Synaustrus and the euthycarcinoid puzzle

Published accounts of the Australian Triassic euthycarcinoid Synaustrus bro okvalensis have not documented all known material, and are inconsistent in several respects with better known euthycarcinoids. Synaustrus is most clos ely related to Euthycarcinus. New morphological findings and interpretation s (e.g., a slender seta on each leg annulation; a series of articulated cep halic sternites) confirm the similarity of Synaustrus to other euthycarcino id taxa. The evidence presented here allies euthycarcinoids with atelocerat es, but they cannot be positioned higher than the stem-lineage of Atelocera ta. Synaustrus and other genera possess trunk apodemes analogous to those o f symphylans. Sternal pores in euthycarcinoids resemble coxal vesicles, tho ugh this conflicts with other morphological indications of aquatic habits.