Systematics
Order: Phyllodocida Dales, 1962.
Family: Polynoidae Kinberg, 1856.
Genus: Harmothoe Kinberg, 1856.
Species: Harmothoe aspera (Hansen, 1879).
Material examined
The two specimens of H. aspera have the following specifications. Both were incomplete and damaged at their posterior end, had no sexual products and had most of their elytra missing. Specimen one measured 3.5 mm long with 19 segments. Segment 18–19 were damaged and only 3 elytra remained (reference collection Rijkswaterstaat). Specimen two measured 2.6 mm long with 15 segments. The left half of segment 14 was missing with 1 elytron left (reference collection Rijkswaterstaat).
Remarks
The two specimens showed ventrally inserted lateral antennae, a bilobed prostomium with cephalic peaks and a digitform supra-acicular process on the neuropodia. The specimens were identified and confirmed as H. aspera by their elytra (Fig. 2). The margin of their elytra had fringing papillae, the microtubercles were pointed (thorn-shaped/triangular) and the macrotubercles near the posterior margin were large and pyramid shaped. All characteristics fit within the normal range of shapes of H. aspera. The key characteristic used to identify H. aspera were the large pyramid shaped macrotubercles.
The presence of large pyramid shaped macrotubercles, as described by Barnich and Fiege (2000), is a clear key characteristic. Nonetheless, H. aspera can be confused with three other species: Harmothoe globifera, Harmothoe bellani and Harmothoe lagiscoides serrata. H. globifera differs by having much longer marginal papillae on the outer lateral margin of their elytra and the macro- and microtubercles are rounded, globose and covered with small nodular papillae. H. bellani differs by having thorn-shaped microtubercles and no macrotubercles. H. lagiscoides serratai differs by having slender and thorn-shaped macrotubercles (Barnich and Fiege 2000).
Habitat
The L15-A platform has a steel jacket foundation which is standing in waters 22 m deep with a sandy bottom that is locally covered with rock dump to prevent scouring of the seabed. The two H. aspera specimens were found in fouling communities growing on steel in vertical orientation. The community at the sampled depths was dominated by Metridium senile and Tubulariidae covered with Jassa herdmani turf. In total, 60 benthic species where present in the 8 samples obtained at these depths, with representatives from Annelida (15 spp), Arthropoda (20 spp), Bryozoa (5 spp), Cnidaria (3 spp), Echinodermata (3 spp), Mollusca (10 spp) and Porifera (4 spp). H. aspera was observed close to the seabed, but was not present in samples taken from the rocks at the bottom of the platform.