As with other valviferan
isopods, the uropods
to the pleotelson,
forming a valvelike covering over the pleopods
wosnesenskii is one
of the largest intertidal isopods in this area. It has a
flattened body with 7 free pereonites
and all pereopods
similar (with sharp claws) (photo).
margin of the cephalon
does not have a deep incision. The eyes are lateral (photo).
has 2 free pleonites
plus the pleotelson
1 is narrower laterally than in the middle (photo).
has lateral incisions indicating the end of another partly free pleonite
(photo). The palp
of the maxilliped
has 5 articles
posterior margin of the pleotelson
is convex and usually ends with a small apical tooth. The
margin of the coxal
plate of the 7th pereonite
is pointed (acute)
1 is wider by at least 1/10 than the cephalon
(photo), and the pereonites
near the middle of the body are wider than the anterior or posterior
is also wider than the cephalon. The eyes are kidney shaped
when viewed from the side.
Usually dark colored, dark olive green to brown but sometimes red (when
among coralline algae) or nearly black. May have a few white
on the body, especially at the posterior end. Up to 3.5 cm
Pentidotea wosnesenskii (Brandt,
Common name(s): Rockweed isopod,
Olive green isopod, Vosnesensky's
|Pentidotea wosnesenskii from Padilla
|(Photo by: Dave Cowles,
How to Distinguish from
Of the species with a convex posterior margin to the pleotelson,
species look similar but pleonite
1 is not narrower laterally than in the
center. Several others have a more slender body with all the pereonites
about the same width. Idotea aculeata, in
the southern part
of the range, looks similar but has round eyes instead of
Alaska to central CA;
Sea of Okhotsk, USSR.
Mid intertidal to 16
Often abundant in kelp, in
mussel beds, and under intertidal rocks.
May eat the egg capsules of Nucella emarginata.
include fish such as the spotted kelpfish Gibbonsia elegans
dwarf perch Micrometrus minimus. This
species can swim well,
using its pleopods (it opens the flaps of the uropods
to expose the
Males are usually larger and paler than females and have thicker
Ovigerous females have been found in July, and a female was seen
3-4 mm young in November in SE Alaska.
The species is named for the Russian zoologist Ilya
who collected and studied species from Siberia, Alaska, and California
and Fairbanks, 1966
and Carlton, 1975
and McConnaughey, 1985
et al., 1980
and O'Clair, 1998
et al., 1985
General Notes and
Observations: Locations, abundances,
In this closeup of the head (cephalon)
one can see the lateral eyes (kidney-shaped when viewed from the side)
and the fact that the first pereonite
is much wider than the cephalon.
In this view of the underside of the head one can see the palp
along the side of the third maxilliped,
which is covering the mouth (the dark mandibles
are visible between the third maxillipeds).
has 5 segments.
This view shows the last two pereonites
(at top), then the two free pleonites
and the front of the pleotelson.
The lateral plates seen on the pereonites
are actually coxal
plates. Note that the posterolateral margin of the coxal
plate from the last (7th) pereonite
is pointed (acute)
The first pleonite
is narrow or acute
at the edge, much narrower than it is mid-dorsally.
Note the notch at the sides of the front of the pleotelson
showing the margin of a third partly free pleonite.
In this ventral view one can see the 7 similar pereopods
on the pereon,
and the flaplike ventral uropods
which are characteristic of suborder Valvifera and cover the pleopods
on the pleotelson.
This individual crawls across a student's hand after being found in the
intertidal. Photo by Dave Cowles, July 2017
Authors and Editors of Page:
Dave Cowles (2006): Created original page