Darkfield Images of tangential sections, showing connectivity within cyclosystems.

 

A Gastrozoid showing four club tentacles.

Macro study of the skeletal material, ongoing. Tabulae.

Other closeups of Skeletal Material

Images of ampullae are found in a previous post.

Earlier images of tabulae and coenosteum are found in a previous post, here.

Tubes: fossil houses of polyps, with tabulae:

Fragment of Millepora platyphylla, with fracture exposed.

A compelling  description of formation of tabulae in Millepora is found in Kaestner's  Invertebrate Zoology:

The polyps stand in little pits into which they can contract. In many species, five to eight defensive zooids form a circle, 0.25 mm in diameter, around a feeding zooid. New growth slowly thickens the crust while the lower layers die. As the polyps grow outward within their tubes, their aboral surfaces produce a new calcareous layer.

Focus stack of fracture, showing tabulae.

General appearance of surface, with irregular cyclosystems:

Kaestner again:

The polyps stand in little pits into which they can contract. In many species, five to eight defensive zooids form a circle, 0.25 mm in diameter, around a feeding zooid.

Entry of Zooxanthellae into the Ovum of Millepora spp. and Skeletal events at liberation

Methods and concepts:  

cursory description

I began collecting fragments of Millepora spp. in August, 1984, with the intention of eventual statistical analysis of the times of reproductive activity.  Observation of a liberation event of medusoids, on an evening in early April, 1985, removed any question of synchronous spawning: study of Millepora platyphylla turned a corner.  I would collect and preserve tissue specimens to pair with the hard parts fragments, to ferret out the sequence of events---development of medusae and gametes, opening of ampullae, and liberation of medusae.   At that point, it became. feasible to focus collection within certain meaningful time frames.  

The Moon that night was 4 or 5 days past Full.  I had reason to believe that this was a synchronized event; if this was the case, it would be useful to focus future collection effort on the days leading up to this night of the Moon.  A question remained: was this a synchronous event among populations on Guam?  Immediately on the next morning, I made forays on other accessible reefs, all on the Western Coast of Guam.  Other colonies demonstrating similar appearance were observed elsewhere, suggesting that this was a synchronous event on a scale greater than a single reef.   

Since I had been focusing my attention on this single species complex, I recalled that a few days prior to this liberation event, an unusual spectacle was observed among a number of colonies at Gun Beach (Fafai), North of Tumon Bay.  Some proportion of colonies had turned a darker brown color; and tiny white rings--less than 1mm in diameter---had appeared, densely scattered irregularly on various parts of colonies.  The stark white of the rings presented a very pleasing contrast against  the dark backgrounds of these colonies.  I suspected the darker colored colonies might betray proliferation of symbiotic dinoflagellates (probably Symbiodinium sp., here called zooxanthellae), or an increase of photosynthetic pigments.   

Since Millepora spp. are widely reported to exhibit vertical transmission of symbionts---ova being imbued with zooxanthellae before their fertilization---proliferation of zooxanthellae might actually be required to generate a supply sufficient for infection of the egg.  Remarkably, as of this writing, 37 years later, I have neither met nor heard of anyone else who has observed this remarkable event.  This points to the importance of focusing field studies on a single species (pointed out by George Barlow as a watchword of the biologist Karl Roehder).  It is one of the most remarkable exhibitions I have ever witnessed.

At this point, due to a previous interest in gametogenesis, field collection took on a new aspect.  Follows a cursory description of field and laboratory treatment of specimens.

• Fragments of Millepora platyphylla (and sometimes M. dichotoma) were broken off from identified colonies with a masonry hammer, and immediately collected into zip loc bags with a good quantity of sea water.  Each specimen---or perhaps specimens from the same colony---was isolated in its own bag.   Each specimen was marked in graphite pencil with date and place of collection.
• On the beach, or perhaps in the laboratory, part of each specimen was fixed in one of various solutions, and matching part was immersed in a tank of Calcium Hypochlorite (swimming pool chlorine) for a few days.  
• Fixation: some specimens were fixed in an acidic fixative, like Bouin's, or Formaldehyde with Formic Acid and other solutions.  After a few days, others were immersed in various decalcifying solutions.  
• The tissue of Millepora spp. comprises as thin sheet, <=1mm thick, that lifts off of the CaCO3 skeleton in the dish during decalcification.  These sheets were cut with scissors into smaller sheets that could be handled, for dehydration and embedment in paraffin wax.  
• Some blocks were sectioned on a rotary microtome and slides prepared. 
• Casson Trichrome was relied upon for staining, for the most part.  

I left Guam and moved to Chuuk, in late 1996.  I did not have a microscope, but had a number of the the slides I had prepared on Guam.  These slides mysteriously disappeared from my classroom at Chuuk High School, a year or two later.  

Thanks to a friend, my remaining blocks and some of the matching skeletal material was recovered some years later, and brought to Saipan.  I have observed and collected a few skeletal fragments on Saipan, between 1999 and 2001.  A spring timing similar to that on Guam, and similar lunar synchrony seemed to be indicated by these sparse observations.  I did not have the wherewithall to preserve tissue specimens during those years. 

Thanks to the interest of coral pathologist Esther Peters, a number of blocks were sectioned, slides produced and stained, which I am still studying some 20 years later.

In Berkeley, a opportunity arose to section about 4 blocks, out of the nearly 200 that remain.  Out of the kindness of a laboratory manager, slides were then stained with Hematoxylin and Eosin.  I had almost randomly selected blocks to section, based on my hunch that darker tissues represented darker colonies that could be endowed with medusae in a state of near readiness for exodus from their home colonies, and spawning.   The results of this   selection seem to support the supposition that darker colonies are reproductively active: at least three blocks yielded sections displaying medusoids.  

 

I hypothesize that reproduction is seasonal on Guam, that the first reproductive event  happens in late March or early April, and that medusoids are released 3 to 5 days after Full Moon (with some exceptions), just after Sunset.   This evening is the first of the lunar cycle when a short period of full darkness happens after the setting of the sun, before the rising of the Moon.  This mode of reproductive timing seems common among marine animals.

 Induction of Zooxanthellae into the Ovum

Here are presented   images  from the ongoing study of existing slides, portraying stages in the approach and incorporation of zooxanthellae into the egg.

Cluster of Zooxanthellae in Immature Medusoid

Above, within a medusoid---apparently flattened during sectioning---zooxanthellae are dividing.  One possibility seems to be that zooxanthellae proliferate during the events leading up to and during the process of entering the medusoid and ovum.

Early movement of zooxanthellae toward developing ova

Phase contrast image.   Note zooxanthellae crossing the field of lipid droplets.

Among the presumptive ova, only three in each medusa, develop into mature eggs.  As seen below, other cuboidal cells provide nutritional support for the growing ovum.  These are termed here "nurse cells." 

Zooxanthellae are nestling up to the Ovum and Nurse Cells.

In the above image, the larger cell at the bottom is one of the row of rectangular cells that are potential ova, but are here called nurse cells, because they nurture the successful ovum,  coalescing with it.  The nuclei of the nurse cells are not as distinctive as the large nucleus of the ovum.  Small zooxanthellae are embedded in the matrix of Lipid Droplets, and are apparently approaching the egg.  They are not yet incorporated.  The definition of "ovum" seems unclear: are the lipid droplets part of the ovum, or not?

Zooxanthellae swarming and dividing

Ovum at a more advanced stage, with zooxanthellae well along in the process of invasion.  
Numerous zooxanthellae are dividing, even within the egg.  

The above image is a brightfield focus stack (with a 40X objective; scale to follow) showing a medusa well along in maturity.  At top and bottom are nuclei of nurse cells; the nucleus of the ovum is distinctive, and larger.  Zooxanthellae at the bottom left, outside the medusa, are not as actively dividing.  

Below, the same subject is shown in Phase Contrast.  

Phase Contrast, Focus stack by Helicon Focus

Opening up of Ampullae

Medusoids---medusae that are incompletely developed---develop within closed pits, the ampullae.  In order for the medusoid to escape, the covering of an ampulla must give way, or (thought it seems unlikely) be broken open by a flailing medusoid.  In the first image below, several ampullae appear to be fully open. 

The following image presents a conundrum, in that one ampulla still retains its covering, while an open one is seen farther to the right.  This begs the question whether a subsequent release may happen.  I have not made sufficiently detailed inquiries to determine whether medusoids may be released over more than one day in, as I presume, a monthly event.  This specimen has been cleaned in

Above, the encircled ampulla is intact, possibly slightly eroded in center.  The depressed condition was identified by Boschma as a diagnostic character for Millepora platyphylla.  On the right, the ampulla is open.  Smallest pores are dactylopores; they are arranged in a "cyclosystem" around the somewhat larger gastrozoids.  Boschma also noted that M. platyphylla cyclosystems are irregular, not neat encirclements as in at least some other species.

Historical concepts of the medusoid of Millepora spp. and Hickson's follies

Dick Randall, my mentor at the University of Guam Marine Laboratory, alerted me to Sydney Hickson's having mangled the systematics of Millepora spp., in the early days of my study.   Hickson, the ultimate lumper decided to spell it Millepora sp.(1)   He had determined that all of the then-known species of Millepora were eco-variants of a single Atlantic species, Millepora alcicornis.  Hullbrandt Boschma, decades later, restored sanity to the taxonomic picture of the group  but the grand synonymization of Hickson lives on as a footnote in taxonomic history.

This was far from the only blasphemy conducted by Hickson.  I will not treat here his fantastical description of the developmental cell biology of Millepora sp., which, to be fair, he retracted in a succeeding publication.  But in his error of judgement about the structure of the medusoid of Millepora spp. Hickson promulgated a misconception of a different kind: his drawing of the medusoida  portrayed a deformed, post-spawning individual, apparently turned inside-out, possibly dead.  This erroneous image was co-opted at some point as a component of a representation of the structure of Millepora spp., based upon the remarkable line drawing from H. N. Moseley's reports from the Challenger Expedition.   The composite has propagated through almost every textbook of Invertebrate Zoology until recently, illustrating the medusa (or, more properly, medusoid) swimming above the cross section of the colony. 

If Hickson committed an absurdly erroneous lumping the species of Millepora, another chapter in the history of misunderstandings of  the medusoid of Millepora spp. involves an over-zealous splitting. In his tome, a taxonomy of the medusae of the world, Mayer had split the medusae of Millepora spp.---as the Medusae Milleporinae---out from all other hydrozoan medusae, the "veiled medusae,"  on account of its purported absence of a velum (veil).  A question remains: did Hickson originate this misconception as well?   

 I was thrilled when I collected medusae (or medusoids) of Millepora platyphylla in April, 1985, I was able to observe them in a dish, at the University of Guam Marine Laboratory.  Luckily, Professor Lucius Eldredge was on hand, and I asked him to check whether they had a velum; he  verified the presence of a velum.   The medusae I observed had not yet spawned.  It was immediately apparent that they differed substantially from the drawing I had seen, I think from Hickson.  It seemed to me that the configuration of the medusae in Hickson's drawing would be that of a spent individual---one that had already expelled its gametes. 

Mangan or Duerden may have been the last person to report observing medusae of Millepora alcicornis., in 1909 or 1910.  

Hickson wove a fantastical tale based on misinterpretations 

I just re-read Hickson's fantasy analysis of the reproductive biology of Millepora plicata, based on a remarkable degree of mis-interpretation of histology.  He weaves an entirely fantastical tale of the origin of the ovum, it's development, internal fertilization (which does not happen at all), and growth of a larva and it's expulsion.  

My blog post does not treat of this.  It is incredible.  Literally.  I am not suggesting you read it, but cite it here.  In his favor, he was indeed prolific, and he ultimately retracted this story.  But it's not the only issue among Hickson's publications.  Or among the other leading lights of Zoology in the latter part of the 19th Century who failed to critically examine or repeat his work, but built entire new stories upon Hickson's foundation.  

Hickson SJ. VIII. On the sexual cells and the early stages in the development of millepora plicata. Philosophical Transactions of the Royal Society of London.(B.). 1888 Dec 31(179):193-204

  

It is tempting to suggest that Sydney Hickson, one of the most prominent marine zoologists of his day (around the turn of the 19th to the 20th century), as a charlatan.   Indeed, one of my long-languishing projects has been to track down the life of the anomalous drawing of Medusae Milleporinae and prove whether he was the originator of this long-lived false cartoon of the medusa of Millepora spp.  After reading through one of his anatomical studies recently, I have come to appreciate what a remarkable observer he was.  However, he certainly suffered from a massive level of presumption.  

And, in a sense, it's a reflection of the nature of Zoology of that era, that he was so highly respected as a zoological authority that his errors persisted for so long, without being tested.  This reflects badly upon the assumption that science proceeds by the testing of hypotheses.  And re-testing.  Hickson obviously took the massive level of respect he enjoyed to heart.  

In Chuukese, there is a word that applies: baatá.  This verb refers to persons who takes flattery to heart.  An example would be a boy who, having been singled out as a good basketball player, goes out and buys basketball gear, and inhabits the cloak of the praise he has enjoyed.  In Chuuk, this is taken to a remarkable extreme: one can "abaatá" (cause to baatá) another person through disingenuous flattery.  

Hickson is an unfortunate example of someone whose entire body of work is perfused with the fruits of his baatá.  But it is on the greater community that he was placed on such a pedestal. 

Another example is found in a previous post of mine: https://millepora.blogspot.com/2022/10/an-obscure-mention-of-millepora-work-by.html

(1)  spp. designated multiple species; sp. a single species, though it be unnamed.  I will use the correct "spp." herein.

ADDENDA

  As I searched via google (scholar?), an amazing thing happened: I saw my on name

  on a Google citation, from a mailing list thread of many years ago.  

  Remarkably, I had written about Hickson's blunders in a post to a

  microscopy mailing list (which, I need to determine).  

Davis, A. E. (2002). Microscopic Artifacts In The History Of Biology. Microscopy Today, 10(2), 18-21.

I had discussed the issue of Hickson's fantasy development cycle, referring to it as a consequence of microscopic artifacts.  Artifacts have been referred to as   “artificial structure(s) or tissue alteration(s) on a prepared microscopic slide as a result of an extraneous factor.”  

From my query on that mailing list:

(About) Sydney Hickson's early work on Millepora spp. (Cnidaria:Hydrozoa) fire corals. It seems an incredible lapse, a wholly fabricated natural history account, one that persisted for a considerable period in the fabric of the mythology of biological knowledge. I am interested because reproduction of Millepora platyphylla is the subject of incompleted thesis research of mine.

Hickson published a report on reproduction of "Millepora" around the end of the 19th Century. ... In this report, which I do not have available at this time, he included several plates of drawings depicting a putative sequence of reproductive events in this organism. We now understand that his depiction is not even close to the way that Millepora spp. (which were later redesignated as proper individual species through painstaking work by Boschma-notwithstanding the issues recently raised by molecular work) reproduce.  The depiction involved dozens of drawings, and a sequence of events based on a misinterpretation of what are apparently artifacts....

Also,.   

... Hickson's erroneous drawings of the meduse of Millepora lived on for over 3/4 of a century in virtually every Invertebrate Zoology textbook published until the late 1980s or 1990s. His erroneous description of the medusa of Millepora as lacking a velum led to the designation of a separate branch of hydromedusae by Mayer, as the only hydrozoan medusa without a velum. My unpublished observations in the 1980s as well as published observations by John Lewis of McGill University showed that the medusae of Millepora spp. clearly possess a velum. I apologize for monopolizing the bandwidth. I hope this is as fascinating a topic for others as for myself, and not considered off-topic.

  

In 1900 Hickson was able to examine material that included medusoids.  The following is a correction in his paper on the subject,, wherein he reported on these findings.  

Hickson, Sydney John. "The medusae of Millepora." Proceedings of the Royal Society of London 66.424-433 (1900): 3-10. 

Correction.—In a former communication to the Royal Society, 1 described certain cells in the cenosarc of Millepore from Celebes as ova. Since the discovery of the female medusa, I have carefully re-examined my preparations, and satisfied myself that I made a mistake. These cells are not ova, but the cells which ultimately give rise to the large kind of nematocyst.

 

My earliest introduction to Millepora spp.

 Professor Richard Randall had been disallowed from being an MSc thesis advisor by the big shots at the University of Guam Marine Laboratory, I think unfairly.  

Shortly after I had arrived on Guam to begin graduate studies in Early August of 1984,  Dick Randall made himself known to me by stopping to offer me a ride down the hill to the Laboratory, and introducing himself as a coral biologist (he is also a geologist).  Immediately he engaged me in discussion of ideas for a thesis topic. 

I explained that I was interested in reproductive periodicity in Tridacnid clams, particularly in endocrine control of gametogenesis.  Such a study would necessarily involve elucidating the phenology, the seasonality, indeed, every aspect of the timing of reproductive events.  This topic was a huge turn-on for me.   

 

  At that point he introduced me to Millepora spp., the fire corals.  He explained that the Calcium Carbonate hard parts of these corals bore outward evidence of reproductive status---the Ampullae that sheltered the medusae within them.  Thus, it seemed, it would be possible to study the reproductive periodicity by the most expedient of all possible methods: examination of hard parts over time.  

(Professor Lu Eldredge stood in his stead.  It is on me and me alone that I did not complete the thesis that was required to earn an MSc from UJ. of Guam.  Had there been a plan B, I would certainly have the MSc. degree today.  Dick Randall deserved to be treated with more respect, as I might add.

So it was I started collecting fragments of Millepora spp.   At that time, I took every opportunity to snorkel, and each time I did I collected at least one fragment of Millepora spp., usually M. platyphylla.  That first term, I was enrolled in a statistics class; I hoped I would be able to draw some conclusions using some statistical means or another on the timing of reproductive efforts.  I had learned from R. K. Trench at UCSB about Tridacnids.  and the interesting variations in the patterns of timing.  I had hoped to be able to study neurosecretory control of gametogenesis of the giant clams.  This interesting twist regarding the biology of Millepora would provide an opportunity to complete a study on the side, in my spare time, no sweat, while engaged in other pursuits.

Professor Randall kept a large plastic tank of Calcium Hypochlorite out on the lanai behind his lab/office, for cleaning corals.  I gradually built up a number of bleached coral specimens, but had not recognized ampullae.  Perhaps I would be able to find time later on to examine the coral skeletons and create a database.

Dick warned me about the work of Sydney Hickson, a prominent british zoologist of the late 19th Century---one of the big names.  Hickson had made the error of synonymizing all species of the genus Millepora as a single species, M. alcicornis, an Atlantic species found prominently in the Caribbean.  Boschma would, much later, correct the record in  a series of long papers on the specific characters, and revised the systematics of the genus.  

When I first laid eyes on the medusae of Millepora platyphylla, I was on the beach at Toguan Bay, Guam.  it was obvious to me that the illustrations by Hickson of the medusa of Millepora had also promulgated an egregious error; this illustration was widely disseminated, as part of a revised drawing of Moseley in most Invertebrate Textbooks.