Nauplii of Tegastes Falcatus (Norman, 1869) (Harpacticoida, Tegastidae), a Copepod with an Unusual Naupliar Mouth and Mandible

There are six stages in the naupliar phase of development of Tegastes falcatus (Norman, 1869). The labrum is expressed as a simple fold which does not cover the mouth. A poorly-sclerotized mouth tube was observed on some specimens of all stages except NI (= naupliar stage 1); NI and Nil are the only stages without an anus and presumably do not feed. The antennal endopod is a subchela against itself at Nil; its distal endopodal segment becomes bifurcate at NIII. A chela on the naupliar mandible consists of the endopod opposite a distoventral attenuation of the basis on NII-NVI. The segmental elements of a chela are present at NI, although the endopod does not oppose the basis at this stage. The maxillule is a unilobe bud with one seta at NIII that gains a second seta at NV and is transformed into a simple bilobe bud with three setae at NVI. The maxilla and maxilliped are each an asetose, ventral attenuation at NVI. Naupliar stages, found in large numbers along with all six copepodid stages of T. falcatus, apparently feed on suctorian ciliates growing on colonies of the bryozoan Flustra foUacea (Linnaeus, 1758). This is the first description of six naupliar stages for a species of Tegastidae Sars, 1904.