Ralpharia coccinea
General description:
Holotype: NMV G2602, Male colony from reef, Crawfish Rock, Western Port, Victoria. 3 m deep, on the alcyonacean Parerythropodium membranaceum.
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Taxon
Ralpharia coccinea Watson, 1984
Ralpharia coccinea
General description:Ralpharia coccinea is easily recognised by its small size and robust, brilliantly coloured hydranths and gonophores. The extreme difference in size and certain differences in the cnidome distinguish this species from its congener, R. magnifica.
Of ecological interest is the obligate association of the two closely related species with the same alcyonacean substrate- Parerythropodium membranaceum. R. magnifica grows from the alcyonacean in sparse colonies of up to 20 stems while R. coccinea may form colonies of up to 200 hydranths growing close to the alcyonacean surface. The hydrorhizas of the two species are often intergrown through the thin, sheet like tissue of the alcyonacean. The growth and reproductive seasons of the two species overlap only slightly: R. magnifica is a summer hydroid, reproducing at maximum water temperature, whereas R. coccinea grows, and is reproductive in the rising temperatures of late winter to spring.
Ralpharia coccinea
General description:Hydrorhiza tubular, 0.3-0.5 mm diameter, embedded in the alcyonacean substrate.
Stems short, robust, to 20 mm long, widening to 0.5-0.8 mm diameter below hydranth. Perisarc thickest proximally, with faint annular striations, thinning distally, becoming a loosely wrinkled sheath below hydranth, coenosarc longitudinally striated.
Hydranths variable in size, distinctly separated from stem by a platform-like base. Mature hydranth 5-7 mm across the extended tentacles (living material), aboral tentacles 2 mm long, 20-24 in a single verticil, and 20-24 short oral tentacles in a tuft 2 or 3 deep surrounding an elongate hypostome.
Gonophores arising from a wide shelf between the hydranth body and aboral tentacles, 8-10 borne singly on short, unbranched blastostyles, balloon-shaped , distally truncated, up to 1.5 mm long at maturity, with 4 conspicuous radial canals and circular canal and 4 rudimentary tentacle knobs; without mouth or tentacles at liberation.
Nematocysts of five kinds present on hydranth and gonophores:
Stenoteles of two sizes: (i) large, capsule spherical, 10-11 µm diameter, common on hydranth body and aboral tentacles, butt 10-12 µm long; (ii) smaller stenoteles, capsule spherical, 5-6 µm diameter, butt 5-6 µm long, very abundant in tentacles and on gonophores.
(iii) Macrobasic mastigophores, capsule subglobose, 12-13 µm long, 8-9 µm wide, thread very long, thick, of same diameter and spinose throughout, spines longer and thicker, near base. Very abundant at base of aboral tentacles and on hydranth body.
(iv) Desmonemes, capsule bean-shared, 5 µm long, 3 µm wide.
(v) ?Atrichous isorhizas, capsule flask-shaped , 10- 12 µm long, 4-5 µm wide, with a short cylindrical neck. When discharged, neck everts into a short thick thread. Moderately common in oral tentacles.
Colour: Stems pale green to brown, coenosarc orange in distal region, tentacles transparent , sometimes with a faint orange longitudinal stripe; hydranths and gonophores brilliant scarlet, radial canals of immature gonophore of a glistening frosted white appearance. Umbrella of liberated medusa clear, radial canals purplish, spadix orange.
Distribution:Victoria, Australia.
Habitat:Subtidal, epizoic on the soft coral Parerythropodium membranaceum.