General
E. complanata possesses an elongate, posteriorly tapering and ventrally flattened bodyplan, demonstrating bilateral symmetry (figure 1). Belonging to the Polycheate superclass, it exhibits clear segmentation and a developed, specialised prostomium (head) region (Ruppert et al, 2004).
Figure 1. E. complanata, exhibiting a bilaterally symmetrical body plan.
Prostomium
The prostomium, or head segement, is located anteriorly and bears a variety of sensory and feeding appendages. E complanata exhibits a strong reliance on its chemosensory system for food acquisition, despite bearing 2 pairs of eyes. This region also exhibits short sensory tentacles, in conjunction with buccal masses associated with it eversible mouthparts (Ruppert et al, 2004). The distinct lack of jaws, teeth or papillae signifies the importance of the animal’s nuchal (chemosensory) organ (Pardo and Amaral, 2005).
- Nuchal organ
A seemingly paired organ, this ciliated pit is actually a single structure separated by central groove. The nuchal organ is the fireworms key sensory appendage in regards to its nocturnal feeding forays, with potential use in light detection in mating as indicated in other polychaete species (Pardo and Amaral, 2005; Wilkens and Purschke, 2009).
Parapodia and chaetae
The parapodia and calcareous chaetae, unique to the Ampinomidae order, allow E. complanata a slow, but steady, rate of peristaltic locomotion (Pardo and Amaral, 2005; Ruppert et al, 2004). The paired parapodia are well developed, with the chitinous setae protruding laterally to provide a solid anchoring point required for its locomotion technique. The hollow, harpoon-like chaetae radiate from a tightly bunched origin in the parapodia (figure 2). The distinct red gill masses are also associated with the parapodia, being located near the base of the setae, providing diffusive respiration.
Figure 2. The chitineous chaetae of the fireworm |