Jellyfish evolution involved an increase in the amount of water in their tissues, allowing them to become larger, more gelatinous, and exceptionally efficient hunters.
While the fossil record for jellyfish is sparse due to their soft bodies, and therefore direct evolutionary lineage is difficult to trace, research suggests the following key adaptations contributed to their evolution:
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Increased Water Content: The primary evolutionary driver highlighted by researchers is the increasing proportion of water within their tissues. This allowed them to achieve larger sizes and a more gelatinous form. Larger size enables them to capture a wider range of prey.
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Efficient Hunting Strategy: The gelatinous body form, made possible by increased water content, likely contributes to their efficient hunting style. Their bell-shaped body allows them to passively drift and ambush prey, expending minimal energy.
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Simple Body Plan: Their simple, radially symmetrical body plan, with a nerve net instead of a centralized brain, has proven remarkably successful and has remained relatively unchanged for hundreds of millions of years. This suggests early evolutionary adaptations were highly effective.
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Early Divergence: Jellyfish belong to the phylum Cnidaria, which is one of the oldest animal groups. Molecular clock studies suggest that cnidarians, including jellyfish, diverged from other animal lineages very early in the history of multicellular life. This implies that their basic body plan was established long ago.
In summary, the evolution of jellyfish centers around an increased proportion of water in their tissues, leading to a gelatinous body form that facilitates efficient hunting. Coupled with a simple, yet effective, body plan, this strategy has enabled jellyfish to thrive for hundreds of millions of years.
