Peramphithoe humeralis

How to Distinguish from Similar Species: All Peramphithoe have the peduncular tooth between the two rami of uropod 1. Peramphithoe mea is also large like this species but has articles 5 and 6 on gnathopod 1 of equal length and also has pereopods 6 and 7 of equal length. P. mea is found mostly in Alaska and Russia. Other local Peramphithoe are usually < 1 cm long and the proximal flagellar articles of antenna 2 are fused. Cymadusa uncinata has an accessory flagellum.

Biology/Natural History: Female amphipods, such as this one, brood their eggs and young on a ventral thoracic brood pouch formed by flaplike inner branches of the legs 3-5 called oostegites. The oostegites can be seen in the photo above as a second set of flaps behind the large flaplike coxae of the legs. This female was carrying at least 11 young in an advanced stage of development. Peramphithoe and the closely related Amphithoe are common on kelp and eelgrass.

On kelp and seagrass, curls blades to form a tube.

Depth Range: Low intertidal and subtidal

Peramphithoe humeralis has a biramous uropod 3, with both rami shorter than the peduncle. The inner ramus of uropod 3 is paddle-like while the outer ramus has 2 curved spines. The antennae have no accessory flagellum. Uropod 1 has a distinct tooth based on the peduncle and extending ventrally between the two uropod rami. The proximal flagellar articles of antenna 2 are not fused. Article 5 of gnathopod 1 is longer than article 6, and pereopod 7 is longer than pereopod 6.