Euprymna

Euprymna is a genus of small cephalopods in the family Sepiolidae, commonly known as bobtail squids. Members have rounded mantles, measure a few centimeters in length, with eight arms and two long tentacles, well-developed eyes, and a flexible, bulbous body adapted for a benthic lifestyle. They are typically found in tropical and subtropical marine waters, occupying shallow coastal habitats such as sandy or muddy bottoms, seagrass beds, and coral reef margins.

A distinctive feature of Euprymna is a light-organ system that houses symbiotic bioluminescent bacteria, usually Vibrio fischeri, which provide counter-illumination at night. Light production is regulated by the host and its circadian clock, allowing the squid to blend with downwelling moonlight to hide from predators.

Reproduction involves separate sexes; males transfer spermatophores to females via a specialized appendage, and females lay gelatinous egg masses attached to the substrate, with young emerging as free-swimming paralarvae. Euprymna comprises several species, including Euprymna scolopes and Euprymna tasmanica, among others.

These squids are of particular interest in biology and ecology due to their model role in studying host-microbe symbiosis, development, and sensory biology. Conservation status varies by species; while some have broad distributions, others are more restricted and sensitive to habitat degradation.