124 CRUSTACEA PERACARIDA chap. 



lends some support to this view, since the smaller species with 

 feeble chelae do appear to be compensated by a greater develop- 

 ment of sensory hairs on the antennae, but the specific differences 

 are so difficult to appreciate in the Tanaidae that it is possible 

 that the two forms of the male in Mliller's supposed single 

 species really belonged to two separate species. 



Sub-Order 2. Flabellifera. 



The Flabellifera include a nnmber of rather heterogeneous 

 families which resemble one another, however, in the uropods 

 being lateral and not terminal, and being expanded together with 

 the telson to form a caudal fan for swimming. The pleopods are 

 sometimes natatory and sometimes branchial in function. Some 

 of the families are parasitic or semi-parasitic in habit. 



Fam. 1. Anthuridae. — These are elongated cylindrical 

 creatures found in mud and among weeds upon the sea-bottom ; 

 their mouth-parts are evidently intended for piercing and sucking, 

 but whether they are parasitic at certain periods on other animals 

 is not exactly known. Antliura, Paranthura, Cruregens. 



Fam. 2. Gnathiidae.'' — These forms appear to be related to the 

 Anthuridae ; they are ectoparasitic on various kinds of fish during 

 larval life, but on assuming the adult state they do not feed any 

 more, subsisting merely on the nourishment amassed during the 

 larval periods. The larvae themselves are continually leaving 

 their hosts, and can be taken in great numbers living freely among 

 weeds on the sea-bottom. The larvae, together with the adults 

 of Gnathia maxillaris, are extremely abundant among the roots 

 of the sea-weed Poseidonia cavolinii in the Bay of Naples. The 

 young larvae hatch out from the body of the female in the state 

 shown in Fig. 8 2, A. This minnte larva fixes upon a fish, 

 and after a time it is transformed into the so-called Praniza 

 larva (B), in which the gut is so distended with the fluid 

 sucked from the host that the segmentation in the hind part 

 of the thorax is entirely lost. When this larva moults it may, 

 however, reacquire temporarily its segmentation. After a 

 certain period of this parasitic mode of life the Praniza finally 

 abandons its host, and becomes transformed into the adult male 

 or female. This may take place at very different stages in the 



1 G. Smith, Mitth. Zool. Stat. Neapcl, xvi., 1903, \\ 469. 



