Diversidade morfológica e molecular de Syconidae Poléjaeff, 1883 (Porifera, Calcarea) do Brasil

Abstract

Syconidae Poléjaeff, 1883 was proposed to group calcareous sponges that exhibit a syconoid aquiferous system and lack a cortex, which may or may not have tufts of diactines. Currently, it comprises Sycetta Haeckel, 1872 and Sycon Risso, 1827. The identification of its species is challenging due to morphological similarity in skeletal composition, and phylogenetic analyses have indicated that neither of these two genera is monophyletic. Sycetta has few known species, but several new species have been described over the years for Sycon, which is common in various regions of the world and in scientific collections. To date, no revisionary studies have been conducted on the family or its genera, despite incomplete descriptions, distribution patterns inconsistent with what is expected for Calcarea, and a lack of information on intraspecific morphological variability. In light of this, the aim of this study was to investigate the diversity of Syconidae in Brazil (southwestern Atlantic ocean), using an integrative approach combining morphological and molecular data (LSU region C). For this purpose, type materials of the species already known from Brazil were redescribed, and new specimens – both from scientific collections and recent samplings – were examined. A new species of Sycetta, Sycetta papillata sp. nov., was described based on collection material gathered decades ago. This is the first record of the genus in the southwestern Atlantic. Detailed images of the morphology of these individuals and a comparative table of Sycetta species were also provided, contributing to future taxonomic identifications. Regarding Sycon, the types of six of the seven species found in Brazil were redescribed, and the first photographic records of the skeletons of some of these species were made. Additionally, three new species were described. DNA sequences were made available, including those from the holotypes of Sycon avus Chagas & Cavalcanti, 2017 and S. bellum Chagas & Cavalcanti, 2017. These data allowed confirmation of the conspecificity of specimens and exploration of their geographic distributions – interestingly, the DNA sequence of one of the new species grouped with others available in GenBank from Hawaii. It was not possible to analyze in deeply the specimens corresponding to those sequences, but preliminary analyses do not rule out that the morphology may indeed be similar. Other noteworthy findings include the discovery of spined diactines in S. avus and the suspicion that S. vigilans Sarà & Gaino, 1971 does not occur in Brazil. Although species within Sycon and Sycetta are morphologically very similar, some morphological characteristics, such as the shape of the spicules and the type of insertion of diactines on the body surface, can be used to differentiate the species analyzed here. Thus, both morphological and molecular data were essential for understanding the diversity of Syconidae found in Brazil. The results presented here may encourage future studies on the revision of its genera and represent an important step forward in the complex systematics of this family.