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Asai M, Miyazawa H, Yanase R, Inaba K, Nakano H. A New Species of Acoela Possessing a Middorsal Appendage with a Possible Sensory Function. Zoolog Sci 2022; 39:147-156. [DOI: 10.2108/zs210058] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2021] [Accepted: 11/03/2021] [Indexed: 11/17/2022]
Affiliation(s)
- Masashi Asai
- Shimoda Marine Research Center, University of Tsukuba, 5-10-1, Shimoda, Shizuoka, 415-0025, Japan
| | - Hideyuki Miyazawa
- Shimoda Marine Research Center, University of Tsukuba, 5-10-1, Shimoda, Shizuoka, 415-0025, Japan
| | - Ryuji Yanase
- Shimoda Marine Research Center, University of Tsukuba, 5-10-1, Shimoda, Shizuoka, 415-0025, Japan
| | - Kazuo Inaba
- Shimoda Marine Research Center, University of Tsukuba, 5-10-1, Shimoda, Shizuoka, 415-0025, Japan
| | - Hiroaki Nakano
- Shimoda Marine Research Center, University of Tsukuba, 5-10-1, Shimoda, Shizuoka, 415-0025, Japan
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Atherton S, Jondelius U. Phylogenetic assessment and systematic revision of the acoel family Isodiametridae. Zool J Linn Soc 2021. [DOI: 10.1093/zoolinnean/zlab050] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Abstract
Isodiametridae is a large family of Acoela with 22 nominal genera and nearly 100 species. Unfortunately, systematics of Isodiametridae, as it stands, is highly problematic. Genera frequently have been proposed without reference to an explicit phylogenetic hypothesis, such that the current classification system holds little or no predictive power. Many taxa do not fit with the family diagnosis, and it is increasingly difficult to determine in which taxon a new species should be described. Herein, we reconstruct the phylogenetic relationships of Acoela with a focus on Isodiametridae using both previously published and new ribosomal and mitochondrial sequence data. Our dataset comprises sequences from 45 species representing 16 of the 22 isodiametrid genera. Our results recovered a well-supported Isodiametridae, but provided further evidence that the family and several genera within require revision. We have updated the classification system of Isodiametridae to be consistent with its phylogeny, including the transference of Otocelis to Otocelididae, Postaphanostoma and Faerlea to Mecynostomidae and Alluna to Actinoposthiidae. Six other genera are placed in synonymy. We review the morphological taxonomy and provide an identification key of the genera in the revised family.
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Affiliation(s)
- Sarah Atherton
- Department of Zoology, Naturhistoriska riksmuseet, Stockholm, Sweden
| | - Ulf Jondelius
- Department of Zoology, Naturhistoriska riksmuseet, Stockholm, Sweden
- Department of Zoology, Systematics and Evolution, Stockholm Universitet, Stockholm, Sweden
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Ultrastructure of spermatozoa and female copulatory organs in preferably asexually-reproducing acoel Convolutriloba retrogemma (Acoelomorpha). ZOOMORPHOLOGY 2020. [DOI: 10.1007/s00435-020-00505-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Haszprunar G. Review of data for a morphological look on Xenacoelomorpha (Bilateria incertae sedis). ORG DIVERS EVOL 2015. [DOI: 10.1007/s13127-015-0249-z] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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Cooper C, Clode PL, Thomson DP, Stat M. A Flatworm from the GenusWaminoa(Acoela: Convolutidae) Associated with Bleached Corals in Western Australia. Zoolog Sci 2015; 32:465-73. [DOI: 10.2108/zs140245] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Perea-Atienza E, Botta M, Salvenmoser W, Gschwentner R, Egger B, Kristof A, Martinez P, Achatz JG. Posterior regeneration in Isodiametra pulchra (Acoela, Acoelomorpha). Front Zool 2013; 10:64. [PMID: 24160844 PMCID: PMC3816570 DOI: 10.1186/1742-9994-10-64] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Accepted: 10/17/2013] [Indexed: 01/30/2023] Open
Abstract
INTRODUCTION Regeneration is a widespread phenomenon in the animal kingdom, but the capacity to restore damaged or missing tissue varies greatly between different phyla and even within the same phylum. However, the distantly related Acoelomorpha and Platyhelminthes share a strikingly similar stem-cell system and regenerative capacity. Therefore, comparing the underlying mechanisms in these two phyla paves the way for an increased understanding of the evolution of this developmental process.To date, Isodiametra pulchra is the most promising candidate as a model for the Acoelomorpha, as it reproduces steadily under laboratory conditions and is amenable to various techniques, including the silencing of gene expression by RNAi. In order to provide an essential framework for future studies, we report the succession of regeneration events via the use of cytochemical, histological and microscopy techniques, and specify the total number of cells in adult individuals. RESULTS Isodiametra pulchra is not capable of regenerating a new head, but completely restores all posterior structures within 10 days. Following amputation, the wound closes via the contraction of local muscle fibres and an extension of the dorsal epidermis. Subsequently, stem cells and differentiating cells invade the wound area and form a loosely delimited blastema. After two days, the posterior end is re-patterned with the male (and occasionally the female) genital primordium being apparent. Successively, these primordia differentiate into complete copulatory organs. The size of the body and also of the male and female copulatory organs, as well as the distance between the copulatory organs, progressively increase and by nine days copulation is possible. Adult individuals with an average length of 670 μm consist of approximately 8100 cells. CONCLUSION Isodiametra pulchra regenerates through a combination of morphallactic and epimorphic processes. Existing structures are "re-modelled" and provide a framework onto which newly differentiating cells are added. Growth proceeds through the intercalary addition of structures, mirroring the embryonic and post-embryonic development of various organ systems. The suitability of Isodiametra pulchra for laboratory techniques, the fact that its transcriptome and genome data will soon be available, as well as its small size and low number of cells, make it a prime candidate subject for research into the cellular mechanisms that underlie regeneration in acoelomorphs.
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Affiliation(s)
- Elena Perea-Atienza
- Department of Genetics, University of Barcelona, Av. Diagonal 643, edifici annex, planta 2a, 08028 Barcelona, Spain
| | - Maria Botta
- Department of Evolutionary Developmental Biology, University of Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria
| | - Willi Salvenmoser
- Department of Evolutionary Developmental Biology, University of Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria
| | - Robert Gschwentner
- Department of Evolutionary Developmental Biology, University of Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria
| | - Bernhard Egger
- Department of Evolutionary Developmental Biology, University of Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria
- Department of Genetics, Evolution and Environment, University College London, Darwin Building, Gower Street, London WC1E 6BT, UK
| | - Alen Kristof
- Department of Integrative Zoology, University of Vienna, Althanstrasse 14, UZA 1, 1090 Vienna, Austria
| | - Pedro Martinez
- Department of Genetics, University of Barcelona, Av. Diagonal 643, edifici annex, planta 2a, 08028 Barcelona, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig Lluís Companys 23, 08010 Barcelona, Spain
| | - Johannes Georg Achatz
- Department of Genetics, University of Barcelona, Av. Diagonal 643, edifici annex, planta 2a, 08028 Barcelona, Spain
- Department of Evolutionary Developmental Biology, University of Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria
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Achatz JG, Martinez P. The nervous system of Isodiametra pulchra (Acoela) with a discussion on the neuroanatomy of the Xenacoelomorpha and its evolutionary implications. Front Zool 2012; 9:27. [PMID: 23072457 PMCID: PMC3488495 DOI: 10.1186/1742-9994-9-27] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2012] [Accepted: 10/09/2012] [Indexed: 12/21/2022] Open
Abstract
Introduction Acoels are microscopic marine worms that have become the focus of renewed debate and research due to their placement at the base of the Bilateria by molecular phylogenies. To date, Isodiametra pulchra is the most promising “model acoel” as it can be cultured and gene knockdown can be performed with double-stranded RNA. Despite its well-known morphology data on the nervous system are scarce. Therefore we examined this organ using various microscopic techniques, including histology, conventional histochemistry, electron microscopy, and immunocytochemistry in combination with CLSM and discuss our results in light of recently established phylogenies. Results The nervous system of Isodiametra pulchra consists of a bilobed brain with a dorsal posterior commissure, a frontal ring and tracts, four pairs of longitudinal neurite bundles, as well as a supramuscular and submuscular plexus. Serotonin-like immunoreactivity (SLI) is displayed in parts of the brain, the longitudinal neurite bundles and a large part of the supramuscular plexus, while FMRFamide-like immunoreactivity (RFLI) is displayed in parts of the brain and a distinct set of neurons, the longitudinal neurite bundles and the submuscular plexus. Despite this overlap SLI and RFLI are never colocalized. Most remarkable though is the presence of a distinct functional neuro-muscular system consisting of the statocyst, tracts, motor neurons and inner muscles, as well as the presence of various muscles that differ with regard to their ultrastructure and innervation. Conclusions The nervous system of Isodiametra pulchra consists of an insunk, bilobed brain, a peripheral part for perception and innervation of the smooth body-wall musculature as well as tracts and motor neurons that together with pseudostriated inner muscles are responsible for steering and quick movements. The insunk, bilobed brains with two to three commissures found in numerous acoels are homologous and evolved from a ring-commissural brain that was present in the stem species of acoelomorphs. The acoelomorph brain is bipartite, consisting of a Six3/6-dependend animal pole nervous system that persists throughout adulthood and an axial nervous system that does not develop by exhibiting a staggered pattern of conserved regulatory genes as in other bilaterians but by a nested pattern of these genes. This indicates that acoelomorphs stem from an ancestor with a simple brain or with a biphasic life cycle.
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Affiliation(s)
- Johannes Georg Achatz
- Department of Evolutionary Developmental Biology, University of Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria.
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Achatz JG, Chiodin M, Salvenmoser W, Tyler S, Martinez P. The Acoela: on their kind and kinships, especially with nemertodermatids and xenoturbellids (Bilateria incertae sedis). ORG DIVERS EVOL 2012; 13:267-286. [PMID: 24098090 PMCID: PMC3789126 DOI: 10.1007/s13127-012-0112-4] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Acoels are among the simplest worms and therefore have often been pivotal in discussions of the origin of the Bilateria. Initially thought primitive because of their “planula-like” morphology, including their lumenless digestive system, they were subsequently dismissed by many morphologists as a specialized clade of the Platyhelminthes. However, since molecular phylogenies placed them outside the Platyhelminthes and outside all other phyla at the base of the Bilateria, they became the focus of renewed debate and research. We review what is currently known of acoels, including information regarding their morphology, development, systematics, and phylogenetic relationships, and put some of these topics in a historical perspective to show how the application of new methods contributed to the progress in understanding these animals. Taking all available data into consideration, clear-cut conclusions cannot be made; however, in our view it becomes successively clearer that acoelomorphs are a “basal” but “divergent” branch of the Bilateria.
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Affiliation(s)
- Johannes G. Achatz
- Department of Genetics, University of Barcelona, Av. Diagonal, edifici annex, planta 2a, 08028 Barcelona, Spain
- Department of Evolutionary Developmental Biology, University of Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria
| | - Marta Chiodin
- Department of Genetics, University of Barcelona, Av. Diagonal, edifici annex, planta 2a, 08028 Barcelona, Spain
| | - Willi Salvenmoser
- Department of Evolutionary Developmental Biology, University of Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria
| | - Seth Tyler
- School of Biology and Ecology, University of Maine, 5751 Murray Hall, Orono, ME 04469 USA
| | - Pedro Martinez
- Department of Genetics, University of Barcelona, Av. Diagonal, edifici annex, planta 2a, 08028 Barcelona, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig Lluís Companys, 23, 08010 Barcelona, Spain
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Boone M, Willems M, Claeys M, Artois T. Spermatogenesis and the structure of the testes in Isodiametra pulchra (Isodiametridae, Acoela). ACTA ZOOL-STOCKHOLM 2010. [DOI: 10.1111/j.1463-6395.2010.00481.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Achatz JG, Hooge M, Wallberg A, Jondelius U, Tyler S. Systematic revision of acoels with 9+0 sperm ultrastructure (Convolutida) and the influence of sexual conflict on morphology. J ZOOL SYST EVOL RES 2010. [DOI: 10.1111/j.1439-0469.2009.00555.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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Semmler H, Bailly X, Wanninger A. Myogenesis in the basal bilaterian Symsagittifera roscoffensis (Acoela). Front Zool 2008; 5:14. [PMID: 18803837 PMCID: PMC2562460 DOI: 10.1186/1742-9994-5-14] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2008] [Accepted: 09/19/2008] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND In order to increase the weak database concerning the organogenesis of Acoela - a clade regarded by many as the earliest extant offshoot of Bilateria and thus of particular interest for studies concerning the evolution of animal bodyplans - we analyzed the development of the musculature of Symsagittifera roscoffensis using F-actin labelling, confocal laserscanning microscopy, and 3D reconstruction software. RESULTS At 40% of development between egg deposition and hatching short subepidermal fibres form. Muscle fibre development in the anterior body half precedes myogenesis in the posterior half. At 42% of development a grid of outer circular and inner longitudinal muscles is present in the bodywall. New circular muscles either branch off from present fibres or form adjacent to existing ones. The number of circular muscles is higher than that of the longitudinal muscles throughout all life cycle stages. Diagonal, circular and longitudinal muscles are initially rare but their number increases with time. The ventral side bears U-shaped muscles around the mouth, which in addition is surrounded by a sphincter muscle. With the exception of the region of the statocyst, dorsoventral muscles are present along the entire body of juveniles and adults, while adults additionally exhibit radially oriented internal muscles in the anterior tip. Outer diagonal muscles are present at the dorsal anterior tip of the adult. In adult animals, the male gonopore with its associated sexual organs expresses distinct muscles. No specific statocyst muscles were found. The muscle mantles of the needle-shaped sagittocysts are situated along the lateral edges of the animal and in the posterior end close to the male gonopore. In both juveniles and adults, non-muscular filaments, which stain positively for F-actin, are associated with certain sensory cells outside the bodywall musculature. CONCLUSION Compared to the myoanatomy of other acoel taxa, Symsagittifera roscoffensis shows a very complex musculature. Although data on presumably basal acoel clades are still scarce, the information currently available suggests an elaborated musculature with longitudinal, circular and U-shaped muscles as being part of the ancestral acoel bodyplan, thus increasing the possibility that Urbilateria likewise had a relatively complicated muscular ground pattern.
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Affiliation(s)
- Henrike Semmler
- University of Copenhagen, Department of Biology, Research Group for Comparative Zoology, Universitetsparken 15, DK-2100 Copenhagen Ø, Denmark.
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