522 



PYCNOGONIDA 



CHAP. 



majority of cases studied the larval Pycnogon is at first provided 

 with three pairs only, the three anterior pairs of the typical 

 adult. 1 Numerical coincidence, and that alone, has often led this 

 " Protonymphon " larva to be compared with the Crustacean 

 Nauplius. In the annexed figure of a young larval Ammothea 

 (Achelici), we see the unsegmented body, the already chelate 



chelophores (furnished with 

 the provisional cement-glands 

 already described), the other 

 two pairs of appendages each 

 with a curious spine at its 

 base, the gut beginning to 

 send out diverticula (of which 



the first pair approach the 

 chelophores) but still desti- 

 tute of the anus (which is 

 only to be formed after the 

 development of the abdomen), 

 the proboscis, and one pair of 

 eyes situated close over the 

 pre-oral ganglia. The subse- 

 quent changes are in this 

 genus extremely protracted, 

 FIG. 280. Young larva (nat. size -i mm.) of and terminate with the loss 



Ammothea fibulifera, Dohrn. O. G, Brain ; ,, , , , , . , 



ff i, gid, gilmd ami duct of cheiophore ; ot the chelae, a process which 



pr, proboscis ; I, II, III, IV, appendages. 

 (After Dohru.) 



occurs so late in life that the 

 chelate individuals were long 

 looked upon as belonging to a separate genus, the original 

 Ammothea of Hodge, until Hoek proved their identity with 

 the clawless Aclielia. 



The developmental history of Phoxichilidium and Anoplo- 

 dactylus is peculiar. The young larvae have the claws of the 

 second and third appendages hypertrophied to form enormous stiff 

 tendril-like organs, with which they affix themselves to the bodies 

 of Hydroid Zoophytes (Coryne, Eudendrium, Tubularia, Hydrac- 



1 The correspondence is not universally admitted. Meinert (Ingolf Expedition, 

 1899) believes that the second and third appendages of the larva disappear, and 

 that the palps and ovigerous legs are new developments ; so giving to the normal 

 Pycnogon nine instead of seven appendages. See also Carpenter "On the Relation- 

 ship between the Classes of the Arthropoda," Proc. Ji. Irish Acad. xxiv., 1903, 

 pp. 320-360. The latest observer (Loman) inclines to the older view. 



