Developmental and Functional Morphology of Ishikawa, 1895 (Branchiopoda: Spinicaudata) Feeding Structures: Combination of Filtering and Scraping Feeding Mechanisms.

Large branchiopods inhabit diverse continental habitats worldwide. Their feeding ecology, nevertheless, remains largely unknown. The few functional morphology studies that have been conducted have mostly focused on adults or larvae, seldom have the two been compared collectively. In this study, we examined the feeding structures in Ishikawa, 1895 from nauplius to adult to clarify their feeding mechanisms and then compared them with the other two sympatric branchiopods ( and ) in Siangtian Pond, Taiwan. Naupliar second antennae and mandibles are similar to those of other species, suggesting filter-feeding. The naupliar feeding structures, including the mandibular palp and naupliar process, gradually degenerate during the juvenile stage. Simultaneously, the molar surface, maxillae, and second antennae continue developing, reaching their adult form in later juvenile substages. The molar surface and thoracopod setal morphology are similar to those of other filter-feeding branchiopods, but adults also have scraping setae on the first several thoracopod pairs. Nearly all naupliar primary feeding structures change through development, particularly during the early juvenile substages, whereas late juvenile substages and adult morphology are similar. transforms from pelagic filtering nauplii to adults that combine benthic filtering and scraping. Comparisons of molar and thoracopod morphology between coexisting branchiopod species show some similarities and differences in filtering and scraping feeding structures, implying potential foraging resource differentiation among species.