Fig. 2From: The internal morphology of primary spines of extant regular echinoids in the tropical western Atlantic: a SEM atlasStylocidaris affinis (Philippi), USNM 27840, SE micrographs of broken sections through primary spines. a Stub A4, b Stub A4 (different specimen from a). c Stub A5. d Stub A6. Scale bars a, b represent 500 µm, c, d represent 1 mmBack to article page