Comprehensive Description

Polychaetes are a major class of the phylum of segmented worms, Annelida. They have a significant diversity of forms and habitats making them. Polychaetes are entirely marine worms which inhabit a number of marine ecosystems including coral reefs, mangrove and wetland areas, sand flats and rocky intertidal zones (Beesley et al., 2000). Fossil records have shown a positive correlation between the abundance of polychaete jaws and the increasing levels of bioturbation (Eriksson & Frisk, 2011); as benthic organisms polychaete worms in general are important bioturbators and bioirrigators in marine systems (Piot et al., 2008).

Intertidal zones are arguably some of the most variable and harshest marine environments. With the movements of the tide intertidal areas are frequently exposed to high temperatures, low or high salinities (Bartels-Hardege et al., 1996) and are faced with the significant risk of dessication through water loss. The rocky intertidal shores of Redcliffe, South-East Queensland are no exception. But despite the dramatic forces at work on the system there is still an enormous diversity and abundance of organisms along the rocky shore.

Like other members of the phylum Annelida, polychaetes consist of presegmental prostomium and peristomium regions, a metastomium or segmented trunk and a postsegmental pygidium (Beesley et al., 2000). Polychaetes can only be distinguished from other annelids by the presence of nuchal organs which are chemosensory structures located on the prostomium (for more information see ‘Internal Anatomy’). It is important to note that there is an enormous morphological variation and diversity of life styles among polychaetes; this includes (but is certainly not limited to) tube-dwellers, entirely sedentary as well as errant species, body lengths which range from very small to very large, species with amazingly bright-coloured cuticles as well as some dangerous, jaw-bearing individuals.

Nereidids are possibly the most frequently encountered polychaetes in intertidal environments. They have also been known to inhabit deep-sea hydrothermal vents and some unusual freshwater environments (Beesley et al., 2000). Species of Nereis are errant, benthic organisms which burrow into rocks and form an important link in intertidal food chains. Nereids are commonly deposit-feeders and herbivores. A pair of large, lateral jaws can be everted during feeding to scrape algae, small invertebrates or detritus from the substrate.













Unlike other burrowing polychaetes Perenereis do not typically occupy a tube, however, in extreme conditions such as a lack of suitable habitat or a significant reduction in food availability they are able to secrete a mucous suspension-feeding net which can also function as temporary housing (own research). The peristomium and first segment of nereids are fused and cephalised otherwise there is little regionalisation of the body. The form of parapodia and chaetae vary from the anterior to posterior of the polychaete. Nereids use parapodia and associated chaetae to move around in their environment. Slow walking involves only the movement of parapodia which alternate between power and recovery strokes. Chaetae are important to grip the substratum. Fast walking involves the lateral waves of muscular contractions or undulations passing from the anterior to the posterior of the body (Ruppert et al., 2004). They may occasionally be forced to swim in which case they use rapid, lateral body undulations to propel through the water. These movements are also important in predatory avoidance.

Nereis spp. are semelparous and able to reproduce by both sexual and asexual methods. Globally, both epitoky and nocturnal swarming behaviours have been observed in sexually reproducing individuals (for more information see ‘Internal anatomy – Sexual Reproduction’). Asexual reproduction is typically via regeneration of lost or damaged body segments (for individually conducted research and more information see ‘Cell Biology').

Nereids are abundant on the rocky intertidal shore of Redcliffe, QLD making them an extremely accessible, unusual and exciting organism to study. Their habitat, behaviour and ability to asexually regenerate parts of their body are intriguing and the methods by which they are able to do this is strongly sought after by scientists in the medical profession. It’s truly amazing the wonders that the ‘big blue’ beholds if we only take the time to look beneath the surface.