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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.


Thaidasys tongiorgii gen. et sp. nov. Differential interference contrast photomicrographs.A, close-up of the anterior region, ventral view, showing the locomotor ciliation and the anterior adhesive tubes (arrow); B, close-up of the internal view of the anterior region of a different specimen, showing the pharynx, pharyngeal pores (arrows) and pharyngo-intestinal junction (arrowhead). C, D, Posterior region of the trunk of two subadult specimens, showing the caudal organ (arrows) at different development stages. E, a juvenile. Scale bars A, B, E = 100 μm, C, D = 50 μm.
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pone.0130278.g003: Thaidasys tongiorgii gen. et sp. nov. Differential interference contrast photomicrographs.A, close-up of the anterior region, ventral view, showing the locomotor ciliation and the anterior adhesive tubes (arrow); B, close-up of the internal view of the anterior region of a different specimen, showing the pharynx, pharyngeal pores (arrows) and pharyngo-intestinal junction (arrowhead). C, D, Posterior region of the trunk of two subadult specimens, showing the caudal organ (arrows) at different development stages. E, a juvenile. Scale bars A, B, E = 100 μm, C, D = 50 μm.

Mentions: Based mostly on the adult specimens with a total body length of 782 μm shown in Fig 2. Body elongate and rather narrow, flattened ventrally and vaulted dorsally, with gently undulating sides due to the presence of numerous epidermal glands; cuticular covering smooth, devoid of scales and/or spines (Figs 1A, 1B, 2A, 3D and 5A). Body attaining the maximum width in the mid- to hindgut, and then narrowing again to an ovoidal caudum (Figs 1A, 1B, 2A, 2B and 5A, 5E). Head consisting of two distinct portions. The anterior one, roughly trapezoidal, with rounded angles, appears clearly demarked by a posterior constriction and with a pair of peculiar leaf-like structures, interpreted as sensory organs at U03; it bears sparse sensory cilia on the lateral side, but neither piston pits nor eye spots are present (Figs 1, 2A, 2C, 3B and 4). The posterior portion of the head hosts the brain (see below), it appears slightly inflated and delimited to the rear by a second constriction at U10.


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)

Thaidasys tongiorgii gen. et sp. nov. Differential interference contrast photomicrographs.A, close-up of the anterior region, ventral view, showing the locomotor ciliation and the anterior adhesive tubes (arrow); B, close-up of the internal view of the anterior region of a different specimen, showing the pharynx, pharyngeal pores (arrows) and pharyngo-intestinal junction (arrowhead). C, D, Posterior region of the trunk of two subadult specimens, showing the caudal organ (arrows) at different development stages. E, a juvenile. Scale bars A, B, E = 100 μm, C, D = 50 μm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0130278.g003: Thaidasys tongiorgii gen. et sp. nov. Differential interference contrast photomicrographs.A, close-up of the anterior region, ventral view, showing the locomotor ciliation and the anterior adhesive tubes (arrow); B, close-up of the internal view of the anterior region of a different specimen, showing the pharynx, pharyngeal pores (arrows) and pharyngo-intestinal junction (arrowhead). C, D, Posterior region of the trunk of two subadult specimens, showing the caudal organ (arrows) at different development stages. E, a juvenile. Scale bars A, B, E = 100 μm, C, D = 50 μm.
Mentions: Based mostly on the adult specimens with a total body length of 782 μm shown in Fig 2. Body elongate and rather narrow, flattened ventrally and vaulted dorsally, with gently undulating sides due to the presence of numerous epidermal glands; cuticular covering smooth, devoid of scales and/or spines (Figs 1A, 1B, 2A, 3D and 5A). Body attaining the maximum width in the mid- to hindgut, and then narrowing again to an ovoidal caudum (Figs 1A, 1B, 2A, 2B and 5A, 5E). Head consisting of two distinct portions. The anterior one, roughly trapezoidal, with rounded angles, appears clearly demarked by a posterior constriction and with a pair of peculiar leaf-like structures, interpreted as sensory organs at U03; it bears sparse sensory cilia on the lateral side, but neither piston pits nor eye spots are present (Figs 1, 2A, 2C, 3B and 4). The posterior portion of the head hosts the brain (see below), it appears slightly inflated and delimited to the rear by a second constriction at U10.

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.