The large, wide, rounded and deep carapace (especially adult females), separates C. canni immediately from C. steindachneri, C. reimanni, C. novaeguineae, most C. longicollis and most C. pritchardi. The wide, robust head of C. canni readily separates it from all C. longicollis, C. pritchardi, C. steindachneri, and most C. novaeguineae and C. mccordi. Chelodina mccordi has a narrower head and plastron than C. canni. In C. mccordi the total dorsal surface area of the second marginal (M2) scute is always larger than that of it's first marginal scute (Rhodin, 1994b), however, in C. canni M1 and M2 are not noticeably different in total dorsal surface area. In C. mccordi both the anterior and posterior plastral lobes diminish in width distally from the axillary notch and inguinal notch. This contrasts with C. canni where only the posterior plastral lobe diminishes in width distally from the inguinal notch but the anterior plastral lobe of the plastron increases in width moving forward from the axillary notch, before rounding off to form the anterior border of the plastron. The plastral (midline sulcus) formula of C. canni has an interanal seam longer than the interabdominal, whereas in adult C. mccordi (in contrast to Rhodin, 1994b) the interabdominal sulcus is longer than the interanal.

     Etymology.- This species is named in honour of John Cann of Sydney, Australia for his lifetime of work with the freshwater turtles of Australia.

     Related Taxa.- The nearest living (based on allozyme data Georges et al., 2002) relative of this species is C. novaeguineae Boulenger, 1888, Lectotype: BMNH 1946.1.22.36; Paralectotype: MSNG C.E. 8407 both from Katow = Mawatta, Binituri River, Papua New Guinea. Lat. 09°: 05' S, Long. 143° 00' E.

DESCRIPTION

External Morphology

See all photo's labelled "Chelodina novaeguineae" with Australian locality data in Cann (1998:61-68).

Carapace.- Carapace length (CL) to at least 169mm in males (mean adult CL, 161mm) and at least 240 mm in females (mean adult CL, 221 mm). Carapace broadly oval, but widest at the seam between marginals M7-M8 (maximum carapace width/maximum CL= 0.76- 0.82; mean =0.79; n = 8; for this and subsequent ratios, compare Figs. 6 and 7 in Rhodin, 1994b). Carapace of juvenile distinctly rounded (Plate 2).

Carapace surface, except on marginals, highly rugose, with a relatively smooth posterior margin and without obvious growth annuli. Hindmost marginals (M12, supracaudals), only slightly raised over tail. Juveniles with individual tiny rugosities organised into a radiating pattern on carapace scutes. Seam between M1 and M2, instead of being perpendicular to carapace margin, curves medially, producing a relatively short medial (i.e., in contact with the first vertebral and the first costal scutes) seam on the first marginal (53-90% of dorsal width of M2; mean = 71%; n = 8); however, M1 and M2 equal or nearly equal in total dorsal surface area. M4, 5, and 6 much shorter than other marginals; M7-10 distinctly flared. Lateral margins of M4-M7 slightly upturned, forming a very narrow trough along the rim of the shell. Cervical scute large, rectangular, slightly wider anteriorly than posteriorly, and longer than wide. Vertebrals (V) in order of decreasing width are 1~5>2~3>4. Regions of costal-vertebral contact distinctly elevated longitudinally, and these two smooth ridges separated by a moderately deep mid-vertebral trough in which there is no evidence of a median keel in western populations, however, a minimal median keel is present in the easterly populations. Carapace brown to almost black (especially dark in juveniles), with the outer margin of the shell rimmed in yellow. Ventral surfaces of marginals faded yellow and flecked to mostly covered with reddish-brown staining.

Plastron.- Plastron slightly upturned anteriorly. Plastron wide in comparison to the other wide-plastroned species of the C. longicollis group (width at axillary notch averaging 50% of CL; range 47% to 52%; n = 8). Front plastral lobe wider than hind plastral lobe. Plastral hindlobe with distinct anal notch. Bridge moderately long, and lacking axillary and inguinal scutes. Large intergular present, much wider anteriorly than posteriorly, and not reaching the margin of the plastron. Average plastral midline seam length formula (Plate 1): intergular (midline length) > anal > abdominal > femoral > pectoral > gular. Plastron uniformly yellow (Plate 1), with seams darkly marked with brown, and with the scutes variably stained reddish-brown. Hatchling plastron with bright red-orange markings ventrally, extending over the margin of the carapace on the dorsal aspects of the marginal scutes (similar and more pronounced than C. mccordi, (Plate 2). Juvenile plastron generally very dark gray-black to black (Plate 2).

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