Life History & Behaviour


Image 1: Plebidonax deltoides

Feeding
Like most bivalves, pipis are suspension feeders, using both their mouths and gills to catch the microscopic plankton that they consume (Ruppert et al., 2004). P. deltoides have lamellibranch gills which are highly folded, making them efficient at both gas exchange and food capture. They have a stomach and intestines for the processing of food particles brought in through the mouth and a digestive ceca for intracellular digestion (Ruppert et al., 2004).

Reproduction

There is little detailed information available for P. deltoides though through lab fertilisation and subsequent observation it is now known that P. deltoides develop into trochophore larvae after approximately 24 hours and have a 6-8 week larval stage in which complete metamorphosis occurs (O’Connor & O’Connor, 2011). The characteristic foot has generally developed by the end of the second week in the initial stages of metamorphosis. Upon the completion of this larval stage, P. deltoides comes to settle in the intertidal zone on high energy beaches (O’Connor & O’Connor, 2011). P. deltoides have separate sexes and the gonads in each are a creamy or pale yellow and appear to be able to reproduce year round (O’Connor & O’Connor, 2011).

Movement

P. deltoides has the ability for movement through the use of its characteristic muscular foot and the waves on the beaches where they are found. When a wave comes in pipis on the surface are moved about without control until they settle where they are dropped by the wave. They use their muscular foot to dig into the ground where they pull themselves upright and dig down. The smaller animals that do not dig as deep each time are more susceptible to movement by the waves while the larger animals may return to the surface when a new location is required.

Internal transport

The pipi has a hemal system that includes a basic heart and blood vessels that take oxygenated blood around the body. Gases are exchanged across the gills and the siphons that form part of the mantel aid in respiration.

Image 2: P. deltoides

Research

A brief study was conducted to investigate the burrowing behaviour of P.deltoides. Pipis of varying sizes were collected from South East Queensland beaches and measured for length. The measurements were used to place each individual into adult or juvenile categories for the purposes of minimising error and comparison. Pipis reach sexual maturity at 6 months of age when they are approximately 3.6cm in length (O’Connor & O’Connor, 2011) and as such any individual measuring over 3.6cm was classified as an adult for the purposes of this experiment.

Image 3: Adult pipi


Image 4: Juvenile pipi

The pipis were place flat on the beach at mid-tide and the time was measured until the animal had successfully buried itself. The animal was determined to have successfully buried itself when it was no longer visible from the surface.

The mean burrowing time was 2 minutes 48 seconds though disturbance may have impacted that animals as an outlier of 9 minutes 31 seconds was observed.