Search

Emplectonema viride Stimpson, 1857, a barnacle predator, is one of the most common and conspicuous intertidal nemerteans found along the West Coast of North America from Alaska to California, but it is currently referred to by the wrong name. Briefly described without designation of type material or illustrations, the species was synonymized with the Atlantic look-alike, Emplectonema gracile (Johnston, 1837) by Coe. Here we present morphological and molecular evidence that E. viride is distinct from E. gracile. The two species exhibit differences in color of live specimens and egg size and are clearly differentiated with species delimitation analyses based on sequences of the partial regions of the 16S rRNA and cytochrome c oxidase subunit I genes. In order to improve nomenclatural stability, we re-describe E. viride based on specimens from the southern coast of Oregon and discuss which species should be the type species of the genus. Emplectonema viride was one of the two species originally included in the genus Emplectonema Stimpson, 1857, but subsequent synonymization of E. viride with E. gracile resulted in acceptance of the Atlantic species, E. gracile, as the type species of the genus. We resurrect E. viride Stimpson, 1857 and following Corrêa’s designation, this should be the type species of the genus Emplectonema.

Emplectonema viride Stimpson, 1857, a barnacle predator, is one of the most common and conspicuous intertidal nemerteans found along the West Coast of North America from Alaska to California, but it is currently referred to by the wrong name. Briefly described without designation of type material or illustrations, the species was synonymized with the Atlantic look-alike, Emplectonema gracile (Johnston, 1837) by Coe. Here we present morphological and molecular evidence that E. viride is distinct from E. gracile. The two species exhibit differences in color of live specimens and egg size and are clearly differentiated with species delimitation analyses based on sequences of the partial regions of the 16S rRNA and cytochrome c oxidase subunit I genes. In order to improve nomenclatural stability, we re-describe E. viride based on specimens from the southern coast of Oregon and discuss which species should be the type species of the genus. Emplectonema viride was one of the two species originally included in the genus Emplectonema Stimpson, 1857, but subsequent synonymization of E. viride with E. gracile resulted in acceptance of the Atlantic species, E. gracile, as the type species of the genus. We resurrect E. viride Stimpson, 1857 and following Corrêa’s designation, this should be the type species of the genus Emplectonema.

The structure of pseudocnidae of 16 species of Palaeonemertea clade Archinemertea (= Cephalotrichida s.l.) was investigated with confocal laser, scanning, and transmission electron microscopy (TEM). All species of the genus Cephalothrix possess two kinds of pseudocnidae, large and small. Only one type of pseudocnida is present in Balionemertes and Cephalotrichella. TEM revealed variation in the ultrastructure of large and small pseudocnidae of four species of Cephalothrix. Pseudocnidae of Balionemertes, Cephalotrichella, and Cephalothrix differ in substructure: in Balionemertes and Cephalotrichella the medulla is located in the basal half of the pseudocnidae with а precore layer situated in the apical half, whereas in Cephalothrix spp. and other palaeonemerteans the medulla surrounds a precore layer. Our results confirm the division of archinemerteans into Cephalotrichidae (with genus Cephalothrix) and Cephalotrichellidae (with genera Cephalotrichella and Balionemertes). The synapomorphy of Cephalotrichidae is pseudocnida dimorphism and the synapomorphies of Cephalotrichellidae are the position of the pseudocnidae on epithelial ridges and the distinct organization of pseudocnida layers, specifically the relative position of the medulla and precore layers. The pseudocnida lateral process, one or more of which is present in most species observed, is a probable synapomorphy of the clade Archinemertea. This is the first application of pseudocnida features to distinguish super-generic nemertean taxa and the results suggest that pseudocnidae provide a useful source of characters for nemertean systematics.

Resolving the deep relationships of ancient animal lineages has proven difficult using standard Sanger-sequencing approaches with a handful of markers. We thus reassess the relatively well-studied phylogeny of the phylum Nemertea (ribbon worms)-for which the targeted gene approaches had resolved many clades but had left key phylogenetic gaps-by using a phylogenomic approach using Illumina-based de novo assembled transcriptomes and automatic orthology prediction methods. The analysis of a concatenated data set of 2,779 genes (411,138 amino acids) with about 78% gene occupancy and a reduced version with 95% gene occupancy, under evolutionary models accounting or not for site-specific amino acid replacement patterns results in a well-supported phylogeny that recovers all major accepted nemertean clades with the monophyly of Heteronemertea, Hoplonemertea, Monostilifera, being well supported. Significantly, all the ambiguous patterns inferred from Sanger-based approaches were resolved, namely the monophyly of Palaeonemertea and Pilidiophora. By testing for possible conflict in the analyzed supermatrix, we observed that concatenation was the best solution, and the results of the analyses should settle prior debates on nemertean phylogeny. The study highlights the importance, feasibility, and completeness of Illumina-based phylogenomic data matrices.

Strand, Malin ... et al.-- 2 pages, Nemertean classification has closely followed Stiasny‐Wijnhoff's scheme (1936) that was based on Schultze's (1851) division of the taxon into the two classes Anopla and Enopla. In August 2018, the 9th International Conference of Nemertean Biology took place in the Wadden Sea Station of the Alfred Wegener Institute in List auf Sylt, Germany. At this meeting, the community reached consensus to revise nemertean taxonomy at the class level, based on the compiled evidence from studies on nemertean systematics published in the last 15 years (Andrade et al., 2012, 2014 ; Thollesson & Norenburg, 2003). Previous classifications (e.g., Stiasny‐Wijnhoff, 1936) are not based on phylogenetic grounds, and the use of these names is therefore nowadays not wholly informative. With the purpose of facilitating the practical use of the nemertean taxonomy and also making nemertean taxonomy reflect a wealth of more recent information, we conclude that the ranks Anopla and Enopla should be eliminated with the following argumentation: “Enopla” has for long held no more information than the name “Hoplonemertea”. “Anopla” is paraphyletic and the name usually corresponds to the following traits: (a) not bearing stylet; and (b) mouth and proboscis having separate openings. This information is equally well presented in a system that also bears information on natural groups. The names “Anopla” and “Enopla” are hence dismissed and the following system of the Nemertea phylum is implemented: Class: Palaeonemertea Currently no Orders Class: Pilidiophora Order: Heteronemertea Class: Hoplonemertea Order: Monostilifera Order: Polystilifera The changes do not affect lower levels of taxonomy, but in accordance with Thollesson and Norenburg (2003), who first presented Pilidiophora, genus Hubrechtella is transferred from class Palaeonemertea to the class Pilidiophora

Understanding the impact of environmental stressors on predator activity is a prerequisite to understanding the underlying mechanisms shaping community structure. The nemertean Prosorhochmus nelsoni is a common predator in the mid-intertidal zone on rocky shores along the Chilean coast, where it can reach very high abundances (up to 260 ind m−2) in algal turfs, algal crusts, barnacle crusts, and mixed substrata. Tidal and diurnal scans revealed that the activity of P. nelsoni is primarily restricted to night and early-morning low tides and is relatively low when air temperatures are high. On average, larger worms crawled faster than smaller worms, with their maximum velocity being influenced by substratum type. Their estimated rate of predation is 0.092 prey items nemertean−1 day−1, just below the laboratory rate of ~0.2 amphipods nemertean−1 day−1 previously estimated for this species. P. nelsoni consumes a diverse spectrum of prey items (i.e., amphipods, isopods, decapods, barnacles, and dipterans) and is possibly exerting a significant influence on its prey populations. We suggest that the opportunistic predatory behavior of this intertidal predator is caused by the trade-off between immediate persistence (e.g., avoidance of desiccation) and long-term survival through successful foraging.

We conducted a phylogeographic study of the meiofaunal nemertean Ototyphlonemertes parmula, an apparent species complex from the littoral zone of coarse-grained beaches, using a 494-bp fragment of the mitochondrial cytochrome oxidase 3 gene (cox3). Six populations from the Gulf and Atlantic coasts of Florida, two from New England, and one from the Caribbean were sampled in March and August 2005. Three major lineages were identified, separated by cox3 sequence divergence of 16–18%, with partially overlapping ranges. Tests for hybridization using ISSR markers detected nuclear gene exchange within but not between the major mitochondrial lineages, indicating the presence of cryptic species. One lineage dominating the Atlantic coast of Florida shows no evidence of geographic structuring. Another lineage shows a phylogenetic break between the Atlantic and Gulf coasts, suggesting that unsuitable habitat may act as a barrier to dispersal. Long-distance migration is evidenced by shared haplotypes between Florida and the eastern Caribbean. Overall, the widespread distribution of individual haplotypes and lack of structuring within geographic regions contrast with O. parmula’s strongly sediment-bound lifestyle. We speculate that dispersal of adults by storms and/or sediment transport may be more important than few and potentially short-lived planktonic larvae to explain geographic diversity in O. parmula and may be important for meiofauna in general.

Thousands of microsatellite loci were identified in the nemertean Prosorhochmus americanus through enrichment-isolation and next-generation sequencing protocols. We tested 48 loci for amplification and subsequently genotyped 17 loci in 30 individuals from three North American populations. Most loci were polymorphic within and across populations; six were monomorphic. The number of alleles per locus ranged from 1 to 9 (mean 4.35, SD 2.37). Cross-species amplification in four nemertean species revealed extended marker utility. These loci will enable investigations of colonization potential and natural history in this selfing, putatively introduced species.

Organisms capable of self-fertilization ("selfing") typically exhibit two evolutionary syndromes: uniting high inbreeding depression with low levels of selfing, or low inbreeding depression with high levels of selfing. We examined the effect of inbreeding on fecundity and time to first reproduction in an apparently self-compatible, simultaneously hermaphroditic marine nemertean worm Prosorhochmus americanus. Adult and juvenile worms were raised in isolation or in pairs. Isolated worms produced significantly more offspring than paired worms (in the adult experiment), and did not exhibit inbreeding avoidance (in the juvenile experiment). The selfing rate of six natural populations was evaluated using 17 species-specific, microsatellite markers, and was consistent with preferential selfing (mean: 0.843, SD: 0.027). Our results showed that P. americanus exhibited an interesting suite of life-history traits, uniting high colonization potential through self-fertilization and high fecundity, with no dispersive larval stage, and with moderate levels of gene flow. We believe that P. americanus is an ideal model system for studies of mating system evolution, inbreeding, and sex allocation.

The proboscis of Hubrechtella juliae was examined using transmission electron microscopy, scanning electron microscopy, and confocal laser scanning microscopy to reveal more features of basal pilidiophoran nemerteans for morphological and phylogenetic analysis. The proboscis glandular epithelium consists of sensory cells and four types of gland cells (granular, bacillary, mucoid, and pseudocnidae-containing cells) that are not associated with any glandular systems; rod-shaped pseudocnidae are 15-25 μm in length; the central cilium of the sensory cells is enclosed by two rings of microvilli. The nervous plexus lies in the basal part of glandular epithelium and includes 26-33 (11-12 in juvenile) irregularly anastomosing nerve trunks. The proboscis musculature includes four layers: endothelial circular, inner diagonal, longitudinal, and outer diagonal; inner and outer diagonal muscles consist of noncrossing fibers; in juvenile specimen, the proboscis longitudinal musculature is divided into 7-8 bands. The endothelium consists of apically situated support cells with rudimentary cilia and subapical myocytes. Unique features of Hubrechtella's proboscis include: acentric filaments of the pseudocnidae; absence of tonofilament-containing support cells; two rings of microvilli around the central cilium of sensory cells; the occurrence of subendothelial diagonal muscles and the lack of an outer diagonal musculature (both states were known only in Baseodiscus species). The significance of these characters for nemertean taxonomy and phylogeny is discussed. The proboscis musculature in H. juliae and most heteronemerteans is bilaterally arranged, which can be considered a possible synapomorphy of Hubrechtellidae + Heteronemertea (= Pilidiophora).

Most animal phyla appeared in the Cambrian radiation, and many have a rich fossil record. The phylogenetic relationships among phyla are, however, still poorly understood. Although systematics based on morphological characters has been revitalized by cladistic methods, incongruent results have been obtained for most relationships. Gene sequence data offer the potential for adding substantial new characters for evaluating phylum level relationships. Molecular studies of the Cambrian radiation are just beginning, and only a few of the potential characters available from genes have been examined. The achievements and controversies between molecular studies are reviewed and compared to corresponding studies based on morphological data. Because molecular systematics is intensely dependent upon the methods used to infer trees, important methodological considerations that affect the studies of phylum-level

The arthropods constitute the most diverse animal group, but, despite their rich fossil record and a century of study, their phylogenetic relationships remain unclear. Taxa previously proposed to be sister groups to the arthropods include Annelida, Onychophora, Tardigrada and others, but hypotheses of phylogenetic relationships have been conflicting. For example, onychophorans, like arthropods, moult periodically, have an arthropod arrangement of haemocoel, and have been related to arthropods in morphological and mitochondrial DNA sequence analyses. Like annelids, they possess segmental nephridia and muscles that are a combination of smooth and obliquely striated fibres. Our phylogenetic analysis of 18S ribosomal DNA sequences indicates a close relationship between arthropods, nematodes and all other moulting phyla. The results suggest that ecdysis (moulting) arose once and support the idea of a new clade, Ecdysozoa, containing moulting animals: arthropods, tardigrades, onychophorans, nematodes, nematomorphs, kinorhynchs and priapulids. No support is found for a clade of segmented animals, the Articulata, uniting annelids with arthropods. The hypothesis that nematodes are related to arthropods has important implications for developmental genetic studies using as model systems the nematode Caenorhabditis elegans and the arthropod Drosophila melanogaster, which are generally held to be phylogenetically distant from each other.