Hydroids of Australia

The ringed tubularia looks somewhat like a small bouquet of pink flowers. A colony consists of a bushy bunch of stems, each ending with a polyp with tentacles. Ringed tubularia reproduce in two ways. Small jellyfish-like organisms reproduce sexually while attached to the ends of the stems. New polyps hatch immediately out of the eggs. The second manner is asexual: loose pieces of the colony are carried by the sea current and can 'take root' at a new location. less ↑

Branching among the colonies is due to the settling of actinulae on adjacent stems of the parent colony, the annulated stem of the young hydranth forming the base of the new branch. There is a tendency for all hydranths on the one colony to be the same sex; however, both male and female may occur on the one colony.

Both the hydranth and blastostyles are very active, the pendulous blastostyles performing rhythmic lashing movements at intervals. less ↑

Colonies up to 20 mm in height.

Hydrorhiza tubular, wandering over and through the substrate, becoming erect at intervals as single stems.

Stems thick and smooth, unfascicled, sparingly and irregularly branched with up to 10 branches, rebranching common. Stems with 6-12 distinct proximal annulations, ringed at intervals throughout length, branches with 6-10 annulations just above origin.

Hydranths terminal on branches, pedicels indistinctly annulated at intervals, widening distally, sometimes terminating obliquely below hydranth. Hydranths large, with 24-30 tentacles (very long in life), a distinct proximal groove in the lower body of some, but not all hydranths.

Hypostome large, annular to clavate in preserved material.

Sexes on separate colonies, the gonophores scattered on all but the most distal branches. Male gonophores in all stages of maturity borne in a single crowded verticil below a hydranth with a fully-developed hypostome and a full number of partially-atrophied tentacles. Mature gonophore 3 or 4-chambered, immature gonophore with a rod-shaped spadix and a small apical knob without nematocyst pad. Mature gonophore globular or bun shaped, apical tubercule lost at this stage. Female gonophores borne low on stem, clustered in all stages of development below a hydranth with hypostome and a full number of partially-atrophied tentacles. Young gonophores on a long, thin pedicel, disk-shaped with unbranched spadix, mature gonophores retained below hydranth, oval, containing a single egg encased in a tough gelatinous pellicle.

Nematocysts, microbasic euryteles of two sizes present:

— Small microbasic euryteles, capsule 8-9 x 3-4 µm, shaft 6-8 µm long, with very long thread. Abundant in tentacles.

— Large microbasic euryteles, capsule 38-43 x 15-18 µm, bean-shaped, shaft discharging sideways, 30-36 µm long, distal end inflated and spirally annulated, with numerous bristles arising from the annulations, thread very long with distinct spines. Abundant around hypostome and scattered in groups over spadix of immature female gonophore.

Colour: Stems golden brown, body of living hydranth yellow or orange pink, tentacles pale yellow to pink, spadix of female gonophore purplish pink, mature eggs orange, male gonophores pearly pink, spadix orange pink. less ↑

Stems plumose, arising from a ramified hydrorhiza; stolons tubular, perisarc very thick, internally longitudinally striated.

Hydrocaulus tubular, becoming narrower distally, divided into internodes of variable length by 4-5 deeply indented transverse nodes; hydrocladia distal on internodes, gracefully recurved from stem, up to eight annulations at junction with stem; internodes same as those on stem, one hydranth given off on a short expanding pedicel on upper, distal side of each internode; pedicel indistinctly ringed at base, perisarc thinner than on hydrocladium.

Hydranths clavate to pyriform, terminal hydranth on each hydrocladium usually larger than others, all hydranths with a whorl of 10-14 semi-filiform aboral tentacles and 14-16 scattered pedunculate capitate tentacles on upper body, aboral tentacles with a longitudinal band of nematocysts on outward facing side, peduncle of oral tentacles long, transversely wrinkled, capitulum richly armed with nematocysts.

Cnidome:

i) Stenoteles, capsule ovoid, 45 -46 x 27-30 µm, shaft 58-60 µm, 10 µm wide armed with four or five curved spines 30 µm long spines and spirals of fine bristles, tubule at least 180 µm long; abundant in capitate tentacles.

ii) Stenoteles, capsule ovoid, 37 x 25 µm, shaft 60 µm, tubule at least 60 µm, in capitate tentacles; none discharged, not common.

iii) Stenoteles, capsule ovoid, 15- 18 x 13- 17 µm, shaft 15-20 µm; in capitate tentacles.

iv) Stenoteles, capsule ovoid, 6.5-10 x 4-7 µm shaft 8 µm, very abundant; in aboral and capitate tentacles, few discharged.

v) Desmonemes ovoid to pyriform capsules, 6-8 x 4-4.5 µm, in aboral tentacles, only one seen discharged.

vi) ?Haploneme, capsules small bean shaped, 9- 12 x 3-6 µm; abundant in aboral tentacles, none discharged.

vii) Capsule ovoid narrower at anterior end, 12.5-15 x 6.5-7 µm with inclusion body; in aboral tentacles, none discharged.

viii) ?Isorhiza capsule almost spherical 10 x 7 µm, site unknown, several partially discharged, tubule with very fine spines. less ↑