[Illustration: FIG. 96.—_Caprella grandimana_, × 4. _a_, Abdomen; _g_, gills; _t_, 3rd (first free) thoracic segment; _t′_, 8th thoracic segment. (After P. Mayer.) ] =Fam. 1. Caprellidae=[113] are also chiefly littoral forms, swarming among rocks covered by algae, though they are by no means so easy to detect as the Gammaridae and Tanaidae which haunt similar situations. In a basinful of algae or Polyzoa taken from the rocks fringing the Bay of Naples, the latter are easily collected, the Tanaidae always crawling out of the weeds in the direction of the light, while the Gammarids dart about in all directions; but the Caprellidae, with their branching stick-like forms, harmonise so well with their surroundings that it requires an experienced eye to detect them. The body is elongated and thin, resembling that of a stick-insect. The first two thoracic segments are more or less completely fused with the head; the second and third thoracic limbs end in claws; the two following thoracic limbs are normal in the genus _Proto_, rudimentary in _Protella_, and absent in the remaining genera, though their gills remain as conspicuous flabellate structures. The three hind legs are normal, and the abdomen is reduced to a tiny wart at the hind end of the greatly elongated thorax. P. Mayer has described cases of external hermaphroditism as being fairly common in certain species, _e.g._ _Caprella acutifrons_, and this is interesting if we take into consideration the frequent partial hermaphroditism exhibited by the gonad of _Orchestia_ at certain times of year (see p. 104). =Fam. 2. Cyamidae.=—These are closely related to the Caprellidae in the form of the limbs and the reduced state of the abdomen. _Cyamus ceti_, which lives ectoparasitically on the skin of whales, has the body expanded laterally instead of being elongated, as in the Caprellids. =Sub-Order 3. Hyperina.= [Illustration: FIG. 97.—_Phronima sedentaria_, ♀, in a _Pyrosoma_ colony, × 1. (After Claus, from Gerstaecker and Ortmann.) ]