New insights into the phylogeny, systematics and DNA barcoding of Nemertea

Abstract

Schima is an ecologically and economically important woody genus in tea family (Thea-ceae). Unresolved species delimitations and phylogenetic relationships within Schima limit our understanding of the genus and hinder utilization of the genus for economic purposes. In the present study, we conducted comparative analysis among the complete chloroplast (cp) genomes of 11 Schima species. Our results indicate that Schima cp genomes possess a typical quadripartite structure, with conserved genomic structure and gene order. The size of the Schima cp genome is about 157 kilo base pairs (kb). They consistently encode 114 unique genes, including 80 protein-coding genes, 30 tRNAs, and 4 rRNAs, with 17 duplicated in the inverted repeat (IR). These cp genomes are highly conserved and do not show obvious expansion or contraction of the IR region. The percent variability of the 68 coding and 93 noncoding (>150 bp) fragments is consistently less than 3%. The seven most widely touted DNA barcode regions as well as one promising barcode candidate showed low sequence divergence. Eight mutational hotspots were identified from the 11 cp genomes. These hotspots may potentially be useful as specific DNA barcodes for species identification of Schima. The 58 cpSSR loci reported here are complementary to the microsatellite markers identified from the nuclear genome, and will be leveraged for further population-level studies. Phylogenetic relationships among the 11 Schima species were resolved with strong support based on the cp genome data set, which corresponds well with the species distribution pattern. The data presented here will serve as a foundation to facilitate species identification , DNA barcoding and phylogenetic reconstructions for future exploration of Schima.

Tubulanus tamias sp. nov. (Nemertea: Palaeonemertea) with Two Different Types of Epidermal Eyes

“…As has been already indicated in Andrade et al (2012) and Kvist et al (2014), the genus Tubulanus is likely to be paraphyletic with respect to Callinera. In this paper, we could have established a new genus for the clade comprised of T. punctatus, T. rhabdotus, T sexlineatus, and T. tamias, and transferred T. pellucidus to Callinera, thereby made the name Tubulanus applied only to the clade containing its type species T. polymorphus.…”

A histology-free description of the branched-proboscis ribbonworm Gorgonorhynchus albocinctus sp. nov. (Nemertea: Heteronemertea)

“…unicolor (Stiasny-Wijnhoff, 1925), since Baseodiscus has been shown to be sister to 'Schizonemertini' (i.e., heteronemerteans with lateral cephalic slits) in recent molecular phylogenetic analyses (cf. Andrade et al, 2012;Kvist et al, 2014). Sequence alignment was carried out gene by gene with MUSCLE (Edgar, 2004a, b) implemented in MEGA ver.…”

DNA barcoding supports identification of Malacobdella species (Nemertea: Hoplonemertea)

“…The combination of molecular and morphological methods has been useful in elucidating nemertean taxonomy in other genera (Sundberg et al 2009;Junoy et al 2010;Puerta et al 2010;Kajihara et al 2011;Taboada et al 2013). DNA barcoding accelerated the discovery ratio of new species (Wiens 2007) and identified some inconsistencies between species assignment and previously sequenced specimens (Kvist et al 2013). Nevertheless, only a small number of nemerteans have been analysed through DNA barcoding (Sundberg et al 2009;Chen et al 2010;Fernández-Álvarez and Machordom, 2013;Kvist et al 2013;Strand et al 2014).…”

“…Recently, molecular methods have been a useful tool for ascertaining the actual biodiversity of these worms and increasing our knowledge of several of the problematic species (Chen et al 2010;Fernández-Álvarez and Machordom 2013;Kvist et al 2013). The nemertean genus Malacobdella de Blainville 1827 originally contained 13 nominal species, of which six are currently regarded as valid (Gibson 1995;Ivanov et al 2002).…”

“…However, the most complete morphological description of M. grossa, reported by Riepen (1933), was based on material from Arctica islandica (Linnaeus 1767) (Heterodonta: Arcticoidea). Nemerteans are traditionally identified and classified using morphological criteria, but the relatively low number of qualitative morphological characters, the lack of adequate fixation procedures for histological studies, vague descriptions in the original papers and the paucity of species-specific characters make species delimitation problematic, especially when comparing closely related species (Chen et al 2010;Fernández-Álvarez and Machordom 2013;Kvist et al 2013). The difficulty of morphological recognition of a great part of the more than 1,280 species included in the phylum Nemertea has been previously discussed (Andrade et al 2012;Kvist et al 2013, among others), and different authors have advocated new tools and comprehensive studies for correctly identifying species and thus providing accurate biodiversity knowledge.…”