Differences between the sensory organs of phytal and bottom-dwelling Loxoconcha (Ostracoda, Crustacea)

Abstract. The morphology and distribution patterns of pores with a bristle were studied on two Loxoconcha species living in adjacent but different habitats: the phytal species L. japonica and the bottom-dwelling species L. uranouchiensis. Both species have only one kind of pore – sieve-pore – from which either of two kinds of bristles emerges. The two types of bristles are here called the “smooth”– and the “twisted”–type according to their morphological features. The sieve-pore orifice of the phytal Loxoconcha remains completely open, whereas that of the bottom-dwelling species has a special morphology both in the sieve-plate and the basal part of the bristle to cope with the adhesion of dirt. The number and distribution pattern of “twisted”-type bristles (chemo-receptors?) are the same in both species. The “smooth”-type bristles (mechano-receptors?), however, are distributed more densely in the ventral area of the bottom-dwelling species compared with those of the phytal species. This difference seems to be related to the mode of life, specifically the difference in the manner of ventral contact with substrata. Some adaptive characters of ostracod pores are clarified and their significance to ostracod taxonomy and palaeocology is discussed.