Phyllidia varicosa
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- Name / Latin
- Phyllidia varicosa — Phyllidia varicosa
- Brief description
- Phyllidia varicosa is a large, colourful sea slug (nudibranch) of the family Phyllidiidae. The body is elongated-oval with 3–6 longitudinal ridges on the back bearing yellow-tipped tubercles; the ridges and tubercle bases are usually bluish-grey or blue with dark lines between them. The foot sole often has a clear dark longitudinal stripe. It lives on coral reefs and rocky areas, feeds on sponges and uses their chemicals for defence; it is considered toxic and has warning coloration.
- Size:
- 8–12 cm
- Depth:
- 1–30 m
- Habitat:
- Indian Ocean, Pacific Ocean, Red Sea, Andaman Sea
- Family:
- Phyllidiidae
- Type:
- Mollusc
- Activity:
- Diurnal
- Conservation status:
- Not Evaluated (NE) — species has not been assessed by IUCN
Phyllidia varicosa is a large, colourful sea slug and a dorid nudibranch. This member of the family Phyllidiidae has a striking appearance and plays an important role in coral reef ecosystems.
Phyllidia varicosa is widespread in the Indo-Pacific. This mollusc is found in the tropical waters of the Indian Ocean, the western Pacific and the Red Sea. It lives on coral reefs and rocky underwater areas, where it often crawls over sponges, which form the main part of its diet. The mollusc takes in sponges together with their toxins, which makes it poisonous and protects it from predators.
Besides its wide range, Phyllidia varicosa is notable for its size. Average length is 8–10 cm, but some individuals grow to 12 cm.
Phyllidia varicosa has an elongated oval body with characteristic longitudinal ridges that make it easy to recognise. The ridges and tubercle bases are grey-blue or blue, and the tubercle tips are bright yellow. The ridges may be continuous or broken, with black space between them. The mantle edges also have semicircular ridges with yellow tubercles. The rhinophores (sensory organs) are bright yellow. The foot sole has a black longitudinal stripe.
They usually live alone but sometimes form small groups. Occasionally several individuals can be seen together, probably when breeding. Phyllidia varicosa is protected from predators by its ability to release toxic substances. Its bright colour acts as a warning signal, showing that it is toxic and helping to avoid attack.
Phyllidia varicosa is a hermaphrodite: each individual has both male and female reproductive organs. When mating, the slugs exchange sperm. The reproductive organs are on the right side at the front of the body, and the slugs line up side by side to mate. Eggs are laid on hard surfaces, and the larvae hatch and spend some time in the plankton before becoming adults.
This species not only adds colour to the underwater world but also has an important ecological role, controlling sponge populations and helping to keep coral reefs healthy.
