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.
