Chelophores.—The first pair of appendages or chelophores are wanting in the adult Pycnogonum, Phoxichilus, Rhynchothorax, and Colossendeis.[[396]]
In Ammothea and its allies they are extremely rudimentary in the adult, being reduced to tiny knobs in Tanystylum and Trygaeus, and present as small two-jointed appendages in Ammothea; in this last, if not in the others also, they are present in complete chelate form in the later larval stages.
Fig. [266].—A, B, Chelophores of Ascorhynchus abyssi, G.O.S. A, Young; B, adult. (After Sars.) C, Anterior portion of Ammothea hispida, Hodge, Jersey: late larval stage (= Achelia longipes, Hodge), showing complete chelae. D, Chela of Eurycide hispida, Kr.
In Eurycide, Ascorhynchus, and Barana they are usually less atrophied, but yet comparatively small and with imperfect chelae, while in some Ascorhynchi (A. minutus, Hoek) they are reduced to stumps.
Fig. [267].—Chelae of species of Nymphonidae: A, Nymphon brevirostre, Hodge; B, Boreonymphon robustum, Bell; C, Chaetonymphon macronyx, G.O.S.; D, Nymphon elegans, Hansen.
Fig. [268].—Proboscis and chelophores of Cordylochele longicollis, G.O.S. (After Sars.)
In Pallenopsis the scape of the chelophore consists of two joints, as also in Decolopoda and some Ascorhynchus: in Nymphon, Phoxichilidium, Pallene, and Cordylochele of one only; in all these the terminal portion or “hand” forms a forcipate “chela,” of which the ultimate joint forms the “movable finger.” In some species of Nymphon the chela is greatly produced and attenuated, and armed with formidable serrate teeth on its opposing edges; in others it is shortened, with blunter teeth; in Boreonymphon robustum the claws are greatly curved, with a wide gap between. In this last, and in Phoxichilidium, the opposing edges are smooth and toothless. In Cordylochele the hand is almost globular, the movable finger being shortened down, and half enclosed by the other.