Milleporidae

Amaral, Fernanda M. D., Steiner, Andrea Q., Broadhurst, Matt K. & Cairns, Stephen D., 2008, An overview of the shallow-water calcified hydroids from Brazil (Hydrozoa: Cnidaria), including the description of a new species, Zootaxa 1930, pp. 56-68 : 57-58

The Milleporidae

Distribution. Millepora are abundant throughout the world’s tropical oceans and are a significant component of coral reefs, where they form large, conspicuous colonies ( Lewis 1989). In Brazil, as elsewhere in the tropics, Millepora can be easily found on coral reefs, beach rocks, and other similar habitats. They are an important constituent of Brazilian reefs and often occur in extensive colonies up to 2 m in diameter, especially in the northeastern region.

Using a range of morphological characters, 112 colonies of Millepora (collected at numerous locations in northeastern Brazil) were recently identified as four species ( Amaral et al. 2002): M. alcicornis , M. braziliensis , M. nitida and M. laboreli n. sp. Millepora alcicornis was identified at nine locations from Cabo Frio (Rio de Janeiro) to the Manuel Luiz Coral Banks (Maranhão) and was easily distinguished from its congeners. It is the only species in common with the Caribbean fauna (according to presently available studies). The remaining species seem to be endemic to Brazil. Figure 1 shows the geographical distribution of the four species of Millepora .

Synonyms. Laborel (1970) admitted that Brazilian Millepora had several synonym problems. Boschma (1948) described M. braziliensis as M. alcicornis , probably due to the varied shape of M. alcicornis (incrusting in agitated waters and ramified in calmer areas), while Laborel (1970) observed that M. braziliensis takes a honeycombed shape in wave-disturbed areas and a ramified, leaf-like form in the back-reef area, becoming similar to M. complanata and M. squarrosa . In fact, M. squarrosa has been cited for Brazil based on studies using material from scientific collections: Boschma (1962) affirmed that M. squarrosa and M. braziliensis coexisted on the Brazilian coast, while de Weerdt (1990) suggested that it might be a synonym of M. braziliensis . However, M. squarrosa was never found again on the Brazilian coast or oceanic islands. Furthermore, despite having found no significant differences in gastropore and dactylopore diameter, a morphometrical study suggested that it is in fact a different species from M. braziliensis (Amaral 1997; Amaral et al. 2002) because of overall differences in skeletal morphology. Yet, it is difficult to distinguish between the various species of Millepora in the field, particularly M. braziliensis and M. squarrosa , due to their high phenotypic plasticity.

To add to the synonym problems, de Weerdt (1984) stated that the holotype for M. alcicornis is unknown and is probably lost. Boschma (1948) and de Weerdt (1984) provide further details on synonyms.

Morphometry. Owing to their plasticity and lack of definitive morphological characters, in any study that seeks to identify Millepora , it would seem appropriate to collect information on as many different characters as possible. Using this logic, Amaral et al. (2002) measured more than 20 variables, which included the growth form and the height of colonies, along with the density and diameter of the dactylopores and gastropores. Data were analyzed and compared to earlier studies to successfully separate the different species of Millepora occurring in Brazil ( Amaral et al. 2002). The key morphological characters used to distinguish the different species from their congenerics along with their general descriptions are summarized below.

Character M. alcicornis M. braziliensis M. nitida M. laboreli

(34 colonies) (45 colonies) (13 colonies) (11 colonies)

Figures

FIGURE 1. Geographical distribution of the Milleporidae from Brazil (map not to scale).