Photographs: structure of Millepora platyphylla skeleton

The Tabulae are apparent in the following photographs of Millepora platyphylla Skeletons

 

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I was attracted to the study of Millepora platyphylla because of their hard parts, their skeleta.  My overriding interest was in reproductive timing.  The Milleporid  Hydrozoan corals had me from where I learned that their reproductive status is heralded by certain characters in their hard parts, the ampullae, which are exhibited only when they are reproductively active: the ampulla is a protective cove in the skeleton that houses the medusae, the reproductive individual that carries forth the gametes.  I reasoned that information regarding seasonality of reproduction could be learned by studying time series of their the hard parts.  

I have to admit that I have learned little about the hard parts of Millepora.  Much more could be learned.  

 

Recently I have been awakened to a seriously interesting aspect of the biology of Millepora spp.: the degradation of the tissues, and the zooxanthellae, especially in the lower layer of the living tissue.   This, in turn, has turned my attention to another aspect of the morphology of their skeleta:  as the tissues lay down more and more layers of the Calcium Carbonate---the skeletal tissue---the polyps produce a sequence of new basement plates.  Akin to the sequence of corallites in scleractinian corals, these plates leave behind a sequence of consecutive chambers, evidence of the progressive accretion of the massive skeletal structure, the corallum. 

These plates are termed the tabulae.  Interestingly, tabulae are also described for the extinct rugose corals, in the _Treatise on Invertebrate Paleontology_.  

 

I note, in part:

• The distance between successive tabulae varies.  One wonders to what extent growth rate of the corallum is determined by, or alternatively determines, the gaps between deposition of these tabulae.  
• The surface of the colony is planar.
• Structure is organized at several levels: (1) gross morphology (tabulae and apparent palisades forming a corallite wall-figure 5);  (2) orthogonal crystalline (trabulae?)--figure 3; and over the broken surface may be seen grains, as in figure 1 and others.
• thick bands orthogonal to the tabulae are visible 

 

Photographs

The following photographs are presented.  It is planned to continue to capture other views of the hard parts of Millepora spp.

 

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3

4

5

Much remains to be learned from studies of the skeletal remains of Millepora platyphylla.

These images were made with a Canon EOS M50, with the 28mm EF-M macro lens.  This is the maximum magnification with this lens, without additional add-on supplementary lenses.  This lens does not accept an extension tube.

 

 

Note to me: Processes during development of the Ova in the medusa

My interest in Millepora spp. (or just Millepora) begins with reproductive timing.  My interests range into seasonality and annual cycles, lunar cycles, daily (circadean) cycles.  I started paying attention to Millepora when I learned that the Ampullae were present in the hard parts (the rock, the skeleton) during reproduction; thus, if I collected a few pieces of their skeleta every time I went to the reef, I would eventually have a record of reproductive activity, enabling deeper understanding into the seasonality of this hydrozoan coral.  I was actually interested in neurosecretory control of gametogenesis,and had hoped to study giant clams.  But these charismatic and delicious macro-molluscs were too few and too far between for such a study on Guam.   Millepora was an interesting option.  Although I did not intend this to be my thesis topic, thse proved to be an intensely interesting organisms.

One night, I was invited to tag along on a night fishing foray with  friends from Pingelap Island.  That night, in early April, 1985, I was thrilled to observe Millepora shedding medusae!   The next day, I drove around the Western side of Guam and sampled Millepora at several sites: these sites also proved to be reproductively active. 

So, it was actually possible to observe reproduction in real time.  My study caught fire at this point.  I started collecting tissue specimens along with the pieces of skeletal material.  I made a point of collecting paired specimens from each colony, and I marked the colonies. 

I have some 200 specimens, collected from different colonies at different times over two seasons on Guam.  Much of my second year at the University of Guam was spent working on these specimens.  Over 200 tissue samples were fixed and embedded in paraffin.   John Starmer rescued them from Guam, when they were about to be thrown out.  

To make a long story short, my interest in Millepora has been focused at the microscopic level.  While I've been trying to grok tha variables involved in attaching a camera to a microscope, I have been focusing on primarily events at the level of developing medusae.  Millepora  hydrocorals are hydroids, that produce ephemeral medusoids (short lived free swimming medusae that exist to carry gametes off and spawn).  

Is it not obvious that the timing of the development of these medusoids is part of the complicated dance that led to the synchronized liberation of medusae observed on the reef that night, at Toguan Bay, Guam.

Here I will post some photos made with a cell phone of a slide from a specimen collected on 9 April 1986, the night of the New Moon.  I have made some assumptions about the timing of reproductive events in Millepora.

 Assumptions (for Millepora platyphylla)

1. Liberation of Medusae is sychronous, on the same night.  At several sites on Guam, liberation was evident on the same night, as far as I could tell.
   
2. Medusae are released/liberated (or alternately break free) on the fourth or fifth evening after Full Moon.
3. Reproduction is seasonal.  The season is about three or four months long.  The first event is in early April or late March.
   
4. Reproduction happens each month during season.  

 

Millepora dichtoma was reproductively active later in the Summer.