Chlamydoselachus

Ebert, David A. & Compagno, Leonard J. V., 2009, Chlamydoselachus africana, a new species of frilled shark from southern Africa (Chondrichthyes, Hexanchiformes, Chlamydoselachidae), Zootaxa 2173, pp. 1-18 : 13-14

Comparison of Chlamydoselachus Species

Comparison of proportional measurements from Chlamydoselachus species from different regions revealed a high degree of differences in proportional measurements between regions. It may be that in addition to the southern African C. africana there may be one or more different Chlamydoselachus species involved or the group may eventually prove to be a species complex. However, we identified a subset of measurements that showed consistent proportional differences between the new species and Chlamydoselachus species from elsewhere. These included a greater head length of 17.3–17.9% for C. africana versus 13.1–16.2% for C. anguineus , a greater prepectoral length, 17.0% versus 13.6–15.9%, a broader interorbital width of 6.0% versus 4.2–5.5%, greater internarial width of 4.4% versus 3.1–3.9%, a broader mouth width of 7.0% versus 4.0–6.3%, and proportionally longer gill openings. Direct comparison of Japanese (including the holotype of C. anguineus ) and Taiwanese material revealed a further subset of measurements including differences in the anal-caudal space; shorter in C. africana 0.8% versus C. anguineus at 1.5–1.6%, a broader head height (7.3% versus 5.4–6.5%) and head width (7.5% versus 5.0–5.8%), a greater caudal peduncle height (4.5% versus 3.2–3.5%), a greater pectoral fin length (9.2% versus 7.0–8.1%), and a greater pelvic fin length (13.2% versus 11.5–11.6%).

The total mean number of upper jaw tooth counts is slightly higher in the four Namibian C. africana specimens (x = 28.8) relative to all C. anguineus examined from other regions. The upper jaw tooth count for the Angolan specimen fell within the range of C. anguineus ( Table 2). The lower tooth counts were slightly higher in the Namibian specimens, with the exception of the North Atlantic specimens. The Angolan C. africana fell within the mid-range of the C. anguineus examined ( Table 2).

The pectoral fin radials of C. africana are slightly higher for the mesopterygium (7 versus 5–6) and lower (8 versus 9–12) for the metapterygium relative to C. anguineus ( Table 3). The number of pelvic fin radials was similar to those of specimens from Japan and Taiwan as were the number of dorsal fin radials ( Table 3). The number of anal fin radials is also slightly higher in C. africana (30) relative to C. anguineus (r = 20–28).

Chlamydoselachus africana and C. anguineus strongly differ from each other in total vertebral counts, precaudal vertebral counts, and in the position of the MP/DP transition ( Table 4). Total vertebral counts were 147 for a Namibian specimen of C. africana while New Zealand and Taiwanese specimens of C. anguineus were 160 and 171, respectively. The variability in the MP-DP counts was especially high. Two C. anguineus , one each from New Zealand and Taiwan, had an MP range of 72–75 and a DP precaudal count range of 21–27, while a C. africana had an MP of 18 and a precaudal DP of 76. The caudal counts (DC) differed widely, with C. anguineus having 58–78 and C. africana having 52. The transition between the MP and DP for C. anguineus was over the pelvic fins between the 72–75 vertebrae, while the transition in C. africana was just posterior to the pectoral fins at the 18th vertebrae.

The crania of the two Chlamydoselachus species exhibit a number of morphological differences ( Figure 6 ). These include the entire ethmoid region of the Taiwanese C. anguineus specimen (DAE 881204) being more elongated, and with a longer rostrum that is more ventrally thrust or angled, and has a slightly greater bend in the subethmoid fossa when compared to the C. africana paratype (SAM 36076). Other differences include the ventral edge of the rostrum in C. anguineus is opposite the mid-nasal capsule in the Taiwanese specimen, and in illustrations of Japanese C. anguineus (e.g. Allis, 1923), and is quite distinct when compared to the opposite dorsal surface in the Namibian C. africana . The ectethmoid processes are more elongate, broader, and more posteriorly expanded in the C. anguineus cranium, to the point of obscuring the front end of groove for orbital process in lateral, whereas in the C. africana cranium one can see space in front of these grooves, such that the basal angle is obvious. The subethmoid fossa is more antero-posteriorly elongated in C. anguineus , where as it is more laterally expanded and broad in C. africana . Comparison of the nasal fenestrae between the two species reveals that it is much smaller in C. anguineus when compared to C. africana . The orbital process grooves on the basal plate is more anterior in C. africana , but more posterior in C. anguineus . The basal plate between anterior grooves for the orbital processes is much more ventrally arched, convex and ridged in C. anguineus , but nearly flat in C. africana . The basal plate is more waisted behind the grooves in C. africana than in C. anguineus . The orbits are more upthrust and are slightly raised above the cranial roof in C. africana , but about opposite that in C. anguineus . The postorbital processes of C. africana are more elongated and bent or twisted, although not extreme in dorsal-ventral view; in lateral view it is less ventral, but higher than in C. anguineus , in which they extend to the ventral edge of the hyomandibular facet. The otic processes of C. africana are more laterally projecting (or sphenopterotic ridges less laterally expanded). The sphenopterotic ridge is higher in C. africana . The otic processes by comparison in C. anguineus are more angled posteriorly, and with a notch. The occiput is much more elongate and with greatly elongated occipital condyles in C. africana , but much shorter in C. anguineus ( Figure 6 b; Allis, 1923).

Spiral valve counts are significantly lower in C. africana than in C. anguineus . The range of spiral valve turns for C. africana was fairly narrow, between 26 and 28, while the number of turns for C. anguineus ranged between 35 and 49 ( Table 6).

Chlamydoselachus africana individuals were clearly distinguished from those of C. anguineus based on PCA results. Principal components (PCs) 1 and 2 were interpretable and accounted for a considerable proportion (PC 1 = 38.6%, PC 2 = 17.2%) of total variation in morphological data. Principal component 1 was strongly bipolar (i.e., influenced by the differential contribution of two variables), with dorsal fin length (0.575) and, to a lesser extent, anal fin anterior margin (0.32) loading heavily to the positive. Conversely, several variables contributed similarly to negative loadings. Foremost among them were anal fin posterior margin (-0.358) and head length (-0.343). Results of the t -test conducted for PC1 case scores revealed highly significant differences between species (t = 4.859, P <0.001), indicating that they could be reliably distinguished by the indicated variables ( Figure 7 ). Species did not separate on PC2 (t = 0.632, P = 0.538; Figure 7 ). Chlamydoselachus anguineus individuals tended to load more positively, however, based primarily on proportional longer anal-caudal (0.137), dorsal-caudal (0.127), and head width (0.88) measurements.

Figures

FIGURE 6. Cranial skeleton, including dorsal, ventral, and lateral views of (a) Chlamydoselachus africana (SAM 36076) and (b) C. anguineus from Taiwan (DAE 881204).

FIGURE 7. Euclidean bi-plot of Principal Component 1 (PC 1) and Principal Component 2 (PC 2) case scores calculated from 28 morphological variables measured for Chlamydoselachus africana (n = 5) and C. anguineus (n = 10) individuals.