Background

Polynoidae (scale worms) is a highly diverse family of polychaetes including more than 700 species (Martin and Britayev 1998). Members of this family are easily recognizable by their dorsal elytra. Polynoidae are mainly considered to be free-living carnivorous-polyphagous (Fauchald and Jumars 1979). Their life strategies and known diets are highly diverse, with more than 20% being symbiotic species. Polynoidae feed on and interact with all kinds of prey including small crustaceans, echinoderms, sponges, gastropods, hydroids and other polychaetes (Fauchald and Jumars 1979).

Harmothoe aspera (Hansen, 1879) is a species of which little is known. Throughout the years, reports of H. aspera have been made from the Strait of Georgia, the Skagerrak, and the Barents, Mediterranean and Japanese sea (Table 1). Depths at which H. aspera has been found varies in range from circa 50 m (Swedish Agency for Marine and Water Management), to circa 200–270 m (Holte 2014; Hassel 2014) and even circa. 1500 m (Nishimura 1966).

Table 1 A sample of locations, year and depth in meters of previous observations of H. aspera a
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The first record of H. aspera was made by Hansen (1879) during the Norwegian North-Atlantic Expedition at station 48 (Lat, 64° 36′ N. Long 10° 22′ W) near the coast of Iceland. The recorded depth was 547 m. The habitat in which H. aspera was found was characterized as dark grey porous clay which contained granite, a few quartz pebbles and a few calcareous shells. The bottom temperature was recorded at −0,3 degrees Celsius (Schmelk, 1882). This article is the first report of H. aspera in the Dutch Exclusive Economic Zone (EEZ) and the first report for H. aspera in a depth range between 15 and 20 m.

Methods

Two specimens of Harmothoe aspera were observed in a mixed macrofauna sample obtained with a surface supplied airlift as described in Coolen et al. (2015) during marine growth sampling for the RECON (Reef effects of structures in the North Sea) project. Marine growth in these samples consisted out of fouling communities on artificial substrates. Samples were taken 11 km from the coast of the island of Vlieland within the Dutch EEZ of the North Sea from an artificial substrate at petroleum platform L15-A (53.3295°N 4.8301°E), at a depth of 15 and 20 m in June 2014 (Fig. 1). Samples where fixed in a borax buffered 6% formaldehyde sea water solution, which was replaced with a mix of 70% ethanol and 3% glycerol before identification. H. aspera was identified by classic taxonomy using the following keys: “Identification of scale worms in British and Irish waters” (Barnich 2011) and “Revision of the Mediterranean species of Harmothoe” (Barnich and Fiege 2000). Both specimens are stored in the Rijkswaterstaat benthic reference collection.

Fig. 1
figure 1

Locations of the samples platforms for the RECON project (black & red bullets). The two specimens of H. aspera were found on platform L15-A (53.3295°N 4.8301°E; red bullet)

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Results

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.

Fig. 2
figure 2

Elytron of Harmothoe aspera. Characteristic for of H. aspera are the large pyramid shaped macrotubercles on the posterior margin of the elytra. The Photo was taken by Martijn Spierings during the discovery of the first H. aspera specimen

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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.

Discussion

The presence of H. aspera of the coast of Vlieland represents its first ever record in the Dutch EEZ. Since its first discovery in 1879 information on H. aspera has been scarce with only a few records since the 1970’s.

The original description from Hansen (1879) contains habitat information on bottom materials, depth and temperature. Besides this account no further descriptions can be found within other records that give information about the habitat of H. aspera. There are also no recorded descriptions about its lifecycle or reproduction. There are only species records containing a year and sometimes a depth is listed. Harmothoe aspera is found in different seas all over the world. In 1876–1878 it has been recorded during the Norwegian North-Atlantic Expedition (Hansen 1879), in 1973 it was recorded in the Strait of Georgia on a 52 year old telephone cable (Levings and McDaniel 1974), in the 1990’s it was found for the first time in the Western Mediterranean (Barnich and Fiege 2000) and around 2006–2008 it was recorded in the Barents Sea (Anisimova et al. 2010). It appears that H. aspera is mostly observed at a depth range between 200 and 300 m, although it has also been observed at shallower depths of 48 m in the waters of Sweden. It must be noted that our depth record (15–20 m) is the shallowest depth record for H. aspera to date.

H. aspera remains a species of which very little is known. The observation of H. aspera on artificial hard substrate in the North Sea emphasizes the importance of investigations of benthic communities on these structures. This finding increases the diversity of Polynoidae found on artificial hard substrates.