n. pl.1.(Zool.) A large division of Mollusca, including all except the bivalves; - so called because the head is distinctly developed. See Illustration in Appendix.
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cephalata Verrill, 1910 but differs in the possession of alternating long (5-9) and short (1-4) dorsal cirri in mid body setigers.
Populations belonging to a specific group invariably showed close morphological similarity, and each corresponded to a different species, with the exception of two clusters, which both possessed morphological features attributed to Daphnia cephalata.
Daphnia longicephala was the sole species at six sites and was common at most others although three other species (carinata, cephalata, and projecta) were also detected.
cephalata had a heterozygosity less than half those of D.
1] hybrids (with cephalata, longicephala, or thomsoni), suggesting that they represented backcrosses.
Prior work (Hebert 1981) has shown some obligately parthenogenetic populations of Daphnia cephalata near Sydney, and this study confirmed the prevalence of populations showing fixed heterozygosity in this species.
cephalata were divisible into two genetically distinctive subspecies - one with a coastal and the other with an inland/montane distribution.
cephalata are known to have low fitness (Hebert 1985), suggesting that genetic divergence among taxa is now sufficient to ensure its protection from erosion by introgression.