Going deep into Parazoanthus axinellae (Anthozoa: Zoantharia) complex: description of two species in the Alboran Sea based on an integrative approach

Abstract Parazoanthus axinellae Schmidt, 1862 (Anthozoa: Zoantharia) has been historically divided into different taxa at various levels (varieties, morphotypes, or subspecies) and is considered a species complex by some authors. This species has a wide distribution, is a key part of coralligenous habitats, and constitutes one of the main ecosystems in the Alboran and Mediterranean Seas. In this work, we propose the reclassification of one subspecies and a new species of Parazoanthus : Parazoanthus brevitentacularis stat. nov. and Parazoanthus franciscae sp. nov. The first was described as a morphotype (named “stocky”) and as the subspecies P. axinellae brevitentacularis , while the second is described here for the first time. An integrative approach, combining morphological, ecological, histological, and genetic analyses, allowed us to detect enough variability to establish this new species and led us to better understand the diversity of this group. Morphological and ecological analyses have been performed in situ by observing the main different features of the species. Histological examinations to propose the systematics of the species and the main diagnostic characters to identify them were performed based on the macro-anatomy, micro-anatomy, and the features of the cnidome. Genetic analyses were performed using common molecular markers ( COI and ITS ) and mitochondrial genome sequencing (MGS). The COI region was limited in establishing informative relationships within the species. MGS was a powerful tool to assess diversity, although somewhat limited due to the small number of genome sequences available, and the slow evolution of mitochondrial genomes in Anthozoa. Ribosomal ITS showed wider distances between taxa, resulting in the phylogenetic trees being most congruent with the ecological, morphological, and histological analyses.