by Jenny Edwards
Some excited children on the Nature Coast Marine Group’s last excursion to a rock platform found many mysterious creatures that they had never seen in the wild before. Elephant snails, brittle stars, nudibranchs, peanut worms and sea hares were just some of their finds.
The sea hares found on this exploration were Dolabrifera dolabrifera which, as far as I have been able to find out, do not have a common name. There were many in the shallow rocky areas at low tide probably because spring is the time of year when they gather to mate and lay their eggs under boulders.
Dolabriferas are small sea hares, growing to about 40mm. They vary in colour from mottled olive-green or brown, like the ones we saw, to shades of pink. This allows them to blend in with their background. Their body shape resembles a pear cut in half with a longer thinner neck and head and a wide rear end.
Unlike any pear, the head end has four tentacles for sensing chemicals in the water and for touch. The rear pair look a bit like rabbit ears and are probably why this group of animals are called sea hares. The eye spots are tiny dots probably only capable of sensing light and are at the base and just forward of the “ear” tentacles.
The wide rear end of Dolabrifera allows it to cling tightly to rocks and algae. It moves with a leech-like motion.
Sea hares graze on algae and Dolabrifera seems to prefer the thin, hairy type of sea weed. It is frequently sold for salt water aquariums as an “algae eater”.
All sea hares are hermaphrodites. Each animal is a functioning male and female at the same time but cannot fertilise itself. The thousands of eggs are fertilized internally and laid in jelly-like strings. Dolabrifera is unusually tidy in this respect. Its transparent pinkish egg ribbons are attached to the underside of boulders in neat zig-zag patterns. The ribbons turn brown just before the eggs hatch.
When the young emerge they spend a period as planktonic larvae before settling as miniature adults.