Synaustrus and the euthycarcinoid puzzle

Abstract

Published accounts of the Australian Triassic euthycarcinoid Synaustrus brookvalensis have not documented all known material, and are inconsistent in several respects with better known euthycarcinoids. Synaustrus is most closely related to Euthycarcinus. New morphological findings and interpretations (e.g., a slender seta on each leg annulation; a series of articulated cephalic sternites) confirm the similarity of Synaustrus to other euthycarcinoid taxa. The evidence presented here allies euthycarcinoids with atelocerates, but they cannot be positioned higher than the stem-lineage of Atelocerata. Synaustrus and other genera possess trunk apodemes analogous to those of symphylans. Sternal pores in euthycarcinoids resemble coxal vesicles, though this conflicts with other morphological indications of aquatic habits.