Coenobita variabilis McCulloch, 1909

Coenobita variabilis McCulloch, 1909 View in CoL ( Figs. 18‒21 View Fig View Fig View Fig View Fig )

Cenobita rugosa – Heller 1865: 82 (Sydney, Australia). (not Coenobita rugosus H. Milne Edwards, 1837 View in CoL ).

Cenobita olivieri – Haswell 1882: 160–161 (N. W. Coast of Australia). (not Coenobita olivieri Owen, 1839 View in CoL ).

Coenobita spinosus variabilis McCulloch, 1909: 305–306 , pl. 88 (2, 2a) (type locality: Cape York, N Queensland, Australia); Springthorpe and Lowry 1994: 91 ( syntypes).

Coenobita spinosus View in CoL – Morgan 1987: 167 (North Territory, N Australia); Morgan 1990: 8 (NW Australia). (not Coenobita spinosus H. Milne Edwards, 1837 View in CoL ).

Coenobita variabilis View in CoL – Harvey 1992: 196–209, figs. 2–6 (Darwin, Northern Territory, Australia); Jones and Morgan 1994: 123, 4 unnumbered figs. (N Australia); Davie 2002: 35; Davie 2005: 149 (Bentinck Is., N Queensland, Australia); McLaughlin et al. 2010: 16; Tan et al. 2018: 322, 324 (mitogenome); Wang et al. 2019: 2646 (mitogenome); Gong et al. 2020: 1805, 1810 (mitogenome); Schäfer 2020: 106–107, 2 unnumbered figs.; Sasaki 2023: 6404 (list).

Material examined: West Papua, Indonesia: 4 òò (16.8, 17.0, 18.2, 18.2 mm) (NCHUZOOL 15257), 2 òò (19.7, 21.8 mm) (NCHUZOOL 15258), 2022.

Additional material: Australia: 4 òò (5.8, 7.7, 11.1, 11.8 mm), 2 ññ (5.5, 8.6 mm) ( QM W21232), West Governor Is., NW side, Napier Broome Bay, Kimberley Coast, WA, coll. J. Short, 26 Nov. 1995; 7 òò (10.2, 10.4, 10.8, 11.6, 11.8, 11.9, 16.4 mm) ( QM W20272), Bedford Is., Kimberley coast, WA, coll. J. Short, 19 Nov. 1994; 1 ò ( 12.8 mm) ( QM W9028), 1 ñ ( 7.9 mm) ( QM W9025), mouth of E. Alligator R., NT, coll. P. Davie, 30 Apr. 1979; 1 ñ ( 13.7 mm) ( QM W9091), West Alligator R., NT, 30 Apr. 1979; 2 òò (9.8, 14.7 mm) ( QM W23491), Karumba Pt, Cape York Peninsula, Far North QLD, coll. T. Stevens, 24 Nov. 1993.

Diagnosis: Shield ( Figs. 18A View Fig , 21A View Fig ), transversely convex, about 1.7 times as long as broad; dorsal surface punctate. Ocular peduncles reaching third proximal of ultimate article of antennular peduncles; basal article of antennular peduncles 0.8 times as long as penultimate article ( Fig. 18B View Fig ); antennal peduncles ( Fig. 18C View Fig ) exceeding ocular peduncles by half length of fifth article, second article stout, short, with flattened tubercles. Chelipeds ( Fig. 19A, C View Fig ) unequal and dissimilar, left larger than right, brush of setae on half proximal of upper margin of both palms; left cheliped palm with row of 5‒6 small and large stridulatory apparatus (laminar ridge) on upper outer surface, outer surface with widely-spaced tubercles, sometimes corneous-tipped; lower margin of palm sinuous; lower proximal angled rounded. Merus of both chelipeds each with a dense tuft of bristles on middle lower inner margin ( Fig. 19B, D View Fig ), comparatively sparse in left one. Left P2 and P3 dissimilar ( Fig. 20A, C View Fig ), P2 more slender than P3. Lateral surfaces of dactylus and propodus of left P2 ( Fig. 20A View Fig ) punctate or with sparse flattened tubercles, ventral surface of dactylus ( Fig. 20B View Fig ) with longitudinal ridge consisting of row of closely-spaced tiny corneous teeth proximally, widely-spaced distally. Right P2 slightly shorter, armament similar. Left P3 ( Fig. 20C–E View Fig ) with lateral surfaces of dactylus and propodus broad, smooth, sparsely punctate; ventral surface of dactylus slightly concave, median longitudinal ridge consisting of row of tiny corneous teeth, closely-spaced proximally, widely-spaced distally. Right P3 ( Fig. 20F View Fig ) slightly more slender than left. Dactylus and propodus ( Fig. 20F View Fig ) densely punctate; ventral surface of dactylus ( Fig. 20G View Fig ) with low corneous-tip tubercles. In male, coxae of P5 thick, each forming calcified sexual tube, left tube narrower than right; small, subtriangular sternal protuberance between both coxae ( Figs. 18D View Fig , 19F View Fig ). Telson ( Fig. 18E View Fig ) posterior lobes slightly asymmetrical, separated by narrow median cleft; margins truncate, with row of setae.

Variation: The stridulatory apparatus row on the outer surface of the palm of the left cheliped is variable ( Fig. 19A View Fig ), being either distinct or indistinct, and this variation is not related to the sex or size of the individual. The sexual tubes are nearly the same length ( Figs. 18D View Fig , 19F View Fig ), although in some individuals, the tubes are slightly unequal.

Color in life ( Fig. 21 View Fig ): Whole body and pereopods typically brown, with variations including light brown and reddish-brown. Palms of chelipeds with outer surface darker than other parts of body.

Size: Largest male SL 21.8 mm; largest female: 13.7 mm.

Ecological notes: According to the local people in West Papua, the habitat consists of sandy beaches, often near river estuaries and bordered by jungle with a humus substrate. Compared to C. brevimanus , larger individuals of this species tend to inhabit the humus area closer to the coastline, while smaller ones are typically found nesting under piles of rocks or dead corals on the sandy beach. This species tends to live further inland compared to C. perlatus .

Distributions: Northern part of Australia to the western (Indonesian) part of New Guinea Island, particularly along the coastline of the Arafura Sea in South Papua Province.

Remarks: Coenobita variabilis is similar to C. scaevola in having a tuft of bristles on the middle of the lower inner margin of the right cheliped merus ( Figs. 19D View Fig , 22D View Fig ). However, C. variabilis differs in the following characters: 1) with a variable stridulatory apparatus row on the outer surface of the left cheliped palm ( Fig. 19A View Fig ) [vs. a regular row of stridulatory apparatus in C. scaevola ( Fig. 22A View Fig )]; 2) sexual tubes nearly the same length or slightly unequal ( Figs. 18D View Fig , 19F View Fig ) [vs. right sexual tube robust, longer than left, curved laterally in C. scaevola ( Fig. 22C View Fig )]; and 3) a bristle tuft on the middle of the lower inner margin of the left cheliped merus in large specimens ( Fig. 19B View Fig ) [vs. none in C. scaevola ( Fig. 22B View Fig )].

Regarding the bristle tuft on the left cheliped merus of C. variabilis , all specimens from West Papua exhibit this distinct character, whereas it only appears in some from Australia ( e.g., QM W23491, QM W21232, QM W23491). This character is presumed to typically appear in large males (all specimens from West Papua are large males with SL 16.8–21.8 mm), but it is inconsistent in smaller individuals (all Australian specimens with SL ≤ 16.4 mm). In other Australian literature, the sizes reported were also smaller ( e.g., SL 14.3 mm in Morgan 1987; SL 11.1 mm in Morgan 1990). Notably, Jones and Morgan (1994) mentioned a carapace length of about 40 mm. This may suggest that suitable habitats for Australian populations are comparatively limited.

Coenobita variabilis View in CoL was generally thought to be endemic to Australia ( e.g., Davie 2005; Schäfer 2020). However, McCulloch (1909) included other localities near Papua New Guinea (Muray Islands and Torres Straits), as well as Vanuatu ( New Hebrides) and Fiji. It is, therefore, not unexpected that the distribution of this species has extended to the southern coast of West Papua, Indonesia.

Molecular analyses

A 545 bp segment of the 16S rDNA and a 658 bp segment of COI from specimens (or tissue samples), including 16 from C. moluccensis , 36 from C. patsyae (16S failed for NCHUZOOL 15274), 9 from C. celebensis , 20 from C. granularis , and 7 from C. variabilis , were amplified and aligned ( Table 1). A total of 34 haplotypes of the 16S and 71 haplotypes of COI were found for the above species ( Table 1). The phylogenetic tree ( Fig. 23 View Fig ), based on the combined 16S and COI data, was constructed using ML analysis, with respective support values from the BI analysis. Support values greater than 50% are shown. The tree shows that the four new species and C. variabilis are well-supported by both ML and BI methods. While C. patsyae , C. moluccensis , and C. celebensis are closely related and sister to C. lila , C. granularis is a sister species to C. pseudorugosus . The Indonesian and Australian sequences of C. variabilis form a well-supported clade.

A total of 61 specimens of C. moluccensis , C. patsyae , C. celebensis were used to construct the 16S+ COI haplotype network ( Fig. 24 View Fig ). There are 11 haplotypes in C. moluccensis , 28 in C. patsyae , and 8 in C. celebensis . Three clade can be clearly separated by 16S+ COI: C. celebensis differs from C. patsyae by ≥ 25 bp and from C. moluccensis by ≥ 32 bp, with ≥ 39 bp differences between C. patsyae and C. moluccensis . The pairwise nucleotide divergences and total bp number differences of COI within and between the related species are shown in table 3. The genetic distances (and bp differences) are 0–3.3% (0–21 bp) within species, and 3.6–17.39% (23–100 bp) between species.