Larval development and metamorphosis of Berthella californica (Gastropoda, Heterobranchia, Pleurobranchoidea) including phylogenetic implications




LaForge, Nicole Laura

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Larval development of Berthella californica, a pleurobranchoidean heterobranch from the Northeastern Pacific, is described using histological sectioning, SEM, TEM, and immunolabelling. Current phylogenetic hypotheses place the Pleurobranchoidea as sister to all nudibranchs, or as sister to only the anthobranch nudibranchs. Deciding between these alternatives is difficult due to extensive homoplasy among heterobranchs. Analysis of larval morphology may help resolve this issue by identifying additional phylogenetically informative characters. Larval development has been well documented for many nudibranchs, but there are few studies on pleurobranchoideans. Larvae of B. calfornica dissolve internal shell whorls, a trait uniquely shared with nudibranch larvae. Additionally, mantle fold tissue inflates and reflects dorsally during metamorphosis to form the notum, which also occurs in anthobranchs. B. californica possesses several unusual developmental traits, as revealed by a review of current knowledge of heterobranch development. Morphological characters of B. californica larvae support hypotheses of nudibranch paraphyly and the clade Pleuroanthobranchea.



gastropoda, development, classification