Halisotoma maritima (formerly Isotoma maritima) is a widespread and common inhabitant of the seashore. It is greyish blue in colour and reaches a length of 2.5 mm. The mucro has only three teeth and the outer side of the tibiotarsus of the second leg bears a pair of distinctive fan setae (Fig. 1). Halisotoma maritima differs from the scarce Halisotoma poseidonis in the fine structure of the maxilla (Fig. 2). My thanks to Arne Fjellberg for spotting this and bringing it to my attention.
Fig. 1: Halisotoma maritima collected from Dumanus Bay, Cork in January 1953 by Peter Lawrence. The outer side of the tibiotarsus of the second leg (tt) bears a pair of distinctive fan setae (*only one clearly visible in the photo above).
Fig. 2: Maxilla of Halisotoma maritima collected from Hood's Ferry, Maghee Isle in November 1938 by Bagnall. Note that lamella 1 (max) has about five 'ciliated' fringes (lamella 1 of Halisotoma poseidonis has only two 'ciliated' fringes).
