RESUMEN
Diverse and extensive macrofouling of the left-hand (eyed) side has been observed in multiple films and photographs of different specimens of Eckström's topknot Zeugopterus regius. Identified foulers include macroalgae and tunicates. Photographs of unfouled specimens and preserved juveniles have also been inspected. Macrofouling is not universal in this species; unfouled fish were observed around the strongly tidal British Isles, whereas the worst-fouled topknots were seen in the eutrophic, microtidal northern Adriatic.
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Incrustaciones Biológicas , Animales , Peces Planos , Algas Marinas , Urocordados/anatomía & histologíaRESUMEN
The vertebrate intestinal system consists of separate segments that remarkably differ in morphology and function. However, the origin of intestinal segmentation remains unclear. In this study, we investigated the segmentation of the intestine in a tunicate ascidian species, Ciona savignyi, by performing RNA sequencing. The gene expression profiles showed that the whole intestine was separated into three segments. Digestion, ion transport and signal transduction, and immune-related pathway genes were enriched in the proximal, middle, and distal parts of the intestine, respectively, implying that digestion, absorption, and immune function appear to be regional specializations in the ascidian intestine. We further performed a multi-species comparison analysis and found that the Ciona intestine showed a similar gene expression pattern to vertebrates, indicating tunicates and vertebrates might share the conserved intestinal functions. Intriguingly, vertebrate pancreatic homologous genes were expressed in the digestive segment of the Ciona intestine, suggesting that the proximal intestine might play the part of pancreatic functions in C. savignyi. Our results demonstrate that the tunicate intestine can be functionally separated into three distinct segments, which are comparable to the corresponding regions of the vertebrate intestinal system, offering insights into the functional evolution of the digestive system in chordates.
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Intestinos , Urocordados , Intestinos/anatomía & histología , Intestinos/metabolismo , Intestinos/fisiología , Urocordados/anatomía & histología , Urocordados/genética , Urocordados/fisiología , Animales , Perfilación de la Expresión Génica , Evolución BiológicaRESUMEN
AbstractColonial animals are composed of clonal individuals that remain physically connected and physiologically integrated. Salps are tunicates with a dual life cycle, including an asexual solitary stage that buds sexual colonies composed of jet-propelling zooids that efficiently swim together as a single unit by multijet propulsion. Colonies from different species develop distinct architectures characterized by their zooid arrangement patterns, but this diversity has received little attention. Thus, these architectures have never been formally defined using a framework of variables and axes that would allow comparative analyses. We set out to define an ontology of the salp colony architecture morphospace and describe the developmental pathways that build the different architectures. To inform these definitions, we collected and photographed live specimens of adult and developing colonies through offshore scuba diving. Since all salp colonies begin their development as a transversal double chain, we characterized each adult colonial architecture as a series of developmental transitions, such as rotations and translations of zooids, relative to their orientation at this early shared stage. We hypothesize that all adult architectures are either final or intermediate stages within three developmental pathways toward bipinnate, cluster, or helical forms. This framework will enable comparative studies on the biomechanical implications, ecological functions, evolutionary history, and engineering applications of the diversity of salp colony architectures.
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Urocordados , Animales , Urocordados/crecimiento & desarrollo , Urocordados/fisiología , Urocordados/anatomía & histología , Estadios del Ciclo de Vida/fisiología , Ontologías BiológicasRESUMEN
Two expeditions EXBODI (2011) and SPANBIOS (2021) sampled the invertebrate fauna of deep bottoms on each side of New Caledonia. Many ascidians were collected and the most part are already known species. Among the 13 species described and figured, two are new to science. All have typical characters of a deep habitat. Variability of the internal anatomy is described for abundant specimens of the same species from the same location. There is no concordance with the littoral ascidian fauna.
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Expediciones , Urocordados , Animales , Urocordados/anatomía & histología , Nueva Caledonia , Invertebrados , EcosistemaRESUMEN
A central question in chordate evolution is the origin of sessility in adult ascidians, and whether the appendicularian complete free-living style represents a primitive or derived condition among tunicates1. According to the 'a new heart for a new head' hypothesis, the evolution of the cardiopharyngeal gene regulatory network appears as a pivotal aspect to understand the evolution of the lifestyles of chordates2-4. Here we show that appendicularians experienced massive ancestral losses of cardiopharyngeal genes and subfunctions, leading to the 'deconstruction' of two ancestral modules of the tunicate cardiopharyngeal gene regulatory network. In ascidians, these modules are related to early and late multipotency, which is involved in lineage cell-fate determination towards the first and second heart fields and siphon muscles. Our work shows that the deconstruction of the cardiopharyngeal gene regulatory network involved the regressive loss of the siphon muscle, supporting an evolutionary scenario in which ancestral tunicates had a sessile ascidian-like adult lifestyle. In agreement with this scenario, our findings also suggest that this deconstruction contributed to the acceleration of cardiogenesis and the redesign of the heart into an open-wide laminar structure in appendicularians as evolutionary adaptations during their transition to a complete pelagic free-living style upon the innovation of the food-filtering house5.
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Evolución Biológica , Corazón/anatomía & histología , Corazón/crecimiento & desarrollo , Urocordados/anatomía & histología , Urocordados/fisiología , Animales , Linaje de la Célula , Redes Reguladoras de Genes , Locomoción , Miocardio/citología , Miocardio/metabolismo , Urocordados/citología , Urocordados/genéticaRESUMEN
The endostyle is a ventral pharyngeal organ used for internal filter feeding of basal chordates and is considered homologous to the follicular thyroid of vertebrates. It contains mucus-producing (glandular) and thyroid-equivalent regions organized along the dorsoventral (DV) axis. Although thyroid-related genes (Nkx2-1, FoxE, and thyroid peroxidase (TPO)) are known to be expressed in the endostyle, their roles in establishing regionalization within the organ have not been demonstrated. We report that Nkx2-1 and FoxE are essential for establishing DV axial identity in the endostyle of Oikopleura dioica. Genome and expression analyses showed von Willebrand factor-like (vWFL) and TPO/dual oxidase (Duox)/Nkx2-1/FoxE as orthologs of glandular and thyroid-related genes, respectively. Knockdown experiments showed that Nkx2-1 is necessary for the expression of glandular and thyroid-related genes, whereas FoxE is necessary only for thyroid-related genes. Moreover, Nkx2-1 expression is necessary for FoxE expression in larvae during organogenesis. The results demonstrate the essential roles of Nkx2-1 and FoxE in establishing regionalization in the endostyle, including (1) the Nkx2-1-dependent glandular region, and (2) the Nkx2-1/FoxE-dependent thyroid-equivalent region. DV axial regionalization may be responsible for organizing glandular and thyroid-equivalent traits of the pharynx along the DV axis.
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Factores de Transcripción Forkhead/fisiología , Hormonas Tiroideas/fisiología , Factor Nuclear Tiroideo 1/fisiología , Urocordados/embriología , Animales , Moco , Glándula Tiroides/embriología , Glándula Tiroides/fisiología , Urocordados/anatomía & histología , Urocordados/fisiologíaRESUMEN
Ascidians are invertebrate chordates, with swimming chordate tadpole larvae that have distinct heads and tails. The head contains the small brain, sensory organs, including the ocellus (light) and otolith (gravity) and the presumptive endoderm, while the tail has a notochord surrounded by muscle cells and a dorsal nerve cord. One of the chordate features is a post-anal tail. Ascidian tadpoles are nonfeeding, and their tails are critical for larval locomotion. After hatching the larvae swim up toward light and are carried by the tide and ocean currents. When competent to settle, ascidian tadpole larvae swim down, away from light, to settle and metamorphose into a sessile adult. Tunicates are classified as chordates because of their chordate tadpole larvae; in contrast, the sessile adult has a U-shaped gut and very derived body plan, looking nothing like a chordate. There is one group of ascidians, the Molgulidae, where many species are known to have tailless larvae. The Swalla Lab has been studying the evolution of tailless ascidian larvae in this clade for over 30 years and has shown that tailless larvae have evolved independently several times in this clade. Comparison of the genomes of two closely related species, the tailed Molgula oculata and tailless Molgula occulta reveals much synteny, but there have been multiple insertions and deletions that have disrupted larval genes in the tailless species. Genomics and transcriptomics have previously shown that there are pseudogenes expressed in the tailless embryos, suggesting that the partial rescue of tailed features in their hybrid larvae is due to the expression of intact genes from the tailed parent. Yet surprisingly, we find that the notochord gene regulatory network is mostly intact in the tailless M. occulta, although the notochord does not converge and extend and remains as an aggregate of cells we call the "notoball." We expect that eventually many of the larval gene networks will become evolutionarily lost in tailless ascidians and the larval body plan abandoned, with eggs developing directly into an adult. Here we review the current evolutionary and developmental evidence on how the molgulids lost their tails.
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Evolución Biológica , Larva/anatomía & histología , Cola (estructura animal) , Urocordados , Animales , Notocorda , Urocordados/anatomía & histologíaRESUMEN
Ascidians (Phylum Chordata, Class Ascidiacea) are a large group of invertebrates which occupy a central role in the ecology of marine benthic communities. Many ascidian species have become successfully introduced around the world via anthropogenic vectors. The botryllid ascidians (Order Stolidobranchia, Family Styelidae) are a group of 53 colonial species, several of which are widespread throughout temperate or tropical and subtropical waters. However, the systematics and biology of this group of ascidians is not well-understood. To provide a systematic framework for this group, we have constructed a well-resolved phylogenomic tree using 200 novel loci and 55 specimens. A Principal Components Analysis of all species described in the literature using 31 taxonomic characteristics revealed that some species occupy a unique morphological space and can be easily identified using characteristics of adult colonies. For other species, additional information such as larval or life history characteristics may be required for taxonomic discrimination. Molecular barcodes are critical for guiding the delineation of morphologically similar species in this group.
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Filogenia , Urocordados/anatomía & histología , Urocordados/genética , Animales , Código de Barras del ADN Taxonómico , Estadios del Ciclo de Vida , Biología Marina , Especificidad de la Especie , Clima Tropical , Urocordados/clasificación , Urocordados/fisiologíaRESUMEN
The larvacean Oikopleura dioica is a planktonic chordate and an emerging model organism with a short life cycle of 5 days that belongs toTunicata (Urochordata), the sister clade of vertebrates. It is characterized by the rapid development of a tadpole-shaped body. Organ formation in the trunk proceeds within 7 h after the hatching of the tailbud larvae at 3 h after fertilization (hpf) and is completed at 10 hpf, giving rise to fully functional juveniles as miniature adult form. Serial block face scanning electron microscopy was used to acquire ~ 2000 serial transverse section images of a 3 hpf larva and a 10 hpf juvenile to characterize the structures and cellular composition of the trunk and organs using 3D images and movies. Germ cells were found to fuse and establish a central syncytial cell in the gonad as early as 10 hpf. Larval development gave rise to functional organs after several rounds of cell division through trunk morphogenesis. The feature would make O. dioica ideal for analyzing cellular behaviors during morphogenetic processes using live imaging. The detailed descriptions of the larvae and juveniles provided in this study can be utilized as the start and end points of organ morphogenesis in this rapidly developing organism.
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Imagenología Tridimensional , Urocordados/anatomía & histología , Urocordados/fisiología , Animales , Larva/anatomía & histología , Larva/fisiologíaRESUMEN
The Origin of Chordates has fascinated scientists from the time of Charles Darwin's publication "Descent of Man" in 1871. For over 100 years, it was accepted that chordates evolved from tunicates, our sessile invertebrate sister group. However, genomic and embryonic analyses have shown that lancelets have a body plan and genome much more like vertebrates than do tunicates. In 2000, we proposed a worm-like hypothesis of chordate origins, and genomic and embryonic studies in the past 20 years have supported this hypothesis. This hypothesis contends that the deuterostome ancestor was worm-like, with gill slits, very much like a chordate. In contrast, tunicates have a very derived adult body plan that evolved independently. Here, we review the current understanding of deuterostome phylogeny and supporting evidence for the relationships within each phylum. Then we discuss our hypothesis for chordate origins and evidence to support it. We explore some of the evolutionary changes that ascidians have made to their adult body plan and some of the key gene regulatory networks that have been elucidated in Ciona. Finally, we end with insights that we have gained from studying tailless ascidians for the past 30 years. We've found that differentiation genes, at the end of the gene regulatory networks, become pseudogenes and nonfunctional, even though they are still expressed in tailless ascidians. We expect that eventually these pseudogenes will not be expressed and the ascidian larval body plan is abandoned, leaving the embryo to develop directly into an adult.
Asunto(s)
Evolución Biológica , Urocordados , Vertebrados , Animales , Cordados no Vertebrados/genética , Ciona/genética , Embrión no Mamífero , Regulación del Desarrollo de la Expresión Génica , Redes Reguladoras de Genes , Filogenia , Seudogenes , Urocordados/anatomía & histología , Urocordados/embriología , Urocordados/genéticaRESUMEN
Ciona robusta (Ciona intestinalis type A), a model organism for biological studies, belongs to ascidians, the main class of tunicates, which are the closest relatives of vertebrates. In Ciona, a project on the ontology of both development and anatomy is ongoing for several years. Its goal is to standardize a resource relating each anatomical structure to developmental stages. Today, the ontology is codified until the hatching larva stage. Here, we present its extension throughout the swimming larva stages, the metamorphosis, until the juvenile stages. For standardizing the developmental ontology, we acquired different time-lapse movies, confocal microscope images and histological serial section images for each developmental event from the hatching larva stage (17.5 h post fertilization) to the juvenile stage (7 days post fertilization). Combining these data, we defined 12 new distinct developmental stages (from Stage 26 to Stage 37), in addition to the previously defined 26 stages, referred to embryonic development. The new stages were grouped into four Periods named: Adhesion, Tail Absorption, Body Axis Rotation, and Juvenile. To build the anatomical ontology, 203 anatomical entities were identified, defined according to the literature, and annotated, taking advantage from the high resolution and the complementary information obtained from confocal microscopy and histology. The ontology describes the anatomical entities in hierarchical levels, from the cell level (cell lineage) to the tissue/organ level. Comparing the number of entities during development, we found two rounds on entity increase: in addition to the one occurring after fertilization, there is a second one during the Body Axis Rotation Period, when juvenile structures appear. Vice versa, one-third of anatomical entities associated with the embryo/larval life were significantly reduced at the beginning of metamorphosis. Data was finally integrated within the web-based resource "TunicAnatO", which includes a number of anatomical images and a dictionary with synonyms. This ontology will allow the standardization of data underpinning an accurate annotation of gene expression and the comprehension of mechanisms of differentiation. It will help in understanding the emergence of elaborated structures during both embryogenesis and metamorphosis, shedding light on tissue degeneration and differentiation occurring at metamorphosis.
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Desarrollo Embrionario/fisiología , Larva/anatomía & histología , Larva/crecimiento & desarrollo , Metamorfosis Biológica/fisiología , Urocordados/anatomía & histología , Urocordados/crecimiento & desarrollo , Animales , Diferenciación Celular , Larva/citología , Larva/ultraestructura , Microscopía Confocal , Urocordados/embriología , Urocordados/ultraestructuraRESUMEN
The appendicularian tunicate Oikopleura epitomizes the degree to which evolution can constrain both genome and cellular composition, while at the same time unleashing fantastic specializations.
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Urocordados , Animales , Encéfalo/anatomía & histología , Genoma/genética , Movimiento , Polisacáridos/metabolismo , Urocordados/anatomía & histología , Urocordados/genética , Urocordados/metabolismoRESUMEN
Many animals build complex structures to aid in their survival, but very few are built exclusively from materials that animals create 1,2. In the midwaters of the ocean, mucoid structures are readily secreted by numerous animals, and serve many vital functions3,4. However, little is known about these mucoid structures owing to the challenges of observing them in the deep sea. Among these mucoid forms, the 'houses' of larvaceans are marvels of nature5, and in the ocean twilight zone giant larvaceans secrete and build mucus filtering structures that can reach diameters of more than 1 m6. Here we describe in situ laser-imaging technology7 that reconstructs three-dimensional models of mucus forms. The models provide high-resolution views of giant larvacean houses and elucidate the role that house structure has in food capture and predator avoidance. Now that tools exist to study mucus structures found throughout the ocean, we can shed light on some of nature's most complex forms.
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Organismos Acuáticos/metabolismo , Moco/metabolismo , Urocordados/anatomía & histología , Urocordados/metabolismo , Animales , Ciclo del Carbono , Conducta Alimentaria , Cadena Alimentaria , Imagenología Tridimensional/instrumentación , Rayos Láser , Conformación Molecular , Moco/química , Océanos y Mares , Conducta Predatoria , Agua de MarRESUMEN
With approximately 3000 marine species, Tunicata represents the most disparate subtaxon of Chordata. Molecular phylogenetic studies support Tunicata as sister taxon to Craniota, rendering it pivotal to understanding craniate evolution. Although successively more molecular data have become available to resolve internal tunicate phylogenetic relationships, phenotypic data have not been utilized consistently. Herein these shortcomings are addressed by cladistically analyzing 117 phenotypic characters for 49 tunicate species comprising all higher tunicate taxa, and five craniate and cephalochordate outgroup species. In addition, a combined analysis of the phenotypic characters with 18S rDNA-sequence data is performed in 32 OTUs. The analysis of the combined data is congruent with published molecular analyses. Successively up-weighting phenotypic characters indicates that phenotypic data contribute disproportionally more to the resulting phylogenetic hypothesis. The strict consensus tree from the analysis of the phenotypic characters as well as the single most parsimonious tree found in the analysis of the combined dataset recover monophyletic Appendicularia as sister taxon to the remaining tunicate taxa. Thus, both datasets support the hypothesis that the last common ancestor of Tunicata was free-living and that ascidian sessility is a derived trait within Tunicata. "Thaliacea" is found to be paraphyletic with Pyrosomatida as sister taxon to monophyletic Ascidiacea and the relationship between Doliolida and Salpida is unresolved in the analysis of morphological characters; however, the analysis of the combined data reconstructs Thaliacea as monophyletic nested within paraphyletic "Ascidiacea". Therefore, both datasets differ in the interpretation of the evolution of the complex holoplanktonic life history of thaliacean taxa. According to the phenotypic data, this evolution occurred in the plankton, whereas from the combined dataset a secondary transition into the plankton from a sessile ascidian is inferred. Besides these major differences, both analyses are in accord on many phylogenetic groupings, although both phylogenetic reconstructions invoke a high degree of homoplasy. In conclusion, this study represents the first serious attempt to utilize the potential phylogenetic information present in phenotypic characters to elucidate the inter-relationships of this diverse marine taxon in a consistent cladistic framework.
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Urocordados , Animales , Sistema Digestivo/anatomía & histología , Sistema Digestivo/metabolismo , Sistema Nervioso/anatomía & histología , Sistema Nervioso/metabolismo , Fenotipo , Filogenia , ARN Ribosómico 18S , Reproducción , Serotonina/metabolismo , Urocordados/anatomía & histología , Urocordados/clasificación , Urocordados/genética , Urocordados/fisiologíaRESUMEN
In the second half of the eighteenth century, Schlosser and Ellis described the colonial ascidian Botryllus schlosseri garnering the interest of scientists around the world. In the 1950's scientists began to study B. schlosseri and soon recognized it as an important model organism for the study of developmental biology and comparative immunology. In this review, we summarize the history of B. schlosseri studies and experiments performed to characterize the colony life cycle and bud development. We describe experiments performed to analyze variations in bud productivity, zooid growth and bilateral asymmetry (i.e., the situs viscerum), and discuss zooid and bud removal experiments that were used to study the cross-talk between consecutive blastogenetic generations and vascular budding. We also summarize experiments that demonstrated that the ability of two distinct colonies to fuse or reject is controlled by a single polymorphic gene locus (BHF) with multiple, codominantly expressed alleles. Finally, we describe how the ability to fuse and create chimeras was used to show that within a chimera somatic and germline stem cells compete to populate niches and regenerate tissue or germline organs. Starting from the results of these 60 years of study, we can now use new technological advances to expand the study of B. schlosseri traits and understand functional relationships between its genome and life history phenotypes.
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Estadios del Ciclo de Vida , Investigación , Urocordados/embriología , Animales , Regeneración , Reproducción , Células Madre/citología , Urocordados/anatomía & histología , Urocordados/genéticaRESUMEN
Regenerative ability is highly variable among the metazoans. While many invertebrate organisms are capable of complete regeneration of entire bodies and organs, whole-organ regeneration is limited to very few species in the vertebrate lineages. Tunicates, which are invertebrate chordates and the closest extant relatives of the vertebrates, show robust regenerative ability. Colonial ascidians of the family of the Styelidae, such as several species of Botrylloides, are able to regenerate entire new bodies from nothing but fragments of vasculature, and they are the only chordates that are capable of whole body regeneration. The cell types and signaling pathways involved in whole body regeneration are not well understood, but some evidence suggests that blood borne cells may play a role. Solitary ascidians such as Ciona can regenerate the oral siphon and their central nervous system, and stem cells located in the branchial sac are required for this regeneration. Here, we summarize the cellular and molecular mechanisms of tunicate regeneration that have been identified so far and discuss differences and similarities between these mechanisms in regenerating tunicate species.
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Regeneración/genética , Urocordados/citología , Urocordados/fisiología , Animales , Sistema Nervioso Central/fisiología , Epitelio/fisiología , Células Madre/citología , Urocordados/anatomía & histología , Urocordados/genéticaRESUMEN
Haematopoiesis is an essential process that evolved in multicellular animals. At the heart of this process are haematopoietic stem cells (HSCs), which are multipotent and self-renewing, and generate the entire repertoire of blood and immune cells throughout an animal's life1. Although there have been comprehensive studies on self-renewal, differentiation, physiological regulation and niche occupation in vertebrate HSCs, relatively little is known about the evolutionary origin and niches of these cells. Here we describe the haematopoietic system of Botryllus schlosseri, a colonial tunicate that has a vasculature and circulating blood cells, and interesting stem-cell biology and immunity characteristics2-8. Self-recognition between genetically compatible B. schlosseri colonies leads to the formation of natural parabionts with shared circulation, whereas incompatible colonies reject each other3,4,7. Using flow cytometry, whole-transcriptome sequencing of defined cell populations and diverse functional assays, we identify HSCs, progenitors, immune effector cells and an HSC niche, and demonstrate that self-recognition inhibits allospecific cytotoxic reactions. Our results show that HSC and myeloid lineage immune cells emerged in a common ancestor of tunicates and vertebrates, and also suggest that haematopoietic bone marrow and the B. schlosseri endostyle niche evolved from a common origin.
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Hematopoyesis , Sistema Hematopoyético/citología , Mamíferos/sangre , Filogenia , Urocordados/citología , Animales , Diferenciación Celular , Linaje de la Célula , Citotoxicidad Inmunológica , Femenino , Citometría de Flujo , Células Madre Hematopoyéticas/citología , Células Madre Hematopoyéticas/inmunología , Inmunidad Celular , Isoantígenos/inmunología , Masculino , Mamíferos/anatomía & histología , Células Mieloides/citología , Células Mieloides/inmunología , Fagocitosis/inmunología , Nicho de Células Madre , Transcriptoma/genética , Urocordados/anatomía & histología , Urocordados/genética , Urocordados/inmunologíaRESUMEN
Neurobiology in ascidians has made many advances. Ascidians have offered natural advantages to researchers, including fecundity, structural simplicity, invariant morphology, and fast and stereotyped developmental processes. The researchers have also accumulated on this animal a great deal of knowledge, genomic resources, and modern genetic techniques. A recent connectomic analysis has shown an ultimately resolved image of the larval nervous system, whereas recent applications of live imaging and optogenetics have clarified the functional organization of the juvenile nervous system. Progress in resources and techniques have provided convincing ways to deepen what we have wanted to know about the nervous systems of ascidians. Here, the research history and the current views regarding ascidian nervous systems are summarized.
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Sistema Nervioso/anatomía & histología , Neurogénesis , Urocordados/anatomía & histología , Potenciales de Acción , Animales , Animales Modificados Genéticamente , Encéfalo/citología , Linaje de la Célula , Ciona intestinalis/citología , Ciona intestinalis/crecimiento & desarrollo , Conectoma , Epéndimo/citología , Predicción , Ganglios de Invertebrados/citología , Genes Reporteros , Imagenología Tridimensional , Microscopía Intravital , Larva/citología , Larva/ultraestructura , Células Musculares/citología , Sistema Nervioso/crecimiento & desarrollo , Fenómenos Fisiológicos del Sistema Nervioso/genética , Neurogénesis/genética , Neuronas/citología , Optogenética , Órganos de los Sentidos/citología , Natación , Cola (estructura animal)/inervación , Urocordados/crecimiento & desarrollo , Urocordados/fisiologíaRESUMEN
Aplousobranchia ascidians from two different families were integrated with morphological characteristics and molecular phylogenetic analysis for the first time. The present study employed morphological descriptions (colony structures, tunic, zooids, spicules stigmata and test) and a molecular approach, using a fragment of the mitochondrial cytochrome oxidase I (COI) gene of four Aplousobranchia colonial ascidians Aplidium conicum (98%), Aplidium elegans (98%), Didemnum fulgens (92%) and Trididemnum cyanophorum (94%) from Andaman and Nicobar Islands. Bar-coded sequences were extracted with BLAST format from NCBI and the heritable diversity of the submitted sequences were compared with associated ascidian species. Study revealed that the evolutionary relationship among the ascidian species exhibited the constant clades, which may help for rapid reassessment of morphological characters of the species distributed worldwide.