Quantitative three-dimensional morphological analysis supports species discrimination in complex-shaped and taxonomically challenging corals

The morphological diversity encompassed by the tree of life displays an extraordinary range of forms and shapes. Beyond contributing to characterize the biodiversity of these otherwise “endless forms”(Darwin, 1859), assessing their variation spectrum is key to gaining a better understanding of shape function and evolution (Klingenberg, 2010). Indeed, delimiting groups of individuals based on their morphological resemblance (morphogroups), or more broadly on their phenotypic distinctiveness (phena; sensu Mayr, 1969), has been traditionally the first step in taxonomic approaches and also often a preliminary step for sorting specimens in ecological, physiological, and evolutionary studies (MacLeod, 2002; Pereira et al., 2021). As such, morphology is the tie that connects the samples used for a variety of contemporary approaches, the designated type specimens used for species description, and the placement of extant species in relation to extinct life forms (Budd and Olsson, 2006; Schlick-Steiner et al., 2007; Saraswati and Srinivasan, 2016). Thus, morphological assessments are crucial to disentangle the confused and sometimes obscure categorisation of the diversity of life forms that inhabit the planet (Wheeler, 2005).