A new species of sponge crab of the genus Epigodromia McLay 1993 (Crustacea: Brachyura: Dromiidae) from the southeastern Arabian Sea, with notes on the Zoogeography Author Prema, Mani Ministry of Earth Sciences, Centre for Marine Living Resources and Ecology, Kochi - 682508, Kerala, India. Author Cubelio, Sherine Sonia Ministry of Earth Sciences, Centre for Marine Living Resources and Ecology, Kochi - 682508, Kerala, India. text Zootaxa 2024 2024-08-19 5496 2 247 260 http://dx.doi.org/10.11646/zootaxa.5496.2.6 journal article 10.11646/zootaxa.5496.2.6 1175-5326 13346677 37F8B010-2897-448B-8593-0F8A7F62D35D Epigodromia mclayi sp. nov. ( Figs. 1A–B , 2 , 3A–E , 4 , 5A–B , 6A–B ) Material examined. Holotype : 1 male (cw 11.43, cl 10.33 mm ), ( IO /SS/BRC/00370), FORVSS stn. 39217, slope, off the coast Tamil Nadu , southeastern Arabian Sea , 7°25’12’’N , 77°31’12” E , 113 m , coll. Vinay Padate , 04 December 2019 .— Paratype : 1 male , (cw 10.29, cl 9.04 mm ), ( IO /SS/BRC/00371), FORVSS stn. 23631, off the coast Tamil Nadu , southwestern Bay of Bengal , 107 m , 11°58’48” N , 80°05 60” E , coll. Smitha C.K , 16 July 2005 . Comparative material examined. Epigodromia areolata (Ihle, 1993) : 1 male (cw 13.2, cl 11.9 mm ) ( ZRC 2001.521), Balicasag Island, Panglao, Bohol , Visayas, Philippines , 200–300 m , coll. 28 November 2001 [examined by Peter K.L. Ng, photographs received]; 1 male (cw 16.0, cl 14.0 mm) ( WAM-C 50514), Queensland, 164 m , coll. W. Goode, 1965 [specimen examined by late Prof. Colin McLay; photographs received]. — Epigodromia gilesii ( Alcock, 1900 ) : holotype , male ( ZSI 5621-34/9), Malabar coast, Marine Survey; 2 males (cw 6.8, cl 6.64; cw 5.8, cl 6.05 mm ) ( IO /SS/BRC00/372), FORVSS stn. 34324, Malabar coast, Southeastern Arabian Sea, India , 32 m , 9°57’36” N , 75°35’24” E , coll. Ishwarya Gopal, 15 August 2015 .— Epigodromia ebalioides ( Alcock, 1900 ) : holotype , male ( ZSI 182-3/10), Karachi, Marine Survey. [Note: E. gilesii Alcock, 1900 and E. ebalioides ( Alcock, 1900 ) which are preserved in the ZSI has been examined by the first author but unable to take the measurements of the specimens due to its fragile condition. The photographs were received upon request from: https://zsifis.nic. in/ImageRequest/GetByCategory/10] Etymology . This species is dedicated to and named in honour of the late Prof. Colin McLay (University of Canterbury ) for his tremendous contribution to the taxonomy and systematics of the brachyuran families, particularly the Dromiidae , which has been most helpful in the present study and for his generous mentorship and help to the authors. FIGURE 1 . Dorsal habitus.A, B, Epigodromia mclayi sp. nov. , holotype, male (cw 11.43 mm, cl 10.33 mm), (IO/SS/BRC00370), southeastern Arabian Sea, Tamil Nadu, India; C, D, Epigodromia areolata ( Ihle, 1913 ) , male (cw 16.0 mm, cl 14.0 mm), (WAMC50514), Queensland, Australia (Photograph by McLay, C.). E, F, Epigodromia areolata (Ihle, 1993) , male (cw 13.2, cl11.9 mm), (ZRC 2001.521), Balicasag Island, Philippines (Photograph by Ng, P.K.L.). Scale bars = 5.0 mm. Description . Carapace wider than long, subcircular, areolate; entire carapace granulated, small granules on anterior region, larger and dense granules posteriorly; grooves between areolae smooth; regions well defined; short frontal groove between rostral and first anterolateral lobe ( Figs. 1A, B , 2A , 4A , 5A , 6A ). Cervical and branchial grooves distinct; mesogastric region convex, with prominent, fine granules, three poorly defined protuberances, anterior one small, rounded, followed by two larger protuberances; small oval-shaped protuberances side by side in protogastric region; urogastric region with two equally divided small protuberances; cardiac region broadly convex, nearly triangular, granulated, well defined by grooves ( Figs. 1A, B , 5A ). Branchial region anteriorly with four fused, prominent protuberances, connected with supraorbital ridge longitudinally and with second anterolateral lobe forms concave surface and deep groove; branchial notch visible with posterolateral node and larger conical tooth; posterior branchial areas convex, evenly granulated with larger granules ( Figs. 1A, B , 5A ). Rostrum tridentate, lateral teeth long, separated by a U-shaped sinus; borders of lateral rostral teeth granulated, concave, median tooth short, pointed, triangular, clearly visible dorsally ( Fig. 1A, B , 2A– C ). Anterolateral margin armed with two granulated lobes, first lobe at the level of anterior corner of buccal frame, and separated from it by a concave groove, second lobe smaller, rounded, projected laterally, continuous with posterolateral margin, covered in larger rounded granules; posterior carapace margin distinctly concave ( Figs. 1A , 2A, B , 4A , 5A ). Supraorbital border slightly concave, smooth, small pointed tooth followed by post-supraorbital border integration with carapace surface, no orbital fissure, and visible tooth at inner corner ( Figs. 2B , 5A ). Suborbital lobe triangular, pointed, granular ( Fig. 2C ). First segment of antenna much wider than long, tuberculate, second segment longer, surface rough, third segment inserted at an angle ( Figs. 2B–C , 4B ). Subhepatic area deeply concave, densely granulated ( Fig. 2C ). Chelipeds well developed, covered with line of larger, rounded granules; merus long, but shorter than propodus; carpus with two obtuse, distal tubercles; propodus with two tubercles near carpal articulation along anterior and posterior margins, three tubercles at base of fingers; outer surface of movable finger with rounded granules, fixed finger surface smooth, possesses numerous setae; fingers strongly curved with 6 or 7 teeth, meeting at tips, pointed tip of dactylus fitting in the bifid tip of pollex ( Figs. 1A , 2E–H ). Ambulatory legs, first two pairs shorter than chelipeds, tuberculate, largely granulated, with rounded nodules and few short bristles; dactyli as long as propodi, inner margins with 5–7 tiny spines of similar size; P4–5 reduced, tuberculate, granulated, with short and long setae, outer surfaces of propodi with 3 spines of similar size, inner posterior end with single spine opposed to dactyli, dactyli of both legs deeply curved ( Figs. 1A , 2I–J , 4D–G ). Male pleon with six free somites; telson wider than long, lateral margins with minor acute spine; uropod plates large, visible externally; median ridge strongly developed; outer surface covered with dense, smaller granules; somites 2–6 with two transverse rows of granulated lobules: upper one with continuous lobe and lower one divided into two lobes; somites 2 and 3 with transverse lobules ornamented with continuous flattened granules ( Figs. 3A , 4H , 5B , 6B ). G1 semi-rolled, setose with a pointed lobe, G2 needle-like, pointed tip ( Figs. 3B–E , 4I–K ). Fresh colouration. Brownish in colour with red spots on the carapace. Remarks. Epigodromia mclayi sp. nov. , fits well within the genus as defined by McLay (1993 , 1998 ) and Guinot & Tavares (2003) , particularly in the following characters: wider, subcircular carapace, areolate, anterolateral margin with two broad granulated lobes; rostrum with three lobes with short median lobe, pointed, triangular, bluntly rounded, lateral lobes; coxae of third maxillipeds separated by a gap by triangular shape plate with the sternum; much larger cheliped in males with proximal tooth along the cutting edge; last two ambulatory legs reduced; male pleon having six free somites by a strongly granulated median ridge with transverse lobes. Among the 10 species of Epigodromia currently recognized ( McLay 1998 ; Ng et al . 2008 ; Poore & Ahyong 2023 ), E. mclayi sp. nov. , is morphologically most similar to E. areolata ( type locality: Timor Island, South China Sea), particularly in the general outline of the carapace and the division of the anterolateral margin whereby second lobe is exceptional with 5–9 distinct blunt teeth, and has a concave margin with anterior margin of the buccal frame, and third lobe continues with posterolateral margin, one large granulated conical tooth and covered in larger rounded granules ( Figs. 1B , 4A ), and number of spines in the dactylus of ambulatory legs ( Fig. 4D, E ). Some consistent morphological features, however, distinguish the two species: (1) the carapace is wider than long and subcircular, areolate, outline is more rounded and granular, posterolateral margin with more rounded granules, posterior carapace margin is distinctly concave in E . mclayi sp. nov. ( Figs. 1A, B , 2A , 4A , 5A , 6A ) (versus the carapace slightly wider than a long, more flattened, outline with two granulated lobes and ornamented with sharp granules,the posterolateral margin with sharp granules, posterior carapace margin is moderately concave in E . areolata ; Fig. 1C–F ); (2) mesogastric region convex, prominent, fine granules, three poorly defined protuberances, anterior one rounded and small, followed by two larger protuberances in E . mclayi sp. nov. ( Fig. 1A, B ) (versus mesogastric region convex and comparatively clearly defined protuberances with larger granules, anterior one small and followed by two larger protuberances in E . areolata ; Fig. 1C–F ); (3) cardiac region broadly convex, nearly triangular structure towards posterior margin, finely granulated, and visible grooves in between posterolateral margin in E . mclayi sp. nov. ( Figs. 1A, B , 2A ) (versus cardiac region broadly convex, round appearance with larger granules, posterolateral margin fused in E . areolata ; Fig. 1C–F ); (4) branchial notch clearly visible forming narrow gap between second anterolateral lobe and the posterolateral node, followed by one larger conical tooth present in E . mclayi sp. nov. ( Figs. 1A–B , 2A , 4A ) (versus branchial notch clearly visible, and fused with posterolateral margin, conical tooth absent in E. areolata ; Fig. 1C–F ); (5) rostrum tridentate, lateral teeth distinctly curved out, triangular, longer than median tooth more triangular in E . mclayi sp. nov. ( Fig. 1A–B ) (versus rostrum tridentate, lateral teeth slightly curved out, slightly longer than median tooth, median tooth deflexed in E . areolata ; Fig. 1C–F ); (6) chelipeds equal, larger, outer surface covered with line of rounded granules, including movable finger, and outer surface of fixed finger smooth and possess numerous setae in E . mclayi sp. nov. ( Figs. 1A , 2E–H ) (versus chelipeds equal, larger, outer surface with densely packed with larger sharp granules, including bases of fingers in E . areolata ; see McLay & Hosie 2022 : fig. 16B–C; Fig. 1C, E ); (7) ambulatory legs, inner margins of dactyli of first two pairs ambulatory legs armed with 5–7 tiny spines of similar size in E . mclayi sp. nov. ( Fig. 4D, E ) (versus inner margins of dactyli of first two pairs of legs armed with 7–8 small spines in E . areolata ; see McLay (1993) and it is also confirmed in Philippines specimen (pers. comm P.K.L. Ng)); (8) the telson of the male pleon is much wider than long, pronounced flange on the lateral margins and anterior margin of somite 6 in E . mclayi sp. nov. ( Figs. 3A , 4H , 5B , 6B ) (versus the telson of the male pleon with smooth margins, slightly wider than long; see McLay (1993) ; Serène & Lohavanijaya (1959: fig. 7); Fig. 6H ); (9) G1 semi-rolled, longer distal part, broader basal part, setose with a pointed lobe in E. mclayi sp. nov. ( Figs. 3B–E , 4I, J ) (versus G1 semi-rolled, shorter distal and slender basal part, setose with a sharp tip in E. areolata ; see McLay (1993) ; Serène & Lohavanijaya (1959: fig. 5); Fig. 3F–I ). FIGURE 2 . Epigodromia mclayi sp. nov. , holotype, male (cw 11.43 mm, cl 10.33 mm) (IO/SS/BRC00370), southeastern Arabian Sea, Tamil Nadu, India. A, carapace, dorsal view; B, anterior carapace, dorsal view; C, cephalothorax, ventral view; D, male thoracic sternum, ventral view; E, left cheliped, external view; F, right cheliped, external view; G, left chela, internal view; H, right chela, internal view; I, right P4, dorsal view (broken spine opposed to dactyl); J, right P5, (spine visible opposed to dactyl) dorsal view. Scale bars: A–D = 5.0 mm; E–J = 1.0 mm. FIGURE 3 . A–E, Epigodromia mclayi sp. nov. , holotype, male (cw 11.43 mm, cl 10.33 mm), (IO/SS/BRC00370), southeastern Arabian Sea, Tamil Nadu, India; F–J, Epigodromia areolata (Ihle, 1993) male (cw 13.2, cl11.9 mm), (ZRC 2001.521), Balicasag Island, Philippines (Photograph by Ng, P.K.L.). A, male pleon, ventral view; B, F, G, left G1, pleonal view; C, H, I, left G1, sternal view; D, G, I, magnified view of distal part of G1; E, J, left G2 pleonal view; Scale bars: A–C, E, F, H, J = 1.0 mm; D, G, I = 0.1 mm. Distribution. Epigodromia mclayi sp. n ov., is currently known only from the southeastern Arabian Sea and southwestern Bay of Bengal, off the coast of Tamil Nadu , India . Results and Discussion. The genus Epigodromia McLay, 1993 ( type species: Epigodromia granulata Kossmann, 1878 ) was taxonomically treated by McLay (1993) , in his worldwide systematic revision of Dromiidae , in which he addressed the confused taxonomy of generic names and recognized 29 genera and 109 species. In his work, he proposed 10 new genera including Epigodromia (a replacement name for Epidromia Kossmann, 1878 ; see McLay 1993 & Ng et al . 2008 ) in recognition of 9 species (most of which were transferred from the genus Cryptodromia , Petalomera and Dromia ), including two new species E . rotunda and E . rugosa from New Caledonia . Later, he added one species Petalomera acutidens Sakai, 1983 from Japan (see McLay 1998 ; McLay & Ng 2007 ). McLay (1993) also distinguished the species of Epigodromia from its closest genus, Takedromia McLay, 1993 , by its areolate carapace, poorly developed anterolateral teeth, and truncate or bilobed male telson. Guinot & Tavares (2003) supplemented the information on the differences between Epigodromia & Takedromia in the absence of vestigial male pleopods in the genus Epigodromia . Thus far, the genus Epigodromia McLay, 1993 , comprises 10 valid species (see Ng et al . 2008 ; Poore & Ahyong 2023 ), and the present E . mclayi sp. nov. brings the species number to 11, and it is distributed in two major oceans: (1) Indian Ocean (Northen Indian Ocean: E . granulata (Kossman, 1878) , E . globosa (Lewinshon, 1977) , E . ebaliodes ( Alcock, 1900 ) , E . gilesii ( Alcock, 1900 ) , E . mclayi sp. nov. ; and Southern Indian Ocean: E. nodosa ( Sakai, 1936 ) , E . rotunda McLay, 1993 ); (2) Pacific Ocean (Northwestern Pacific Ocean: E . areolata ( Ihle, 1913 ) , E . nodosa ( Sakai, 1936 ) , E . rotunda McLay, 1993 , E . ruguosa McLay, 1993 ; and Southwestern Pacific Ocean: E . areolata ( Ihle, 1913 ) , E . ruguosa McLay, 1993 , E . sculpta ( Haswell, 1882 ) . Amongst the species, E . areolata has proved abundant in western Pacific (see Takeda & Miyake 1972 ; McLay & Ng 2005 ) and McLay (1998) revealed the distributional records from Japan in the north to New Caledonia in the south ( Table 1 , Figure 7 ). However, no records were found in the Indian Ocean after Ihle (1993)’s record of E . areolata , which was originally described from South coast of Timor Island, Indonesia (Ihle 1993: pl. II. fig. 10). Thus, the species, E. areolata , has been illustrated from different locality by several researchers (see Sakai 1936 , 1965 , 1976 ; Serène & Lohavanijaya 1973 : figs. 5–7, pI. II fig, A; Dai & Yang 1991 : pl. 1 fig. 8; McLay 1993 : fig. 19 e–f); and the recent records of McLay & Ng (2005) , and McLay & Hosie (2022 : figs. 15, 16) clarified the impediments in taxonomy, sexual dimorphism, and its distributions. Accordingly, Epigodromia areolata is known from a large series of specimens, and particularly noting that the larger specimens of McLay (1993 : fig. 19f) (male, cw 14.4, cl 12.3 mm ), and much larger specimen of McLay & Hosie (2022 : fig. 16) from Queensland which is used in this study as a comparative material (male, cw 16.0, cl 14.0 mm) has slight resemblance to E . mclayi sp. nov. , on the dorsal surface of the swollen regions and the apex of the male pleon; however, compared to new species of E . mclayi sp. nov. ( male, cw 11.43, cl 10.33 mm ) with comparably sized male specimen of E . areolata (male, cw 13.2, cl 11.9 mm ) from Philippines clearly shows the distinct white, areolate characters on the carapace, anterolateral margin with sharp granules (see Fig. 1E, F ), the gonopods agreed with Serène & Lohavanijaya (1973 : figs. 5, 6, pI. II, A) and detailed G1, distal part with sharp tip (see Fig. 3G, I ). FIGURE 4 . Epigodromia mclayi sp. nov. , holotype, male (cw 11.43 mm, cl 10.33 mm), (IO/SS/BRC00370), southeastern Arabian Sea, Tamil Nadu, India. A, carapace, dorsal view; B, antenna, ventral view; C, maxilliped 3 with triangular plate between coxa; D–G, right ambulatory legs P2–P5, dorsal view; H, male pleon, dorsal view; I, left G1, distal tip covered with plumose setae, pleonal view; J, left G1, distal tip denuded, sternal view with tip; K, left G2, pleonal view. Scale bars = 1.0 mm. FIGURE 5 . Micro-computed tomography 3D images. A–D, dorsal view; B–C, frontal view with chelipeds outer view. A, B, Epigodromia mclayi sp. nov. , holotype, male (cw 11.43 mm, cl 10.33 mm), (IO/SS/BRC00370), southeastern Arabian Sea, Tamil Nadu, India; C–D, Epigodromia gilesii Alcock, 1900 , male (cw 5.8 mm, cl 6.05 mm), (IO/SS/BRC00372), Malabar coast, southeastern Arabian Sea, India. Epigodromia mclayi sp . nov. ( Fig.6A, B ) resembles E . gilesii ( Fig. 6C, D ; type locality: southeastern Arabian Sea) by its slightly curved out lateral teeth of rostrum; and also resembles to E . ebalioides ( Fig. 6E, F ; type locality: Karachi) in the form of fused anterolateral lobe with anterolateral margin of the buccal frame, larger conical tooth in the posterolateral node, and apex of the male pleon. However, anterolateral margin of the buccal frame is concave in E . mclayi sp. nov. , and convex in E . ebalioides , while E . gilesii does not possess this character; larger tooth in the posterolateral node in E . mclayi sp. nov. is conical and smooth, but round shape with 4–5 granules in E . ebalioides while the tooth is absent in E. gilesii ; the apex of the male pleon in E. mclayi sp. nov. is differs from without emargination as on E. gilesi ( Gordon 1950 : fig. 2C; Fig. 6D ). Additionally, the last two pairs of legs in the present specimens are very small and not accompanied by any object for camouflage ( Fig. 6A–H ) corroborating a similar observation by McLay (1993) , and Guinot &Tavares (2003) . The present observation of E . gilesii from the southeastern Arabian Sea is only the second record of this species from the type locality ( Fig. 5C, D ) and E . mclayi sp. nov. is the second species of the genus from India . The present discovery suggests that brachyuran species richness is highly underestimated in Indian waters, particularly the southern coasts and adjoining waters as evidenced by the recent discoveries in the region ( Ng et al . 2024 ), and it emphasizes the importance of extensive surveys of poorly explored, unique, and deeper habitats (Wafer et al . 2011; Ng et al . 2019 , 2024 ; Prema et al . 2023 ). An identification key to the species of the genus Epigodromia is provided below based on McLay (1993) , Sakai (1983) , and the present contribution.