Medusa: A Review of an Ancient Cnidarian Body Form

Abstract

Medusae (aka jellyfish) have multiphasic life cycles and a propensity to adapt to, and proliferate in, a plethora of aquatic habitats, connecting them to a number of ecological and societal issues. Now, in the midst of the genomics era, affordable next-generation sequencing (NGS) platforms coupled with publically available bioinformatics tools present the much-anticipated opportunity to explore medusa taxa as potential model systems. Genome-wide studies of medusae would provide a remarkable opportunity to address long-standing questions related to the biology, physiology, and nervous system of some of the earliest pelagic animals. Furthermore, medusae have become key targets in the exploration of marine natural products, in the development of marine biomarkers, and for their application to the biomedical and robotics fields. Presented here is a synopsis of the current state of medusa research, highlighting insights provided by multi-omics studies, as well as existing knowledge gaps, calling upon the scientific community to adopt a number of medusa taxa as model systems in forthcoming research endeavors.

Box, stalked, and upside-down? Draft genomes from diverse jellyfish (Cnidaria, Acraspeda) lineages: Alatina alata (Cubozoa), Calvadosia cruxmelitensis (Staurozoa), and Cassiopea xamachana (Scyphozoa)

“…Some of the most fascinating and outstanding mysteries related to the genomic underpinnings of metazoan biology are centered around cnidarians [1]. Active areas of research include the basis of venom evolution and diversification [2–4], mechanisms of independent evolution of image-forming vision (lens eyes) [5–7], and the emergence of a pelagic adult stage within a biphasic (or multiphasic) life cycle [8].…”

“…There are ∼3,900 described species within Medusozoa, classified into 4 diverse lineages: Hydrozoa (hydroids, hydromedusae, siphonophores), Staurozoa (stalked jellyfish), Cubozoa (box jellyfish), and Scyphozoa (true jellyfish) (Fig. 1A−C) [1, 11]. There exists much debate regarding the phylogenetic relationships among these lineages [10, 16, 18–20].…”

“…The mechanisms of medusa formation are variable amongst medusozoans, often involving 2 phenotypically distinct life stages—polyp and medusa—that are genotypically identical (reviewed by Lewis Ames [1]). Cubozoan polyps undergo partial or complete metamorphosis and develop into the adult medusoid form capable of sexual reproduction, although in some cases a polyp rudiment remains [23].…”

“…The basal portion of the adult forms a stalk, or peduncle, while coronal muscles and gastric filaments, among other features, characterize the apical portion (calyx) of the adult [20, 25–27]. Hydrozoans exhibit the greatest variation in life history strategies and often lack a medusa form [1]. Species that give rise to the medusoid form do so via lateral buds generated by asexual polyps, while others possess sexual polyps without a free-swimming stage [28, 29].…”

“…In addition, the genome for the cubozoan Morbakka virulenta has also recently been released [59]. While the majority of Medusozoa species are represented by hydrozoans (>90%), both cubozoans and scyphozoans garner significant attention as a result of their impact on economy and tourism [1, 60]. Largely due to venom being used as a mechanism of defense and prey capture, the inherent risk of jellyfish sting has been exacerbated by uncertainty about how cnidarians will respond to modern-day anthropogenic disturbances [61, 62].…”