*imminuta (Bagnall, 1937)
*thalassophila (Bagnall, 1937)
Thalassaphorura (formerly Protaphorura) debilis is confined to the littoral zone. There are records from salt marshes, and under stones below the high tide level. In some localities it is found together with Thalassaphorura halophila with which it has sometimes been confused. Steve has examined all the available specimens of Thalassaphorura evansi (Bagnall, 1935) and Thalassaphorura thalassophila (Bagnall, 1937) in the NHML collection; it is clear that these two species are junior synonyms of Thalassaphorura debilis (the latter already noted by Fjellberg 1998).
Distinctive characters of Thalassaphorura debilis include the complete absence of any trace of a furca, a broadly oval post-antennal organ with a maximum of 20 vesicles (Fig. 1), a short empodial appendage about a third of the length of the claw with a distinct lamella (Fig. 2), and the arrangement of pseudocelli (PSO) on the dorsal side of the abdomen (Fig. 3). The typical PSO formula is 32/233/33343. There are two anal spines (Fig. 4). Also illustrated is the male genital plate on the ventral side of the fifth abdominal segment (abd5).