抄録
A new species of Euphausiacea, Thysanoëssa inspinata, from the North Pacific is described. Thysanoëssa inspinata has been included in the part of the spineless form of Thysanoessa longipes, but it is divided from T. longipes in following points.
1) Thysanoëssa inspinata has the lateral denticle in the far posterior position in the lower margin of the carapace.
2) The terminal process and proximal process of the male copulatory organ are nearly the same size and shorter in T. inspinata
. 3) A specimen of Thysanoëssa longipes lacking abdominal spines which is considered to be the real spineless form is found, which has the different taxonomical character from Thysanoëssa inspinata. Other taxonomical points and ecological features of Thysanoëssa inspinata are also discussed.
