Bijdragen lot de Dierkunde, 54 (2): 243-262—1984 Taxonomic characters in Caribbean Millepora species (Hydrozoa, Coelenterata) by Walentina H. de Weerdt Institute of Taxonomie Zoology, University of Amsterdam, P. 0. Box 20125, 1000 HC Amsterdam, The Netherlands Summary size of the and gastropores dactylopores, pore density and structure of the ampullae, have In order to find characters in Millepora species with a been studied in the or were higher diagnostic value than the growth form (on which hardly past con- sidered useless because species delimitation is hitherto based) a comparison is of high intraspecific made of the surface structure, microstructure of the variation 1948 1949 (Boschma, a & b, a, 1950, skeleton, structure of the ampullae coverings, size of the 1964; Martinez Estalella, 1982). In some Atlan- and and in gastropores dactylopores, pore density tic the form of the species, however, growth cor- specimens of the four species occurring in the Caribbean allum is which often im- M. M. and variable, region: Millepora alcicornis, complanata, squarrosa, extremely identification. This M. striata. While most characters are of little taxonomic pedes a good variability sizes and densities useful. The value, pore are surprisingly be the fact may partly explained by that species are diagnosed and some biogeographical remarks various Millepora has a high adaptability to en- are given. vironmental circumstances, like depth, water movement, current, and turbidity. Résumé In in a previous paper (De Weerdt, 1981), Afin de trouver dans les espèces de Millepora des caractères which I reviewed the taxonomie problems in de valeur caractè- diagnostique supérieure par rapport aux Millepora, the need to search for other characters res du habitus (sur lesquels la délimitation des espèces est is stressed. However, when it is attempted to jusqu’à présent fondée), on a effectué des comparaisons the of sur: les structures superficielles, les microstructures du distinguish species Millepora on a more squelette, la structure des revêtements des ampullae, la sound base than the growth form, only few taille des des gastéropores et dactylopores, ainsi sur la que characters are available for taxonomie in- densité des dans des des pores, exemplaires quatre espèces Another vestigation. problem is the scarceness des Caraïbes: M. M. M. M. alcicornis, complanata, squarrosa, of type-specimens and the lack of ecological striata. La de ces caractères s’avèrent être de de plupart peu valeur la mais la taille la densité des data in museum collections. these im- pour taxonomie, et Despite pores se montrent remarquablement utiles. Des diagnoses perfections it seemed nevertheless worth while fournies des formu- sont et remarques biogéographiques the results from of to present obtained a study lées les mentionnées. pour espèces morphological characters of a collection of tropical Western Atlantic Millepora species. INTRODUCTION This study is restricted to species occurring in the Caribbean region, viz. Millepora alcicornis Species delimitation in the hydrocoral Millepora Linnaeus, 1758; M. complanata Lamarck, 1816; M. M. (Milleporidae, Capitata, Hydrozoa), with squarrosa Lamarck, 1816; and striata about Indo-Pacific & 1864. The latter eight and six Atlantic spe- Duchassaing Michelotti, the form of Boschma cies, was hitherto based on growth species was synonymized by (1948a) the corallum and with M. it here geographical distribution squarrosa, but is regarded as a valid in with (Boschma, 1948 a & b, 1961, 1962, 1966; Weis- species, accordance an unpublish- ed of Boschma. bord, 1968; Roos, 1971; Stearn & Riding, 1973; manuscript The taxonomie De Weerdt, 1981). Other characters, such as validity of the following 244 W. H. DE WEERDT - CARIBBEAN MILLEPORA is examined: of the Goreau characters growth form cor- 1969; Mergner, 1969; Roos, 1971; & allum, texture of the surface, microstructure of Goreau, 1973; Stearn & Riding, 1973; Colin, De Martinez the skeleton, structure of the ampullae cover- 1978; Weerdt, 1981; Estalella, ings, time of reproduction, size of the 1982). It will be explained here how this and and of lead to identifica- gastropores dactylopores, density polymorphy can easily wrong the tions, and which form be exhibited pores. growth may the four Caribbean The species are diagnosed and some by Millepora species. biogeographical remarks are given. In Boschma's revision of Millepora (Boschma, MATERIAL AND METHODS 1948 a), extensive descriptions of the growth forms of the the species are given. Briefly, Most corals were collected by the author in the period from till 1977 the Carib- forms of the Caribbean January 1976 January during a stay at growth species are, ac- bean Marine Biological Institute Curaçao. (Carmabi), cording to his descriptions: Several localities off the coast of Curaçao and Bonaire, M. alcicornis: extremely variable, at the growing edge representing a wide variety of biotopes, were visited and divided into branches which as a rule are laterally com- all growth forms encountered between 0 and 50 m were but be less Some pressed may more or finger-like. colonies gathered. About 250 specimens were collected, and others of are decidedly delicately branched, are a Taxonomische very deposited at the Instituut voor Zoölogie, compact growth form. Zoölogisch Museum, Amsterdam (ZMA), the M. complanata: upstandingplates, growingout from a com- Netherlands. mon basal part. from Additional specimens were borrowed the Rijks- M. thin with lateral squarrosa: upstanding plates, numerous Leiden the museum van Natuurlijke Historie, (RMNH), which each other united form expansions, among are to a Muséum National d'Histoire Naturelle, Paris (MNHN), more or less honeycombed complex. and the Hessisches Landesmuseum, Darmstadt, Ger- M. striata (Boschma, unpubl. ms.): "pronouncedly in the British Museum many. Specimens present (Natural branching in all directions". History), London (BMNH), were also studied. During this work I received great help from some un- The growth forms of the other two Atlantic published manuscripts of the late Prof. Dr. H. Boschma, which Prof. Dr. W. Vervoort known from the Brazilian were put at my disposal by species, only region, (RMNH). are described as: M. braziliensis: "erect cylindrical branches that at their tops divide into smaller branches" (Boschma, 1961: 293). RESULTS M. nitida: "low rounded clumps, consisting of short, rapid- ly forking, rounded or slightly compressed branches, VARIATION AND TAXONOMIC USEFULNESS OF which are obtuse, rounded, or even davate at the ends" MORPHOLOGICAL CHARACTERS [abbreviated after Verrill, 1868: 362. In Boschma's revi- the sion 1948 this with Growth form of corallum (Boschma, a) species was synonymized M. alcicornis. Later he considered it (Boschma, 1962) as a to Boschma a & who According (1948 b), valid species, but he did not redescribe it.] revised the genus Millepora after a period of and different splitting lumping by authors From these descriptions it is easily, but er- concluded thatM. is the (Duchassaing & Michelotti, 1864; Hickson, roneously, squarrosa on- 1898 the the form which a & b; Wood-Jones, 1907), growth ly species showing growth is form of the corallum is the only character which sometimes called "honeycombed", sometimes is sufficiently distinct in most species to warrant "boxwork" (terminology used by Stearn & identification. reliable From recent studies on Riding, 1973; Colin, 1978; and De Weerdt, Millepora and coral reefs in general it has, 1981). It is the growth form in which "upstand- become that identificationof thin with lateral however, apparent ing plates, numerous expan- the in the Atlantic Ocean still each other united form species occurring sions, are among to remains very difficult, because of the high a more or less honeycombed complex" of the three degree polymorphy expressed by species (Boschma, 1948 a: 19). However, of the four Caribbean (Goreau, 1959; Weisbord, 1968; Mattraw, species may exhibit such a - 245 BIJDRAGEN TOT DE DIERKUNDE, 54 (2) 1984 able resist the growth form, viz. M. complanata, M. squarrosa strong masses, quite to high and M. striata. This mistake is other in the surf Corals with an among water energy zone. form the other things demonstrated by Boschma's identifica- exclusively plate-like growth on tion of in the ZMA collection and and four specimens hand were rare at Curaçao Bonaire, M. from and (ZMACoel. 8370, 8371, 8372, and 8373) as judging descriptions photographs in the Carrión squarrosa (Boschma, 1948 a: 102), and one (Almy & Torres, 1963; Colin, 1978), collection Even be restricted to RMNH (RMNH 16876). this phenomenon seems not to Boschma identified them as M. these islands. though squar- Boschma's rosa, he remarked that all specimens have a Using descriptions sensu stricto, M. would be growth form intermediate between M. com- complanata turn out to a rare and M. the basis whereas M. would be planata squarrosa. However, on species, squarrosa quite The is M. of criteria discussed below, two of the specimens common. reverse, however, true: of the in the ZMA collection belong to M. complanata complanata is one most common Millepora (ZMA Coel. 8372, 8373), whereas the other two species in the Caribbean region, extremely M. striata Coel. and main constituents specimens belong to (ZMA polymorphous one of the the other 8370, 8371). of the recent reefs. M. squarrosa on Another of this iden- hand is not example misleading very rare, probably polymorphous criterion is and it does contribute the tification the following: in a previous