Elseya (Hanwarachelys) rhodini, Thomson, Scott, Amepou, Yolarnie, Anamiato, Jim & Georges, Arthur, 2015

Thomson, Scott, Amepou, Yolarnie, Anamiato, Jim & Georges, Arthur, 2015, A new species and subgenus of Elseya (Testudines: Pleurodira: Chelidae) from New Guinea, Zootaxa 4006 (1), pp. 59-82 : 69-73

Elseya (Hanwarachelys) rhodini sp. nov.

Southern New Guinea Stream Turtle

2015 Elseya rhodini sp. nov., Thomson et al., this study.

Type data: Holotype—PNGM R25204 ( Figure 8 ), adult female (carapace length: 255 mm), collected at Rue Creek (tributary of Wau Creek), Gulf Province, Papua New Guinea (07˚11’ 67.3” S, 144˚37’ 13.8” E) by Yolanie Amepou on 6 January, 2015 ( Figure 9 ). Paratype: PNGM R25203, adult male (carapace length: 205 mm), herein set as Allotype, collection data as per Holotype. For basic measurements of these types and others from the genus Elseya see Table 1.

Etymology —Named in honor of Anders G. J. Rhodin; Chairman Emeritus of the IUCN/SSC Tortoise and Freshwater Turtle Specialist Group; Founder and Director, Chelonian Research Foundation. He also researched the turtles of Papua New Guinea describing two species, Chelodina (M.) parkeri ( Rhodin and Mittermeier, 1976) and Chelodina (C.) pritchardi ( Rhodin, 1994) . He was also one of the first to collect this new species ( Rhodin and Rhodin, 1977), and the first to recognize it as new ( Rhodin and Genorupa 2000).

Distribution —Streams draining into rivers in New Guinea, south of the central ranges, from the Sitekwa River region of Papua, Indonesia, to the Kikori-Purari rivers region of Papua New Guinea. Aru Islands. ( Figure 1 )

Diagnosis –Distinguished by gold speckling usually present in the sclera of the eye, which partially obscures the iris; base color green ( Figure 10 ). In Elseya novaeguineae and Elseya schultzei the sclera is bright green and the iris is starkly contrasted, though the base colors of the sclera in the later is a duller and plainer green. The head shield in E. rhodini is reduced when compared to other species of this subgenus. The lateral edge of the head shield at its midpoint between the eye and the tympanum is above the level of the eye, below it in the other species. The ventral extension of the head shield down the parietal arch is also reduced, typically still reaching the tympanum, but narrower throughout its length. Posterior to the eye in E. novaeguineae and E. schultzei is a variable but generally present extension of the head shield that extends down behind the eye, in some specimens to nearly the midpoint of the eye. This is absent in E. rhodini . On the carapace the spots on the scutes of E. rhodini are visible in all growth stages, whereas in the other two species they are often faded or absent in adults. The cervical is generally present in the members of this group however it is narrower (approximately 30% of length) in E. rhodini whereas it is usually 50% of length in the other two species. The lateral sulcus of the first vertebral scute in both E. schultzei and E. novaeguineae contacts the center of the second marginal scute, whereas in E. rhodini it contacts the anterior ¼ of the second marginal. The skull of E. rhodini can be diagnosed by the contact of the vomer with the pterygoids posteriorly and the premaxillae anteriorly.

Description

External Morphology

Carapace —The carapace is broadly oval slightly flattened at the anterior from the 2nd marginal. The first vertebral scute is approximately the same width as the second. The outer sulci of the first vertebral tend to intersect the 2nd marginal close to the sulcus between the 1st and 2nd marginal, differing from E. novaeguineae where it is in the center of the 2nd marginal. There is some flaring of the marginal over the hind legs, though it tends to be more pronounced in E. novaeguineae and E. schultzei than is apparent in similarly sized individuals of E. rhodini . Cervical scute is present for all three taxa, though it is usually relatively narrower in E. rhodini than in the other two species of the subgenus. The carapace is brown in color for all three species, spots may be present at the center of each major scute, these persist into adult hood in E. rhodini , are faded if present in E. schultzei and may be absent altogether in E. novaeguineae .

Plastron —The plastra of all three species are very similar, being rectangular in general shape but widest at the posterior of the anterior lobe and with lateral flanging in older individuals just anterior to the rear legs on the posterior lobe. The plastral formula is generally pec>fem>abd>ana>int>hum with the gulars excluded from the midline by the intergular. The plastron is cream to yellow in color, very occasionally there is a slight pink suffusion.

Head and soft parts —The color of the sclera of E. rhodini is gold flecked green, 2.5 Y 7/8 to 2.5 Y 8/8 ( Munsell 2000) with the iris gold and relatively indistinct. Compared with the color of the sclera of E. novaeguineae is green with no flecks, 5y7/3 to 5y8/3 ( Munsell 2000) with a very distinct gold iris, and in E. schultzei it is also green with no flecks, 5y7/6 to 5y8/6 ( Munsell 2000) again with a very distinct gold iris. The dorsal surface of the head of E. rhodini is variegated in color between yellow brown to dark brown, a similar pattern is seen in E. schultzei , however E. novaeguineae tends to be far less variegated without the striking patterns seen in the other species.

Size and Sexual Dimorphism —This species attains a size of approximately 240mm carapace length with females being slightly larger than males. This is similar for all members of the subgenus Hanwarachelys. The species attains a smaller adult size than Elseya branderhorsti with which it is sympatric throughout parts of its range.

Osteology

Skull ( Figs. 11–13 )—Dermal roofing elements of the skull are similar in all species of Elseya , the frontals are paired and the anterior process separates the nasals almost in their entirety. Parietals are large and postero-laterally suture to the squamosal to form the parietal arch. The arch is narrow in the Elseya (Elseya) much wider in Elseya (Hanwarachelys) . This feature also determines the degree of lateral extension of the head shield as it requires bone for its support.

On the palatal surface there are significant differences at the species level. The vomer of E. rhodini completely divides the maxillae anteriorly to meet the pre-maxillae and posteriorly the palatines to meet the pterygoids. In E. novaeguineae both the maxillae and palatines meet at the midline. In the description of Elseya (Pelocomastes) albagula ( Thomson et al, 2006) the form of the alveolar ridge was further defined and we follow this here. The lingual ridge (sensu Thomson et al, 2006) is completely absent in all members of both Elseya (Elseya) and Elseya (Hanwarachelys) its presence being a synapomorphy for the Elseya (Pelocomastes) . However the alveolar ridge is present in members of the Elseya (Elseya) and is only partially present in the members of Elseya (Hanwarachelys) . In E. rhodini there is no obvious alveolar ridge on the ramphotheca of the upper jaw whereas there is a reduced, though present ridge consisting of a row of raised nodules in E. novaeguineae .

Cervicals—The articulation formula is the same in all three species and follows the typical chelid condition of (2(3(4(5)6)7(8) (sensu Williams 1950).

Shell—The carapace of members of the Elseya (Elseya) differ from members of the Elseya (Hanwarachelys) in the structure of the bridge strut suture, the former having a medial constriction, present in all three species, whereas this is absent in all members of the latter. Further the sutural scar of the ileum in the E. ( Elseya ) is separated from the anterior suture of the 8th pleural with this scar occupying the posterior 2/3 of the 8th pleural and continuing onto the pygal. In E. (Hanwarachelys) this scar is adjacent to the anterior suture of the 8th pleural occupying the full width and also continuing on to the pygal (Figure 2). All members of the E. (Hanwarachelys) normally possess a cervical scute, absent in E. ( Elseya ) and E. ( Pelocomastes ).

All three species of Elseya (Hawarachelys) lack exposed neural bones (sensu Thomson & Georges 1996) a feature common to the entire genus. There are slight differences in the general morphology of the shell between the three species within E. (Hanwarachelys), but subject to considerable within species variation.

Figures

FIGURE 1. Map of New Guinea showing the distribution of Elseya novaeguineae (Birds Head), E. schultzei (north of Central Ranges) and E. rhodini (south of Central Ranges). The locations of the holotypes for each species are shown as red dots; the type locality for the neotype of Elseya branderhorsti is shown as a green square.

FIGURE 8. Dorsal, ventral and lateral views of the holotype PNGM R 25204 of Elseya (Hanwarachelys) rhodini from Wau Creek, Kikori Drainage, Papua New Guinea. Scale: 20 mm.

FIGURE 9. Habitat of Elseya rhodini Wau Creek, Sirebi River, Kikori drainage (07 ˚ 11 ’ 67.3 ” S, 144 ˚ 37 ’ 13.8 ” E).

FIGURE 10. Lateral view of the head of Elseya rhodini. Wild caught individual (UC <Aus> AA 42045).

FIGURE 11. Lateral views of the skulls of A. Elseya (Hanwarachelys) rhodini, B. Elseya (Hanwarachelys) novaeguineae, C. Elseya (Elseya) dentata, and D. Elseya (Pelocomastes) albagula. po—postorbital, sq—squamosal, q—quadrate, j—jugal, mx—maxilla.

FIGURE 12. Ventral views of the skulls of A. Elseya (Hanwarachelys) rhodini, B. Elseya (Hanwarachelys) novaeguineae, C. Elseya (Elseya) dentata, and D. Elseya (Pelocomastes) albagula. pm—premaxilla, mx—maxilla, pal—palatine, vo—vomer, bs—basisphenoid, bo—basooccipital. Also labelled are the alveolar and lingual ridges.

FIGURE 13. Dorsal view of the skulls of A. Elseya (Hanwarachelys) rhodini, B. Elseya (Hanwarachelys) novaeguineae, C. Elseya (Elseya) dentata, and D. Elseya (Pelocomastes) albagula. fr—frontal, po—postorbital, pa—parietal, sosupraoccipital.