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 Miiller’s supposed single 
species really belonged to two separate species. 
Sub-Order 2. Flabellifera. 
The Flabellifera include a number 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. <Anthura, 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. 82, A. This minute 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 hfe 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 
1G. Smith, Witth. Zool. Stat. Neapel, xvi., 1903, p. 469. 
