Hymenocera

Lore & Background

The harlequin shrimp is usually cream colored or white with spots. In the Pacific Ocean many individuals have red spots, while Indian Ocean shrimp typically have purple spots; the Hawaiian H. picta has both purple and red spots. The shrimp has two walking legs on each side and large, flattened claws (chelipoda). Its head bears petal-like sensory antennules used to smell out prey. The male is slightly smaller than the female. These shrimp are typically found from Hawaii through the Indo-Pacific below the intertidal zone on coral reefs, preferring temperatures of 72–82°F, but are very rare because of changing coral reefs. They move slowly and in waves, and may carry toxins from their prey that make them distasteful to predators. The female produces between 100 and 5,000 eggs per season depending on environmental factors. Males and females are often seen together in the wild and cooperate in reproduction and foraging.

Reader's Guide

Hymenocera is notable for its specialized diet: it feeds almost exclusively on starfish, including the crown-of-thorns starfish. The shrimp are skilled at flipping a slow starfish onto its back and eating the tube feet and soft tissues until reaching the central disk, usually killing the starfish within a few days. While they prefer smaller, more sedentary starfish, those are generally not sufficiently numerous, so they commonly attack crown-of-thorns starfish, reducing its consumption of coral while under attack. The starfish may shed an attacked arm and regrow it, but is usually too wounded to recover. Occasionally the shrimp will feed on sea urchins if starfish are not available. The genus is usually considered monotypic, but some split it into two species: H. picta from the central and east Pacific, where spots are deep pinkish-purple with a yellow edge, and H. elegans from the Indian Ocean and west Pacific, where spots are more brownish with a blue edge. The shrimp's slow pace, waving movement, and constant claw motion are characteristic behaviors.

Did You Know?

• Some authorities split the genus into two species: H. picta and H. elegans.
• The shrimp may carry toxins from its prey that make it distasteful to predators.