Significance of head and carapace pores in Ceriodaphnia (Crustacea, Cladocera)

Abstract

Twelve species of Ceriodaphnia were examined by light and scanning electron microscopy for the presence of head and carapace pores. Rostral pores, similar to those in the Scapholeberinae (Dumont & Pensaert, 1983) were found in all species, situated just anterior to or between insertions of the antennules. With two exceptions, the pattern of reticulations around the pores was distinctive for each species. Oval ‘head pores’ or fenestrae occur consistently on the anterior surface of the cervical notch of juvenile and adult C. dubia, cf. dubia (from Australia), lacustris, and reticulata. The patterns of reticulations around a fenestra are unique to each species. It appears that C. cornuta (s.l.) in the Americas has a fenestra, whereas Australian C. cornuta (s.s.) has none. Minute pores often occur bilaterally anterior and posterior to the cervical notch in heavily reticulated individuals of several species but are not constant enough to be taxonomically useful. Well-defined small pores are situated within narrow reticulations just medial to the ventral and posterior valve margins of C. dubia, lacustris, and reticulata. These open into carapace glands of unknown, perhaps secretory, nature. Similar glands have been observed in related taxa. Such glands and marginal pores occur only occasionally or not at all in other Ceriodaphnia. Other small pores sometimes occur among reticulations of the head, fornix, and lateral and antero-ventral surfaces of the valves. They are found more often in juvenile or heavily reticulated individuals. As yet no consistent pattern to their occurrence among species has emerged. Head and carapace pores in Ceriodaphnia may be most useful in identifying species rather than in determining species groups or evolutionary patterns within the genus.