Species Key of Genus Diodon* 1a Two or more spines wholly on the dorsal or dorsolateral surfaces of the caudal peduncle (Figure 2A); color pattern of the adults dominated by (smaller than eye) spots; at least dorsal, pectoral, and caudal fins of adults with dark spots ....go to 2a 1b No spines wholly on the caudal peduncle (Figure 2B); color pattern of adults dominated by large dorsal and lateral bars or blotches; fins of adults without spots except in some cases at base ....go to 3a 2a 19-22 pectoral fin rays, 16-18 dorsal fin rays and anal fin rays; dorsal and anal fins of adults falcate; 14 or less spines in longitudinal row over the ventrum from the lower jaw to the anus; head width less than 30% standard length Diodon eydouxii 2b 22-25 (rarely 21) pectoral fin rays, 14-17 dorsal fin rays, 14-16 anal fin rays; anal and dorsal fins rounded; 14 or more spines in a longitudinal row over the ventrum from the lower jaw to the anus; head width greater than 30% standard length Diodon hystrix       3a No small, fixed, tribase spine immediately above the gill opening; no small, flat spines on the anterior border of the depression surrounding the gill opening; 11 or less spines in longitudinal row over the ventrum from the lower jaw to the anus; adult color pattern dominated by four large lateral bars, dorsum uniformly dark Diodon nicthemerus 3b One or two small, fixed, tribase spines above the gill opening; three or four small, flat spines forming the anterior border of the depression surrounding the gill opening; 12 or more spines in longitudinal row over the ventrum from the lower jaw to the anus; adult pattern dominated by several dorsal blotches ....go to 4a       4a Ratio of frontal spine length to standard length 0.04-0.10, much shorter than pectoral axil spines; 12-15 spine in longitudinal row over the ventrum from the lower jaw to the anus; a small downward-pointing spine below the anterior margin of the eye present; dorsal blotches with a distinct light border; a dark gular band from eye to eye under the lower jaw Diodon liturosus 4b Ratio of frontal spine length to standard length 0.13-0.28, slightly shorter to much longer than pectoral axil spines; 12-15 spines in a longitudinal row over the ventrum from the lower jaw to the anus; a small downward-pointing spine below the anterior margin of the eye absent (Indo-Pacific specimens) or present (most Atlantic specimens); dorsal blotches without a distinct light border; no gular band Diodon holocanthus From: Leis, J.M. 1978. Systematics and zoogeography of the porcupinefishes (Diodon, Diodontidae, Tetraodontiformes), with comments on egg and larval development. Fishery Bulletin (U.S.) 76(3): 535-567.