Phylogeny of Gastrotricha: a morphology-based framework of gastrotrich relationships

Abstract

Currently, the phylum Gastrotricha is divided into the orders Macrodasyida and Chaetonotida, with the structure of the myoepithelial pharynx being an important distinguishing feature. Macrodasyida currently has six recognized families, and Chaetonotida comprises seven families. However, within-group relationships are poorly understood. To arrive at a better understanding of gastrotrich systematics and phylogeny, we performed the first cladistic analysis of nearly all known gastrotrich genera using 71 morphological characters. Results suggest that the Gastrotricha is a monophyletic group (supported by 82% of bootstrap replications) with its most primitive taxa distributed among the families Dactylopodolidae and Neodasyidae. Monophyly of Macrodasyida and Chaetonotida was supported by 90% and 52% bootstrap replications, respectively. Within the Macrodasyida, the families Dactylopodolidae, Turbanellidae, Macrodasyidae, and Thaumastodermatidae all formed monophyletic clades. The families Planodasyidae and Lepidodasyidae were paraphyletic. Among the Chaetonotida, the marine family Xenotrichulidae was monophyletic, supported by 51% of bootstrap replications. A second clade containing all freshwater families was supported by 62% bootstrap values. However, Chaetonotidae were paraphyletic. Using this analysis as a framework, we now can explore possible patterns of evolution within it, and arrive at a consensus of the gastrotrich ground pattern. Moreover, in future molecular studies of metazoan phylogeny, we will be able to select gastrotrich species that are more appropriate representatives of the phylum.

Diuronotus aspetos (Gastrotricha): new morphological data and description of the spermatozoon

“…The presence of pedunculated scales in addition to the ones fully adhering to the cuticle distinguishes Diuronotus from Musellifer. Among Chaetonotida pedunculated scales are present only in Aspidiophorus and Xenotrichula, two genera greatly differing in morphology from the Muselliferidae, and belonging to separate evolutionary lines (Hochberg and Litvaitis 2000).…”

“…Within the Chaetonotida, the families Muselliferidae and Xenotrichulidae are marine, the Chaetonotidae include both marine and freshwater species, while Dasydytidae, Dichaeturidae, Neogosseidae and Proichthydiidae are exclusively freshwater. The monophyly of the strictly freshwater families has never been questioned, and has gained support from an inclusive cladistic analysis of the Gastrotricha based on 81 morphological and reproductive traits (Hochberg and Litvaitis 2000). On the contrary, the phylogenetic relationships within Chaetonotidae and between Chaetonotidae and Xenotrichulidae are still unclear, due in part to the uncertain status of the genus Musellifer, originally assigned to the Chaetonotidae.…”

Unusual spermatozoa and reproductive modalities ofXenodasys eknomios(Gastrotricha: Xenodasyidae)

“…As the most inclusive phylogenetic analyses based on morphological characters (Hochberg & Litvaitis 2000, 2001a have set Xenodasys among the most basal taxa along the Macrodasyida evolutionary branch, it is likely that in a larger framework the new information might assume relevance for reconstructing the morphological ground pattern of the whole phylum.…”

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

“…Os Gastrotricha são microinvertebrados comumente encontrados na meiofauna de ambientes marinhos e de água doce, que apresentam no máximo três milímetros de comprimento (a maioria tem menos de 0,5 milímetros), quando adultos, e movem-se predominantemente pela ação de cílios presentes nas superfícies ventral, lateral e ventrolateral (Hochberg & Litvaitis, 2000;Balsamo & Todaro, 2002;Balsamo et al, 2005). Apesar do grande número de populações em distintos ambientes, este táxon não é muito estudado, possivelmente por características que torna seu estudo difícil como seu diminuto tamanho e fragilidade de seus corpos.…”

“…O táxon, com distribuição cosmopolita, é composto por mais de 760 espécies tradicionalmente dividido em duas grandes ordens: Chaetonotida e Macrodasyida (Hochberg & Litvaitis, 2000;Balsamo et al, 2008;2009;Todaro & Hummon, 2008;Hummon & Todaro 2010; mas veja Kieneke et al, 2008). O grupo Chaetonotida apresenta mais de 450 espécies, ou seja, compreende a maioria dos Gastrotricha, e possui representantes com uma morfologia externa que lembra o formato de um "pino de boliche".…”