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Medusoid release and spawning of Macrorynchia philippina Kirchenpauer, 1872 (Cnidaria, Hydrozoa, Aglaopheniidae)
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International audience. The life cycle of the aglaopheniid Macrorynchia philippina Kirchenpauer, 1872, is re-described from examination of live specimens collected from Réunion Island, Indian Ocean. Fertile colonies were collected on the outer slope of the coral reef and medusoid release happened a few hours later. Video sequences were recorded. Colonies were hermaphroditic: each phylactocarp contained one female and one male gonotheca. Sexual dimorphism was remarkable: sex could be recognized by colour, the female being red ochre, including about 40 oocytes disposed in a mosaic feature, and the male yellow ochre, having a homogeneous mass of spermatozoa. The blastostyle ran all around the gonangium near the closure of the two valves of the gonotheca, forming gubernacula. A ring of refringent corpuscles was clearly visible near the apex. Medusoids were indistinguishable inside the gonotheca. Male and female medusoids were released simultaneously at gamete maturity. Medusoid release involved the basal rupture of the blastostyle and the rupture of the links between the ectoderm surrounded the medusoid (the mantle), including the blastostyle (the mantle), and the gonothecal perisarc. While the two valves of the gonotheca were pushed and drew aside, the medusoid emerged by slipping out of the mantle that ruptured distally, forming a sheath; the bell of the medusoid did not contract. Immediately after emergence, quick and strong contractions of the bell allowed the medusoid to swim and induced spawning by breaking the ectoderm surrounding the gametic mass around the spadix. Spawning lasted only a few minutes: both oocytes and spermatozoa were expelled at each contraction. Spent medusoids remained alive only about 2 h. External fertilization gave rise to planulae 1 day later.
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