Two Compelling Features Observed in ~1.2X Macro Images of a Skeletal Fragment of Millepora platyphylla

The specimen

A  small number of skeletal fragments are available to me from my collection of Millepora spp. on Guam between 1984 and 1986.  As I have come to examine these specimens more closely, through macro and ultra-macro photography, many interesting features have been revealed.   

I had read of a method, referred to in one paper (that I have lost track of) as Koch's Method, used early in the history of study of Millepora spp., wherein a preserved coral together with its skeleton were ground down to a thin section, that revealed the nature of the relationship of the coral animal with it's stony exoskeleton.  Why not, I thought, grind a broken edge of a fragment with fine stone, file,  or sandpaper?  With that in mind, I picked up a piece and started filing with a cheap diamond jewelers file. and various grits of sandpaper along one promising edge.   

This particular fragment of, I think, Millepora  platyphylla bore pencil markings (as I used to write upon them before cleaning), with the date and site of collection: Obyan Beach, Saipan, on 8 June 2001.  Upon further examination of this piece, it occurred to me a macro study might be revealing.  Using a Canon EOS EF-M 28mm f/3.5 macro lens I photographed this piece at the maximum magnification of 1.2X.  on a Canon EOS M50 camera, by built-in flash. The following features were observed, providing surprising insights into the morphology of the skeleton, and the organization of the animal.   These are presented in two images.  As it appears, this piece seems to have  been collected at a time of especially intense  Calcium Carbonate production.  So far, two special features have attracted my attention.  Here are presented images of them.

A line of pores of identical diameter along a ridge

Ordinarily, the surface of Millepora platyphylla exhibits tightly packed cyclosystems, wherein larger gastropores are encircled by dactylopores in various arrangements referred to by Hulbrandt Boschma determined to be species specific.  In this case,  the variation in diameter of the pores in this row.  Also, smaller pores appear, at first glance, to flank them along the sides of the ridge; further study is also planned at higher magnifications to measure and compare the diameters of these pores for uniformity, and determine whether they are similar in size to gastropores in cyclosystems---which may be observed, however blurry, elsewhere in this image.  Not so obvious are parallel lines along either side of this row, of apparently smaller diameter.  If these two sets of pores are indeed related in size to gastrozoids and dactylozoids, a very interesting parallel is suggested with the sylasterid hydrocoral Distichopora spp, a group of hydrozoans closely related to the Milleporidae, the family of Millepora spp.  

Puce et al. have published a study of the development of the arrangement of rows of pores along the branch tips of Distochopora sp. from a cyclosystem.  It would be incredible if something like that is going on here. 

Puce, S., Pica, D., Brun, F., Mancini, L., & Bavestrello, G. (2012). Genus Distichopora (Cnidaria, Hydrozoa): from primary cyclosystem to adult pore organisation. Coral Reefs, 31(3), 715–730. doi:10.1007/s00338-012-0885-0 

I have taken the liberty to copy an image of this character of Distichopora from their paper:

This seeming parallel may be a stretch of the imagination; but even the slightest similarities of these systems are especially interesting, given their close evolutionary relationship. 

A lattice pattern of new growth  

 In the following image, taken from another area of the same fragment, illustrates a striking latticework of blank areas, like pathways, devoid of pores.  These appear to surround and delineate cyclosystems.  Boschma had much to say about the details of cyclosystems of Millepora spp.: he, in fact, utilized differences of the pattern of pores in cyclosystems as characters to delineate and redefine species that had been lumped as a single species by Hickson half a century earlier.

A flush of new skeletal production is suggested, as within these broad and pale pathways may be observed smaller pores that have been obscured by overgrowth.

The two features illustrated here are suggestive.  They seem to point to a time of intense calcification, following Full Moon in June.  How does this fit the overall pattern of reproductive periodicity of Millepora spp. on Guam?