Larval development of japanese “conchostracans”: Part 3, larval development of lynceus biformis (crustacea, branchiopoda, laevicaudata) based on scanning electron microscopy and fluorescence microscopy



For comparison with the remarkable larvae of the laevicaudatan (clam shrimp) Lynceus brachyurus, a basic description of the larval sequence of another laevicaudatan branchiopod, the Japanese Lynceus biformis, is provided. Four larval stages have been identified, ranging in size from 258 to 560 μm in length. The first stage has no flattened dorsal shield, in contrast to the three following stages, in which such a shield is present. During development, the only significant changes to the naupliar appendages occur in the antenna at the molt from stage 1 to 2, with the addition of a fourth apical seta to the endopod and a change in the form of the naupliar process, used for food manipulation, from a long, unbranched, pointed spine to a bifid structure. In addition, buds of trunk limbs (five pairs) first appear externally in stage 4 but can be recognized through the cuticle in the previous stage. The larval sequence and larval morphology of L. biformis differ from those of L. brachyurus in at least two respects. L. brachyurus has a dorsal shield in the earliest known stages, but such a shield is lacking in the first stage of L. biformis. Another difference is that L. brachyurus has a huge, flattened, kidney-shaped labrum, whereas that of L. biformis is smaller and bears four robust, denticulate spines on the distal margin. Based on out-group comparison, the morphology of L. biformis, at least in these respects, is likely to represent the ancestral morphology. Despite the partly peculiar morphology of the larvae of Lynceus species, they share many similarities with other branchiopod larvae, at least two of which, the naupliar swimming/feeding apparatus and the mode of development of the trunk limbs, could be considered synapomorphies for the Branchiopoda. J. Morphol., 2013. © 2012 Wiley Periodicals, Inc.