Chelodina oblonga, Gray, 1841

Smales, Ian, 2021, Morphology of the lectotype of Chelodina oblonga Gray 1841 (Testudines: Chelidae), Zootaxa 5068 (4), pp. 547-571 : 554

Chelodina oblonga lectotype specimen

The lectotype of C. oblonga ( Figure 1 ) is a taxidermied specimen mounted on a detachable wooden plinth. The plastron has been cut from the rest of the specimen, permitting many, but not all internal bony structures of the shell to be examined ( Thomson 2000) ( Figure 6 ). As Gray (1873) noted, it has a carapace 6¾ inches (171 mm) in length. The carapace maximum width is 113 mm while total length of the plastron is 143 mm. The sex of the specimen is not known.

The carapace has a slight anterior taper from its greatest width at marginal 8. Anterior and posterior edges of the carapace are broadly and smoothly rounded, while its lateral edges are relatively straight-sided from the posterior part of marginal 4 to the anterior part of marginal 8. There is a depression across the width of the vertebrals extending from the posterior end of V1 to the posterior end of V4. Within it there is a very slightly raised medial portion coinciding with the underlying vertebrae. The anterior lobe of the plastron is broadly rounded and both lobes taper evenly from their greatest width at the pectoral/abdominal sulcus. There is no ‘step’ in the posterior plastral lobe as occurs in many Chelodina at the femoral/anal region. The anal notch is shallow and is straight-sided, with no curvature. As noted by Gray (1841), the plastron is quite uniformly reddish-brown, although the medial portion of the posterior lobe has an underlying yellowish tinge.

The dorsal and lateral surfaces of the head, neck, limbs and entire tail are plain dark grey. Ventral portions of the head, neck, limbs and skin of the axillary and inguinal pockets are yellowish tinged heavily with greyish brown. External colouration of the specimen may have been affected by age or preservation processes.

Taxidermy of the specimen includes wiring to hold the head, neck, limbs and tail in position and the inclusion of glass eyes. The neck and limbs are stuffed with fibre and remnants of fibres in the shell cavity suggest that it may also have been stuffed prior to detachment of the plastron. Various authors ( Goode 1967, Cann 1998, Cann & Sadlier 2017) have noted that the neck of the specimen is considerably shorter than it would have been in life. The cervical vertebrae and all neck musculature have been removed allowing the skin of the posterior portion of the neck to have been inverted back into the interior of the shell ( Figure 7 ), much in the manner in which a sock or sleeve can be inverted into itself. It is conceivable that, if the taxidermist was familiar with cryptodires but not with the neck anatomy of pleurodires, it might have been assumed that the neck would retract somewhat in this fashion. Thomson (2000) provided a low resolution photograph showing the internals of the specimen and said that it showed a disarticulated section of the cervical vertebrae in the specimen. Examination of the specimen ( Figure 6 , 8 ) shows that rather than cervical vertebrae, what can be seen is actually wire and fibres from taxidermy of the specimen.

Radiographs of the specimen show that both bony otic chambers, including quadrate and squamosal on each side, have been fractured and are slightly displaced from the remainder of the cranium ( Figure 8 ). Other aspects of the specimen are discussed below.

Figures

FIGURE 1. Dorsal and ventral aspects of the C. oblonga lectotype specimen NHMUK 40.12.9.81 / 1947.3.5.89 (photos P. Campbell, courtesy of The Natural History Museum, London).

FIGURE 6. Chelodina oblonga lectotype with plastron removed, showing (a) everted neck skin and (b) pale mark in detritus on thoracic costals.

FIGURE 7. Detail of C. oblonga lectotype with plastron removed, showing neck shortened in taxidermy by eversion of neck skin into the thoracic cavity.

FIGURE 8. (A) Radiograph of C. oblonga lectotype. (B) Interpretive detail of skeletal carapace showing shape and size of hyoplastron sutures with costal 1 (arrowed); discernible portions of neurals (red) and sutural contact between nuchal (green) and peripheral 2 (blue) excluding peripheral 1 (yellow) from costal 1 (purple). (radiograph P. Campbell, courtesy of The Natural History Museum, London)