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

Todaro MA, Dal Zotto M, Leasi F - PLoS ONE (2015)

Bottom Line: In sandy samples from Thailand, we found numerous macrodasyidan gastrotrichs belonging to an undescribed species of difficult taxonomic affiliation.Adult specimens exhibit maturing eggs and a bulky, muscular caudal organ, but do not show sperm nor the frontal organ.While the anatomical characteristics of the Asian specimens appear so unique to grant the establishment of a new taxon, for which the name Thaidasys tongiorgii gen. et sp. nov. is proposed, the result of phylogenetic analyses based on the 18S rRNA gene unites the new genus with the family Macrodasyidae.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy.

ABSTRACT

Background: Gastrotricha systematics is in a state of flux mainly due to the conflicts between cladistic studies base on molecular markers and the classical systematisation based on morphological traits. In sandy samples from Thailand, we found numerous macrodasyidan gastrotrichs belonging to an undescribed species of difficult taxonomic affiliation. The abundance and original nature of the specimens prompted us to undertake a deep survey of both morphological and molecular traits aiming at a reliable systematisation of the new taxon.

Methodology/principal findings: Using several microscopical techniques we investigated the external and internal anatomy, including the muscular and nervous systems of the new species. Additional specimens were used to obtain the 18S rRNA gene sequence; molecular data was analysed cladistically in conjunction with data from additional species belonging to the near complete Macrodasyida taxonomic spectrum. Specimens are vermiform, up to 806 μm in total length, and show a well-defined head equipped with peculiar leaf-like sensorial organs and a single-lobed posterior end. The adhesive apparatus includes anterior, ventrolateral, dorsal and posterior tubes. Pharynx is about 1/4 of the total length and shows pores at its posterior 3/4. Adult specimens exhibit maturing eggs and a bulky, muscular caudal organ, but do not show sperm nor the frontal organ. Musculature and nervous system organisation resemble the usual macrodasyidan plan; however, the somatic circular muscles of the intestinal region surround all other muscular components and a third FMRFamide-IR commissure ventral to the pharyngo-intestinal junction appear to be an autoapomorphic traits of the new species.

Conclusions/significance: While the anatomical characteristics of the Asian specimens appear so unique to grant the establishment of a new taxon, for which the name Thaidasys tongiorgii gen. et sp. nov. is proposed, the result of phylogenetic analyses based on the 18S rRNA gene unites the new genus with the family Macrodasyidae.

No MeSH data available.


Phylogenetic relationships of Thaidasys tongiorgii gen. et sp. nov. inferred from Bayesian analysis of 18S rRNA.The analysis includes 45 Gastrotricha Macrodasyida and the outgroup is represented by Xenotrichula intermedia (Chaetonotida, Xenotrichulidae). Number at nodes represents posterior probabilities.
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pone.0130278.g014: Phylogenetic relationships of Thaidasys tongiorgii gen. et sp. nov. inferred from Bayesian analysis of 18S rRNA.The analysis includes 45 Gastrotricha Macrodasyida and the outgroup is represented by Xenotrichula intermedia (Chaetonotida, Xenotrichulidae). Number at nodes represents posterior probabilities.

Mentions: The final rDNA dataset included 1895 alignable positions, 977 of which are constant, and 707 parsimony-informative. The three phylogenetic analyses, carried out with ML, MP and Bayesian approaches, yielded topologies that were congruent with each other, with most of the groups that are in common bearing high nodal support: i.e. bootstrap and Bayesian posterior probability values >70 and 98%, respectively (Figs 12–14). 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]. In contrast, the currently recognised Macrodasyidae and Cephalodasyidae never appear as monophyletic due to the scattering along the evolutionary tree of their respective species and/or the alliances between members of different families. Genera represented by two or more species were also recovered as monophyletic in the analyses (except Ptychostomella Remane, 1926 and Tetranchyroderma Remane, 1926). With regard to the new species from Thailand, all of the three analyses strongly indicate (bootstrap ≥ 87, Bayesian posterior probability = 1) a sister-group relationship with the clade containing the two species of Macrodasys Remane, 1924 (Fam. Macrodasyidae) involved in the study (Figs 12–14). Finally, the inclusion of the Thaidasys tongiorgii gen. et sp. nov., did not produce a consistent find a steady position for the recently described Hummondasys jamaicensis Todaro, Leasi & Hochberg, 2014 (Fam. Hummondasyidae, see [21]) in the Macrodasyida phylogenetic tree.


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

Todaro MA, Dal Zotto M, Leasi F - PLoS ONE (2015)

Phylogenetic relationships of Thaidasys tongiorgii gen. et sp. nov. inferred from Bayesian analysis of 18S rRNA.The analysis includes 45 Gastrotricha Macrodasyida and the outgroup is represented by Xenotrichula intermedia (Chaetonotida, Xenotrichulidae). Number at nodes represents posterior probabilities.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4496097&req=5

pone.0130278.g014: Phylogenetic relationships of Thaidasys tongiorgii gen. et sp. nov. inferred from Bayesian analysis of 18S rRNA.The analysis includes 45 Gastrotricha Macrodasyida and the outgroup is represented by Xenotrichula intermedia (Chaetonotida, Xenotrichulidae). Number at nodes represents posterior probabilities.
Mentions: The final rDNA dataset included 1895 alignable positions, 977 of which are constant, and 707 parsimony-informative. The three phylogenetic analyses, carried out with ML, MP and Bayesian approaches, yielded topologies that were congruent with each other, with most of the groups that are in common bearing high nodal support: i.e. bootstrap and Bayesian posterior probability values >70 and 98%, respectively (Figs 12–14). 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]. In contrast, the currently recognised Macrodasyidae and Cephalodasyidae never appear as monophyletic due to the scattering along the evolutionary tree of their respective species and/or the alliances between members of different families. Genera represented by two or more species were also recovered as monophyletic in the analyses (except Ptychostomella Remane, 1926 and Tetranchyroderma Remane, 1926). With regard to the new species from Thailand, all of the three analyses strongly indicate (bootstrap ≥ 87, Bayesian posterior probability = 1) a sister-group relationship with the clade containing the two species of Macrodasys Remane, 1924 (Fam. Macrodasyidae) involved in the study (Figs 12–14). Finally, the inclusion of the Thaidasys tongiorgii gen. et sp. nov., did not produce a consistent find a steady position for the recently described Hummondasys jamaicensis Todaro, Leasi & Hochberg, 2014 (Fam. Hummondasyidae, see [21]) in the Macrodasyida phylogenetic tree.

Bottom Line: In sandy samples from Thailand, we found numerous macrodasyidan gastrotrichs belonging to an undescribed species of difficult taxonomic affiliation.Adult specimens exhibit maturing eggs and a bulky, muscular caudal organ, but do not show sperm nor the frontal organ.While the anatomical characteristics of the Asian specimens appear so unique to grant the establishment of a new taxon, for which the name Thaidasys tongiorgii gen. et sp. nov. is proposed, the result of phylogenetic analyses based on the 18S rRNA gene unites the new genus with the family Macrodasyidae.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy.

ABSTRACT

Background: Gastrotricha systematics is in a state of flux mainly due to the conflicts between cladistic studies base on molecular markers and the classical systematisation based on morphological traits. In sandy samples from Thailand, we found numerous macrodasyidan gastrotrichs belonging to an undescribed species of difficult taxonomic affiliation. The abundance and original nature of the specimens prompted us to undertake a deep survey of both morphological and molecular traits aiming at a reliable systematisation of the new taxon.

Methodology/principal findings: Using several microscopical techniques we investigated the external and internal anatomy, including the muscular and nervous systems of the new species. Additional specimens were used to obtain the 18S rRNA gene sequence; molecular data was analysed cladistically in conjunction with data from additional species belonging to the near complete Macrodasyida taxonomic spectrum. Specimens are vermiform, up to 806 μm in total length, and show a well-defined head equipped with peculiar leaf-like sensorial organs and a single-lobed posterior end. The adhesive apparatus includes anterior, ventrolateral, dorsal and posterior tubes. Pharynx is about 1/4 of the total length and shows pores at its posterior 3/4. Adult specimens exhibit maturing eggs and a bulky, muscular caudal organ, but do not show sperm nor the frontal organ. Musculature and nervous system organisation resemble the usual macrodasyidan plan; however, the somatic circular muscles of the intestinal region surround all other muscular components and a third FMRFamide-IR commissure ventral to the pharyngo-intestinal junction appear to be an autoapomorphic traits of the new species.

Conclusions/significance: While the anatomical characteristics of the Asian specimens appear so unique to grant the establishment of a new taxon, for which the name Thaidasys tongiorgii gen. et sp. nov. is proposed, the result of phylogenetic analyses based on the 18S rRNA gene unites the new genus with the family Macrodasyidae.

No MeSH data available.