Cladonema radiatum
A miniature hydromedusa in the Seagrass Meadow, tiny enough to fit on a fingernail, that both swims and crawls along surfaces on branched stinging tentacles, capturing copepods and small zooplankton; a sessile polyp stage on the glass wall may persist unseen between medusa sightings.
The Cladonema Jelly (Cladonema radiatum) is a miniature hydromedusa (not a true jellyfish but a member of the hydroid lineage) that alternates between a sessile polyp stage on hard substrate and a tiny free-swimming medusa stage that can also crawl along surfaces using its branched tentacles. Two individuals are on record, but no introduction date, source, or observation record documents their presence or current status in the Seagrass Meadow.
Cladonema radiatum has a cosmopolitan distribution in temperate to subtropical coastal marine environments, recorded in the Mediterranean, Atlantic, Pacific, and Gulf coasts. It is a common aquarium hitchhiker and a frequently observed hydromedusa in enclosed marine systems worldwide. In natural settings it is found in shallow coastal waters, seagrass beds, tidal pools, and sheltered bay environments, habitats broadly comparable to miniBIOTA's Seagrass Meadow.
Cladonema radiatum has a two-stage life cycle: a sessile polyp stage that attaches to hard surfaces (glass, rock, shell, coralline algae) and a medusa stage that both swims and crawls. The medusa can use its branched, adhesive tentacles to anchor to surfaces and creep along the substrate, a behavior uncommon among medusae and useful in low-flow enclosed systems. The polyp stage is cryptic and easily overlooked; medusae are more visible but still very small. In miniBIOTA, both stages would be expected on hard surfaces in the Seagrass Meadow.
Cladonema radiatum medusae are micro-predators, capturing copepods, amphipod larvae, small worms, and other small zooplankton with stinging tentacles. The polyp stage also captures small prey. In a closed system with limited zooplankton production, Cladonema can place measurable predation pressure on copepod populations.
Cladonema alternates between asexual polyp reproduction (budding new polyps and releasing medusae) and sexual medusa reproduction (release of eggs and sperm, producing planula larvae that settle to form new polyps). In an enclosed system, the polyp stage can persist and bud medusae repeatedly if food and substrate are available, making Cladonema capable of establishing a self-sustaining population in marine aquarium systems without external input. This is notable and potentially relevant to miniBIOTA population dynamics.
Cladonema radiatum tolerates a range of marine to near-marine salinities and temperatures across its cosmopolitan range. It is recorded in systems from 15-30 degrees C. Sensitive to extremes of salinity and temperature; not documented for specific miniBIOTA conditions.
Cladonema Jelly is a micro-predator in the Seagrass Meadow water column and on hard surfaces, consuming copepods and small zooplankton. In a system with active microcrustacean populations, it can suppress copepod densities. The polyp stage occupies hard-surface biofouling niches alongside barnacles, bryozoans, and encrusting algae. Unlike most species in the Seagrass Meadow, Cladonema is capable of reproducing in place through asexual polyp budding, which means even a small founding population could theoretically persist or grow without external introduction.
No introduction date, source, or method is on record. Cladonema radiatum is a known aquarium hitchhiker, arriving most commonly on live rock, coral rubble, or macroalgae. Hitchhiker arrival with an early saltwater introduction is the most probable pathway. Two individuals are documented; neither has a dedicated observation record.
No observation files found.
Two individuals documented but no observation file documents the sighting. Polyp stage can reproduce asexually; population dynamics in a closed system may be more persistent than a single-count snapshot suggests. Current status unknown.
Micro-predator of copepods and small zooplankton at both medusa and polyp stages. In closed systems with limited zooplankton production, can place meaningful predation pressure on copepod populations. No feeding observed in miniBIOTA.
Cosmopolitan hydromedusa tolerating a range of marine salinities and temperatures (recorded 15-30 degrees C across its range). Specific tolerance ranges for miniBIOTA conditions not measured.
Capable of self-sustaining closed-system population through asexual polyp budding. Medusa stage can reproduce sexually. No reproductive observation in miniBIOTA. Whether a polyp colony is established in the Seagrass Meadow is unknown.
Micro-predator of copepods and small zooplankton. Polyp stage occupies hard-surface biofouling niches. Species is capable of establishing a self-sustaining population through asexual budding, which distinguishes it from broadcast-spawning species that require larval settlement. No ecological observations in miniBIOTA.
Follow this species across the habitats where it currently appears in the miniBIOTA biosphere.
