83
DIAGNOSTIC FEATURES AND DESCRIPTION
In contrast to most of our native
crayfishes, the Rusty crayfish does
have some rather distinctive
markings. Overall they are a gray-
green with a darker rusty red
coloration on the dorsal surfaces.
Underneath they are a grayish color
as can be seen
below. The
distinctive
markings are
the rust-red
spots on the
rear of the
carapace seen
in the photo
above. Older
individuals
can become a
very dark
brown/olive
with age.
Colors are
their brightest
immediately
after a molt.
Algae growth in summer can make
them as black as tar.
One of the key
identification
characters of many
crayfishes is the
shape of the first
pleopod of a Form I
male. The terminal
elements of the first
pleopod of the Rusty
crayfish are straight
with the mesial process having a
slightly flattened end. In non-
breeding season the pleopod reverts to
a juvenile form (Form II) that is of
limited use for identification. Note
that this is very similar to the first
pleopod of the Ringed crayfish. .
The aureola in
the Rusty
crayfish is quite
wide with room
for several rows
of punctuations.
The rostrum of the Rusty crayfish is
similar to that of the Northern
crayfish. It has a dished center with
strong ridges on both sides. There is a
fairly sharp tip and no median carina.
Juveniles have much more pronounced
spines on
the tip and
on each side
which get
smaller as
they get
older.
