TRIBE II. ISOKERANDRIA.
The first antennae are short, similar in the two sexes, and are never used by the male as clasping organs. This function may be subserved by the second maxillae.
Fams. Oncaeidae, Corycaeidae, Lichomolgidae, Ergasilidae, Bomolochidae, Chondracanthidae, Philichthyidae, Nereicolidae, Hersiliidae, Caligidae, Lernaeidae, Lernaeopodidae, Choniostomatidae.
The families Oncaeidae and Corycaeidae contain pelagic forms of flattened shape and great swimming powers, but the structure of the mouth-parts in the Corycaeidae points to a semi-parasitic habit.
Fam. 1. Oncaeidae.—This family, including the genera Oncaea, Pachysoma, etc., does not possess the elaborate eyes of the next family, nor is the sexual dimorphism so marked.
Fam. 2. Corycaeidae.—These are distinguished from the Oncaeidae, not only by their greater beauty, but also by the possession of very elaborate eyes, which are furnished with two lenses, one at each end of a fairly long tube. The females of Sapphirina are occasionally found in the branchial cavity of Salps, and their alimentary canal never contains solid particles, but is filled with a fluid substance perhaps derived by suction from their prey. S. opalina may occur in large shoals, when the wonderful iridescent blue colour of the males makes the water sparkle as it were with a sort of diurnal phosphorescence. The animal, however, despite the opinion of the older observers, is not truly phosphorescent. It may be that the ornamental nature of some of the males is correlated with the presence of the curious visual organs, which are on the whole better developed in the females than in the males. As in so many pelagic Copepods, the body and limbs may bear plumed setae of great elaboration and beautiful colour, e.g. Copilia vitrea (Fig. [37]).
We now pass on to the rest of the parasitic Copepods,[[51]] which probably belong to the tribe Isokerandria, and we meet with the same variety of degrees of parasitism as in the Ampharthrandria, often leading to very similar results.
Fig. [37].—Copilia vitrea (Corycaeidae), ♀, × 20. (After Giesbrecht.)
In the first seven families mentioned below there is no siphon. The Lichomolgidae and Ergasilidae have not much departed from the free-living forms just considered, retaining their segmentation, though in the Ergasilidae the body may be somewhat distorted (Fig. [39]). In both families the thoracic swimming feet are of normal constitution.