Fig. 4From: The internal morphology of primary spines of extant regular echinoids in the tropical western Atlantic: a SEM atlasPhormosoma placenta sigsbei A. Agassiz, USNM E12320, SE micrographs of broken sections through primary spines. a Stub A10. b, c Stub A11, both ends of broken spine. d Stub A11 (different specimen from b, c). Scale bars a, d represent 500 µm, b, c represent 200 µmBack to article page