New data from an enigmatic phylum: evidence from molecular sequence data supports a sister-group relationship between Loricifera and Nematomorpha

Abstract

Loricifera is one of the most recently discovered animal phyla. So far, the group has been considered closely related to Kinorhyncha and Priapulida, and assigned to the ecdysozoan clade Cycloneuralia. Using Bayesian inference, we present the first phylogeny that includes 18S rRNA and Histone 3 sequences from two species of Loricifera. Intriguingly, we find support for a sister-group relationship between Loricifera and Nematomorpha. Such relationship has not been suggested previously and the results imply that a revision of our conception of early ecdysozoan evolution is required. Additionally, the data suggest that evolution through progenesis (sexual maturation of larvae) may have played an important role among the ancestral cycloneuralians.

MicroRNAs and phylogenomics resolve the relationships of Tardigrada and suggest that velvet worms are the sister group of Arthropoda

“…Morphological and embryological evidence suggests a close affinity among Arthropoda, Onychophora, and Tardigrada (the Panarthropoda) (8,9), although the interrelationships among these three taxa are uncertain. Despite the concordance between these morphological studies and a few molecular analyses (10)(11)(12)(13)(14), most molecular studies instead support a close relationship between the water bears and the cycloneuralian ecdysozoans (nematodes, priapulids, and their close relatives), particularly the nematodes (2,(15)(16)(17)(18)(19)(20)(21)(22). These alternative hypotheses of tardigrade relationships have important consequences for our understanding of morphological evolution within Ecdysozoa.…”

Evidence of Priapulid Scavenging From the Early Cambrian Chengjiang Deposits, Southern China

“…In addition, some recent molec− ular data appear to support the latter view. Thus, Sørensen et al (2008) linked the nematomorphs to the loriciferans, even though the general consensus had allied the latter group to the kinorhynchs and priapulids. In their scheme these scalidopho− rans would form the sister−group to the other cycloneuralians (plus arthropods, with onychophorans).…”

“…In their scheme these scalidopho− rans would form the sister−group to the other cycloneuralians (plus arthropods, with onychophorans). Importantly Sørensen et al (2008) also outlined a phylogenetic scenario whereby the most primitive ecdysozoans possess a life cycle that includes a loriciferan−like larva and a priapulid−like adult. We would suggest that the palaeoscolecidans and related forms are equi− valent to this stage of ecdysozoan evolution (Fig.…”

“…So far as the priapulids in the Cam− brian are concerned, most likely they only occur as stem− group forms (see Wills 1998) represented by such taxa as Ottoia prolifica (Conway Morris 1977). Moreover, whilst the phylogeny of Sørensen et al (2008) appears to drive a wedge between the scalidophorans and other priapulid−like cyclo− neuralians, it is necessary to stress that the morphological (and most likely genetic) differences in the earliest stages of this ecdysozoan radiation were most likely trivial, even though their end−products include the disparate phyla represented by the arthropods, nematoids, kinorhynchs, and priapulids. , Mount 1976, Mount , 1980.…”

First record of Loricifera from the Iberian Peninsula, with the description of Rugiloricus manuelae sp. nov., (Loricifera, Pliciloricidae)

“…Recently, loriciferans have been reported living permanently in extreme environments, such as a hypersaline, anoxic basin of the Mediterranean Sea (Danovaro et al 2010(Danovaro et al , 2012. The phylogenetic position of Loricifera remains still controversial (for review, see Sørensen et al 2008). …”