Both species, with no intermediate forms, were frequent in samples containing much Hydrallmania falcata and some other hydroids, including Kirchenpaueria pinnata (prey of D. dunnei) .

The dark specimen above fits the morphological features of D. hydrallmaniae which feeds on H. falcata. Visible features, as described in the original description of the species (Morrow,Thorpe & Picton, 1992), www.int-res.com/articles/meps/84/m084p053.pdf include:
1) Up to 12 mm long
2) Cerata are long and club-shaped, with a narrow base, reaching maximum diameter at just over half of their length, then tapering to a blunt terminal tubercle.
3) Wing-like ridges of typical pseudobranch structure are almost entirely absent.
4) Dark red pigment spots (dark reddish-brown on this one) cover the dorsum and the sides of the body, but leave a well-defined, clear circle around the bases of the cerata. Spots continuous from dorsum to flank between cerata.
5) Well defined spots extend onto the basal inner surfaces of the rhinophore sheaths.
6) White marks are present in the distal half of the rhinophores, becoming more concentrated towards the tips.
7) An area of dark brown-red pigment marks the inner face of each ceras.

The pale specimen above, Doto sp. 1, fits none of the points 2-7 listed for D. hydrallmaniae. Several members of Seasearch N. Wales on the diving expedition identified it as Doto eireana using the information and illustrations in Picton & Morrow, 1994, ‘A field guide to the Nudibranchs of the British Isles’ by B. E. Picton & C. C. Morrow, 1994 (referred to as P&M below). This and further reading of Thompson & Brown, 1976 ‘Biology of opisthobranch molluscs’ (T&B) show a similarity to D. eireana but with some differences that prevent positive identification as it. Below are listed features of the specimens found corresponding to those given above for D. hydrallmaniae:

Doto sp. 1.
1) Specimens up to 9.5mm were found on the Menai dives. If the 7mm maximum for D. eireana in T&B is correct, the species pictured is not it but, as it is a little known species that is yet to be confirmed by DNA sequencing, it might grow longer or not be a valid species.
2) Cerata are stout, with up to 5 circlets of blunt tubercles, becoming widest just below the tip. ( Similar in shape to D. eireana in B&P, but that species usually has 4, or fewer, circlets.)
3) Wing-like ridges of typical pseudobranch structure are large and well formed. See Doto sp. 1 pseudobranchs. .(Similar to D. dunnei and D. millbayana in T&B, but indistinct on D. eireana.)
4) Two pale longitudinal areas link the ceratal bases, so spots are not continuous from dorsum to flank between cerata. (“D. eireana may be distinguished” by this feature, T&B, but on some of the Menai specimens there are a very few spots encroaching onto the pale longitudinal areas; their significance is open to interpretation).
5) A few reddish dorsal pigment spots may extend onto the basal inner surfaces of the translucent white rhinophore sheaths and there are a few white spots on the rim.
6) The rhinophores have white pigment spots for almost their entire lengths.
7) There are no red or dark brown-red pigment marks on the inner face of each ceras like those found on D. coronata. s.s. and D. hydrallmaniae.