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.

Briefly: A note from the Coral List about Millepora spp. decline in the Red Sea

On a mailing list a recent post to a discussion thread about effects of warming on coral reefs included this remark:

 

... There was a massive coral bleaching south of latitude 20 degrees (Al Lith) during the 2023 summer, correlating with water temperatures of 33-34 degrees. Many of the bleached corals have subsequently died and there has also been a near-complete loss of Millepora hydrozoans.

 

I had lunch next to Zvi Dubinsky, at the International Coral Reef Symposium on Guam, in 1992.  I discussed my interest in Millepora spp.  He said: "Millepora is always the first to go."

 

 

 

Note about Millepora taxonomy

 History of the taxonomy of Genus Millepora is tortured.   In the mid-20th Century, work by Hulbrandt Boschma resulted in the separation of the Genus into a number of species that are, substantially, still recognized today.  Hickson had synonymized all species of Millepora as ecomorphs of M. alcicornis. 

 In 1898, Hickson decided that the variations in morphology were due to environmental factors and that Millepora alcicornis was the valid name for all these species. This conclusion has since been questioned.

                                          ---Wikipedia

A number of workers have recently applied molecular methods to the classification of Millepora spp., and to be sure some question has been cast on the global homogeneity of, for example, Millepora platyphylla and especially M. dichotoma.  

Sidney Hickson was a  widely recognized zoological authority.  A lesson can be drawn by looking at the number of workers---themselves also authorities---who accepted the word of Hickson without, it seems, questioning the validity of a remarkable act of mass synonymization of a suite of species as ecomorphs of a single species.    Hickson could do no wrong.  

The species question of corals in general is a thorny one.  Even the definition of species needs to be examined, when discussing corals.  The fact of mass spawning of numerous species of corals at various places, including the Great Barrier Reef, and Guam, for example, would seem to leave open the possibility, in my mind, of hybridization. 

In his treatment of _The Species Problem in Millepora,  Boschma he discussed  characters that could distinguish various Millepora species, citing Hickson's earlier list:

• The form of the corallum
• The texture of the corallum and its surface
• The size of the pores
• The shape of the pores
• The degree of isolation of the cycles
• The relative number of Dactylopores and Gastropores
• The distribution of the pores in various parts of the corallum
• The Presence or absence of ampullae
• The anatomy of the soft parts
• The stinging properties
• The distribution of the various forms in different parts of the reefs

 

 In one paper, Duchassiang and Michelotti (in 1864) named "not less than 22 (or 24) West Indian species."  (Boschma,  Very few have not tripped over the thorny problem of the species of Millepora.  

 

To be extended.  Boschma's paper is noteworthy.  

 Boschma, Hilbrand. "The species problem in Millepora." Zoologische Verhandelingen 1, no. 1 (1948): 1-116.

Randomly, here is a reference to Arigoni et al, a recent approach to systematics of Millepora spp.

 Arrigoni, Roberto ; Maggioni, Davide ; Montano, Simone et al. / An integrated morpho-molecular approach to delineate species boundaries of Millepora from the Red Sea. In: Coral Reefs. 2018 ; Vol. 37, No. 4. pp. 967-984.

 Boisson et al. approached the species of Millepora at Reunion in a similar manner:

Boissin, E., J. K. L. Leung, V. Denis, Chloé A-F. Bourmaud, and Nicole Gravier-Bonnet. "Morpho-molecular delineation of structurally important reef species, the fire corals, Millepora spp., at Réunion Island, Southwestern Indian Ocean." Hydrobiologia 847, no. 5 (2020): 1237-1255.

 

 Another parallel:

Manchenko, Gennady P., Alexander V. Moschenko, and Vyatcheslav S. Odintsov. "Biochemical genetics and systematics of Millepora (Coelenterata: Hydrozoa) from the shore of south Vietnam." Biochemical systematics and ecology 21, no. 6-7 (1993): 729-735.

 

 

 

 

 

A lost slide found: Some thoughts: Putative Dying Dinoflagellaes; and Overview Images of Zooid Distribution

 As I was cleaning out my drawers, a slide appeared, caked in grime, that I had carefully labelled at some point using a crow quill pen wit, waterproof drawing ink, coated with clear nail polish.  The label provides the following information:  

Slide    : 530 ["A"]

Colony: Tog BE

Date.    : 15 April 1986

                    Fixative:  Bouin's 

                    Stain.    : #2 = Hematoxylin and Eosin

  

Green Cells: Putative dying Dinoflagellates, and date Medusae were Liberated

This slide is particularly interesting because of the date, and the presence of clusters of green entities that are probably deteriorating dinoflagellate symbionts.  Full Moon that month was on March 26 (need to double check this).   Medusae would have been liberated between 2 and 5 days after Full Moon.  This specimen may have been taken 20 days after Full Moon.  

Why are these clusters interesting?  Seeing the date, I have at least one new hypothesis to test:

 Since this date is 20 after full moon and the liberation of medusa was two to five days after Full Moon, does this suggest that after liberation, the entire colony reorganizes itself, the symbionts in certain regions being killed off?

I will revisit this idea at another time.

 Overviews of zooid distribution: a cyclosystem and random dactylozoids.

Two images are presented here of the same area of the slide mentioned above.  Actually, the date is inconsequential, as I was merely aiming for an, if one will, aerial overview of a small region, including a single Gastrozoid and its associates, the Dactylozoids, arranges in a Cyclosystem, .  The first is a single  brightfield image taken through a 4X AmScope objective; the second image is a 4x4 panorama assembled through Helicon Focus, software I have also used to take focus stacks of especially Millepora spp. skeletal material.  

Image I: A single brightfield image, 4X.  

I have not yet inserted a scale bar.

Image II: Darkfield panorama of 16 images taken at a higher magnification.

Panorama built up from 16 (4x4) images.  16X Objective.   

 

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?