LEIS: SYSTEMATICS AND ZOOGEOGRAPHY OF THE POKCT'PINEKISHKS 



pectoral fin base. Approximately 20 vertebrae. 

 Dorsal and anal fins usually rounded, set far back 

 on body, with 12-18 rays. Caudal rounded, with 9 

 rays (there are no secondary rays). Pectoral fin 

 slightly emarginate, with 19-25 rays, the upper- 

 most ray (not counted) greatly reduced in adults. 

 No pelvic fins. Body covered with long spines, all 

 but a few (around the gill opening, dorsal fin base, 

 and caudal peduncle! of which are erectile. Erec- 

 tile spines consisting of a long pointed shaft, tw'o 

 subdermal lateral bases lying in nearly the same 

 plane as the shaft, and usually a shaft extension 

 which is shorter than the shaft. The shaft exten- 

 sion may be greatly reduced. Nasal organs consist- 

 ing of a short tentacle with a pair of lateral open- 

 ings near the tip. In larger individuals of some 

 species the tissue closing the end of the tentacle 

 may be absent, giving rise to a bifid nasal tentacle 

 without nostrils. Both species whose reproductive 

 habits are known (D. hystnx and D. holocanthus) 

 spawn pelagic spherical eggs of 1.6-2.1 mm in 

 diameter. 



Ren2arks. — Only Bleeker's (1865) proposal of 

 Paradiodon for the species here considered to be- 

 long in Diodon (because of page priority, he be- 

 lieved Diodon should apply to those species usu- 

 ally referred to Chilomycterus) has disturbed the 

 stability of the usage of the name Diodon. 

 Trichodiodon and Trichocyclus are names applied 

 to juvenile stages oi Diodon. 



Although subgeneric status seems unwar- 

 ranted, Diodon can be broken into two groups on 

 the basis of body width, caudal peduncle length, 

 and squamation. The species of the slender-bodied 

 group, D. eydouxii and D. hystrix, have a rather 

 narrow body (Figure 3, Table 2), long caudal 

 peduncle (Figure 3, Table 2), and several small 

 spines in the dorsal and dorsolateral surfaces of 

 the peduncle. The species of the round-bodied 

 group, D. holocanthus, D. liturosus, and D. nicth- 

 emerus, have a wider body, shorter caudal pedun- 

 cle (Figure 3), and lack spines on the caudal 

 peduncle (although there are strong spines, pro- 

 jecting over the peduncle, at the base of the dorsal 

 and anal fins). Upon inflation, the dorsal and anal 

 fins are engulfed by the expanding skin. In the 

 round-bodied group, the caudal peduncle and fin 

 are also largely obscured in inflated specimens 

 and the large spines mentioned above provide 

 added protection. In the slender-bodied group, the 

 peduncle remains largely uncovered and is pro- 

 tected only by the relatively small spines on its 



upper surfaces. Diodon nivthemerus, although 

 clearly a member of the round-bodied group, ap- 

 pears to have undergone a reduction in spine 

 number and base size, and is thus separable from 

 D. holocanthus and D. liturosus. 



70-1 



E 60- 



E 



-LITUROSUS 



-EYDOUXII 



-HYSTRIX 



-NICTHEMERUS 



-HOLOCANTHUS 



X 



100 



150 



200 



Figure 3. — Plotted regression lines of (top) caudal peduncle 

 length vs. standard length and (bottom) body width vs. stan- 

 dard length for the five species of Diodon. Lines plotted only- 

 over size range of specimens examined. The line with arrow- 

 head for D. hystrix extends to 571 mm SL. Regression data in 

 Table 2. 



Table 2. — Regression equations for caudal peduncle length 

 (PL) and body width (BW) vs. standard length (SL) in the five 

 species of Diodon (see also Figure 3). 



539 



