ON THE DEVELOPMENT OF PARASITIC COPEPODA I. -SARCOTACES PACIFICUS KOMAI (CYCLOPOIDA : PHILICHTHYIDAE)-

Abstract

1. The free-living larval stages of Sarcotaces pacijicus Komai are described and figured on the specimens reared under the laboratory conditions. 2. About ten thousand eggs or the first nauplius larvae may be found together with a couple of parasitic copepods in a single gall. Probably, the hatching of eggs takes place inside the gall, but further development does outside it after the napuplii have escaped into the sea through a pore. There are noted five nauplius stages to the first copepodid stage within 45 hours under laboratory conditions at 20-22°C. 3. The nauplii have three appendages typical to usual nauplii, but the appendages are devoid of feeding apparatus, gnathobase and masticatory setae. They are nonfeeding throughout all the stages, and no growth of the body is gained. All appendages become gradually simplified and no rudiments of post-mandibular mouth-parts are recognized. The rudimentary first and second legs appear at the fifth stage. 4. The first copepodid is the infective stage. Most of them survive more than a week on the yolk contained in them. The apparent mouth-parts are completely m1ssmg. The first pedigerous segment is separated by a distinct suture from the cephalothorax which is provided with only two pairs of antennae. 5. The systematic position of Sarcotaces is discussed briefly. The morphology offreeliving larvae clearly shows that Sarcotaces belongs to Cyclopoida and that the genus is to be included in the family Philichthyidae. Further, a close relation between the Philichthyidae and the Chondracanthidae is ovbious. The difference between these two families in the number of nauplius stages, five in the Philichthyidae and three in the Chondracanthidae, may depend upon the conditions of the adult habitat or upon the mode of parasitic life, or be referable to the phylogenetic feature.