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Research Article
Carcinoplax mistio Ng & Mitra, 2019 (Crustacea, Decapoda, Goneplacidae): additional records and genetic differentiation of allied taxa
expand article infoMani Prema§, Chien-Hui Yang|, Samuthirapandian Ravichandran, Peter K. L. Ng#
‡ Annamalai University, Parangipettai, India
§ Ministry of Earth Sciences, Kochi, India
| National Taiwan Ocean University, Keelung, Taiwan
¶ Government Arts & Science College, Nagercoil, India
# National University of Singapore, Singapore, Singapore
Open Access

Abstract

The goneplacid crab, Carcinoplax mistio Ng & Mitra, 2019, was originally described from West Bengal, India, in the northern Indian Ocean. Additional material of C. mistio from off Tamil Nadu in the southeast of India revealed a high degree of size-associated variation in the structures of the anterolateral tooth of the carapace, chelipeds, and male and female pleons. In addition to an in-depth morphological examination of C. mistio, this study also records the natural coloration of the species and conducts a genetic comparison (with mitochondrial COI and 16S rRNA genes) with its close relatives, C. haswelli (Miers, 1884) and C. purpurea Rathbun, 1914. Molecular comparison of C. mistio with its morphologically closest congener, C. haswelli from northern Australia and the western Pacific, corroborates their status as separate species. The genetic sequence of C. mistio, however, is similar to that of C. purpurea from the West Pacific, although these two species can easily be distinguished by distinct carapace and ambulatory leg characters. The present study provides some possible explanations for the genetic and morphological incongruence observed between C. mistio and C. purpurea and highlights the need for a detailed molecular study for Carcinoplax H. Milne Edwards, 1852, to appreciate the evolution of various morphological characters in the genus.

Key words

Brachyura, COI, genetic and morphological incongruence, goneplacid crab, Goneplacoidea, India, systematics, 16S rRNA

Introduction

The goneplacid crab genus, Carcinoplax H. Milne Edwards, 1852, comprises 26 species from the Indo-West Pacific (Castro 2007, 2009; Ng and Kumar 2016; Ng and Mitra 2019; Ng and Castro 2020). Six species of Carcinoplax are known from India: C. longimanus (De Haan, 1833); C. longipes (Wood-Mason, in Wood-Mason & Alcock, 1891); C. indica Doflein, 1904; C. specularis Rathbun, 1914; C. fasciata Ng & Kumar, 2016; and C. mistio Ng & Mitra, 2019 (see Trivedi et al. 2018; Ng and Mitra 2019).

While describing C. mistio from West Bengal, India, Ng and Mitra (2019) compared it with two close congeners, C. sinica Chen, 1984, and C. purpurea Rathbun, 1914, noting that C. mistio has a combination of diagnostic characters of other species. Carcinoplax sinica has since been synonymised with C. haswelli (Miers, 1884) (cf. Ng et al. 2022). Ng and Mitra (2019) had only three specimens of C. mistio available for study, so they were unable to assess allometric variation, which can be pronounced in some species of Carcinoplax (Guinot 1989; Castro 2007). A good series of C. mistio was recently collected from Tamil Nadu, southeast coast of India, allowing the present evaluation of morphological variation in the species. The present study also takes the opportunity to document the natural coloration of C. mistio and compare the genetics of allied C. mistio, C. haswelli and C. purpurea.

Material and methods

Material

The material used for morphological examination is deposited in the Zoological Survey of India, Kolkata (ZSIK); and Centre of Advanced Study in Marine Biology, Annamalai University, Parangipettai, Tamil Nadu (CASAU). Details of all specimens examined are provided in the material examined subsection of the systematic account below. Measurements provided, in millimetres (mm), are of the maximum carapace width (inclusive of spines) and length (taken at the midline from the tips of the frontal margin to the median part of the posterior margin), respectively. The terminology used follows Davie et al. (2015) and Ng and Mitra (2019). Abbreviations used in this study are as follows: coll. = collector; juv. = juvenile; G1 = male first gonopod; and G2 = male second gonopod; ovig. = ovigerous.

Molecular analysis

In addition to C. mistio, C. haswelli and C. purpurea, four other species of Carcinoplax [C. ischurodous (Stebbing, 1923), C. longimanus, C. nana Guinot, 1989 and C. tomentosa Sakai, 1969], are also included for the molecular analysis. Goneplax rhomboides (Linnaeus, 1758) was selected as the outgroup. The samples for molecular analyses were from the Zoological Reference Collection of the Lee Kong Chian Natural History Museum, National University of Singapore (ZRC), and National Taiwan Ocean University (NTOU) (Table 1).

Table 1.

Material, sampling localities and GenBank accession numbers of Carcinoplax and outgroup used in this study. “#” sequences downloaded from GenBank. N.C. - no sequence available.

Species Locality Voucher Nos. GenBank Accession Nos.
(code) COI 16S rDNA
C. haswelli (1) Gulf of Tonkin ZRC 2011.0607 OP163291 PQ163823
C. haswelli (2) Off Singapore ZRC 1984.5693 OP163292 N.C.
C. ischurodous MZ434779 # MZ424933 #
C. longimanus (1) Taiwan NTOU B00138 OP163293 PQ163824
C. longimanus (2) MZ434781 # MZ424935 #
C. longimanus (3) MZ434783 # MZ424936 #
C. mistio (1) India ZRC 2022.0812 (male) OP163294 PQ163825
C. mistio (2) India ZRC 2022.0812 (female) OP163295 PQ163826
C. nana Philippines ZRC 2019.0361 OP163296 PQ163827
C. purpurea (1) Taiwan ZRC 2001.0017 OP163297 PQ163828
C. purpurea (2) Taiwan NTOU B00139 OP163298 PQ163829
C. purpurea (3) Philippines ZRC 2006.0216 OP163299 PQ163830
C. tomentosa Taiwan NTOU B00140 OP163300 PQ163831
Goneplax rhomboides MG935224 # JN591672 #

Crude genomic DNA was extracted from the muscles of the pleon using a DNeasy® Blood and Tissue Kit (Qiagen, Hilden, Germany) following the protocol of the manufacturer. Molecular markers were selected as the mitochondrial COI and 16S rRNA genes, while the sequences amplification using LCO1490/HCO2198 (~657 bp, Folmer et al. 1994) and 16Sar/16S1472 (~550 bp) (Simon et al. 1994; Crandall and Fitzpatrick 1996), respectively. PCR reactions, cycling profiles, product checking and sequencing procedures followed those used in Ng et al. (2018). The output sequences were edited for contig assembly by SeqMan ProTM (Lasergene®; DNASTAR, Madison, WI, USA), then blasted on the GenBank (National Center for Biotechnology Information, NCBI) to check for any potential contamination. EditSeq (Lasergene®; DNASTAR) was used to translate into the corresponding amino acid sequences to avoid the inclusion of pseudogenes for the COI dataset (Song et al. 2008). Sequence alignment and nucleotide pairwise distance for each of the two datasets were calculated based on the Kimura 2-parameter model (K2P, Kimura 1980) by MEGA v.11 (Tamura et al. 2021). The maximum-likelihood (ML) tree was constructed based on the combined sequences (COI+16S rDNA) using MEGA v.11 by 1000 bootstrap replicates (Felsenstein 1985). We failed to get a complete 16S rDNA sequence on C. haswelli (ZRC 1984.5693), and the missing sequence was filled up by the fifth nucleotide “N” for the combined dataset.

Systematic account

Superfamily Goneplacoidea MacLeay, 1838

Family Goneplacidae MacLeay, 1838

Genus Carcinoplax H. Milne Edwards, 1852

Carcinoplax mistio Ng & Mitra, 2019

Figs 1, 2, 3

Carcinoplax (purpurea) ? – Stephensen 1946: 166, 208, fig. 44 (not Carcinoplax purpurea Rathbun, 1914).

Carcinoplax purpureaGuinot 1967: 276 (list); Titgen 1982: 252 (list) (not Carcinoplax purpurea Rathbun, 1914).

Carcinoplax sinicaGuinot 1989: 285, fig. 14A, B, pl. 5 figs A, B, B1, C, C1, D, E, E1; Apel 2001: 101; Naderloo and Sari 2007: 449; Naderloo 2017: 69, text-fig. 11.2d, e, fig. 12.1 (not Carcinoplax sinica Chen, 1984) [= Carcinoplax haswelli Miers, 1884)].

Carcinoplax mistio Ng & Mitra, 2019: e2019004, figs 1, 2, 6A, 7A, G, H, 8A–G, 9A, B.

Carcinoplax haswelliSureandiran et al. 2024: figs 2–7 (not Carcinoplax haswelli Miers, 1884).

Material examined

Holotype. India • ♂ (29.2 × 19.0 mm); northern Bay of Bengal, Fresargunj Fishing Harbour; 24 Feb. 2017; coll. local fishermen by trawl; ZSIK C7123/2. Paratypes. India • 1 ♀ (36.4 × 24.2 mm); same collection data as for holotype; ZSIK C7124/2 • 1 ♀ (36.7 × 27.5 mm); northern Bay of Bengal, Fresargunj Fishing Harbour; 28 Jul. 2018; ZSIK.

Other material

India • 4 ♂♂ (35.1 × 30.0 mm, 29.2 × 22.3 mm, 25.1 × 18.2 mm, 23.2 × 29.2 mm), 5 ♀♀ (37.1 × 31.0 mm, 36.2 × 30.1 mm, 32.1 × 25.2 mm, 31.0 × 25.2 mm, 26.1 × 24.0 mm); southern Bay of Bengal, eastern Tamil Nadu, Pazhayar Fishing Port; 11°21'N, 79°50'E; depth 50–100 m; 2016–2020; coll. M. Prema & S. Ravichandran; CASAU CR-1031 • 1 ♂ (29.7 × 19.6 mm), 1 ♀ (43.2 × 29.2 mm); same collection data as for preceding; 2016–2020; CASAU CR-1032 • 2 ♂♂ (37.6 × 25.8 mm, 32.0 × 21.3 mm), 7 ♀♀ (37.9 × 24.5 mm, 37.0 × 25.1 mm, 34.0 × 22.9 mm, 32.3 × 21.6 mm, 31.2 × 21.1 mm, 29.5 × 19.6 mm, 27.6 × 25.6 mm,); same collection data as for preceding; 18 Mar. 2018; CASAU CR-1033 • 1 ♂ (26.4 × 18.0 mm), 1 juv. ♀ (19.7 × 13.4 mm); same collection data as for preceding; Mar. 2018; CASAU CR-1034 • 4 ♂♂ (36.0 × 23.8 mm, 33.0 × 22.7 mm, 32.5 × 22.2 mm, 31.5 × 21.4 mm), 1 ovig. ♀ (39.0 × 26.6 mm), 1 ♀ (36.1 × 23.4 mm); same collection data as for preceding; 2020–2021; CASAU CR-1035 • 3 ♂♂ (29.2 × 20.8 mm, 29.2 × 20.5 mm, 27.6 × 19.4 mm); same collection data as for preceding; 12 Jan. 2022; CASAU CR-1036 • 1 ♂ (33.× 23.4 mm); same collection data as for preceding; CASAU CR-1037 • 2 ♀♀ (37.3 × 24.6 mm, 35.9 × 23.7 mm); same collection data as for preceding; 26 Mar. 2023; CASAU CR-1038 • 2 ♂♂ (26.2 × 18.1 mm, 24.8 × 16.4 mm), 2 ♀♀ (32.2 × 22.0 mm, 29.5 × 19.4 mm); same collection data as for preceding; 11 Feb. 2024; CASAU CR-1039 • 7 ♀♀ (37.9 × 26.0 mm, 36.2 × 24.3 mm, 34.7 × 22.5 mm, 33.5 × 24.0 mm, 30.5 × 20.5 mm, 29.2 × 20.1 mm, 25.1 × 17.1 mm); same collection data as for preceding; 11 Feb. 2024; CASAU CR-1040.

Diagnosis

Modified from Ng and Mitra (2019). Carapace broad, dorsal surface gently convex; antero-lateral surfaces generally with small, rounded, densely packed granules, sometimes appearing almost smooth; post-orbital region with small, rounded granules; second anterolateral teeth relatively short in larger specimens, slightly sharp in smaller specimens; gastro-cardiac groove shallow but visible (Figs 1, 2A, B, 3A). Chelipeds unequal, male carpal spine more rounded, that on female more elongate (Figs 1, 2G–I, J–L, 3B–D). Ambulatory legs long, slender; articles laterally flattened, smooth; margins lined with setae (Fig. 1). G1 relatively slender, laterally flattened, tip elongate, tapering, lined with numerous short spines (Fig. 3G–K). G2 longer than G1, distal segment long, curved, tip weakly bifurcated (Ng and Mitra 2019: fig. 8D).

Figure 1. 

Colour in life and overall dorsal view of Carcinoplax mistio Ng & Mitra, 2019 A male (33.3 × 23.4 mm) (CASAU CR-1037) B male (29.2 × 20.5 mm) (CASAU CR-1036) C female (33.5 × 24.0 mm) (CASAU CR-1040). Scale bars: 1.0 cm (A–C).

Figure 2. 

Carcinoplax mistio Ng & Mitra, 2019 A, C, D, E–I male (33.3 × 23.4 mm) (CASAU CR-1037) B, J–L male (24.8 × 16.4 mm) (CASAU CR-1039) A, B dorsal view of carapace C frontal view of cephalothorax D third maxillipeds E thoracic sternites 3–6, pleonal somites and telson E pleonal somites and telson G–L dorsal and outer views of chelae. Scale bars: 5.0 mm (A–L).

Figure 3. 

Carcinoplax mistio Ng & Mitra, 2019 A–F female (33.5 × 24.0 mm) (CASAU CR-1040); G– J male (33.3 × 23.4 mm) (CASAU CR-1037) K male (25.1 × 18.2 mm); A dorsal view of carapace B–D dorsal and outer views of chelae E pleon and telson F thoracic sternites with position of vulvae G dorsal view of left G1 H dorso-lateral view of left G1 I ventral view of left G1 J ventro-lateral view of left G1 K lateral view of left G1. Scale bars: 5.0 mm (A–F); 1.0 mm (G–K).

Habitat

The present specimens of C. mistio were collected from 50–100 m depth, off the coastal waters of Tamil Nadu state, Bay of Bengal, India. The three type specimens were obtained from West Bengal, also from a fishing port but without depth data (Ng and Mitra 2019).

Coloration in life

Carapace orange, cheliped fingers and upper surface of ambulatory legs white (Fig. 1A–C), merus of ambulatory leg generally orange (Fig. 1), and sternopleonal surfaces pale white.

Distribution

Northern Indian Ocean: Bay of Bengal (West Bengal and off Tamil Nadu coast, India; Ng and Mitra 2019; present study); north-western Arabian Sea (Gujarat, India; Sureandiran et al. 2024); and Persian Gulf (Guinot 1989; Naderloo 2017).

Remarks

The present specimens of C. mistio agree well with the type account (Ng and Mitra 2019). The large series of specimens, however, allowed us to document size-related morphological variation. The largest specimens of C. mistio collected in this study have a carapace width of 37.6 mm (male, CASAU CR-1033) and 43.2 mm (female, CASAU CR-1032), respectively; both are larger than the type specimens and are the largest known specimens of the species.

In the types as well as in the smaller males (e.g., 26.4 × 18.0 mm, CASAU CR-1034; 24.8 × 16.4 mm, CASAU CR-1039) and most of the larger specimens of the present collection, the second anterolateral tooth of the carapace is prominent, being sharp and curved (Figs 1B, 2B). In the largest males (e.g., 35.1 × 30.0 mm, CASAU CR-1031; 33.3 × 23.4 mm, CASAU CR-1037), this tooth is relatively lower (Figs 1A, 2A) and comparable to the condition in C. purpurea. In C. purpurea, however, the second anterolateral tooth is even lower and more like a rounded tubercle (cf. Ng and Mitra 2019: fig. 6C, D). As such, the form of the second anterolateral tooth is not a reliable diagnostic character for C. mistio at all body sizes, being sometimes size dependent, though it is usually sharp and longer. The cheliped of the largest males is elongate, with the merus and fingers extremely long (Fig. 1A, B, 2G–I), a condition like that of C. longimanus (see Guinot 1989). In the smaller holotype male of C. mistio as well as in smaller males, the chelipeds are relatively shorter (Fig. 2J–L). Sexual dimorphism is apparent as all females have relatively shorter cheliped fingers (Figs 1C, 3B–D).

The cheliped carpal spine of male C. mistio specimens examined, including the holotype male, is relatively more rounded and relatively shorter (Figs 1A, B, 2G, H, J, L) (versus the cheliped carpal spine being relatively less rounded, more elongate and curved in most of the females; Figs 1C, 3B, D). In the holotype male of C. mistio, the carpal spine is relatively short and rounded (Ng and Mitra 2019: fig. 1A, F) and as such, its length is a sexually dimorphic character (Ng and Mitra 2019: fig. 2A, D, F) that is not size dependent. This is similar to the condition of the cheliped carpal spine that was reported for C. haswelli (as C. sinica, cf. Ng and Mitra 2019: fig. 4E).

The lateral margins of pleonal somite 6 of large males is gently convex, gradually converging towards the telson, which is similar to that of the holotype of C. mistio (Fig. 2E, F; see Ng and Mitra 2019: fig. 7A). In the large male of C. mistio (33.3 × 23.4 mm, CASAU CR-1037), pleonal somite 6 is proportionately broader, width-to-length ratios 2.1 (versus pleonal somite 6 width-to-length ratios in two smaller males (26.2 × 18.1 mm, 24.8 × 16.4 mm, CASAU CR-1040) being 1.96 and 1.98, respectively). The pleon of large females in the present collection is similar to that reported for the paratype C. mistio (36.4 × 24.2 mm, ZSIK C7124/2) (cf. Ng and Mitra 2019: fig. 9A), but in a smaller specimen (26.1 × 24.0 mm, CASAU CR-1031), the pleon is relatively wider than in the paratype. Among the 28 female specimens studied, only one was ovigerous (39.0 × 26.6 mm, CASAU CR-1035). In juvenile females (e.g., 19.7 × 13.4 mm, CASAU CR-1034), the pleon is not expanded, lacking setae on pleopods, and the operculum of the vulva is poorly developed.

The proportions of the male telson vary regardless of size with the width-to-length ratios of three males (33.3 × 23.4 mm, CASAU CR-1037; 26.2 × 18.1 mm, 24.8 × 16.4 mm, CASAU CR-1040) are 0.76, 0.88 and 0.67, respectively. Overall, the male telson is slightly broader with the lateral margins being more concave (Fig. 2E, F) than in C. haswelli (cf. Ng and Mitra 2019: fig. 7D–F).

The mesial margin of the distal two-thirds of the G1 is gently concave in large specimens of C. mistio (Fig. 3G) and almost straight in smaller ones (Fig. 3I), but the tip is always elongate and tapering (Fig. 3G–J). Ng and Mitra (2019) observed that the G1s of the holotype (29.2 × 19.0 mm, ZSIK C7123/2) were distally damaged. Sureandiran et al. (2024) reported “Carcinoplax haswelli” based on one male specimen from Gujarat in western India, but all their figures of the G1 and the carapace (see Sureandiran et al. 2024: figs 2–7), actually correspond to C. mistio.

The genetic comparisons for seven species of Carcinoplax, including C. mistio, are interesting (Fig. 4). The intraspecific divergences of COI (657 bp) and 16S rRNA (552 bp) genes for four morphologically distinct species of Carcinoplax are less than 1.5%: C. haswelli (COI 0.2%), C. mistio (COI 0%, 16S 0.2%), C. purpurea (COI 0.5–1.1%, 16S 0%), and C. longimanus (COI 0.2–0.8%, 16S 0.0–0.4%) (Table 2). As for the interspecific divergences of the three species under study here (Table 2), that between C. haswelli and C. mistio is high (COI 10.3–10.5%, 16S 3.5–3.7%), as is that between C. haswelli and C. purpurea (COI 9.9–10.5%, 16S 3.5%) (Table 2, Fig. 4), corroborating their status as separate species. The genetic divergence between C. mistio and C. purpurea, however, was unexpectedly low (COI 0.3–0.8%, 16S 0.0–0.2%) and within the range normally considered for conspecificity (Fig. 4) when compared with the other four species of Carcinoplax (COI 12.4–21.1%, 16S 6.5–12.1%) (Table 2, Fig. 4). The morphological differences between C. mistio and C. purpurea, however, are substantial. In C. mistio, the carapace is proportionally wider, appearing more rectangular in shape with the posterolateral margins distinctly converging posteriorly (Figs 1A–C, 2A, B, 3A; see Ng and Mitra 2019: figs 1A, 2A, 6A, B) (versus carapace more quadrate with the posterolateral margins subparallel in C. purpurea; see Ng and Mitra 2019: figs 3A, 6C, D); the second (last) anterolateral tooth is usually sharp and curved (Figs 1B, C, 2B, 3A) (versus low and rounded in C. purpurea; see Ng and Mitra 2019: figs 3A, 6C, D); and the ambulatory legs are long and slender (Fig. 1A–C; see Ng and Mitra 2019: figs 1A, 2A, 7G, H) (versus distinctly shorter and stouter in C. purpurea; see Ng and Mitra 2019: figs 3A, 7I, J). Noteworthy is that the G1s of C. mistio and C. purpurea are similar (Fig. 3G–J; see Ng and Mitra 2019: fig. 8E, F, H, I). The characters of the G1 are more conservative in goneplacid evolution than carapace and pereopod differences, which are more plastic. Significant morphological differentiation but with low genetic variation has previously been reported in Armases angustipes (Dana, 1852) (Sesarmidae, Marochi et al. 2017), Carcinus maenas (Linnaeus, 1758) (Carcinidae, Silva et al. 2010), and Pachygrapsus marmoratus (Fabricius, 1787) (Grapsidae, Deli et al. 2015). There are many possible explanations for this observed discordance, ranging from incomplete lineage sorting to retention of ancestral genotypes, etc. (see Meier et al. 2006; Tang et al. 2012; Nabholz 2023).

Figure 4. 

Maximum likelihood phylogenetic tree for seven species of Carcinoplax based on the mitochondrial COI+16S rRNA genes dataset. Goneplax rhomboides (Linnaeus, 1758) was chosen as outgroup. Bootstrap value is represented above the branches. Values < 50 are not shown.

Table 2.

Pairwise distance based on Kimura-2-parameter (K2P) model of partial mitochondrial COI (within and under the diagonal) and 16S rDNA (value in the brackets and above the diagonal) sequences among Carcinoplax species. Goneplax rhomboides (Linnaeus, 1758) was treated as an outgroup.

Carcinoplax haswelli C. ischurodous C. longimanus C. mistio C. nana C. purpurea C. tomentosa Goneplax rhomboides
Carcinoplax haswelli 0.002 0.102 0.098–0.101 0.035–0.037 0.105 0.035 0.134 0.128
C. ischurodous 0.199–0.202 0.078–0.083 0.095–0.097 0.080 0.095 0.093 0.071
C. longimanus 0.172–0.178 0.176–0.178 0.002–0.008 [0.0–0.004] 0.082–0.088 0.078–0.084 0.082–0.086 0.084–0.087 0.113
C. mistio 0.103–0.105 0.190 0.159–0.164 0.0 [0.002] 0.093–0.095 0.0–0.002 0.118–0.121 0.113–0.116
C. nana 0.165–0.167 0.154 0.124–0.127 0.179 0.093 0.065 0.105
C. purpurea 0.099–0.105 0.192–0.195 0.159–0.169 0.003–0.008 0.181–0.184 0.005–0.011 [0.0] 0.118 0.113
C. tomentosa 0.173–0.175 0.209 0.203–0.211 0.203 0.160 0.200–0.203 0.105
Goneplax rhomboides 0.187–0.189 0.122 0.204–0.205 0.198 0.172 0.195–0.203 0.219

A detailed molecular study of Carcinoplax will be necessary to appreciate the evolution of the various morphological characters in the genus as currently defined (sensu Castro 2007). Carcinoplax currently contains 26 species, all from the Indo-West Pacific, with many species morphologically similar and often occurring sympatrically, although several species span both oceans (see Castro 2007, 2009; Ng and Castro 2020). As the present study indicates, genetic and morphological incongruence may be more common in Carcinoplax than expected, and wide-ranging taxa may well prove to be species-complexes (see Ng and Castro 2020). Currently, C. mistio is known from the northern Indian Ocean, ranging from the Bay of Bengal to the Persian Gulf. Carcinoplax purpurea is only known for certain from the western Pacific (Castro 2007). There is also a record of C. purpurea from Madagascar by Castro (2007: 639), but it was based on a badly preserved male specimen, and it more likely belongs to either C. monodi Guinot, 1989, or C. haswelli. Carcinoplax haswelli, however, occurs in the western Pacific, Southeast Asia and eastern Indian Ocean (north-western Australia) (Ng et al. 2022).

Acknowledgements

We sincerely appreciate Dr Paul F. Clark (Department of Life Science, The Natural History Museum, London, England) and Dr Shane T. Ahyong (Australian Museum, Sydney, Australia) for many constructive comments in reviewing the manuscript. Prof. Tin-Yam Chan kindly provided specimens from the National Taiwan Ocean University.

Additional information

Conflict of interest

The authors have declared that no competing interests exist.

Ethical statement

No ethical statement was reported.

Funding

The Earth Watch Institute of India, New Delhi, Citizen Science Fellowship (PR/01/2022-2023) is acknowledged for facilitating funding for the fieldwork along the coast of Tamil Nadu, Bay of Bengal.

Author contributions

MP and SR collected the samples. MP prepared the photographs. CHY conducted the molecular works and prepared Fig. 4. MP and CHY prepared the draft and PN finalized the manuscript.

Author ORCIDs

Mani Prema https://orcid.org/0000-0003-2694-3034

Chien-Hui Yang https://orcid.org/0000-0002-4594-3622

Samuthirapandian Ravichandran https://orcid.org/0000-0002-8632-5062

Peter K. L. Ng https://orcid.org/0000-0001-5946-0608

Data availability

All of the data that support the findings of this study are available in the main text.

References

  • Apel M (2001) Taxonomie und Zoogeographie der Brachyura, Paguridea und Porcellanidae (Crustacea: Decapoda) des Persisch-Arabischen Golfes. PhD Thesis, Johann Wolfgang Goethe-Universität, Biologie und Informatik, Frankfurt am Main, Germany.
  • Castro P (2007) A reappraisal of the family Goneplacidae MacLeay, 1838 (Crustacea, Decapoda, Brachyura) and revision of the subfamily Goneplacinae, with the description of ten new genera and eighteen new species. Zoosystema 29(4): 609–773.
  • Castro P (2009) Two new species of Carcinoplax H. Milne Edwards, 1852, and Pycnoplax Castro, 2007, from the western Pacific, and a description of the female of Thyraplax truncata Castro, 2007 (Crustacea, Decapoda, Brachyura, Goneplacidae). Zoosystema 31(4): 949–957. https://doi.org/10.5252/z2009n4a9
  • Crandall Jr KA, Fitzpatrick JE (1996) Crayfish molecular systematics: using a combination of procedures to estimate phylogeny. Systematic Biology 45: 1–26. https://doi.org/10.1093/sysbio/45.1.1
  • Davie PJF, Guinot D, Ng PKL (2015) Anatomy and functional morphology of Brachyura. In: Castro P, Davie PJF, Guinot D, Schram FR, von Vaupel Klein JC (Eds) Treatise on Zoology – Anatomy, Taxonomy, Biology. The Crustacea (Vol. 9C–I): Decapoda: Brachyura (Part 1). Brill, Leiden, 11–163. https://doi.org/10.1163/9789004190832_004
  • Deli T, Bahles H, Said K, Chatti N (2015) Patterns of genetic and morphometric diversity in the marbled crab (Pachygrapsus marmoratus, Brachyura, Grapsidae) populations across the Tunisian coast. Acta Oceanologica Sinica 34: 49–58. https://doi.org/10.1007/s13131-015-0687-7
  • Folmer O, Black M, Hoeh W, Lutz R, Vrijenhoek R (1994) DNA primers for amplification of mitochondrial cytochrome c oxidase subunit I from diverse metazoan invertebrates. Molecular Marine Biology and Biotechnology 3: 294–299.
  • Guinot D (1967) La faune carcinologique (Crustacea, Brachyura) de l’Ocean Indien occidental et de la Mer Rouge. Catalogue remarques biogéographiques et bibliographie. Mémoires de l’Institut fundamental d’Afrique noire 77: 235–352.
  • Guinot D (1989) Le genre Carcinoplax H. Milne Edwards, 1852 (Crustacea, Brachyura: Goneplacidae). In: Forest J (Ed.) Resultats des campagnes MUSORSTOM, Volume 5. Mémoires du Muséum National d’Histoire Naturelle 144: 265–345.
  • Kimura M (1980) A simple method for estimating evolutionary rate of base substitutions through comparative studies of nucleotide sequences. Journal of Molecular and Evolution 16: 111–120. https://doi.org/10.1007/BF01731581
  • Marochi MZ, Masunari S, Schubart CD (2017) Genetic and morphological differentiation of the semiterrestrial crab Armases angustipes (Brachyura: Sesarmidae) along the Brazilian coast. The Biological Bulletin 232(1): 30–44. https://doi.org/10.1086/691985
  • Meier R, Shiyang K, Vaidya G, Ng PKL (2006) DNA taxonomy and DNA identification in Diptera: a tale of high intraspecific variability and low identification success. Systematic Biology 55(5): 715–728. https://doi.org/10.1080/10635150600969864
  • Nabholz B (2023) Incomplete lineage sorting explains the low performance of DNA barcoding in a radiation of four species of Western European grasshoppers (Orthoptera: Acrididae: Chorthippus). Biological Journal of the Linnean Society 141(1): 33–50. https://doi.org/10.1093/biolinnean/blad106
  • Naderloo R, Sari A (2007) Subtidal crabs of the Iranian coast of the Persian Gulf: new collections and biogeographic considerations. Aquatic Ecosystem Health Management 10: 341–349. https://doi.org/10.1080/14634980701514620
  • Ng PKL, Castro P (2020) A revision of Carcinoplax abyssicola (Miers, 1885) and seven related species of Carcinoplax H. Milne Edwards, 1852, with the description of two new species and an updated key to the genus (Crustacea, Decapoda, Brachyura, Goneplacidae). Zoosystema 42(17): 239–284. https://doi.org/10.5252/zoosystema2020v42a17
  • Ng PKL, Kumar AB (2016) Carcinoplax fasciata, a new species of deep-water goneplacid crab from southwestern India (Crustacea: Decapoda: Brachyura: Goneplacoidea). Zootaxa 4147(2): 192–200. https://doi.org/10.11646/zootaxa.4147.2.6
  • Ng PKL, Ho P-H, Lin C-W, Yang C-H (2018) The first record of an eastern Pacific invasive crab in Taiwanese waters: Amphithrax armatus (Saussure, 1853) (Brachyura: Majoidea: Mithracidae), with notes on the taxonomy of the genus. Journal of Crustacean Biology 38(2): 198–205. https://doi.org/10.1093/jcbiol/rux109
  • Silva IC, Alves MJ, Paula J, Hawkins SJ (2010) Population differentiation of the shore crab Carcinus maenas (Brachyura: Portunidae) on the southwest English coast based on genetic and morphometric analyses. Scientia Marina 74(3): 435–444. https://doi.org/10.3989/scimar.2010.74n3435
  • Simon C, Frati F, Beckenbach A, Crespi B, Liu H, Flook P (1994) Evolution, weighting and phylogenetic utility of mitochondrial gene sequences and a compilation of conserved polymerase chain reaction primers. Annals of the Entomological Society of America 87: 625–701. https://doi.org/10.1093/aesa/87.6.651
  • Song H, Buhay JE, Whiting MF, Crandall KA (2008) Many species in one: DNA barcoding overestimates the number of species when nuclear mitochondrial pseudogenes are coamplified. Proceedings of the National Academy of Sciences of the United States of America 105: 13486–13491. https://doi.org/10.1073/pnas.0803076105
  • Stephensen K (1946) The Brachyura of the Iranian Gulf. With an appendix: The male pleopoda of the Brachyura. Danish Scientific Investigations in Iran 4: 57–237.
  • Sureandiran B, Dave TH, Suyani NK, Karuppasamy K (2024) First record of goneplacid crab, Carcinoplax haswelli (Decapoda: Brachyura: Goneplacidae) from the Indian Ocean. Journal of the Marine Biological Association of the United Kingdom 104: e37. https://doi.org/10.1017/S0025315424000328
  • Tang Q-Y, Liu S-Q, Yu D, Liu H-Z, Danley PD (2012) Mitochondrial capture and incomplete lineage sorting in the diversification of balitorine loaches (Cypriniformes, Balitoridae) revealed by mitochondrial and nuclear genes. Zoologica Scripta 41: 233–247. https://doi.org/10.1111/j.1463-6409.2011.00530.x
  • Titgen RH (1982) The systematics and ecology of the Decapods of Dubai, and their zoogeographic relationships to the Arabian Gulf and the Western Indian Ocean. PhD Thesis, Texas A&M University, USA.
  • Trivedi JN, Trivedi DJ, Vachhrajani KD, Ng PKL (2018) An annotated checklist of marine brachyuran crabs (Crustacea: Decapoda: Brachyura) of India. Zootaxa 4502(1): 1–83. https://doi.org/10.11646/zootaxa.4502.1.1
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