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Review
. 2022 Jan 18:10:e12735.
doi: 10.7717/peerj.12735. eCollection 2022.

A review of the common crab genus Macromedaeus Ward, 1942 (Brachyura, Xanthidae) from China Seas with description of a new species using integrative taxonomy methods

Ziming Yuan  1   2 , Wei Jiang  1   3 , Zhongli Sha  1   3   4
Affiliations
Review

A review of the common crab genus Macromedaeus Ward, 1942 (Brachyura, Xanthidae) from China Seas with description of a new species using integrative taxonomy methods

Ziming Yuan et al. PeerJ. .

Abstract

Macromedaeus is one of the most common xanthid genera in shallow waters of the Indo-West Pacific. In this study, we describe a new species, Macromedaeus hainanensis sp. nov., and report on two newly recorded species, M. quinquedentatus (Krauss, 1843) and M. orientalis (Takeda & Miyake, 1969) from Hainan Island, South China Sea. M. hainanensis is most related to M. distinguendus (De Haan, 1833-1850) and M. orientalis on the carapace shape and granular appearance, but can be distinguished by unique morphological characteristics especially its front, pereopods and male first gonopod. Taxonomic identities of the six Macromedaeus species recorded from China seas are discussed, and a phylogenetic analyzation is performed on Macromedaeus and related taxa based on three mitochondrial and two nuclear markers (12S, 16S, COI, H3, 18S). Integrated taxonomic evidence is used to support the taxonomic status of each species.

Keywords: China Seas; Integrative taxonomy; Macromedaeus; New species; Xanthidae.

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Conflict of interest statement

The authors declare there are no competing interests.

Figures

Figure 1
Figure 1. Holotype of Macromedaeus hainanensis. sp. nov., male, 6.54 × 4.34 mm (MBM286988).
(A) Overall, dorsal view. (B) Carapace, dorsal view. (C) Third maxillipeds and pterygostomian region, anterior view. (D) Thoracic sternites and abdomen. (E) Right cheliped, outer view. (F) Left cheliped, outer view. Scale bars = 2 mm.
Figure 2
Figure 2. Holotype of Macromedaeus hainanensis sp. nov., male, 6.54 × 4.34 mm (MBM286988).
(A) Carapace, dorsal view. (B) Third maxillipeds, external view. (C) Front, dorsal view. (D) Abdomen. (E) P5, dorsal view. (I) G1, left, internal view. (F) Same, distal portion, internal view. (G) Same, external view. (H) G2, right, external view. Scale bars: (A) 2 mm. (B–E) = 1 mm. (F–H) = 0.1 mm. (I) = 0.5 mm.
Figure 3
Figure 3. Paratype of Macromedaeus hainanensis sp. nov., female, 14.69 × 9.21 mm (MBM160965).
(A) Overall, dorsal view. (B) Carapace, dorsal view. (C) Third maxillipeds and pterygostomian region, anterior view. (D) Thoracic sternites and abdomen. (E) Right cheliped, outer view. (F) Left cheliped, outer view. Scale bars = 5 mm.
Figure 4
Figure 4. Macromedaeus orientalis (Takeda & Miyake, 1969), male, 6.85 × 4.43 mm (MBM286994).
(A) Overall, dorsal view. (B) Carapace, dorsal view. (C) Third maxillipeds and pterygostomian region, anterior view. (D) Thoracic sternites and abdomen. (E) Right cheliped, outer view. (F) Left cheliped, outer view. Scale bars = 2 mm.
Figure 5
Figure 5. Front of Macromedaeus species, dorsal view.
(A) M. orientalis (Takeda & Miyake, 1969), male, 6.85 × 4.43 mm (MBM286994). (B) M. distinguendus (De Haan, 1833-1850), male, 27.76 × 18.21 mm (135CC03764). (C) M. distinguendus (De Haan, 1833–1850), male, 28.9 × 18.58 mm (MBM286999). (D) M. quinquedentatus (Krauss, 1843), male, 24.77 × 15.60 mm (MBM286997). (E) M. crassimanus (Milne-Edwards, 1867), male, 29.69 ×18.46 mm (MBM282426). Scale bars: (A) = 1 mm. (B-E) = 2 mm.
Figure 6
Figure 6. P5 of Macromedaeus species, dorsal view.
(A) M. orientalis (Takeda & Miyake, 1969), male, 6.85 × 4.43 mm (MBM286994). (B) M. distinguendus (De Haan, 1833-1850), male, 27.76 × 18.21 mm (135CC03764). (C) M. quinquedentatus (Krauss, 1843), male, 24.77 × 15.60 mm (MBM286997). (D) M. crassimanus (Milne-Edwards, 1867), male, 29.69 × 18.46 mm (MBM282426). Scale bars: (A) = 1 mm. (B–D) = 2 mm.
Figure 7
Figure 7. Left G1 of Macromedaeus species.
(A, E, I) M. orientalis (Takeda & Miyake, 1969), male, 6.85 × 4.43 mm (MBM286994). (B, F, J) M. distinguendus (De Haan, 1833-1850), male, 27.76 × 18.21 mm (135CC03764). (C, G, K) M. quinquedentatus (Krauss, 1843), male, 24.77 × 15.60 mm (MBM286997). (D, H, L) M. crassimanus (Milne-Edwards, 1867), male, 29.69 × 18.46 mm (MBM282426). (A–D) distal portion, internal view. (E–H) same, external view. (I–L) overall, internal view. Scale bars: (A, B, E, F) = 0.1 mm. (C, D, E, H) = 0.2 mm. (I) = 0.5 mm. (J–K) = 1 mm.
Figure 8
Figure 8. Macromedaeus distinguendus (De Haan, 1833-1850), male, 27.76 × 18.21 mm (135CC03764).
(A) Overall, dorsal view. (B) Carapace, dorsal view. (C) Third maxillipeds and pterygostomian region, anterior view. (D) Thoracic sternites and abdomen. (E) Right cheliped, outer view. (F) Left cheliped, outer view. Scale bars = 10 mm.
Figure 9
Figure 9. Macromedaeus distinguendus (De Haan, 1833-1850).
(A, B, C) From Qingdao, Shandong. (D) From Xiamen, Fujian. (E, F) From Ningbo, Zhejiang. Photo by Zhang Xu.
Figure 10
Figure 10. Macromedaeus distinguendus (De Haan, 1833-1850).
(A) Male, 28.9 × 18.58 mm (MBM286999). (B) Male, 27.76 ×18.21 mm (135CC03764). (C) Male, 23.19 × 15.75 mm (MBM160925). (D) Male, 24.14 × 16.04 mm (MBM160943). Scale bars = 10 mm.
Figure 11
Figure 11. Macromedaeus quinquedentatus (Krauss, 1843), male, 24.77 × 15.60 mm (MBM286997).
(A) Overall, dorsal view. (B) Carapace, dorsal view. (C) Third maxillipeds and pterygostomian region, anterior view. (D) Thoracic sternites and abdomen. (E) Right cheliped, outer view. (F) Left cheliped, outer view. Scale bars = 10 mm.
Figure 12
Figure 12. Macromedaeus crassimanus (Milne-Edwards, 1867), male, 29.69 × 18.46 mm (MBM282426).
(A) Overall, dorsal view. (B) Carapace, dorsal view. (C) Third maxillipeds and pterygostomian region, anterior view. (D) Thoracic sternites and abdomen. (E) Right cheliped, outer view. (F) Left cheliped, outer view. Scale bars = 10 mm.
Figure 13
Figure 13. Phylogenetic relationships inferred from combined 12S, 16S, 18S, COI and H3 sequences among Macromedaeus species and related genus in Xanthidae, analyzed by Bayesian Inference (BI) and maximum likelihood (ML) analyses.
(A) BI tree, with posterior probabilities (PP) labeled. (B) ML tree, with bootstrap replications (BS) labeled, “-” represents values below 50.
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