_Laura gerardiae_, described by Lacaze Duthiers,[69] is parasitic on the stem of the “Black Coral,” _Gerardia_ (vol. i. p. 406); it has the shape of a broad bean, the body being entirely enclosed in a soft mantle, with the orifice in the position corresponding to the hilum of a bean. The body lying in the mantle is composed of eleven segments, and is curved into an =S=-shape. Its internal anatomy is entirely on the plan of an ordinary Cirripede. _Petrarca bathyactidis_, G. H. Fowler,[70] was found in the mesenteric chambers of the coral _Bathyactis_, dredged by the _Challenger_ from 4000 metres. The body is nearly spherical, and the mantle-opening forms a long slit on the ventral surface. The mantle is soft, but is furnished on the ventral surface with short spines. The antennae, which form the organs of fixation, remain very much in the state characteristic of the Cypris larvae of other Cirripedes, being furnished with two terminal hooks by which attachment is effected. The thoracic appendages, of which there are the normal number six, are reduced flabellate structures, and the abdomen forms an indefinitely segmented lobe of considerable size. The animal appears to be in an arrested state of development, and so retains some of the characteristics of the Cypris larvae, but it is very doubtful how far these characters can be considered primitive. Other forms are _Dendrogaster astericola_ on Echinoderms, and _Synagoga mira_ on the “Black Coral,” _Parantipathes larix_, at Naples. =Sub-Order 5. Apoda.= [Illustration: FIG. 65.—_Proteolepas bivincta_, × 26. _A_, Antennae; _a_, _b_, 1st and 2nd abdominal segments; _O_, ovary; _P_, penis; _T_, telson; 1–8, thoracic segments. (After Darwin.) ] Darwin described a small hermaphrodite parasite in the mantle chamber of _Alepas cornuta_ from Saint Vincent, West Indies, which he named _Proteolepas bivincta_. The body (Fig. 65) is distinctly segmented into eleven somites, the last three of which are supposed to belong to the abdomen; there are no appendages except the antennae by which fixation is effected. The mouth-parts are of normal constitution. This animal has not been found again since Darwin’s discovery, but Hansen[71] describes a number of peculiar Nauplius larvae taken in the plankton of various regions, which he argues probably belong to members of this group. A wide field of work is offered in attempting to find the adults into which various larvae grow. =Sub-Order 6. Rhizocephala.=[72]