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PACIFIC SCIENCE, VoL XIV, April I960 
2-1-0, e d of tarsus I with basal companion seta. 
S4 of tibia I without companion seta. Supra- 
coxal setae absent on gnathosoma and coxa I; 
vestigial setae absent from patella and tibia of 
all legs. Femora I and II divided, six free seg- 
ments beyond the coxa; III undivided, only five 
free segments beyond the coxa. All tarsi with 
two nearly equal claws, the posterior ones a 
little larger and more erect than the anterior 
ones. Intercoxal area with more than one pair 
of setae between coxae II and III. 
REMARKS: The genus is remarkable for the 
way in which the larval characters have, in many 
cases, been carried over into the adult with little 
change. The general body form is strikingly 
similar in both stages, and the chaetotaxy of the 
body is nearly as simple in the adult as it is in 
the larva. Perhaps the greatest similarity in the 
two instars is in the structure and chaetotaxy of 
the appendages. In the larva of C. delitescens, 
the chaetotaxy of the palpal tarsus is very rem- 
iniscent of that found in Johnstoniana, Dip- 
lot hr ombium, and Centrotrombidium, being 
virtually identical with the latter. In these three 
genera, however, the two or more dorsal and 
distal setae of the tarsus (which evidently are 
modified eupathidia) are replaced in the adult 
by typical eupathidiform setae. In Charadracarus 
delitescens, on the other hand, these setae are 
easily recognizable in the adult and have almost 
precisely the same form that they had in the 
larva. The total number of setae on the palp of 
the adult is increased only a little over that of 
the larva, and there is usually (exception: C. 
aelleni) no development of the paradont on the 
palpal tibia such as occurs in all the other genera 
of the Johnstonianidae. 
The femur, which is undivided in leg III of 
the larva remains undivided in the adult, too, 
and femur IV also has no trace of a subdivision. 
In both larva and adult, the eupathidia are con- 
fined to tarsi I and II; moreover there is no 
proliferation whatever of the eupathidia on 
tarsus II, there being a single eupathid in both 
larva and adult. There is an appreciable increase 
in the number of eupathidia on tarsus I. There 
is a single solenidioni on tarsus I of the adult 
just as in the larva, whereas in other genera 
there is often an increase in the number of Si 
in the transition from larva to adult ( Centro - 
trombidium, Johnstoniana). In all these charac- 
teristics, the members of the genus appear to be 
highly neotenic. The presence of numerous setae 
in the intercoxal area of the larva is, on the 
contrary, a typically postlarval characteristic. 
TYPE SPECIES: Charadracarus hurdi new 
species. 
CHARACTERS SHOWING INTERSPECIFIC 
VARIATION IN THE GENUS CHARADRACARUS 
The known species of this genus show a high 
degree of homogeneity in structure. The ob- 
served differences, in many cases, are so minor 
that the possibility of environmental influences 
can not be dismissed. However, until the exist- 
ence of such influences have been proved ex- 
perimentally, we must assume that the observed 
differences have actual specific value. The struc- 
tures exhibiting variants of specific value are 
discussed here briefly, and are then summarized 
in a formula key. 
Sensilla. At least two types of sensilla oc- 
cur in the genus. In all known species but 
C. hurdi, the sensilla are fusiform, with a club- 
shaped swollen portion at the end of a long 
slender stalk, and beyond this the shaft of the 
seta tapers to a fine point. The portion of the 
shaft proximal to the swelling is nearly the 
same length as the portion distal to the swell- 
ing. In C. hurdi, the distal portion is almost 
completely wanting; an indication of it is seen 
only at high magnification (Fig. 9). In both 
types, the swollen portion of the sensillum bears 
a number of fine points. 
Setae of Hysterosoma. In the adults of all 
described species, there are two series of setae, 
major and minor, the minor setae being smaller 
and much more numerous than the major. 
Cooreman (1954: 14-17) indicated that there 
are six pairs of major setae in C. aelleni. The 
number and arrangement in the three species 
studied by the writer are not especially regular. 
The distinct interspecific differences are found, 
however, in the form of the major setae. In 
C. hurdi and C. aelleni, the major setae are like 
the minor in the filiform tips. In the remaining 
two species, on the other hand, the tips of the 
major setae are distinctly swollen and bear a 
tuft of fine barbs. The terminal tuft of barbs in 
