The phylogenetic position of Brachiopoda remains unsettled, and only few recent data on brachiopod organogenesis are currently available. In order to contribute data to questions concerning brachiopod ontogeny and evolution we investigated nervous and muscle system development in the craniiform (inarticulate) brachiopod Novocrania anomala. Larvae of this species are lecithotrophic and have a bilobed body with three pairs of dorsal setal bundles that emerge from the posterior lobe. Fully developed larvae exhibit a network of setae pouch muscles as well as medioventral longitudinal and transversal muscles. After settlement, the anterior and posterior adductor muscles and delicate mantle retractor muscles begin to form. Comparison of the larval muscular system of Novocrania anomala with that of rhynchonelliform (articulate) brachiopod larvae shows that the former has a much simpler muscular organization. The first signal of serotonin-like immunoreactivity appears in fully developed Novocrania anomala larvae, which have an apical organ that consists of four flask-shaped cells and two ventral neurites. These ventral neurites do not stain positively for the axonal marker alpha-tubulin in the larval stages. In the juveniles, the nervous system stained by alpha-tubulin is characterized by two ventral neurite bundles with three commissures. Our data are the first direct proof for the presence of an immunoreactive neurotransmitter in lecithotrophic brachiopod larvae and demonstrate the existence of flask-shaped serotonergic cells in the brachiopod larval apical organ, thus significantly increasing the probability that this cell type was part of the bauplan of the larvae of the last common lophotrochozoan ancestor.

BackgroundKinorhynchs are ecdysozoan animals with a phylogenetic position close to priapulids and loriciferans. To understand the nature of segmentation within Kinorhyncha and to infer a probable ancestry of segmentation within the last common ancestor of Ecdysozoa, the musculature and the nervous system of the allomalorhagid kinorhynch Pycnophyes kielensis were investigated by use of immunohistochemistry, confocal laser scanning microscopy, and 3D reconstruction software.ResultsThe kinorhynch body plan comprises 11 trunk segments. Trunk musculature consists of paired ventral and dorsal longitudinal muscles in segments 1–10 as well as dorsoventral muscles in segments 1–11. Dorsal and ventral longitudinal muscles insert on apodemes of the cuticle inside the animal within each segment. Strands of longitudinal musculature extend over segment borders in segments 1–6. In segments 7–10, the trunk musculature is confined to the segments. Musculature of the digestive system comprises a strong pharyngeal bulb with attached mouth cone muscles as well as pharyngeal bulb protractors and retractors. The musculature of the digestive system shows no sign of segmentation. Judged by the size of the pharyngeal bulb protractors and retractors, the pharyngeal bulb, as well as the introvert, is moved passively by internal pressure caused by concerted action of the dorsoventral muscles. The nervous system comprises a neuropil ring anterior to the pharyngeal bulb. Associated with the neuropil ring are flask-shaped serotonergic somata extending anteriorly and posteriorly. A ventral nerve cord is connected to the neuropil ring and runs toward the anterior until an attachment point in segment 1, and from there toward the posterior with one ganglion in segment 6.ConclusionsSegmentation within Kinorhyncha likely evolved from an unsegmented ancestor. This conclusion is supported by continuous trunk musculature in the anterior segments 1–6, continuous pharyngeal bulb protractors and retractors throughout the anterior segments, no sign of segmentation within the digestive system, and the absence of ganglia in most segments. The musculature shows evidence of segmentation that fit the definition of an anteroposteriorly repeated body unit only in segments 7–10.Electronic supplementary materialThe online version of this article (doi:10.1186/s13227-016-0062-6) contains supplementary material, which is available to authorized users.

Elysia chlorotica, a sacoglossan sea slug found off the East Coast of the United States, is well-known for its ability to sequester chloroplasts from its algal prey and survive by photosynthesis for up to 12 months in the absence of food supply. Here we present a draft genome assembly of E. chlorotica that was generated using a hybrid assembly strategy with Illumina short reads and PacBio long reads. The genome assembly comprised 9,989 scaffolds, with a total length of 557 Mb and a scaffold N50 of 442 kb. BUSCO assessment indicated that 93.3% of the expected metazoan genes were completely present in the genome assembly. Annotation of the E. chlorotica genome assembly identified 176 Mb (32.6%) of repetitive sequences and a total of 24,980 protein-coding genes. We anticipate that the annotated draft genome assembly of the E. chlorotica sea slug will promote the investigation of sacoglossan genetics, evolution, and particularly, the genetic signatures accounting for the long-term functioning of algal chloroplasts in an animal. Design Type(s) sequence assembly objective • sequence annotation objective Measurement Type(s) genome assembly Technology Type(s) DNA sequencing Factor Type(s) developmental stage Sample Characteristic(s) Elysia chlorotica • whole organism

No abstract

Different features can protect bacteria against protozoan grazing, for example large size, rapid movement, and production of secondary metabolites. Most papers dealing with these matters focus on bacteria. Here, we describe protozoan features that affect their ability to grow on secondary-metabolite-producing bacteria, and examine whether different bacterial secondary metabolites affect protozoa similarly. We investigated the growth of nine different soil protozoa on six different Pseudomonas strains, including the four secondary-metabolite-producing Pseudomonas fluorescens DR54 and CHA0, Pseudomonas chlororaphis MA342 and Pseudomonas sp. DSS73, as well as the two nonproducers P. fluorescens DSM50090(T) and P. chlororaphis ATCC43928. Secondary metabolite producers affected protozoan growth differently. In particular, bacteria with extracellular secondary metabolites seemed more inhibiting than bacteria with membrane-bound metabolites. Interestingly, protozoan response seemed to correlate with high-level protozoan taxonomy, and amoeboid taxa tolerated a broader range of Pseudomonas strains than did the non-amoeboid taxa. This stresses the importance of studying both protozoan and bacterial characteristics in order to understand bacterial defence mechanisms and potentially improve survival of bacteria introduced into the environment, for example for biocontrol purposes.

Background: Despite significant methodological progress, Brachiopoda remains one of the lophotrochozoan phyla for which no recent ontogenetic data employing modern methodologies such as fluorescence labelling and confocal microscopy are available. This is particularly astonishing given the ongoing controversy concerning its phylogenetic position. In order to contribute new morphogenetic data for phylogenetic and evolutionary inferences, we describe herein the ontogeny and myoanatomy of larvae and adults of the rhynchonelliform brachiopods Argyrotheca cordata, A. cistellula, and Terebratalia transversa using fluorescence F-actin labelling combined with confocal laserscanning microscopy.

Ciliates represent an important trophic link between nanoplankton and mesoplankton. Many species acquire functional chloroplasts from photosynthetic prey, being thus mixotrophs. Little is known about which algae they exploit, and of the relevance of inorganic carbon assimilation to their metabolism. To get insights into these aspects, laboratory cultures of three mixotrophic Strombidium spp. were established and 35 photosynthetic algal species were tested as prey. The relative contributions of ingestion and photosynthesis to total carbon uptake were determined, and responses to prey starvation were studied. Ciliate growth was supported by algal species in the 2–12 μm size range, with cryptophytes and chlorophytes being the best prey types. Inorganic carbon incorporation was only quantitatively important when prey concentration was low (3–100 μgCL−1), when it led to increased gross growth efficiencies. Chla specific inorganic carbon uptake rates were reduced by 60–90% compared to that of the photosynthetic prey. Inorganic carbon uptake alone could not sustain survival of cultures and ciliate populations declined by 25–30% during 5 days of starvation. The results suggest that mixotrophy in Strombidium spp. may substantially bolster the efficiency of trophic transfer when biomass of small primary producers is low.

Growing evidence suggests that sexual reproduction might be common in unicellular organisms, but observations are sparse. Limited knowledge of sexual reproduction constrains understanding of protist ecology. Although Teleaulax amphioxeia and Plagioselmis prolonga are common marine cryptophytes worldwide, and are also important plastid donors for some kleptoplastic ciliates and dinoflagellates, the ecology and development of these protists are poorly known. We demonstrate that P. prolonga is the haploid form of the diploid T. amphioxeia and describe the seasonal dynamics of these two life stages. The diploid T. amphioxeia dominates during periods of high dissolved inorganic nitrogen (DIN) and low irradiance, temperature, and grazing (winter and early spring), whereas the haploid P. prolonga becomes more abundant during the summer, when DIN is low and irradiance, temperature, and grazing are high. Dimorphic sexual life cycles might explain the success of this species by fostering high genetic diversity and enabling endurance in adverse conditions.