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The importance of molecular characters when morphological variability hinders diagnosability: systematics of the moon jellyfish genus Aurelia (Cnidaria: Scyphozoa).

ABSTRACT: Cryptic species have been detected across Metazoa, and while no apparent morphological features distinguish them, it should not impede taxonomists from formal descriptions. We accepted this challenge for the jellyfish genus Aurelia, which has a long and confusing taxonomic history. We demonstrate that morphological variability in Aurelia medusae overlaps across very distant geographic localities. Even though some morphological features seem responsible for most of the variation, regional geographic patterns of dissimilarities are lacking. This is further emphasized by morphological differences found when comparing lab-cultured Aurelia coerulea medusae with the diagnostic features in its recent redescription. Previous studies have also highlighted the difficulties in distinguishing Aurelia polyps and ephyrae, and their morphological plasticity. Therefore, mostly based on genetic data, we recognize 28 species of Aurelia, of which seven were already described, 10 are formally described herein, four are resurrected and seven remain undescribed. We present diagnostic genetic characters for all species and designate type materials for newly described and some resurrected species. Recognizing moon jellyfish diversity with formal names is vital for conservation efforts and other studies. This work clarifies the practical implications of molecular genetic data as diagnostic characters, and sheds light on the patterns and processes that generate crypsis.

SUBMITTER: Lawley JW

PROVIDER: S-EPMC8435205 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundAurelia aurita (Scyphozoa, Cnidaria) is an emblematic species of the jellyfish. Currently, it is an emerging model of Evo-Devo for studying evolution and molecular regulation of metazoans' complex life cycle, early development, and cell differentiation. For Aurelia, the genome was sequenced, the molecular cascades involved in the life cycle transitions were characterized, and embryogenesis was studied on the level of gross morphology. As a reliable representative of the class Scyphozoa, Aurelia can be used for comparative analysis of embryonic development within Cnidaria and between Cnidaria and Bilateria. One of the intriguing questions that can be posed is whether the invagination occurring during gastrulation of different cnidarians relies on the same cellular mechanisms. To answer this question, a detailed study of the cellular mechanisms underlying the early development of Aurelia is required.MethodsWe studied the embryogenesis of A. aurita using the modern methods of light microscopy, immunocytochemistry, confocal laser microscopy, scanning and transmission electron microscopy.ResultsIn this article, we report a comprehensive study of the early development of A. aurita from the White Sea population. We described in detail the embryonic development of A. aurita from early cleavage up to the planula larva. We focused mainly on the cell morphogenetic movements underlying gastrulation. The dynamics of cell shape changes and cell behavior during invagination of the archenteron (future endoderm) were characterized. That allowed comparing the gastrulation by invagination in two cnidarian species-scyphozoan A. aurita and anthozoan Nematostella vectensis. We described the successive stages of blastopore closure and found that segregation of the germ layers in A. aurita is linked to the 'healing' of the blastopore lip. We followed the developmental origin of the planula body parts and characterized the planula cells' ultrastructure. We also found that the planula endoderm consists of three morphologically distinct compartments along the oral-aboral axis.ConclusionsEpithelial invagination is a fundamental morphogenetic movement that is believed as highly conserved across metazoans. Our data on the cell shaping and behaviours driving invagination in A. aurita contribute to understanding of morphologically similar morphogenesis in different animals. By comparative analysis, we clearly show that invagination may differ at the cellular level between cnidarian species belonging to different classes (Anthozoa and Scyphozoa). The number of cells involved in invagination, the dynamics of the shape of the archenteron cells, the stage of epithelial-mesenchymal transition that these cells can reach, and the fate of blastopore lip cells may vary greatly between species. These results help to gain insight into the evolution of morphogenesis within the Cnidaria and within Metazoa in general.

Project description:Mohammed Rizman-Idid, Abu Bakar Farrah-Azwa, and Ving Ching Chong (2016) Scientific enquiries into jellyfish blooms and associated problems are often deterred by the lack of taxonomical and ecological studies worldwide. Taxonomic difficulty is attributed to the high degree of morphological variations among and within species. To date, only two scyphozoan jellyfish species have been documented from field surveys in Malaysian waters, whereas another four Malaysian scyphozoan and two cubozoan jellyfish species have been mentioned in toxicological studies. None of these species have; however, been verified. This study thus aimed to document and resolves the uncertainty of earlier identified species in the region using morphology and molecular DNA sequencing. Jellyfish specimens were collected from Malaysian waters in the Straits of Malacca, South-China Sea and the Sulu-Sulawesi Sea over two years (June 2008 to October 2010), and their DNA sequences were compared with those from the Atlantic and Pacific regions. Ten scyphozoan and two cubozoan species were recorded in Malaysian waters (South China Sea and Straits of Malacca). These jellyfish included eight species from the order Rhizostomeae (Rhizostomatidae, Lobonematidae, Mastigiidae, Catostylidae and Cepheidae), two species from Semaestomeae (Pelagiidae and Cyaneidae) and two species from class Cubozoa; one from order Carybdeida (family Carukiidae) and another from order Chirodropida (family Chiropsalmidae). Molecular identification of species using phylogenetic approaches was based on DNA sequences of partial cytochrome oxidase I (COI), 16S and internal transcribed spacer (ITS1) regions. The COI phylogenetic tree of Cubozoa and Scyphozoa species from the Atlantic and Pacific regions showed distinct clustering of six Malaysian jellyfish species. However, most of the deeper divergences and relationships between the families were unresolved, which were also observed in the 16S and ITS1 phylogenetic trees. The Malaysian edible species Lobonemoides robustus, Rhopilema hispidum and Rhopilema esculentum were grouped within Rhizostomeae, whereas other scyphozoans showed phylogenetic affinities to Semaestomeae and Kolpophorae. Chrysaora and Cyanea appeared non-monophyletic; however their paraphyly was not confirmed. This study has provided the much needed baseline information on the taxonomy of Malaysian jellyfish species which have been substantiated by partial COI, 16S and ITS1 sequences. A total of 12 putative species of jellyfish were identified, which encompassed 12 genera.

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The importance of molecular characters when morphological variability hinders diagnosability: systematics of the moon jellyfish genus Aurelia (Cnidaria: Scyphozoa).

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