Structure of the ampullae of Millepora spp. is defined by the structure of the tissues.

An earlier post presented an image of the degradation of the tissue overlying the ampulla---and hence medusoid---of Millepora sp. cf. platyphylla.  An image of lower magnification of the identical slide shows the structure that has been compromised, toward the periphery of the hollow that is the ampulla.  Pylons remain beyond the central part of the disk.

Below, another image, this time of a male medusoid gives a better idea of the structure of tissues of an intact covering of an ampulla.  The pylon-like structure is clearly identifiable.  Individual spermatozoa are also clearly visible.

Ampullae of Millepora spp: Decalcification Prior to Liberation/Escape of Medusoids

This image signals a hallmark event in the life history of Millepora spp., as one of several propitious sections with views of a Millepora sp. (probably M. platyphylla) collected in 1986, likely at Toguan Bay, Guam.  This study derived from the plan to use the condition of hard-part specimens---presence of open ampullae---as an indicator of reproductive activity, as an approach to determining the timing of reproductive activity.  Once open ampullae had been observed, and certain signs in  colonies, in situ,  interest was aroused in histological study of the structural changes.  This slide represents a proof of concept of this approach.  e of  image is the beginning of a story, involving timing of reproductive activity of these spp.; development of medusoids---inside protective cavities, the ampullae; and the dissolution of the coverings of ampullae to allow the medusoids to escape.  

Millepora spp. are colonial calcifying hydroids, exhibiting alternation of generations; each colony bears either male or female medusoids. the "adult" form that spawns within a few hours of liberation into the water column, each of them less than 1mm in diameter.  In order to facilitate successful spawning between ephemeral medusoids, which live a number of hours, they must swarm in the water column en masse. This requires a tight synchrony in time of release.    

 

Distal part of medusoid, degrading covering, concomitant with decalicification of ampulla cover.  Two tentacles shown with developing nematocysts.