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Kelp lice are marine isopods of the genus Paridotea that live and feed on various seaweeds. Kelp lice have a specially developed digestive mechanism to combat the anti-herbivorous chemicals the kelp uses to defend the spore areas on which the lice preferentially feed. 

(Header image: Bernadette Hubbart)

There are four species of kelp lice common in South African waters, all of which are present in the Aquarium from time to time:

  • Green weed-louse (P. ungulata) - The most common species that you will see in the Aquarium. It is small and green with small, jagged projections on the rear edges of its tail fan. Grows up to 5.5cm. Widely distributed between Walvis Bay and East London. This weed-louse is particularly fond of green algae in the genus Ulva, commonly called "sea lettuce".
  • Reticulate kelp louse (P. reticulata) - Its body is green-brown and covered in a yellow net-like pattern. Grows up to 5.5cm. Occurs on the South African West Coast. It feeds on the kelp spores and spore-bearing organs, which usually contain the highest concentration of anti-herbivore toxins, but it has an armoured gut (literally) to overcome this.
  • Red weed-louse (P. rubra) - Very similar to the green kelp-louse, but it dwells on and consumes red algae and thus has a red-brown colour. It also has smooth telson corners. Grows up to 4.5cm. Occurs on the West Coast and in Namibian waters.
  • Brown weed-louse (P. fucicola) - Smaller and narrower than red and green weed-lice, with a tapering, notched telson. They do not feed on algae, but rather on eelgrass. Occurs on the West Coast and in Namibian waters.

What are isopods?

Isopods are small, flat, segmented crustaceans, many of which inhabit marine and freshwater environments. There are also terrestrial examples - such as "wood lice" which you undoubtedly know. Despite often carrying the name "louse" isopods are not true lice - with include parasitic insects such as hair lice, body lice and pubic lice.

Isopods are typically flattened, with seven pairs of legs attached to their thorax, or pereon. All these legs, regardless of their position are identical, hence their name "iso-", meaning "same", and "-pod", meaning "leg".

Their abdomen, or pleon, is divided into five segments, each of which has a pair of "swimming-legs" called pleopods. These pleopods are also used for respiration, i.e. They are the isopod's gills.

The last segment of the isopod's abdomen is the telson, sometimes called a tail-fan.

Approximately 300 species of isopod are found in the waters of Southern Africa. Globally, more than 10 000 species of isopod are known.