Mangan mentions Duerden as describing the medusae of Millepora. Nothing is available of this paper on line, but J. Lewis did cite Duerden.
I do not have Duerden's paper at this time.
A bibtex citation:
@article{duerden1899zcb,
title={{Zoophyte Collecting in Bluefields Bay.}},
author={Duerden, JE},
journal={J. Inst. Jamaica},
volume={2},
pages={619--624},
year={1899}
}
Preliminary Results of a Study of Millepora sp. and its Zooxanthellae
======================================================================
From 1984 until 1986 I studied reproduction of Millepora spp. in Guam.
My initial interest was in determining whether reproduction is
seasonal. Millepora spp. have unique reproductive structures in the
calcium carbonate skeleta (hard parts), the ampullae, which surround
the developing medusa and gametes. These ampullae are only present
when the reproductive zooids, the medusae, are produced, and are
filled in within a matter of days after the medusae have been
liberated. Thus, the presence of ampullae in hard parts specimens is a
sign that the colony was reproductively active at the time of
collection, and their absence a sign, likewise, that the colony was
not reproductively active. I was determined to track reproductive
effort over time using these ampullae as markers. Later on, as the
study of Millepora spp. took on a life of its own, it indeed became
apparent that Millepora spp. are highly seasonal, and other aspects of
their biology, and that of associated species, piqued my interest.
Specimens of hard parts were collected at irregular intervals
beginning in September 1984 until fall 1986. Beginning somewhat after,
some specimens were decalcified, and tissues embedded in wax for
sectioning. Colonies at certain reefs were numbered and labelled to
enable samples to be taken, repeatedly from the same colony.
In both 1985 and 1986, Millepora platyphyla shed medusae about three
or four days after full moon in early April, in what appeared to be
the first event of a summer reproductive season. Each of these events
(except one, see below) was apparently highly synchronized on Guam,
with apparently substially all the ripe Millepora platyphyla colonies
on Guam reefs shedding medusae on the same night.
The first event of each of these seasons was striking to observe on
the reef. Each "spawning" was presaged by an abrupt change in the
appearance of a preponderance of Millepora platyphyla colonies on Guam
reefs: they turned a richer, darker brown. This change of coloration
seemed to be poorly correlated with reproductive condition; color was
apparently not correlated with reproductive condition in other
months. On many (but not all) of the darker colonies could be seen a
myriad of minute white rings about 1 mm in diameter, contrasting with
the background of dark brown. These white rings evidenced the opening
of the ampullae. Within approximately a week after this color change,
the colonies shed their burdens of medusae (bearing female and male
gametes) in a synchronous ”spawning” event. I observed shedding of
medusae in ziploc bags containing colony fragments at about sunset.
Each colony produced either male or female medusae, as Hickson
reported.
Swarming does not occur a uniform number of days after the full moon,
but usually somewhere between one and four days after full moon. Only
once were medusae observed to swarm on
In the material examined it was clear that the vacuolated substance of the ova in the free medusae, in all cases, contained numerous zooxanthellae; but they were equally absent from the ova of the numerous unliberated medusas that had been inspected.
However, after a long search some half a dozen medusae were found which, I think, afforded conclusive evidence that zooxanthellae pass in numbers from the manubrium into the ovum, and that this invasion may commence at a period prior to the liberation of the medusae.
The ovum, until it has attained a considerable size, is sharply
divided off from the vacuolated substance of the manubrium.
Eventually a period is reached when its compact cytoplasm becomes continuous with the central mesh work (fig. 8). This stage could be commonly observed, and zooxanthellae be seen round the margin of the egg, but never in its compact substance. Sometimes the egg cytoplasm displayed small incipient vacuoles.
The subsequent period, during which vacuolisation of the cytoplasm of the ovum occurs, and during which the zooxanthellae are incorporated, could be found only on one piece of Millepora, where half a dozen medusae had reached this stage (fig. 9). Their ova showed a variable amount of vacuolisation, which, so far as I could make out, is in great part inaugurated at the inner borders of the egg substance; as if in some manner the vacuolated portion of the manubrinm with its contained zooxanthellas were drawn in.
That the medusas are liberated at this stage can be concluded from
their mature appearance within the ampullae, and from the fact
that one free medusa (fig. 10) was met with which exhibited an
essentially similar structure.
The other free medusas examined, possessed ova, more completely
vacuolated, and with more numerous zooxanthellae. The egg-cells
showed various phases of an encroachment upon the manubrial
substance, which eventually was almost entirely reduced (fig. 12),
the ova at the same time becoming rounded off and similar to the
extruded ova that were examined.
During all this period the zooxanthellae exhibit their normal appearance, and it can be observed that they divide fairly frequently within the ovum. These cells have been figured by Moseley ('81) who was able to examine fresh material. He remarks that they closely resembled those of other Hydroids. They contained irregular granules of a bright gamboge-yellow colour,
gamboge
n 1: a gum resin used as a yellow pigment and a purgative;
2: a strong yellow color [syn: {gamboge}, {lemon}, {lemon
yellow}, {maize}]the cell-contents frequently dividing into two, and sometimes, more rarely, into four (emphasis mine, AED). In the older portions of the colony the pigment; was of dark-brown hue.
I show their structure as displayed in stained specimens (fig. 18). The spherical nucleus exhibited a mass of closely packed chromatin granules. A pyrenoid was always present, the clear space around which, in most cases, gave the reaction for starch. The pigment-bearing granules varied in number and size, did not always stain to the same degree, and in some cases had a little starch associated with them. The cell membrane did not respond to cellulose tests. I observed in a few cases division of a cell into four. Their average diameter was
somewhat over 9um.
That zooxanthellae pass into the ovum from the parental tissues
appears to be undoubtedly the case from the foregoing evidence;
but the part these play in the future economy of the animal
remains to be solved. It may be that their enclosure is more
accidental than physiologically necessary, for the bulk of the
foreign cells in the canals and tissues of the colony may come
from the surrounding water at a subsequent period. An apparent
increase in the substance of a mature ovum (see below) might be an
indication of their activity. At all events, there is suggested,
an approach to a more complete symbiotic union than that which
exists in Convoluta roscoffonsis, for instance, where ifc has been
definitely shown ('07) that infection takes place after the animal
is hatched, for there the animal undoubtedly plays, in the long
run, the part of a parasite with respect to the alga, as under no
known conditions were algte found to escape alive from the body of
that turbellarian.
