figure 1: D. koenneckeri (length 9 mm) Menai Strait, Anglesey.
It is surprising that such a distinctive species as Doto koenneckeri (figures 1 and 6) was aggregated with Doto coronata (figure 2) until 1976. The dark pigment spots on the cerata (outgrowths on the upper surfaces of the body) of D.koenneckeri compared with the red spots and red pigment on the inner face of the cerata of D.coronata, are among the features which distinguish these species.
figure 2: D. coronata (length 7 mm).
The only records of D. koenneckeri mapped by N.B.N. Gateway http://data.nbn.org.uk/ are from Scilly, Skomer, the Calf of Man and Lyme Bay. There are records in W. Ireland (Biomar), and from Norway to Spain (Thompson and Brown 1984). Most or all records are from divers, but it can be found on the shore.
In August 2010, two specimens of D. koenneckeri were found at low water of a spring tide on the Menai Strait by inspecting the alga, Halidrys siliquosa (figure 3), a preferred attachment surface for the hydroid Aglaophenia pluma, the food of D. koenneckeri.
figure 3: H. siliquosa, Menai Strait.
The alga was found in the water’s edge, but it also lives in deep pools low on the shore, and divers may find a belt of it growing just below the Laminaria zone. It is easily recognised by its long pod-like air bladders, which reveal internal compartments when cut lengthways (figure 4).
figure 4: Air bladder of H. siliquosa (length 60 mm).
If the alga is in water, the hydroid and any spawn of D. koenneckeri can be fairly easily seen If spawn is found, there is a good chance that the adult is nearby, but it is difficult to detect as it is so well camouflaged (figure 5).
It may be possible to find the adult with the help of a hand magnifier if the alga and hydroid are placed in water, but it may be necessary to take a sample for examination at 5 and 10 under a binocular microscope. This especially applies at times when the slugs are 2 or 3 mm juveniles.
Thompson and Brown (1984) stated that the spawn had only been observed in May, but the Menai record shows that it occurs at least in August also. If no spawn is found, it is still worth examining a plant bearing the hydroid for juveniles.
figure 6: Underside of D. koenneckeri.
Reference
Thompson, T.E. and Brown, G.H.. 1984. Biology of Opisthobranch Molluscs 2. London.