3D-microanatomy of the mesopsammic Pseudovermis salamandrops Marcus, 1953 from Brazil (Nudibranchia, Gastropoda)

Multiple paedomorphic lineages of soft-substrate burrowing invertebrates: parallels in the origin of Xenocratena and Xenoturbella

“…While the phylogeny of Aeolidacea is currently actively studied [18][19][20][21], a majority of these nudibranchs as defined within the previously established broad-scope aeolidacean nudibranch phylogenetic framework [19], are complex animals with numerous dorsal papillae (cerata) (Figs 1-3). However, there is a single exclusively infaunal family, Pseudovermidae, with evident paedomorphic features such as vermiform shape and reduced dorsal papillae, which strongly matches early ontogenetic stages of complex aeolidaceans [22]. This unique aeolidacean nudibranch family has never been assessed with molecular phylogenetic methods prior to this study.…”

“…This is particularly well exemplified by the recent discovery of a peculiar new brackish water nudibranch genus and species [44], in a Swedish fjord. Finally, the soft-bottom meiobenthic environment has been considered a strong driver of paedomorphic organisation [6,22], thus being a very reliable example of ecological criterion for paedomorphosis. However, it needs further verification with morphological data and molecular phylogeny on different metazoan groups.…”

“…During ontogeny of all aeolidacean nudibranchs, a few juvenile ceratal rows (1-2 anterior rows in earlier postlarval stages, about 3-4 anterior rows in more advanced juveniles) precede the adult state with numerous ceratal rows (commonly more than ten in total, more than four in anterior rows) [22,71]. Therefore, the presence of a smaller number of ceratal rows in the adult stage is a sign of at least partial paedomorphosis, and not just an overall reduction/loss, especially if such small-sized taxa with a smaller number of anterior ceratal rows are sister to large-sized taxa with numerous cerata.…”

“…According to the present evidence, it is plausible to infer that the common ancestor of cumanotids and pseudovermids may represent early stages of paedomorphosis-related soft bottom-dwelling adaptations, which would have further led to a reduction of the dorsal papillae and the worm-like body shape of the pseudovermids (Figs 1, 2 and 4). It has previously been documented that at early ontogenetic stages, non-burrowing aeolidacean nudibranchs could facultatively occur within the soft-substrata environment [22], and this might have facilitated a further evolutionary shift towards obligate infaunal habitats. Both Xenocratena and Cumanotus occasionally deposit egg masses directly on soft substrata (Fig 2D and 2H), thus favouring a potential evolutionary shift to infaunal habitats.…”

Editorial: diversity of marine meiofauna on the coast of Brazil

“…1 Citation metrics retrieved from Google Scholar using the terms "meiofauna" or "meiobenthos" and further refining for country "Brazil": a) number of publications per year; b) number of citations per year 2014; Venekey et al 2014), Oligochaeta (Prantoni et al 2014), Polychaeta (Di , Platyhelminthes (CuriniGaletti 2014; Reygel et al 2014), and Mollusca (Jörger et al 2014). In total, 18 new species are described and 10 species are re-described (Table 1).…”