Pleurobranchaea eggs are embedded in a jelly in clearly visible long finely woven white strands. The egg-laying process usually takes from 12 to 24 hours. Under laboratory conditions, egg-laying is usually associated with stress, and is especially prevalent in freshly trawled animals. Our trawling data indicates that P. californicaeggs hatch midsummer, mature during the fall to fully mature adults that are ready for reproduction during the winter months: December-March is the period when only large adults (70-200 ml) are caught.
Pleurobranchaea Body Size and Form
Pleurobranchaea has a hydrodynamic body suitable for living in turbulent current that averages 5 cm/sec. Body size typically varies between 10 cm for juveniles to 30 cm in adults.
The foot (ventral view), attached to the tank wall, functions primarily for locomotion in the forward direction. The base is composed of both mucus secreting cells and cilia. The cilia actually cause locomotion whereas the mucus facilitates the cilia movement. Since the cilia can only move in one direction, turning relies on body wall muscle contraction and behaviorally elevating the front of the foot to facilitate twisting on the heel of the foot.
Pleurobranchaea Sensory Organization – Rhinophore and Oral veil
Pleurobranchaea is equipped with a couple of rhinophores (black structures on the top of the head) that presumably sense the water currents, plus a couple of tentacles or prolonged edge of the oral veil. Oral veil is the major chemosensory organ in Pleurobranchaea. Sensory cells are presumed to be located more densely on the tentacles and papillae – the tiny bumps of skin on the oral veil. Usually the papillae are larger along the front edge of the oral veil. The ratio of the number of papillae to oral veil area varies and usually increases with age of the slug.
Pleurobranchaea Gill and Sexual Organs
Pleurobranchaea‘s body is covered with a protective mantle that secretes sulfuric acid and acts as a mechanical shield for the gill (feathery organ) and sexual organs; the white structure below the gill represents the penis, the female structure is not visible in this photo; they are hermaphroditic and hence male and female organs are located close to one another. In order to mate these slugs have to align with each other pointing in opposite directions.