Shell length of C. galea and C. caribaea ranged from 3.4 to 38.9 mm and 4.3 to 25.8 mm respectively. In both species, a clear host-associated size structuring of shell length existed (F = 13.6; p < 0.0001 and F = 5.8; p < 0.0001 for C. galea and C. caribaea, respectively (Fig. 7). The mean length of C. galea, snails differed among host species (29 combinations of host pairs, post-hoc Tukey HSD test), compared to a total of for C. caribaea (Tables S2-S3 in Online Supplementary Material 4). C. caribaea (nine pairs of hosts) associated with alcyonacean host species that were larger (based on shell length) than snails associated with scleractinian hosts (including all specimens; F = 23.8; p < 0.0001; Fig. 7).
C. curacaoensis sp. nov. was on average smaller (shell length 2.5-8.9 mm) than C. galea and C. caribaea. However, C. curacaoensis sp. nov. was only found on Madracis auretenra, which was also a host of C. galea. Coralliophila galea individuals associated with M. auretenra (shell length 5.4-9.7 mm) were not different in size compared to specimens of C. curacaoensis sp. nov. (F = 4.07; p = 0.061).