202
WILLIAM MACNAE
the substratum. All appear to feed by using a technique by means of
which diatoms or particles of edible detritus are separated from the
mineral fraction of the substratum. The process has been studied in
certain species of Uca, Dotilb and Mictyris. Specimens of other gencra
which I have examined (Heloecius, Uca) and of some which have bccn
studied by Ono (Ilyoplax, Scopimera) possess a buccal armature of
similar form and hence may be presumed to feed in a similar manner.
All of these smaller ocypodids feed by picking up portions of the substratum, licking the particles and/or selecting some of them, and
discarding the rest in the form of the subspherical pellets which arc so
notable a feature of the areas inhabited by them.
Male specimens of Uca use only the minor cheliped, females of D’ca
and both sexes of the other genera use both chelipeds more or less
alternately. Chelipeds used for this purpose are slightly hollowed a t thc
tips. Thc material is then transferred to the maxillipeds for sorting.
The third maxillipeds are not greatly concerned in this. The second
and first maxillipeds are modified to serve as sorting agents (Fig, 71).
The setae of these two limbs are highly modified, and particularly those
on the meropodite and to a lesser extent those on the distal segment2
of the limb. Several of these setae havc spoon tips, others are feathery,
such are characteristic of the inner surface of the second maxi1lil;cd.
The setae on the outer surface of the first maxilliped are also modifiej
to form, together, a stiff brush. This is illustrated in Fig. 71. The form
of the spoon-tipped hairs varies. There are more of them and each
individually is larger in those species picking up sand grains, and
smaller individually, and fewer in those species which feed on finc
particles. Figure 71 indicates these variations in a scries of species
of Uca : row I represents the set of maxillipeds of U . lactea which fecds
off sand ; row I1 represents those of U . urvillei which feeds off fine mud,
and row I11 those of U . dussumieri which feeds off very fine mud. The
series illustrated is very similar in appearance to the buccal armature
of Uca pugnax, U . pugilator (Bosc) and U . minax (Le Conte) illustrated
by Miller (1961) and so may be presumed to function in the way hc
described.
A current of water is pumped up out of the branchial chamber by
the scaphognathite. This current assists in the sorting process. It
would appear that the material picked up by the chelipeds is rolled
between the specialized setae on the meropodite of the second maxilliped and the stiff brush of hairs on the outer surface of the meropodite
of the first maxilliped. The spoon-tipped hairs would hold sand grains
against the “ brush ” which would scrape off the diatoms, etc., living
on these grains. The current of water would wash this organic material
WILLIAM MACNAE
the substratum. All appear to feed by using a technique by means of
which diatoms or particles of edible detritus are separated from the
mineral fraction of the substratum. The process has been studied in
certain species of Uca, Dotilb and Mictyris. Specimens of other gencra
which I have examined (Heloecius, Uca) and of some which have bccn
studied by Ono (Ilyoplax, Scopimera) possess a buccal armature of
similar form and hence may be presumed to feed in a similar manner.
All of these smaller ocypodids feed by picking up portions of the substratum, licking the particles and/or selecting some of them, and
discarding the rest in the form of the subspherical pellets which arc so
notable a feature of the areas inhabited by them.
Male specimens of Uca use only the minor cheliped, females of D’ca
and both sexes of the other genera use both chelipeds more or less
alternately. Chelipeds used for this purpose are slightly hollowed a t thc
tips. Thc material is then transferred to the maxillipeds for sorting.
The third maxillipeds are not greatly concerned in this. The second
and first maxillipeds are modified to serve as sorting agents (Fig, 71).
The setae of these two limbs are highly modified, and particularly those
on the meropodite and to a lesser extent those on the distal segment2
of the limb. Several of these setae havc spoon tips, others are feathery,
such are characteristic of the inner surface of the second maxi1lil;cd.
The setae on the outer surface of the first maxilliped are also modifiej
to form, together, a stiff brush. This is illustrated in Fig. 71. The form
of the spoon-tipped hairs varies. There are more of them and each
individually is larger in those species picking up sand grains, and
smaller individually, and fewer in those species which feed on finc
particles. Figure 71 indicates these variations in a scries of species
of Uca : row I represents the set of maxillipeds of U . lactea which fecds
off sand ; row I1 represents those of U . urvillei which feeds off fine mud,
and row I11 those of U . dussumieri which feeds off very fine mud. The
series illustrated is very similar in appearance to the buccal armature
of Uca pugnax, U . pugilator (Bosc) and U . minax (Le Conte) illustrated
by Miller (1961) and so may be presumed to function in the way hc
described.
A current of water is pumped up out of the branchial chamber by
the scaphognathite. This current assists in the sorting process. It
would appear that the material picked up by the chelipeds is rolled
between the specialized setae on the meropodite of the second maxilliped and the stiff brush of hairs on the outer surface of the meropodite
of the first maxilliped. The spoon-tipped hairs would hold sand grains
against the “ brush ” which would scrape off the diatoms, etc., living
on these grains. The current of water would wash this organic material