HEMIGALEIDAE

FAMILY HEMIGALEIDAE View in CoL

Externally, the hemigaleid caudal fin has a large dorsal lobe, elongated terminal lobe and falcate ventral lobe. The thin plate preceding the caudal fin skeleton is absent in Hemigaleidae (arrow in Figs 5A View Figure 5 , 6A View Figure 6 ). The caudal fin skeleton of the examined species of Hemigaleidae has 56–92 VC ( Table 1), rectangular basidorsal and interdorsal cartilages and elongated, slightly curved and tapering supraneural spines. The caudal fin skeletons of Paragaleus , Chaenogaleus , Hemigaleus and Hemipristis are divided into anterior and posterior diplospondylic caudal regions (Table 2). The anterior diplospondylic caudal region comprises six to eight VC ( Table 1) and has basiventral cartilages with the anterior apophysis as a slight prominence (arrow in Figs 5B View Figure 5 , 6B View Figure 6 ) and haemal spines slightly concave anteriorly. The posterior diplospondylic caudal region of Paragaleus and Chaenogaleus has all haemal spines anteriorly convex ( Fig. 5A View Figure 5 ), whereas in Hemigaleus and Hemipristis , most haemal spines are weakly ‘>’ shaped ( Fig. 6A View Figure 6 ). In the terminal lobe, the haemal spines are straight and basiventral cartilages absent.

FAMILY CARCHARHINIDAE

The carcharhinid caudal fin has distinct dorsal and ventral lobes, with a thin cartilaginous plate preceding the caudal fin skeleton (arrow in Figs 7A View Figure 7 , 8 View Figure 8 , 9 View Figure 9 , 10A View Figure 10 ). In all examined carcharhinids, the supraneural spines are elongated and tapering terminally ( Figs 7–11 View Figure 7 View Figure 8 View Figure 9 View Figure 10 View Figure 11 ) and the basidorsal and interdorsal cartilages are rectangular. The caudal fin has a wide range of VC (66–119), which are divided into anterior and posterior diplospondylic caudal regions ( Tables 1, 2).

The anterior diplospondylic caudal region of Isogomphodon has seven VC, Prionace seven to eight VC, Galeocerdo eight VC, Negaprion nine VC and Loxodon nine VC. Among species of the genus Carcharhinus , this region is composed of four to nine VC and in Rhizoprionodon six to eight VC ( Table 1). The basiventral cartilages have an apophysis as a slight prominence on the anterior margin in Galeocerdo , Negaprion , Rhizoprionodon , Loxodon , Carcharhinus plumbeus and Carcharhinus porosus (arrow in Figs 7B View Figure 7 , 10B View Figure 10 ). The basiventrals of Prionace , Isogomphodon , Carcharhinus acronotus , Carcharhinus brevipinna , Carcharhinus melanopterus , Carcharhinus longimanus and Carcharhinus signatus are rectangular, slightly uniform and lack an anterior apophysis ( Figs 8 View Figure 8 , 9 View Figure 9 , 11 View Figure 11 ). In all carcharhinids, the first haemal spines are anteriorly concave, and only Galeocerdo has distal prehypochordal cartilages ( Fig. 7A View Figure 7 ). This structure is absent in all other examined sharks.

Most of the haemal spines in the posterior diplospondylic caudal region are ‘>’ shaped ( Figs 7–11 View Figure 7 View Figure 8 View Figure 9 View Figure 10 View Figure 11 ); however, in Prionace , close to the mid-length of the caudal fin, the haemal spines in the distal portion are posteriorly curved ( Fig. 11A View Figure 11 ). The basiventrals are reduced or absent in the terminal caudal lobe.