated valves. Female gonophore containing several large ova.

Colour: Clear, hyaline. less ↑

Hydrorhiza a coarse undulating tube. Stems to 4 mm long, robust, athecate part very short, with a strong distal constriction. Internodes conspicuously inflated behind hydrotheca, nodes sharply twisted. Hydrothecae large, 2-6 on stem, completely occupying internode; fixed adcauline wall 0.18-0.20 mm, free adcauline wall 0.35-0.40 mm; abcauline wall 0.35-0.40 mm. Thecal wall smooth, with 'a notch on abcauline side below margin, opposite the submarginal tooth. Margin 0.15-0.20 mm in diameter, lateral view. Three internal submarginal teeth, the abcauIine tooth best developed. less ↑

Hydrorhiza a simple tube, loosely wound on substrate.

Stems simple, to 1 cm long, smooth or slightly annulated, diameter Increasing distally, a distinct transverse joint just above junction with hydrorhiza. Pedicels of hydrothecae 1.95-2.7 mm long, 0.25 mm in diameter distally. Hydrothecal margin with 4 teeth, 4 valved operculum, and thickened submarginal ring. Depth of hydrotheca, 1.5 mm; diameter at margin, 0.75-1.21 mm. less ↑

Hydrorhizal stolons tightly entwining substrate. Clusters of up to 20 pinnate stems to 100 mm high arising from hydrorhiza, basal stem region lightly fascicled by hydrorhizal stolons, stems thereafter monosiphonic, tubular, stiff and robust, perisarc of basal region very thick and smooth, thinning distally.

Hydrocladia pinnate, alternate, well separated, long, no secondary branching, two alternate hydrothecae on stem between each branch and one axillar. Stem and hydrocladial internodes fairly long, nodes slightly oblique to transverse, marked by a notch in perisarc. Hydrocladial apophysis long, inclined upwards, proximal side marked by an indentation in perisarc in stem; first hydrocladial internode long, internodes shorter thereafter, nodes transverse, usually distinct.

Hydrothecae alternate, pedicel short, thick, smooth or with several ridges; hydrotheca asymmetrical, abcauline wall straight, proximal third of adcauline wall convex, the curve straightening out distally, diaphragm distinct, down-curved, often asymmetrically tilted , hydrothecal margin circular, rim quadrate with four low, equidistant, sharply pointed cusps separated by four shallow emarginations; operculum thin, of four triangular flaps.

Hydranths stubby, with at least 30 tentacles.

Gonothecae immature, top -shaped, arising in proximal stem region beside a hydrotheca or on stem, hydrocladium or apophysis from which a hydrotheca has been shed; perisarc thin.

Colour: Golden-yellow to golden brown. less ↑