The Beautiful Hypselodoris (Hypselodoris pulchella) is a dorid nudibranch, a marine gastropod mollusc. They are commonly seen on the reefs of Tanzania, usually but not always with one individual trailing another. The smaller individual follows the larger individual.
The background colour of the dorsal area is white, with indistinct purple lines making up random patterns across the body. A large number of yellow spots of varying sizes cover the dorsal area. The edge of the mantle and the foot each have a distinct solid purple line around the edges. The rhinopores are blue purple in colour and are made up of approximately 30 roughly semi-circular plates on either side of the supporting arm. These can be seen in the image below. These plates contain chemoreceptors and maximise the surface area. These chemoreceptors are used to detect small amounts of trace chemicals in the seawater and are used to detect food sources and probably to find other individuals for trailing purposes and mating.
The gills are situated on the rear of the body and are not fixed, rather they move with the currents. They are white with purple edges.
When threatened the gills can be retracted into the body as can be seen below.
IN THE WILD
Hypselodoris pulchella are commonly seen during the day in Tanzanian waters. They are usually seen trailing with one specimen closely following the foot of the specimen in front. There seems to be no explanation for the trailing. In all probability it enables the larger specimen to find food sources and the smaller specimen following benifits as it uses less effort to do so. Whether there is any other advantage to this type of behaviour is open to speculation. One could speculate that an evolutionary advantage is obtained by staying in close proximity to a potential mate, given that they are hermaphrodites. This proximity then facilitates mating and makes it easier for the mating to take place. The need to search for a mate is thus dispensed with and trailing is theoretically more efficient.
Hypselodoris pulchella is found across the Indian ocean and in the west Pacific. They have been seen on mixed rubble and coral areas in Tanzania to depths of 12 meters.
The Beautiful Hypselodoris feed mainly on certain species of sponge. They insert a tube into the sponge and emit fluids which partially digest it. This partially digested meal is then sucked into the body for further digestion.
Nudibranchs are simultaneous hermaphrodites and mating takes place by darting. The reproductive organs are on the right side and mating takes place in a head to tail fashion. The eggs are laid on a solid substrate and when they hatch the larvae become planktonic before growing into adults. The egg coils are reddish in colour.
HYPSELODORIS PULCHELLA CLASSIFICATION
Species: Hypselodoris pulchella
- The Reef Guide fishes, corals, nudibranchs & other invertebrates: East and South Coasts of Southern Africa by Dennis King & Valda Fraser