Millepora alcicornis Linnaeus, 1758

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 : 59

Millepora alcicornis Linnaeus, 1758

Boschma (1948), in a description of Millepora alcicornis , stated that it “is so highly variable in shape that it is impossible to characterize the species in this respect”. A study by Amaral (1997) showed that most colonies are ramified, but can also be incrusting, hemispheric, or a mixture of these forms. The shapes of the ramifications also vary (most are flattened). Yet, despite these variations in form, this species can be easily identified among other Brazilian Millepora . Colonies can exceed 1 m in height; according to Laborel (1970), colonies are 2–3 m high and important building components in Brazilian reefs. Amaral et al. (2002) noted that, of the morphometric characters studied for M. alcicornis , the shape and size of the dactylopores and gastropores were the most distinctive, as these were predominantly rounded and larger than in all of the other species studied ( Table 1 ). This species also had the largest mean number of gastropores and ampullae per cm2, yet the number of cyclosystems per cm2 was relatively smaller. Another distinguishing morphometric feature of M. alcicornis among other Brazilian calcified hydroids is the diameter of the ampullae, which measures 0.41 mm on average (Amaral 1997) ( Table 2 ).