Thimble Jelly

Overview

The Thimble Jelly (Linuche unguiculata) is a small, distinctively shaped scyphozoan jellyfish known for its resemblance to a thimble. It is widely recognized in tropical and subtropical regions, where it often drifts in large, nomadic swarms near the water's surface.

Appearance

This species features a flat-topped, straight-sided bell that can reach approximately 16 mm in diameter and 20 mm in height. Its body is divided by a characteristic coronal groove, and the margin of the bell is scalloped into 16 blunt, oval lappets. The jellyfish typically displays an orangish-brown coloration due to the presence of symbiotic zooxanthellae within its tissues, while its translucent mesoglea is often marked with dark flecks.

Biology & behavior

Linuche unguiculata exhibits a complex life cycle, alternating between a sessile, colonial polyp stage and a free-swimming, solitary medusa stage. The medusae are active swimmers that move via rhythmic bell pulsations. While they do not display complex social hierarchies, they are frequently observed congregating in massive groups. Notably, both the adult medusae and their larval forms possess nematocysts that can cause "seabather's eruption," an itchy skin rash that occurs when the tiny organisms become trapped against a swimmer's skin, such as under swimwear.

Feeding

These jellyfish are carnivores that utilize a combination of active swimming and passive waiting to capture prey. By pulsing their bells, they create water currents that draw small organisms toward them. They then extend their short, inconspicuous tentacles to ensnare prey, using chemical stimuli to help locate food sources.