Kiwa (crustacean)

Lore & Background

The genus Kiwa was named for Kiwa, the Polynesian god of shellfish. The first described species, Kiwa hirsuta, was discovered on the Pacific-Antarctic Ridge. Subsequent species include Kiwa puravida from cold seeps in the East Pacific, Kiwa tyleri (the 'Hoff crab') from the East Scotia Ridge, and Kiwa araonae from the Australian-Antarctic Ridge. Two undescribed species are known from vents on the South West Indian Ridge and at the Galápagos, and a third undescribed species was found in the Atlantic sector of the Southern Ocean. DNA analysis confirms these species diverged millions of years ago; K. araonae and K. puravida are closely related despite being 12,000 kilometers apart. Fossils from the Eocene-Oligocene boundary and mid-Miocene suggest that changes in deep-sea temperature and ventilation influenced species divergence.

Reader's Guide

Kiwa crustaceans are primary consumers in deep-sea hydrothermal vent and cold seep ecosystems, relying on chemosynthetic bacteria as their main food source. These bacteria live on the hair-like setae covering the crab's appendages, particularly the claws. In Kiwa puravida, known as the 'dancing crab,' individuals wave their claws in a rhythmic motion to stir water and increase the flow of methane and hydrogen sulfide to the bacteria, effectively farming their own food. This adaptation allows them to thrive in environments where sunlight cannot provide energy. The setae also show variation: rows of narrow, flexible setae enclose thicker, restricted setae. In brooding females, setae become deteriorated and brown due to reduced carapace health away from vent heat. Males of the South West Indian Ridge species prefer warmer water, while egg-carrying females and juveniles prefer the coldest. Male yeti crabs have larger claws than females, which may serve in antagonistic interactions for mates, resembling a precopulatory guarding mating system. In Kiwa tyleri, males cluster near vents while females stay farther away, likely to protect developing eggs from high temperatures. The propodus of K. tyleri bears a spine that helps the crab cling to steep vent chimneys.

Did You Know?

• Kiwa is the only genus in the family Kiwaidae.
• Kiwa puravida is known as the 'dancing crab' because it waves its claws to farm bacteria.
• Male yeti crabs have larger claws than females, possibly for mating competition.
• Egg-carrying females of the South West Indian Ridge species prefer the coldest water.