Aspidomorphus dimorphus Kraus, 2025, sp. nov.
Creators: name: Kraus, Fred
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Squamata
Serpentes
Elapidae
Aspidomorphus
Aspidomorphus dimorphus

description: Aspidomorphus dimorphus sp. nov.
urn:lsid:zoobank.org:act: 543A1AB7-D294-441D-A7E2-9A9B726877E7
Figs. 1, 3, 4
Aspidomorphus lineaticollis McDowell 1967: 514–520.
Holotype. BPBM 20784 (field number FK 9742), adult male, coll. by F. Kraus, forest NNW Mt. Rio, ~ 5 km S Araeda village, 11.4787°S, 153.4199°E, 170 m a.s.l., Sudest Island, Milne Bay Province, Papua New Guinea, on 21 April 2004.
Paratypes (n = 12). Papua New Guinea: Milne Bay Province: Sudest Island: along Gesirava River, 11.4918°S, 153.4126°E, 130 m a.s.l. (BPBM 20782–83, 20786); N slope Mt. Rio, 11.4961°S, 153.4264°E, 390 m a.s.l. (BPBM 20785); 11.4856°S, 153.4217°E, 300 m a.s.l. (BPBM 20787); ~ 3 km S Araeda, 11.4637°S, 153.4220°E, 200 m a.s.l. (BPBM 20788); ~ 1 km S Araeda, 11.4457°S, 153.4264°E, 90 m a.s.l. (BPBM 20789); Wele River above Kolkol Falls, 11.4462°S, 153.4312°E, 30 m a.s.l. (FK 9519, 9873); Rambuso, 0–100 m a.s.l. (AMNH 76652); W slope Mt. Rio, 250–350 m a.s.l. (AMNH 76653–54).
Diagnosis. A moderately sized species of Aspidomorphus (SVL of males 329–452 mm, of females 330–455 mm; TL/SVL of males 0.13–0.14, of females 0.10–0.14); ventrals 154–161 in seven males, 161–169 in six females; subcaudals 26–29 in seven males, 22–30 in six females; hemipenis short, ornamented proximally with dense array of enlarged spines that gradually decrease in size distally, apex papillose, sulcus bifurcating distally, without membranous septum below point of bifucation; evenly dimorphic for color pattern (Fig. 1), with (1) orange morph uniformly orange brown dorsally except for a narrow, low-contrast, light-brown nuchal collar whose apex points anteriorly, venter uniformly salmon pink (white in preservative), labials white to very pale straw, without bridle, and (2) dark morph unicolor brownish pink dorsally with a darker head, venter gray anteriorly changing to pale salmonorange posteriorly (white in preservative), labials brown, without bridle or with only a faint hint of an amorphous darker region below eye. Neither morph has indications of dark or white lines on the neck nor light lines on the rostral or mental nor ocelli on the top of head.
Comparisons with other species. Aspidomorphus dimorphus sp. nov. differs from all other members of the genus in its striking color-pattern dimorphism, with snakes having two different uniform ground colors (orange and brownish pink) showing no indication of intermediacy between them; and it differs as well in its narrow, forward-pointing nuchal chevron. Concolor individuals occasionally seen in other species of Aspidomorphus involve merely loss of pattern elements on a dark-brown ground color between patterned and concolor specimens but not dimorphism in ground color. Nor do any other populations of Aspidomorphus have an orange ground color or a forward-pointing chevron.
Aspidomorphus dimorphus sp. nov. further differs from A. schlegeli in having more ventrals (154–161 in males, 161–169 in females vs. 137–155 in male and 143–160 in female A. schlegeli), lacking a dark line on the parietals that borders a white stripe below (vs. both present in A. schlegeli), lacking a dark postocular stripe (vs. present in A. schlegeli), and in having a hemipenis with enlarged spines proximally (vs. spines absent in A. schlegeli) and whose apex is papillose (vs. with longitudinal fleshy folds in A. schlegeli).
Aspidomorphus dimorphus sp. nov. further differs from A. muelleri in having fewer ventrals in males (154–161 vs. 160–176 in A. muelleri); having fewer subcaudals in males (26–29 vs. 33–40 in A. muelleri); having a faint chevron on the neck whose apex points forward (vs. a boldly black nuchal chevron that points backward in A. muelleri); lacking ocelli on head scales (including the parietals), a light rostral stripe, and a light mental stripe (vs. all present in A. muelleri); in either lacking (orange morph) or sometimes having only a barely discernible hint (dark morph) of a bridle (vs. bridle conspicuous in A. muelleri); and in lacking a membranous septum proximal to bifurcation of the two branches of the sulcus spermaticus (vs. membrane present in A. muelleri).
Aspidomorphus dimorphus sp. nov. is most similar to A. lineaticollis, from which it differs in lacking dark longitudinal lines on the parietal and neck (vs. present in A. lineaticollis, Fig. 2A, B), lacking an upper light line on the neck (vs. present in A. lineaticollis), and in lacking or with barely an amorphous hint of a dark bridle below the eye (vs. conspicuous in A. lineaticollis). Aspidomorphus lineaticollis never has the faded brown collar and uniformly white labials seen in the orange morph of A. dimorphus sp. nov.
From Aspidomorphus m. lineatus, A. dimorphus sp. nov. differs in lacking an upper light line on the neck, a conspicuous dark bridle below the eye, a broad reddish-brown postocular stripe, and the dark central lines on each dorsal scale on the anterior body, all of which are seen in A. lineatus (Fig. 2C, D).
Description of the holotype. Adult male. Rostral broader (4.0 mm) than high (2.8), notched ventromedially, just visible from above; internasals angulate, pentangular, wider than long, much smaller than prefrontals; prefrontals pentangular, almost as wide as long (3.2 × 3.3 on right), bordered below by preocular and nasal, not reaching supralabials, widely separating internasal from preocular; preocular single, slightly taller than long, bordered anteriorly by nasal and prefrontal, below by second and third supralabials, above by supraoculars, not in contact with frontal; loreal absent; frontal shield shaped, longer (5.5 mm) than supraoculars (4.9 mm); parietals longer than wide (length 8.9 mm, width 5.7 mm on right), widest anteriorly, in contact anteriorly with postoculars. Nares oriented dorsolaterally, centered in nasals, each with wide, shallow groove below naris and broad, shallow depression above naris; postoculars two, lower larger, smaller than eye; one elongate anterior temporal lies above fifth supralabial and temporolabial, separating them from parietal; two posterior temporals, upper larger, lower abutting anterodorsal margin of sixth supralabial; temporolabial wedged between the fifth and sixth supralabials, widely separated from postoculars. Supralabials six, third and fourth contacting eye; infralabials seven, the first pair separated posteriorly by mental groove, the second small, nearly triangular, in point contact with anterior genial. Mental small, triangular, longer (3.1 mm) than wide (2.8 mm); anterior genial shorter (4.5 mm) than posterior (5.2 mm); posterior genials separated along most of length by single diamond-shaped intergenial; first two gulars separate posterior genials from fifth infralabials. Eye relatively small (2.8 mm), less than distance from eye to nostril (EY/EN = 0.82), larger than distance from eye to border of mouth (2.2 mm); pupil round.
Head moderately distinct from neck, flattened, sloping roundly toward snout tip; broadly rounded snout when viewed from side or above; canthus rostralis absent. Body almost cylindrical, without vertebral keel or angulation of the ventrals. Dorsal scale rows 15-15-15, smooth, un-notched posteriorly, without apical pits. Ventrals 154, approximately five times wider than long; cloacal scale divided; subcaudals 26. Dorsal scales on tail reduced to nine rows at level of subcaudal 2, to six rows at level of subcaudal 6, and to four rows at level of subcaudal 13. Tail short (TL/SVL = 0.13), tipped by a pointed conical spine.
Hemipenis short, everted organ 7 mm, extending to third subcaudal, widening toward apex but not bifurcate, densely covered with short spines that are longer basally and gradually decreasing in size distally, tip of organ papillate (Fig. 3). Sulcus spermaticus diverges into two arms approximately two-thirds of distance to apex, no membranous septum proximal to this, lips of sulcus spermaticus closely appressed, making sulcus difficult to see; arms of sulcus spermaticus each ending in a shallow apical pocket, which are separated from each other by an elevated medial ridge.
In preservative, dorsum uniformly tan, anterior of each dorsal scale darker than posterior on first few scales behind head; barely discernable chevron of slightly darker tan forms a faint collar on neck that is 2–3 scales wide and whose apex points forward (Fig. 4A); dark-brown flecking on first 2–3 dorsal scale rows anteriorly, decreasing posteriorly and disappearing after ~40 ventrals; single slightly darker tan marking on frontal and each prefrontal; supralabials pale buff, dusted with tan dorsally. Venter uniformly pale buff (Fig. 4B); no dark medial line on subcaudals. Iris dark gray with few silver flecks along margin of pupil. Tongue dark gray.
Measurements of the Holotype (in mm). —Total length = 509, SVL = 452, TL = 57, EN = 3.4, EY = 2.8, SN = 5.2, HW = 15.2, mass = 56.8 g.
Variation. SVL varies from 329–452 mm in males and from 330–455 mm in females; mass varies from 16.4–56.8 g in males and 15.3–43.6 g in females. Ventrals vary from 154–161 in males and 152–169 in females; subcaudals vary from 26–29 in males and 22–30 in females. AMNH 76652 is an anomalous female whose ventral count is 152 and subcaudal count is 30, which is similar to the counts seen in males. Aside from this specimen, ventral counts in females range from 161–169 and subcaudal counts from 22–25, which are more divergent from the counts seen in males. Otherwise, important scalational variation is non-existent, with numbers of supralabials, supralabials in contact with the eye, infralabials, and temporals invariant.
In preservative, color variation within each of the two color-pattern morphs is minimal. For the orange morph, each paratype is virtually identical to the holotype except that the dark collar on the nape is 1–2 scales wide and not evidently continuous across the vertebral area in BPBM 20782–83 and 20785. For the dark morph, each paratype is brown dorsally, with each scale narrowly margined posteriorly in darker brown; venters are light buff heavily dusted with darker brown, denser anteriorly and lessening posteriorly, primarily by reducing the dark dusting midventrally; venters are darker in the larger specimens, and BPBM 20789 (SVL = 349 mm) is mostly uniform buff ventrally with the brown dusting largely limited to the anterior quarter of the body. A narrow dark forward-directed collar (1–2 scales wide) is barely evident on BPBM 20787 and 20789, may also be present on BPBM 20788, but is not discernible in BPBM 20786. The tops of the heads are punctated or vermiculated with darker brown, there are a few paler-brown flecks present on the supralabials, lower temporolabial, and ending at the rictus (BPBM 20789) or continuing 4–5 scales past that point. These paler flecks apparently comprise the residuum of what would be the lower white line in other species of Aspidomorphus. Among the 13 specimens, six are of the orange morph and seven of the dark morph.
Color in life. Orange morph: BPBM 20782 was uniformly orange-brown dorsally (Fig. 1A) except for the head, which was dark tan and followed by a brown nuchal band that graded imperceptibly into the dorsal color (Fig. 1B). It had a few small brown spots on top of the head; pale-straw supralabials and chin, which darkened slightly and became suffused with salmon pink on the throat; uniformly salmon-pink on most ventrals and all subcaudals; bright red iris; and black tongue. FK 9873 was similar but with the pale-brown nuchal collar incomplete on the sides, the head and just behind the collar were darker brown, and the tongue was dark gray.
Dark morph: BPBM 20787 and 20788 were dark brown dorsally with charcoal-gray heads and a faint trace of a pale-cream labial stripe (Fig. 1C, D); chin charcoal gray; venter medium gray with very pale pinkish-orange cast on posterior third (Fig. 1G); iris charcoal gray with narrow red rim around pupil; and tongue black. BPBM 20786 was dark brown dorsally, with a darker-brown head; there was no light postocular line though there were a few white flecks in that area; face dark brown, including supralabials; chin and throat were dark gray-brown, paler gray brown on first half of venter and acquiring a slightly orange cast on posterior half of venter and tail; iris dark brown with a narrow orange-red rim around pupil. BPBM 20789 was the same as these except for being medium brown dorsally with a slightly darker head (Fig. 1E, F), chin and throat were charcoal gray, and the remainder of the venter pale salmon orange (Fig. 1H).
Etymology. This species name is a compound masculine adjective formed from the Greek adjective di -, meaning “two”, and the feminine Greek noun morphe, meaning “form”. It refers to the unique color-pattern dimorphism that characterizes this species.
Range. This species is restricted to Sudest Island (Fig. 5). It may also occur on the smaller islands of the Calvados Chain, which are contained within the fringing reef that demarcates the larger Sudest Island during glacial periods.
Ecology. The specimens I obtained all came from primary rainforest at elevations ranging from 90–390 m a.s.l. (Fig. 6). Most animals were found active on the forest floor from early to mid-morning, but BPBM 20786 came from a bucket trap placed along a drift fence.
The series of eight BPBM specimens all have small ticks lodged under some of their ventral scales, with one specimen also having adjacent rows of dorsal scales infested. Numbers of these ticks vary from 1–10 ticks/snake.
BPBM 20785 bit one of our field assistants on the hand during the morning of 23 April 2004. His hand swelled to approximately twice its normal size, he was in some pain, and had some joint stiffness. The swelling subsided by mid-afternoon but was still evident late on 24 April. Bites from this species were viewed locally as of no particular concern. This is similar to my experience elsewhere in Papua New Guinea with the attitudes of local villagers toward bites of Aspidomorphus muelleri. These symptoms include those described by Schiefenhövel (1969) for a bite by A. muelleri, though his report has further observations on symptoms as well as treatment, inasmuch as the case was observed and presented by a physician as a medical case study.
Remarks. The Reptile Database (Uetz et al. 2025) claims that the holotype of Aspidomorphus lineaticollis cannot be found. However, both Tiedemann et al. (1994) and Gemel et al. 2019) recorded the holotype as present at Naturhistorisches Museum Wien, and I illustrate that specimen here (Fig. 2A). In his original description, Werner (1903) noted that the specimen was obtained from W[ilhelm] Schlüter (who was a natural-history dealer based out of Halle, Germany), and the jar label for this specimen shows that it was donated by Franz Steindachner. The jar label also records that the specimen came from Astrolabe Bay, which is more information than Werner provided in his original description. This is consistent with the fact that Schlüter obtained many New Guinean specimens from the Geisler brothers (Bruno and Herbert), who collected along Astrolabe Bay in 1890–91 and presumably obtained this specimen during that time. There is no reason to continue to consider the holotype of this species lost.
I should note that I am aware of a self-published vanity paper assigning new names to a number of specimens of Aspidomorphus. For reasons well covered by Kaiser et al. (2013), Kaiser (2014), and Kraus (2019) I do not adopt these names because they lack scientific justification and some of which are based on false information.
description: Published as part of Kraus, Fred, 2025, A new species of Aspidomorphus (Serpentes: Elapidae) from Papua New Guinea, pp. 153-165 in Zootaxa 5631 (1) on pages 155-162, DOI: 10.11646/zootaxa.5631.1.7, http://zenodo.org/record/15327017