Gastrotricha: A Marine Sister for a Freshwater Puzzle

Abstract

BackgroundWithin an evolutionary framework of Gastrotricha Marinellina flagellata and Redudasys fornerise bear special interest, as they are the only Macrodasyida that inhabit freshwater ecosystems. Notwithstanding, these rare animals are poorly known; found only once (Austria and Brazil), they are currently systematised as incertae sedis. Here we report on the rediscovery of Redudasys fornerise, provide an account on morphological novelties and present a hypothesis on its phylogenetic relationship based on molecular data.Methodology/Principal FindingsSpecimens were surveyed using DIC microscopy and SEM, and used to obtain the 18 S rRNA gene sequence; molecular data was analyzed cladistically in conjunction with data from 42 additional species belonging to the near complete Macrodasyida taxonomic spectrum. Morphological analysis, while providing new information on taxonomically relevant traits (adhesive tubes, protonephridia and sensorial bristles), failed to detect elements of the male system, thus stressing the parthenogenetic nature of the Brazilian species. Phylogenetic analysis, carried out with ML, MP and Bayesian approaches, yielded topologies with strong nodal support and highly congruent with each other. Among the supported groups is the previously undocumented clade showing the alliance between Redudasys fornerise and Dactylopodola agadasys; other strongly sustained clades include the densely sampled families Thaumastodermatidae and Turbanellidae and most genera.Conclusions/SignificanceA reconsideration of the morphological traits of Dactylopodola agadasys in light of the new information on Redudasys fornerise makes the alliance between these two taxa very likely. As a result, we create Anandrodasys gen. nov. to contain members of the previously described D. agadasys and erect Redudasyidae fam. nov. to reflect this novel relationship between Anandrodasys and Redudasys. From an ecological perspective, the derived position of Redudasys, which is deeply nested within the Macrodasyida clade, unequivocally demonstrates that invasion of freshwater by gastrotrichs has taken place at least twice, in contrast with the single event hypothesis recently put forward.

An Integrated Morphological and Molecular Approach to the Description and Systematisation of a Novel Genus and Species of Macrodasyida (Gastrotricha)

“…The robustly supported groups include: 1) the densely sampled families Thaumastodermatidae and Turbanellidae and their recognized subgroupings; 2) the recently highlighted alliance between Redudasys fornerise Kisielewski, 1987 and Anandrodasys agadasys (Hochberg, 2003) (Fam. Redudasyidae, see [24]) and their sister-group relationship with a clade composed of Cephalodasys and Dolichodasys (Fam. Cephalodasyidae); and 3) the sister-group relationship between Crasiella Clausen, 1968 and Megadasys Schmidt, 1974, recently united in the family Planodasyidae [33].…”

“…Phylogenetic analysis of the Macrodasyida based on molecular traits (18S rDNA gene alone or in conjunction with the 28S rDNA and Cox 1 genes) have provided support for some of the traditional groupings based on morphological traits but have also unveiled surprising associations, e.g. congeneric species grouping with different families or morphologically disparate species grouping together (e.g., [24, 43, 44]).…”

A new species of Turbanellidae (Gastrotricha, Macrodasyida) from Jamaica, with a key to species of Paraturbanella

“…As of December 2017, the group comprises 840 species divided into the two orders Macrodasyida and Chaetonotida (Todaro 2017). Macrodasyida generally includes taxa living interstitially in marine sandy bottoms (but see e.g., Todaro et al 2012), while Chaetonotida comprises species found from marine to freshwater environments. The alpha biodiversity and systematics of the Phylum are changing at a fast pace, as shown by the continuous finding and description of new taxa (for marine taxa, e.g., Hochberg et al 2014, Todaro et al 2014, 2015, Lee and Chang 2017) and the in-group phylogenetic reassessments (e.g., Kånneby et al 2013, Todaro et al 2014, Kånneby and Todaro 2015).…”

“…Research teams headed by one of us (MAT) have visited three islands: St. John in the US-Virgin islands, Jamaica, and Curaçao. Part of the information and/or taxa found have appeared in several papers (e.g., Hummon et al 2010, Kånneby et al 2012, 2013, 2014, Todaro et al 2012, Schuster et al 2017). Specifically devoted to the Jamaican survey were two papers dealing with the description a new species of Macrodasys and the description of a new species, genus and family (Todaro and Leasi 2013, Todaro et al 2014).…”

Checklist de Gastrotricha do Estado do Mato Grosso do Sul, Brasil

“…A falta de dados sobre essas duas espécies levou os estudiosos a situarem estas espécies como insertae sedis dentro da ordem Macrodasyida. Entretanto, Todaro et al (2012) Garraffoni et al (2010) e Araújo et al (2013), em amostras qualitativas no estado de Minas Gerais, respectivamente, observaram inúmeros espécimes dos gêneros Redudasys e Marinellina.…”