扁形動物多岐腸類の成長と行動に関する研究

筑波大学 (University of Tsukuba)201

Put a tiger in your tank: the polyclad flatworm Maritigrella crozieri as a proposed model for evo-devo

Polyclad flatworms are an early branching clade within the rhabditophoran Platyhelminthes. They provide an interesting system with which to explore the evolution of development within Platyhelminthes and amongst Spiralia (Lophotrochozoa). Unlike most other flatworms, polyclads undergo spiral cleavage (similar to that seen in some other spiralian taxa), they are the only free-living flatworms where development via a larval stage occurs, and they are the only flatworms in which embryos can be reared outside of their protective egg case, enabling embryonic manipulations. Past work has focused on comparing early cleavage patterns and larval anatomy between polyclads and other spiralians. We have selected Maritigrella crozieri, the tiger flatworm, as a suitable polyclad species for developmental studies, because it is abundant and large in size compared to other species. These characteristics have facilitated the generation of a transcriptome from embryonic and larval material and are enabling us to develop methods for gene expression analysis and immunofluorescence techniques. Here we give an overview of M. crozieri and its development, we highlight the advantages and current limitations of this animal as a potential evo-devo model and discuss current lines of research

Systematics and taxonomy of polyclad flatworms with a special emphasis on the morphology of the nervous system

In a first survey of the Colombian polyclad fauna, a total of 25 species were collected from the rocky littoral of the Tayrona National Park, Santa Marta, Colombia and deposited at the Museo de Historia Natural Marina del INVEMAR. Six species represented first records for Caribbean region. Furthermore, a new combination Phrikoceros mopsus nov. comb, was proposed, and a possible new species of Pleioplana Faubel, 1983 was found. In addition, a new polyclad family Anocellidae was erected and four deep-sea species were described; two species from the North Pacific Ocean, Anocellidus profundus gen. nov. sp. nov. and Oligocladus voightae sp. nov., and two from the continental slope of the Gulf of Mexico, Oligocladus bathymodiensis sp. nov. and Didangia carneyi sp. nov. All except D. carneyi, were found in association with bivalves. The type material was deposited at the Field Museum of Natural History, Chicago, Illinois, USA. All taxonomic work was based on major external features and serial sagittal sections of the reproductive system. Finally, the central nervous systems (CNS) of 12 species of polyclad flatworms belonging to 11 families were examined using traditional light microscopic techniques. Even though some morphological features of the CNS probably were related to the body shape and behavior of the species, three categories could be established. These categories were based on the presence and development of globuli cell masses, the cross-sectional shape of the main nerve cords, and the tissue type surrounding the nerve cords. Well-developed globuli cell masses characterize all acotylean species examined. Furthermore, the cotylean Pericelis cata also had well-developed globuli cell masses, providing additional evidence of the close phylogenetic relationship of Pericelidae with the Acotylea. Cotylean polyclads on the other hand, exhibit only weakly developed globuli cell masses. Unique features of the CNS were found in Boninia divae which represent autapomorphies for the family and which can be linked to the behavior and body shape of this taxon. The presence of external globuli cells masses in some polyclads, forming structures similar to arthopod mushroom bodies, may be an indication of an early evolutionary adaptation

An Updated Checklist of Polyclads with a Note on the New Records to Indian Coastal Waters

Polyclads are free-living, exclusively marine and usually bottom dwellers. They are usually carnivorous. Field survey was carried out during November 2023 in Boria Island, Gujarat and February 2024 in Kavaratti Island, Lakshadweep West coast of India as part of the in-house programme of ZSI on the marine faunal exploration.  Snorkeling and scuba diving gear was used up to 5m depth and intertidal collections were also made in the study area. On perusal of literature and examining the species thoroughly two polyclad species i.e., Pseudobiceros sp. and Prosthiostomum sp. were found to be a new record for Indian coastal waters and and new record to Lakshdweep waters respectively. Based on the published literature, an attempt was made to prepare the checklist resulted 85 species under 08 family, 17 genera are reported from India so far.  Further exploration and understanding of polyclad diversity, their associates along the Indian coast may act as a useful indicator of overall marine bio diversity and reef habitat health

Oceanographic and biological influences on recruitment of benthic invertebrates to hard substrata on the Oregon shelf

Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Estuarine, Coastal and Shelf Science 208 (2018): 1-8, doi:10.1016/j.ecss.2018.04.037.The number of anthropogenic substrata in the ocean – structures like oil rigs and offshore renewable energy generators – is increasing. These structures provide hard-bottom habitat in areas previously dominated by sand or mud, so they have the potential to alter species distributions or serve as “stepping-stones” between other hard-bottom habitats. It is thus important to understand what factors influence the composition and abundance of benthic fauna recruiting at these sites. We examined recruitment to hard substrata (fouling panels) deployed on sand at various distances from a large rocky reef (~60 m isobath) on the southern Oregon coast in 2014 – 2015. Recruitment was dominated by the acorn barnacle Hesperibalanus hesperius. For the majority of the study period in 2014, an anti-cyclonic eddy was present near the deployment sites. However, anomalously high recruitment of H. hesperius during August – early October 2014 coincided with dissipation of the eddy, slower bottom currents, and a positive convergence index, suggesting that H. hesperius larvae from the adjacent area may have been accumulated and retained near our study sites. Other sessile species, including hydroids and bryozoans, recruited to the fouling panels in low abundances, and most of these species have long-range dispersal and fast growth. Mobile invertebrates observed on the fouling panels included gastropods and nudibranchs, most of which also have long-range dispersal and fast growth, and are predators as adults. Thus, a community with two trophic levels assembled on the fouling panels in a relatively short time period (<12 weeks). None of the common hard-bottom species from the adjacent rocky reef recruited to the panels, suggesting that there is a specialized assemblage of species that can exploit hard-bottom habitats surrounded by sandy plains. Our results raise many questions about the influences of dispersal and oceanographic conditions on recruitment to hard substrata.This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-0829517. YL is partially supported by the Dr. George Grice Postdoctoral Scholarship from Woods Hole Oceanographic Institution, with support from NSF grant #1634965

Polycladida biodiversity and systematics: an integrative approach

In face of the fact that marine biodiversity is highly threatened by human impacts on the environment, it is important to know what we want to protect. This thesis addresses the biodiversity and systematics of Polycladida, which are free-living Platyhelminthes with highly ramified intestine. Polylclads live in all types of marine environments whereas most areas of the world remain unsampled. From the around 1000 species considered valid many were described based on single or immature specimens and few have designated type material or specimens deposited in museums or research institutions. This is especially the case for Brazilian species that had no type material designated, labeled with codes in the publication or deposited. Characters used traditionally in polyclad taxonomy concern eyespots, type of pharynx, reproductive system, especially prostatic vesicle, but so far, those characters have not been tested against molecular evidence. The order Polycladida has two suborders, Cotylea and Acotylea, and their systematics is based on two conflictive classifications in use, which reflects inadequacy in characters choice. Molecular data from this group is still scarce and there is no morphological or molecular phylogeny that includes the whole order. Three gaps in knowledge are addressed in this work: biodiversity, type material and phylogeny with character evolution. Here I contribute to fill the first one by describing some new species, and by adding novel information, such as color photographs of living animals and microscopic observations to species that are already known. Samplings were made in some previously non-assessed areas in Brazil, Senegal and Cape Verde. One new species from each area is described and distribution ranges are discussed. The genus of the African species Pseudobiceros wirtzi is revised based on literature records. Additionally species associated to aquaculture were sampled for the first time in Brazil. To fill the second gap I studied species from Brazil described by Ernst Marcus and / or Eveline Du Bois-Reymond Marcus. Specimens donated by Eveline Marcus to the Swedish Museum of Natural History were analyzed and I recognized holotypes, paratypes, and designated lectotypes and paralectotypes, as required. Before this work began, most Brazilian species had unknown type material, whereas in this work type specimens of 52 species were designated or recognized. Out the 71 species reported from Brazil, ten remain without information about type material. 4 As a way to fill the third gap I present here a new and comprehensive set of partial 28S nuclear ribosomal DNA (rDNA) data across Polycladida families. Our phylogenetic analysis, despite being based only on a single molecular marker, is the first to test traditional morphology-based hypotheses on relationships inside the order. Remarkably, all our molecular trees were fully resolved and most nodes robustly supported. The overall topology is consistent with evidences from an updated and revised list of morphological and histological characters. Albeit largely congruent at genus and family level, our integrative phylogenetic hypothesis is not compatible with superfamilies and suborders of neither of the two conventional yet conflicting classification systems by Faubel and Prudhoe. The suborders Acotylea and Cotylea, as traditionally considered, were rejected in the hypothesis tests, thus the taxa were amended to reflect molecular monophyly. According to our trees, just two of Prudhoe’s and Faubel’s superfamilies were monophyletic; a novel concept of polyclad superfamily was thus proposed. Molecular results revealed that prominent characters used in previous classifications, such as the position of eyespots, the type of pharynx, and the type of prostatic vesicles were prone to homoplasy in both the Acotylea and the Cotylea branches. A novel scenario of morphological character evolution is suggested and the significance of certain features for taxonomy is discussed. Overall, samples from areas not previously sampled resulted in several new records for Brazil and two new species in this thesis, indicating the potential for future biodiversity exploration. The re-discovery of Ernst and Eveline Marcus’ type material is very important for both the contemporary and future study of Atlantic Polycladida. Our molecular results and its combination to morphological data is a unique effort in Polycladida phylogeny. Even though they are preliminary, the novel hypotheses and the data presented here provide a fresh baseline for future studies on Polycladida systematics

First records of Cotylea (Polycladida, Platyhelminthes) for the Atlantic coast of the Iberian Peninsula

A study of polyclad fauna of the Atlantic coast of the Iberian Peninsula was carried out from 2010 to 2013. The paper reports nine new records belonging to three Cotylean families: the family Euryleptidae Lang, 1884, Pseudocerotidae Lang, 1884 and the family Prosthiostomidae Lang, 1884, and describes one new species, Euryleptodes galikias sp. n. © Carolina Noreña et al.This study was supported by I+D Project grants CGL 2010–15786/BOS and CGL2011–29916, which are financed by the Spanish Ministry of Economy, and by the Spanish Agency for International Cooperation (AECI Project ref.: A/030038/10).Peer Reviewe

Fatal Canine Intoxications Linked to the Presence of Saxitoxins in Stranded Marine Organisms Following Winter Storm Activity.

At the start of 2018, multiple incidents of dog illnesses were reported following consumption of marine species washed up onto the beaches of eastern England after winter storms. Over a two-week period, nine confirmed illnesses including two canine deaths were recorded. Symptoms in the affected dogs included sickness, loss of motor control, and muscle paralysis. Samples of flatfish, starfish, and crab from the beaches in the affected areas were analysed for a suite of naturally occurring marine neurotoxins of dinoflagellate origin. Toxins causing paralytic shellfish poisoning (PSP) were detected and quantified using two independent chemical testing methods in samples of all three marine types, with concentrations over 14,000 µg saxitoxin (STX) eq/kg found in one starfish sample. Further evidence for PSP intoxication of the dogs was obtained with the positive identification of PSP toxins in a vomited crab sample from one deceased dog and in gastrointestinal samples collected post mortem from a second affected dog. Together, this is the first report providing evidence of starfish being implicated in a PSP intoxication case and the first report of PSP in canines

Comparative embryology and muscle development of polyclad flatworms (Platyhelminthes: Rhabditophora)

Polyclads belong to the phylum Platyhelminthes, lineage Rhabdotophora, are simple Bilateria, and represent an interesting and useful group for research in developmental biology. Although polyclads, together with catenulids and macrostomids, have been argued to be most closely related to the ancestral flatworm and hold the key to understand the relationship between development and evolution, knowledge of their embryonic development is still scarce and most of the work on spiralian development has focused on mollusks and annelids. In view of polyclad embryonic significance, a comparative study of their embryonic development including several species of direct and indirect developers was performed. Developing embryos of 16 species representing 10 families were examined and followed through embryogenesis until hatching. Considerable differences in egg plates, egg capsule morphology, size and number of eggs, and developmental time lines were found among the analyzed species. A correlation between developmental times and morphology of egg capsules was found; likewise it was possible to link larger eggs to direct developing species and longer developmental time and for most but not all, indirect developing species to smaller egg sizes. The number of eggs per egg capsule does not appear to be of systematic value, instead the morphology of the female reproductive system may play a significant role in determining the number of embryos per egg capsule. The influence of parental care on hatching success was also determined for two local species. Covering of egg masses by the adult was observed for individuals of both species and although this parental care is not necessary for egg development or hatching, it plays a significant role in the hatching success of Pleioplana atomata embryos. For individuals of Imogine zebra, parental covering of recently laid egg masses may play a role in egg capsule formation. In the polyclad Pericelis cata a case of developmental dimorphism was found. Larvae and juveniles from the same parent hatched simultaneously throughout the three-day hatching period. This represents the first case of true poecilogony reported for polyclad flatworms which may be a bet-hedging strategy in which benthic juveniles are recruited to the parental habitat, and concurrently, siblings disperse as larvae. The most notable feature of the development of P. cata was the unusual appearance of extra-embryonic yolk inside the egg capsules. Similarly, almost all the larvae of this species had only one eye, whereas three eyes characterize typical Muller\u27s and Gotte\u27s larvae. Understanding the origin of the muscular system may have implications for the understanding of bilaterian evolution. Hence, a comparative analysis of body wall formation and muscle organization during embryogenesis was performed. Fluorescent dye-conjugated phalloidin was used to characterize the musculature of Maritigrella crozieri and Melloplana ferruginea which represent an indirect and a direct developing species, respectively. In both species, the first myoblasts were localized in the periphery of the egg. Progressively, myoblasts formed unorganized and rudimentary muscle fibers that further differentiated during development. Muscle differentiation was similar between the two species; however, the process of muscle development progressed quite differently in larvae and juveniles. These results provide additional support that the orthogonal muscle pattern is a symplesiomorphy of Spiralia and it may have been present in the stem species of all Bilateria