Taxonomic studies on brackish copepods in Korean waters - II. Ontogeny and phylogeny of appendages in copepodid stages of Tortanus derjugini Smirnov, 1935 (Copepoda, Calanoida)

Abstract

The development of all copepodid stages of a brackish calanoid copepod Tortanus (Eutortanus) derjugini from western Korea is investigated. Homologies of segmentation and setation in adult characters are traced through all copepodid stages. The fourth and fifth pedigers are secondarily fused at the moult to the adult. Antennulary setation shows sexual dimorphism first at stage IV. The exopod of leg 1 is divided into two segments without addition of any element at the moult to stage II, while an inner seta on the first segment is newly added at the moult to stage III. This pattern differs from the basic pattern proposed for other copepods, in which the division of the exopod is preceded by the formation of an element or both occur at the same time. In the fifth leg of the male some elements are suppressed during the final moult into the adult. The ontogenetic analyses indicate that adult characters of some subgenera of Tortanus are expressed by their suppressions at the developmental phases. Suppression of elements is important for the evolution of Tortanus.