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Many animals go through one or more metamorphoses during their lives, however, the molecular underpinnings of metamorphosis across diverse species are not well understood. Medusozoa (Cnidaria) is a clade of animals with complex life cycles, these life cycles can include a polyp stage that metamorphoses into a medusa (jellyfish). Medusae are produced through a variety of different developmental mechanisms-in some species polyps bud medusae (Hydrozoa), in others medusae are formed through polyp fission (Scyphozoa), while in others medusae are formed through direct transformation of the polyp (Cubozoa). To better understand the molecular mechanisms that may coordinate these different forms of metamorphosis, we tested two compounds first identified to induce metamorphosis in the moon jellyfish Aurelia aurita (indomethacin and 5-methoxy-2-methylindole) on a broad diversity of medusozoan polyps. We discovered that indole-containing compounds trigger metamorphosis across a broad diversity of species. All tested discomedusan polyps metamorphosed in the presence of both compounds, including species representatives of several major lineages within the clade (Pelagiidae, Cyaneidae, both clades of Rhizostomeae). In a cubozoan, low levels of 5-methoxy-2-methylindole reliably induced complete and healthy metamorphosis. In contrast, neither compound induced medusa metamorphosis in a coronate scyphozoan, or medusa production in either hydrozoan tested. Our results support the hypothesis that metamorphosis is mediated by a conserved induction pathway within discomedusan scyphozoans, and possibly cubozoans. However, failure of these compounds to induce metamorphosis in a coronate suggests this induction mechanism may have been lost in this clade, or is convergent between Scyphozoa and Cubozoa.

The catostylid jellyfish, Crambionella annandalei was originally described by Rao (1932) based on a preserved specimen collected from the Andaman Sea. Since then, no detailed taxonomic studies have been conducted and the species is often misidentified. Here, we provide a detailed morphological re-description of C. annandalei from fresh material collected at a variety of locations along the east coast of India. The species can be distinguished from its congeners by a combination of morphological characters, the most important of which are the proportion of terminal club length to oral arm length (0.48 ± 0.031), the proportion of the distal portion of the oral arm to naked proximal portion (7.25 ± 0.268) and the body colour. The occurrence of intra-specific colour variation in fresh specimens was also observed in the present study.

In order to investigate possible differences and patterns of body-plan morphogenesis among Scyphozoa, we described the morphology and development of the bell and oral arms of 11 species. We built a model for the development of the group and provide a guide for recognizing development stages. In general, the bell diameter was more efficient than age (days) to identify the stage of development, which suggests that the events of morphogenesis depend more on body size than on age. We used measurements of bell and oral arm to build growth curves and described the timing of developmental events (e.g., appearance of digitata, velar lappets and oral arms, filling of interlobe gaps) and patterns of morphogenesis (contour of marginal lappets, branching of oral arms, and presence of structures/appendages on the oral arms). The time until the appearance of digitata and velar lappets, the marginal lappet contour, and the presence of lateral folds in oral arms supported a phylogenetic relationship between the “Semaeostomeae” and Rhizostomeae (Dactyliophorae and Kolpophorae) lineages. “Semaeostomeae” jellyfish with digitata (family Ulmaridae) and differentiated velar lappets developed such structures at larger bell diameters than rhizostomes; only Dactyliophorae rhizostomes had serrated contour of the lappets; only species of Rhizostomeae showed development of the lateral folds; and only Ulmaridae and Rhizostomeae had differentiated appearance of the velar lappets. We propose a specific definition of oral arms that is based on morphological and functional features. Therefore, estimating development timing and describing the way that these structures develop can help to understand how jellyfish feeding strategies change during initial growth and how the changes in these structures can reflect the differences in feeding habits among the groups.

Whether a perceived increase in the abundance of jellyfishes is related to changing marine environments has been considered primarily using large-scale analyses of multi-species assemblages. Yet jellyfish blooms—rapid increases in the biomass of pelagic coelenterate species—are single-species demographic events. Using published and new genetic analyses and population surveys, we investigate whether there may be a critical knowledge gap between the scales of recent analyses and the scales of natural phenomena. We find that scyphomedusae may show population genetic structure over scales of tens to hundreds of kilometers, that environments vary regionally and locally, and that populations of medusae can display uncorrelated dynamics on these scales. These findings suggest genetic differences between populations and/or environmental differences between sites are important determinants of population dynamics in these jellyfishes. Moreover, the local abundance of medusae may be most strongly correlated with preceding rather than current local environmental conditions, indicating there is a cumulative time-course to the formation of ‘blooms’. Broad-scale macro-ecological analyses will need to build from coordinated, long-term, fine-grained studies to synthesize, rather than mask, population-level phenomena in larger-scale analyses.

The Indo-Pacific is recognized as a hotspot for marine diversity. The taxonomy of certain taxa, such as Discomedusae jellyfish, has been neglected, despite its importance in the fishery industry. This study documents the first records of Discomedusae for the Java Sea using an integrative approach and provide notes about its distribution in the area. We used up to 53 morphological and meristic characters and amplified one mitochondrial marker (COI). The comparison and assessment of these data resulted in the recognition of seven species of Discomedusae, from which five has been recorded for the Indo-Pacific area. Two other species require a taxonomic revision to confirm the species assignation. The distribution of jellyfish in the coast of Java Sea might be correlated with the jellyfish life history and species-specific ranges of tolerance, and not solely determined by the environmental parameters. These findings provide the foundations for extending the taxonomic research in the area; the description of the biodiversity will increase the understanding of the population dynamics and its implications in the fisheries.

Authors report historical and recent records of the little-known medusa Drymonema dalmatinum in the Adriatic Sea. This large scyphomedusa, which may develop a bell diameter of more than 1 m, was first described in 1880 by Haeckel based on four specimens collected near the Dalmatian island Hvar. The paucity of this species records since its description confirms its rarity, however, in the last 15 years sightings of D. dalmatinum have been more frequent.Original Abstract: Gli autori riportano segnalazioni storiche e recenti della poco conosciuta medusa Drymonema dalmatinumnel mare Adriatico. Questa grande scifomedusa, che puo sviluppare un cappello di diametro di oltre 1 m, e stata descritta per la prima volta nel 1880 da Haeckel, in base a quattro esemplari catturati vicino all'isola di Lesina (Hvar) in Dalmazia. La scarsita delle segnalazioni di questa specie dalla sua prima descrizione conferma la sua rarita. Tuttavia, negli ultimi 15 anni gli avvistamenti di D. dalmatinum sono stati piu frequenti. Avtorji v prispevku predstavljajo malo znano klobucnjasko meduzo Drymonema dalmatinum (dalmatinska lasasta meduza). Prvic jo je opisal Haeckel (1880) ravno na osnovi vzorcev meduz iz Jadranskega morja. Klobuk dalmatinske lasaste meduze lahko doseze premer preko enega metra, vendar so bili primerki iz Jadranskega morja manjsi, najvecji so imeli premer okoli 60 cm. Na osnovi historicnih virov in novejsih opazovanj avtorji v prispevku podajajo casovni pregled opazovanj te meduze od konca 19. stoletja do danes. Stiasny (1940b) je predlagal 30-letni ciklus pojavljanja, vendar smo v zadnjih desetletjih zabelezili pojave l. 1984, 2001, 2010 in 2014. Dalmatinska lasasta meduza je bila bolj pogosto zabelezena v juznem Jadranu, opazovani primerki pa so bili manjsih dimenzij kot v severnem Jadranu, kar nakazuje njen transport z vodnimi masami ob vzhodnojadranski obali proti severu. Podatki iz literature kazejo, da so pomemben plen dalmatinske lasaste meduze uhati klobucnjaki, za katere v obdobju po letu 1980, zlasti pa po l. 2000, v severnem Jadranu ugotavljamo pogostejse masovno pojavljanje.