Peramphithoe humeralis has a biramous
3, with both rami
shorter than the peduncle
of uropod 3 is paddle-like while the outer ramus
has 2 curved spines (photo).
have no accessory
1 has a distinct tooth based on the peduncle
and extending ventrally between the two uropod
articles of antenna 2 are not fused (photo).
Article 5 of gnathopod
1 is longer than article 6 (photo),
and pereopod 7
(the last one) is longer than pereopod 6 (photo).
humeralis (Stimpson, 1864)
Common name(s): Kelp amphipod
humeralis, a large
adult female about 3 cm long + antennae. Found in late
a stone at extreme low tide (-3) at Sares Head. This female
babies between her oostegites.
Two babies can be seen peeking out from below her body behind leg 5
forward) and in front of leg 6 (angled backward).
|(Photo by: Dave Cowles,
October 2007) Identified with the help of Craig Staude
How to Distinguish from
tooth between the two rami
of uropod 1. Peramphithoe
is also large like this species but has articles 5 and 6
1 of equal length and also has pereopods
6 and 7 of equal length. P.
mea is found mostly in Alaska and Russia. Other
are usually < 1 cm long and the proximal
articles of antenna 2 are fused. Cymadusa uncinata
has an accessory
Low intertidal and subtidal
On kelp and seagrass, curls blades to form a tube.
amphipods, such as this one, brood their eggs and young on a ventral
brood pouch formed by flaplike inner branches of the legs 3-5 called oostegites.
can be seen in the photo above as a second set of flaps behind the
of the legs. This female was carrying at least 11 young in an
stage of development.
and the closely
on kelp and eelgrass.
K.E., and E.L. Bousfield. 1982. The amphipod superfamily
the northeastern Pacific region. Family Ampithoidae:
distributional ecology. Publ. Biol. Oceanogr. (Natl. Museums
General Notes and
abundances, unusual behaviors:
In gammarid amphipods the last three abdominal legs are uropods.
This view shows a dorsal view of uropods
1 (lowest) to 3 on the left side of the animal.
Above the base of uropod
3 the telson
can be seen, then uropod
3 on the right side of the animal is visible at the very top.
1 and 2 have two similar rami
composed of flattened blades with setae
along the edges.
3 has a paddlelike inner ramus
(seen on edge on the left, close uropod
and from the flat side on the right, far uropod).
The outer ramus
3 is less flattened and has two apical
teeth, as seen below.
This closeup view of left uropod
3 seen from the dorsal aspect of the left side shows the two apical
teeth on the lateral ramus,
and also shows the paddlelike inner (medial) ramus.
This ventral view of the right uropod
#2 shows the spine which extends from the base (peduncle)
out between the two rami.
In this dorsal view of the tail all three uropods
plus the telson
can be seen.
Uropod 1 is farthest forward (left), uropod 2 is intermediate, and uropod 3 is next to the telson.
is short and evenly rounded.
Neither antenna has an accessory
which would be a short branch based beside the main flagellum
is the flexible, whiplike distal portion of the antennae, with many
articles which allow it to bend easily). The articles at the
of the flagellum
of the second antenna are not fused together. In this photo
antennae are to the left and the second antennae are to their right,
around the first two pereopod
legs (called gnathopods)
This is a view of the left gnathopods
(#1 is to the left, #2 next to it to the right). Gnathopods
have 7 segments, the last two of which form a (usually subchelate)
In this view the 7th segment (the movable tip of the claw) is folding
away from the view plane. Segment 5 of gnathopod 1 is longer
than segment 6.
In this view it can be seen that the last two pereopods
(walking legs), # 6 and 7, are of similar length, but #7 is slightly
A live video of this individual can be viewed here.
This female was carrying at least 11 larvae in her oostegite
brood bpouch, Two of the larvae are shown
are about 3 mm long plus the antennae.
The young appeared to be sticking their heads (cephalon) out and
out from the pouch as the mother moved around, so I am guessing they
nearing the time when they can safely leave the mother.
Authors and Editors of Page:
Dave Cowles (2007): Created original page
CSS coding for page developed by Jonathan Cowles (2007)