Description of Tanystylum caulieri sp. nov. (Ammotheidae, Pycnogonida) in California, USA

A new species of Tanystylum pycnogonid is described, based on 59 specimens simultaneously collected in San Francisco, California, USA. A precise description of each body part is provided, along with population structure, and biometric measurements. Diagnostic criteria include a barrel-shaped proboscis, five-articled palps, 10-segmented ovigers, the abdomen forming an obtuse angle, distally tilted at 45°, reaching the distal margin of the 4th lateral processes, and ornamented legs: coxae 1 with a lateral, front-oriented tubercle, femora with two ventral bumps, tibiae 1 with four dorsal bumps, and tibiae 2 with three. A comparison with several other Tanystylum species, either geographically co-occurring or morphologically similar, is also made. Among them, Tanystylum orbiculare Wilson, 1828 is one of the closest but lacks lateral, front-oriented tubercles on the coxa 1, and ventral bumps on the femur, plus the abdomen shape is different. The proposed name is Tanystylum caulieri sp. nov.