Ctenotus delli Storr, 1974: 92.

Southwestern Heath Ctenotus

(Figures 1, 6‒8, 10)

New synonymy. Ctenotus catenifer Storr 1974: 92

Holotype. WAM R37478, female, from 6 miles [9 km] east of Kalamunda (31°57’S, 116°08’E), Western Australia, Australia, collected by J. Dell on 29 April 1970. Fixed in 10% formalin, stored in 70% ethanol.

Diagnosis. A medium-sized, moderately slender member of the C. labillardieri species group with pale to dark brown ground colour on dorsum. Broad (often ragged-edged) to narrow black laterodorsal stripe or zone enclosing pale blotchy pattern of series of broken dashes and spots. Occasionally with continuous dorsolateral and at most ragged-edged white midlateral stripes. Black peppering or spotting (often longitudinally aligned) on greyish limbs. Body with 24‒30 midbody scale rows. Digits of manus and pes with narrow brown callused subdigital lamellae, 10‒16 on 4 th finger and 20‒26 on 4 th toe. Ear lobules numerous and subequal, either roundish, triangular or acutely pointed.

Description. Mensural characters: N = 63, all measurements in mm. Snout-vent length 39.7‒62.5 mm (mean 50.0), body length 20.2‒34.3 (mean 26.5), body width 3.6‒10.8 (mean 6.8), body depth 3.9‒8.5 (mean 6.0), forebody length 15.5‒22.9 (mean 19.6), tail length 69.0‒114.0 (mean 92.1), tail length % of SVL 161‒205% (mean 183%), forelimb length 10.1‒15.2 (mean 12.3), hindlimb length 13.3‒22.9 (mean 17.7), head length 7.8‒12.9 (mean 10.4), head depth 4.0‒7.1 (mean 5.7), head width 4.6‒8.0 (mean 6.5), snout length 3.7‒6.0 (mean 4.6). Scalation: Midbody scale rows 24‒30 (mean 26). Paravertebral scales 54‒72 (mean 63). Nuchal scales 1‒5 (mean 4). Supralabials 7‒8 (mean 7), fifth and sixth usually subocular. Infralabials 6‒7 (mean 6). Supraciliaries (Figure 1) 7‒9 (mean 8), median fourth to sixth much smaller than first three and last two in series. Supraoculars 4, first 2 (rarely 3) in contact with frontal. Ciliaries 6‒10 (mean 9). Ear aperture moderately large. Ear lobules 0‒5 (mean 3), small and variable in shape either rounded, triangular or occasionally acutely pointed, when numerous, upper lobules tend to be larger than the lower. Nasals are narrowly to widely separated, rarely in point contact. Prefrontals are usually widely separated, occasionally narrowly separated. Frontoparietals paired. Interparietal distinct. Loreals two, first narrower and slightly or much higher than wide, second wider usually as wide as high, occasionally equal in size and height. Preoculars two (Figure 1), upper much smaller, lower squarish and narrowing posteriorly. Two angled presuboculars (rarely one) (Figure 1) between the lower preocular and fifth subocular supralabial, second slightly wedged between fourth and fifth supralabials. One primary temporal between the last two supralabials. Secondary temporals two, upper much larger than lower. Toes compressed, subdigital lamellae under fourth toe 20‒26 (mean 23), each forming a laterally compressed narrow callus. Plantar surfaces of manus and pes conical.

Variation in scalation. Head scales in C. delli display minimal intraspecific variation.All specimens have nasals and prefrontals widely separated, however in fourteen and three respective specimens, the nasals and prefrontals are narrowly separated. Two specimens (WAM R17989, WAM R37477) have nasals in point contact. The first two supraoculars contact the frontal in all except seven specimens (WAM R17942, WAM R21819, WAM R36453, WAM R90124, WAM R90223, WAM R156643, WAM R172949) in which three supraoculars contact the frontal. Other variations include: WAM R40989 has a larger second presubocular contacting lower preocular on left side. WAM R90124 has a single fused presubocular on both sides. WAM R96280 has the first upper labial composed of four smaller scales on right side, with an extra scale wedged between nasal and prefrontal above the first loreal on left side and an elongated scale separating frontoparietals from the interparietal. WAM R144173 has nasal scales composed of three scales on both sides.

Colour in life, preservative and variation. The following description of colour in life is based on Figures 6A‒D and field observations of C. delli in Western Australia. The descriptions in preservative and of variation are based on specimens of C. delli listed in the Appendix and Table A2.

In life, dorsal ground colour pale to dark brown with broad (Figures 6A, B) to narrow (Figures 6C, D) black laterodorsal stripe or zone. Dorsal ground colour extends on to head forming longitudinal pattern intermixed with black pigment (Figures 6A, B) or relatively unmarked, at most flecked with black (Figures 6C, D). Narrower irregular vertebral stripes of ground colour are often present on dorsum that coalesce along tail. (Figures 6A, B). Narrow to broad black laterodorsal zone borders dorsal ground colour and often encloses series of similarly coloured spots to base of tail (Figures 6A‒C). In some individuals the black laterodorsal zone and white dorsolateral series of dashes, spots or stripe can be barely discernible due to broad extent of dorsal ground colour (Figure 6D). Broad black upper lateral zone bordered above by variable extent of either dorsolateral series of broken equal-sized white dashes or spots (Figures 6A, C), or a continuous stripe, at most with some short breaks, extending forward to above eye to base of tail (Figure 6B). When broken, dorsolateral stripe is often more continuous anteriorly. Black upper lateral zone often encloses scattered white spots, occasionally longitudinally aligned, including midlateral series of broken or irregular white dashes (occasionally a continuous ragged edged stripe) extending forward to below eye. Black upper lateral zone extending on to tail, narrowing enclosing white to yellowish dashes or spots. Lower lateral zone whitish to pale grey, obscurely blotched or marbled with darker pigment. Limb base colouration greyish, occasionally with slight pinkish tinge, overlain with black peppering or spotting (often longitudinally aligned) extending on to digits. Ventral surfaces white, occasionally with yellowish tinge.

In preservative, the ground colour has faded slightly but overall retains a brown appearance. Elements of pale pigment remain distinct.

Variation includes: the two irregular lines of ground colour enclosing a black vertebral stripe (Figure 8A) was present in an equal number of specimens with a zone of ground colour enclosing either a light or heavy pigment of black spots (Figures 8B, C) and those specimens with an unmarked zone of ground colour (Figure 8D). The dorsolateral stripe comprising a series of broken white dashes or spots is equally present in a similar number of specimens with an almost continuous stripe at most with short breaks. In some specimens (e.g. WAM R117161, WAM R132008), the dorsolateral stripe was more continuous anteriorly. The black laterodorsal zone either enclosed a series of white spots (e.g. WAM R163142‒43) or was virtually clear with at most a few white spots (e.g. WAM R135711, WAM R143967). One specimen (WAM R36013) has two virtually straight lines of ground colour, and two specimens (WAM R121359, WAM R156643) are heavily spotted.

Etymology. Storr (1974: 92) provided no derivation of name delli, but it is clear that the species was named after Mr John Dell (1943‒2025), esteemed naturalist, and educator, formerly of the Western Australian Museum and Environmental Protection Authority, former president and journal editor of the Western Australian Naturalists’ Club and recipient of the Australian Natural History Medallion in 1988 for increasing popular or scientific knowledge of the Australian flora and fauna and Public Service Medal of Australia in the Queen’s Birthday 2011 Australian Honours list for his service and contribution to the environment. An inspiration to any naturalist fortunate enough to cross his path. We suggest the common name Southwestern Heath Ctenotus.

Distribution. Ctenotus delli is endemic and widespread throughout the temperate Jarrah Forest, southern Swan Coastal Plain, Warren and Esperance Plains bioregions of southwestern Western Australia (Figure 9). Ctenotus delli extends north on the Darling Range to Julimar State Forest, and south to 2.5 km NE of Augusta, Lake Maringup, Walpole-Nornalup, William Bay and Torndirrup National Parks, Two Peoples Bay Nature Reserve, Cheynes Beach, and Cape Le Grand National Park. It extends inland to 7 km E of Sawyers Valley, 7 km NW of North Bannister, Collie area, Ambergate Reserve near Busselton, Tone-Perup Nature Reserve, Stirling Range National Park, 18 km W of Ravensthorpe and Coolinup Nature Reserve, and east to Cape Arid National Park. There is a disjunct population in the southern Geraldton Sandplains bioregion, represented by one specimen (WAM R68924) from Badgingarra National Park (Figure 10, see remarks). Ctenotus delli appears to be patchily distributed in some areas which is possibly an artefact of collecting. For example, noticeable gaps exist between the most northerly record on the Darling Range east of Perth and the Julimar State Forest population and on the south coast east of Stirling Range and Waychinicup National Parks (Figure 9).

The locality entry for Point Dempster in Storr et al. (1999: 50) is not supported by any collection records (OZCAM 2023).

Habitat and ecology. Ctenotus delli occupies a variety of temperate vegetation associations on sandy, lateritic and clay soils, with an overstorey of dry sclerophyll forests or woodlands of mallee and/or other eucalypts (mainly jarrah/marri/wandoo), often mixed with shrublands and trees of Agonis (DC.) Sweet, Allocasuarina Johnson, Banksia L.f. and Melaleuca Linnaeus, usually over a sparse to dense shrub-dominated understorey including coastal low heath and rock outcrops (Wilson & Knowles 1988; Ehmann 1992; Bush et al. 2007, 2010; Cogger 2014; Wilson & Swan 2025). Specimens of C. delli can occasionally be raked from spoil heaps with dead vegetation and abandoned stick-ant Iridomyrmex conifer Forel nests (especially during cooler weather), or found under leaflitter, logs, mallee roots, ground-strewn bark, rocks (laterite and occasionally exfoliated granite on soil bordering outcrops) and rubbish, especially pieces of old iron in disturbed agricultural areas or dumps adjacent to uncleared vegetation. When seasonal activity is optimum, C. delli can be funnel and/or pit-trapped in buckets during biological surveys.

During a series of biological surveys near Dwellingup in the Darling Range, nine C. delli were trapped on different soils in a variety of habitats, including low shrubland adjacent to small granite outcrop with grass trees/ sheoaks and mixed grass trees/ Hakea prostrata Brown over low shrubland including Banksia nivea Labillardière. The habitats where C. delli was present appear to be relatively unburnt and bordered by eucalypt forest with a dominant shrub understorey of Hypocalymma angustifoilum (Endlicher) and Pericalymma ellipticum (Endlicher) in the Myrtaceae family, and Trymalium ledifolium Fenzl in the Rhamnaceae family (B. Maryan & G. Gaikhorst, pers. obs.). In contrast, no C. delli were trapped in the predominantly forest habitats with minimal shrub understorey (B. Maryan & G. Gaikhorst, pers. obs.). This species has been known to utilize rehabilitated mine sites, which may suggest it is to some extent adaptable to an altered habitat (Nichols & Bamford 1985).

Some degree of habitat partitioning occurs in the Stirling Range National Park, where C. delli generally prefers the low-lying Melaleuca on heavier soils near drainage lines and C. gemmula the dry proteaceous heath on lighter soils (B. Van Der Heide, pers. obs.). Bush et al. (2010: 99; J. Dell, pers. comm.), noted that compared to C. labillardieri, it is active at much lower temperatures and can be observed on cool, sunny days in August‒September.

Sympatry with other species. In the eastern parts of its range (e.g. largely Esperance Plains bioregion) C. delli is regionally sympatric with C. gemmula (Bush et al. 2007). Based on collection records instances of syntopy between C. delli and C. gemmula are known from Cape Le Grand National Park and Coomalbidgup (Chapman & Dell 1975; B. Bush & K. Thorn, pers. obs.).

Ctenotus delli shows broad sympatry with C. labillardieri in the Jarrah Forest, Warren, and Esperance Plains bioregions (How et al. 1987; Bush et al. 2007). Where both species are known to occur, records of C. labillardieri substantially outnumber those of C. delli particularly granite outcrops on the south coast (B. Maryan & G. Gaikhorst, pers. obs.). For instance, during a biological survey in the Fitzgerald Biosphere Reserve on the central south coast 29 C. labillardieri from eight sites were recorded versus only a single record of C. delli (Sanders et al. 2012).

At the boundaries of the southern Swan Coastal Plain and western Jarrah Forest bioregions, collection records also suggest C. delli and C. ora are sympatric in the vicinities of Cape Naturaliste and Dunsborough.

Comparison with other species. Ctenotus delli differs from all other members of the C. labillardieri species group in having the pattern of black peppering or spotting on limbs appearing to be longitudinally aligned on greyish limbs (versus contrasting bold black blotches or marbling on yellowish to bright reddish limbs).

Ctenotus delli specifically differs from C. gemmula in typically having seven supralabials (versus typically eight supralabials) and more greyish limbs (versus pale yellowish brown to slightly reddish limbs); from C. labillardieri and C. ora in having a typically broken pale dorsolateral and midlateral series of short dashes (versus more continuous pale dorsolateral and midlateral stripes present, although in south of range this pattern in C. labillardieri becomes wavy or broken), more greyish limbs (versus pale to bright reddish limbs) and further differs from C. labillardieri in smaller adult snout-vent length to 63 mm (versus to 76 mm).

Ctenotus delli differs from C. lancelini and C. youngsoni in its smaller adult snout-vent length to 63 mm (versus to 80 and 84 mm, respectively), typically broken pale dorsolateral series of short dashes (versus continuous pale dorsolateral stripe present), typically broken midlateral series of short dashes (versus in C. lancelini the pale midlateral stripe tends to more continuous while in C. youngsoni it is indistinct or absent) and more greyish limbs (versus yellowish to pale reddish).

Remarks. A specimen (WAM R68924) included in C. catenifer by Storr et al. (1981: 42) from Badgingarra National Park was treated as disjunct on their species map. However, in a revised edition by Storr et al. (1999: 50) this record is erroneously mapped from Badgingarra south and east to Point Dempster, thus incorporating the distribution of C. delli on the Darling Range and most of the Swan Coastal Plain where C. catenifer is absent. We confirm this specimen is C. delli (Figure 10) based on its colour pattern and the following measurements (mm) and meristic counts, due to desiccated condition of specimen some were not taken: SVL 45.9, BL 25.4, BW 3.6, BD 4.4, FL 15.6, TL 69 regenerated, FLL 11.7, HLL 13.2, HL 9.1, HD 4.0, HW 5.1, SnL 4.0, MBSR 26, PS 62, NS 4, SupLab 7, InfLab 6, SupCil n/a, Cil n/a, EarLob 3, SubdigLam 4th F 12, SupradigLam 4th F 10, SubdigLam 4th T n/a, SupradigLam 4th T n/a. This specimen was pit-trapped in the northern part of the national park adjacent Cadda Road on 2 November 1979 (P. Murray, pers. comm.). Further specimens are required to determine the genetic affinities of this disjunct population.

Ctenotus delli as defined here is widespread and is likely considered to be Least Concern under the IUCN criteria, with a combined AOO (area of occupancy) of 504 km 2 and an EOO (extent of occurrence) of 210,022 km 2 (Craig et al. 2017a, b). It occurs in many large, relatively undisturbed state forests, nature reserves and national parks (e.g. Ambergate, Badgingarra, Cape Arid, Cape Le Grand, D’Entrecasteaux, Julimar, Scott, Stirling Range, Tone-Perup, Torndirrup, Two Peoples Bay, Walpole-Nornalup, Waychinicup, West Cape Howe and William Bay).