Figure 1.

Appendage morphology in crustaceans correlates with boundaries in Ubx/abd-A expression. (Upper) In Triops longicaudatus (tadpole shrimp), Ubx/abd-A expression begins in the first thoracic segment (T1), the position in the body where the transition from feeding to locomotory appendages occurs. (Lower) In Mysidium colombiae (opossum shrimp), Ubx/abd-A expression begins in T2 but is rather weak in this segment. Stronger expression is seen in T3 and all thoracic segments more posterior. The transition from the feeding type morphology to locomotory morphology occurs at T2, although T2 is somewhat intermediate between the morphology of T1 and T3. Mxl, morphology of typical feeding appendage seen in the head. [Reproduced with permission from ref. 5 (Copyright 1997, Macmillan Magazines)].