We establish a new genus of planocerid polyclad, Heteroplanocera gen. nov., based on a new species, H. katoi sp. nov., collected at a depth of 245 m off the coast of the Izu Peninsula, West Pacific, Japan. Heteroplanocera gen. nov. is distinguished from other planocerid genera by the following characteristics: (i) a pair of nuchal tentacles, (ii) a muscular bulb, (iii) a pair of spermiducal bulbs (instead of a seminal vesicle), (iv) a free prostatic vesicle, (v) a pair of accessory organs with teeth, (vi) a Lang's vesicle, and (vii) the lack of a bursa copulatrix. We provide a partial sequence of the cytochrome c oxidase subunit I (COI) gene (712 bp) as a DNA barcode of the new species. Furthermore, we estimate the phylogenetic position of Heteroplanocera gen. nov. among Planoceridae based on partial sequences of COI and 16S, 18S, and 28S ribosomal DNA. Based on our findings, we discuss the evolution and function of the (i) vaginal cuticularized structure and (ii) accessory organs among planocerid flatworms.

Invertebrates living in underground environments often have unusual and sometimes unique adaptations and occupy narrow ranges, but there is a lack of knowledge about most micro-endemic cave-dwelling invertebrate species. An illustrative case is that of the flatworm Dendrocoelum italicum, the first survey of which was performed 79 years after its description. The survey revealed that the underground stream supplying water to the pool from which the species was first described had been diverted into a pipe for human use, thus severely reducing the available habitat for the species. Here we describe the results of what we believe is the first habitat restoration action performed in a cave habitat for the conservation of a flatworm. The water-diverting structure was removed, with the involvement of local protected area administrators, citizens and volunteers from local organizations. The intervention resulted in the restoration of a large, stable pool inside the cave, thus creating an optimal habitat for this threatened planarian, with increased availability of prey and a stable population. This report of habitat restoration for a neglected invertebrate offers insights for the protection of other micro-endemic species.

A new final fish host (Stromateus brasiliensis) for the digenean parasite Monascus filiformis from the continental shelf of Patagonia Argentina in the South-western Atlantic Ocean is reported. This demersal-pelagic fish (commonly denominated pampanito) is exclusively a jellyfish consumer. It is well known that larval stages of Monascus filiformis mostly use medusae as secondary hosts. Therefore, the pampanito likely acquires this parasite when it predates upon some species of parasitized medusae in the area. This work improves the knowledge about the final hosts of this parasite and infers which species of medusa may be involved in their life cycle.

Clarification of the life-history traits of a symbiont and its host is necessary to evaluate the relationship between them. Stylochoplana pusilla, a polyclad, inhabits the mantle cavity of the eulittoral snail Monodonta labio. This study elucidated the life-history traits of S. pusilla relative to those of M. labio in a tide pool, which retained seawater, and a boulder shore, which was dry at low tide, in Mutsu Bay, northern Japan, from 2010 to 2012. In these habitats, S. pusilla was semelparous with a 1-year life cycle; it reproduced in midsummer and inhabited the shell of M. labio except for the early juvenile stages, which were planktonic. More juvenile S. pusilla newly settled on hosts in the tide pool than on the boulder shore, however, their survival rate was higher on the boulder shore compared with the tide pool. The growth rate of juvenile S. pusilla was higher in the tide pool than on the boulder shore. The higher growth rate of S. pusilla at the tide pool suggested that they were more actively feeding. Stable isotope analysis showed that S. pusilla acquired food resources outside the host snail both in the tide pool and on the boulder shore. Thus, it was likely that S. pusilla engaged in feeding outside the host snails but resulted in lower survival rates at the tide pool. These results suggest that S. pusilla is semi-free living and uses M. labio as a refuge in the eulittoral zone for protection against desiccation.

Six new records of hydromedusae are reported as secondary hosts of Opechona sp. (Lepocreadiidae) for the Brazilian coast. Among the 392 hydromedusae sampled, 43 (~11%) were harbouring metacercaria. Prevalence (P) and intensity of infection (I) of Opechona sp. varied considerably among the different host species. Gossea brachymera (Limnomedusae) was highly parasitized (P = 30%; I = 1–7), while the other five hydromedusae species were not (P = 1.5–10; I = 1–2). The high parasitism in G. brachymera suggests the importance of this species in the transmission of Opechona sp. to fish, the definitive hosts, and highlights the hydromedusae as a probable noteworthy food item for zooplanktivorous fish in the area.

Six species of polyclads Pseudobiceros damawan, Pseudobiceros flavocanthus, Pseudoceros bifurcus, Pseudoceros concinnus, Pseudoceros gamblei and Pseudoceros goslineri are newly reported from Andaman and Nicobar Islands of India. Not only do all recorded species constitute first records for the Andaman coast of India, but except for Pseudoceros gamblei, all species are new to Indian waters.

Selfing has been considered the most common mode of reproduction in Echinococcus flatworms. However, population genetic studies on the asexual larval stage involving nuclear co-dominant markers have not always revealed significant heterozygote deficiencies – the expected outcome of a regularly and highly inbred population. In this study, we analysed the genetic structure of Echinococcus granulosus sensu lato populations from Southern Brazil during their adult (sexual) stage using 1 mitochondrial and 1 nuclear marker (cox 1 and mdh, respectively). We show that parasite genetic differentiation is largest among definitive hosts (domestic dogs) from different farms, suggesting that transmission is mostly maintained within a farm. Moreover, we show that heterozygote deficiencies are not significant, and we suggest that outbreeding is the most common mode of reproduction of the parasite in that region.

Pseudoceros bicolor and Pericelis cata, species of the turbellarian order Polycladida previously listed for regions of the Caribbean Sea, are here recorded for the first time from Brazil. This is also the first record of the genus Pericelis from Brazil. The morphology of the specimens is described and photographs of living forms are given. The present records expand the known geographical range of both species to a transition zone between tropical and subtropical environments.

The mechanism whereby praziquantel produces a contraction and subsequent flaccid paralysis (a loss of sensitivity to subsequent stimuli) of Schistosoma mansoni in a medium containing an elevated Mg2+:Ca2+ ratio was investigated. In RPMI, praziquantel produced a concentration-dependent tonic contraction of the parasite with an EC50 of 200 nM. Magnesium inhibited the contraction in such a manner as to convert the tonic contraction to a phasic one without altering the peak force generated. The Mg2+-dependent block was non-competitive with praziquantel but was competitive with extracellular Ca2+, ratios of 7·5:1; Mg2+: Ca2+ being needed to inhibit the tonic contraction and to induce flaccid paralysis. Flaccid paralysis was associated with a reduced ability of the parasite to take up 45Ca2+ from the bath compared to parasites that had not entered into flaccid paralysis and flaccid paralysis was reversible. Recovery from flaccid paralysis was accelerated by treatments that are expected to increase Ca2+ uptake by the parasite. At a concentration of 500 nM, praziquantel produced 2 distinct phasic contractions in intact parasites incubated in an elevated [Mg2+] medium but only 1 phasic contraction in parasites lacking their surface tegumental membranes. In zero Ca2+ I-RPMI, 10 μM praziquantel produced a phasic contraction of intact parasites but did not stimulate contraction of detegumented parasites until Ca2+ was reintroduced into the bath. These results indicate that praziquantel interacts with specific Ca2+-permeable sites in the tegumental and sarcoplasmic membranes of the parasite and that under these conditions of elevated Mg2+:Ca2+ ratios, these sites become blocked by Mg2+, leading to flaccid paralysis of the parasite.