COLLECTIONS: Sites 38 (type locality), 43, 46, 48, 63, and 66, all from South Island.

Thalli up to 2300 µm in length, diam. up to 180 µm, decreasing slightly near the ends. Holdfast becoming cup shaped and located laterally at or near the middle of the mature thallus, the thallus often slightly bent in the holdfast region. One arm of the thallus often of greater diam. In hindgut of Ephemeroptera nymphs.

HOSTS: All in C. humeralis or Deleatidium sp. (Ephemeroptera, Leptophlebiidae).

Thalli usque ad 2300 µm longi, ad 180 µm crassi, paulum ad fines attenuati. Tentaculum cupuliforme factum, e latere prope thalli maturi medium positum, ubi thallus saepe paulo flexus, thalli brachium alterum altero crassius. In proctodaeo Ephemeropterorum nympharum.

Paramoebidium bibrachium appears to be fairly well dispersed in different populations of Leptophlebiidae on South Island, but only 28% of the specimens we dissected were infested. We were not able to see the release of amoebae from thalli, but we did observe encysted amoebae in some of the slides we prepared and kept in water.
Paramoebidium is a very widespread genus that is common in many parts of the world in nymphs of Ephemeroptera and Plecoptera and in larvae of Simuliidae. They are often morpholgically variable and difficult to speciate, except on the basis of host differences, and this is a questionable basis for species determination. Paramoebidium spp. have not been cultured; consequently, it is not possible to determine their host ranges experimentally or to study their morphology under common growth conditions.
Only two validly described species of Paramoebidium exist, although eleven nomina nuda can be found in the literature. Our new species, P. bibrachium, has thalli that are very distinctive because of the location of the holdfast. Based on our extensive collections of the genus, we are confident it is a valid new species.
It is interesting to note that, though common in many parts of the world, we did not find any species of Paramoebidium on North Island. Other than the collections of P. bibrachium cited above, we found only one aquatic insect specimen with this genus on South Island, a nymph of Neozephlebia scita (Walker) (Ephemeroptera, Leptophlebiidae) from site 65, with some very young thalli of Paramoebidium that were too young to determine if they were P. bibrachium. The host family and proximity of the nymph to other sites with P. bibrachium suggest the young thalli might have been that species.

HOLOTYPE: Slide ZEA-38-M-4 prepared from the hindgut of Coloburiscus humeralis (Walker) (Ephemeroptera) collected at Orton Bradley Park, Banks Peninsula (site 38), 26.I.87. Deposited with R. W. Lichtwardt, University of Kansas.