Petrolisthes tanmayi Pahari, Das, Das & Maiti, 2025, sp. nov.
Creators: name: Pahari, Priti Ranjan
name: Das, Shubhrajyoti
name: Das, Mitali
name: Maiti, Subhadeep
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Porcellanidae
Petrolisthes
Petrolisthes tanmayi

description: Petrolisthes tanmayi sp. nov.
(Figs. 2–4)
Type material. HOLOTYPE: ZSI CR 751, male (cl 7.8 mm, cw 7.2 mm), G-Plot Island, Sundarbans, West Bengal, India, 21°38'52.25"N 88°24'53.91"E, intertidal zone, from sandy-muddy substratum, under pebbles and bricks, 30 January 2023. PARATYPES: ZSI CR 752, 2 males (cl 6.8 mm, cw 6.3 mm; cl 6.4 mm, cw 6.0 mm), 2 females (cl 6.1 mm, cw 6.1 mm; cl 6.0 mm, cw 6.0 mm), same data as holotype.
Other material examined. TMV/ZOO/CL/CR/PT 1, 1 male (cl 7.5 mm, cw 7.0 mm), same data as holotype; TMV/ZOO/CL/CR/PT 2, 1 female (cl 5.2 mm, cw 5.2 mm), same data as holotype.
Description. Carapace smooth, about as long as broad; lateral margins convex, posterior to epibranchial angle, broadest at mesobranchial region; dorsal surface marked by fine sculpturing of broken transverse lines (Fig. 2A); frontal and orbital region depressed; front narrow about 1/3 width of maximum carapace width (Fig. 3A) with median longitudinal groove on dorsal surface, margins not granulate, trilobate in dorsal view and frontal view, devoid of setae; median lobe triangular, distally subangular, over reaching lateral lobes, lateral lobes rounded; posterolateral carapace surface rugose; posterior margin converging; posterior region depressed, devoid of setae; branchiostegite with longitudinal subparallel wrinkles, without setae, without anterodorsal granular crest.
Thoracic sternite 3 with broad median lobe, subtriangular with protruding tip slightly overreaching lateral lobes; lateral lobes narrow, triangular. Thoracic sternite 4–7 broad, sutures between sternites incomplete, distinct only dorsally. Thoracic sternite 8 with anterior margin convex, posterior margin concave (Fig. 3F).
Cornea small, dilated.
Antennular basal article (Fig. 4B) slightly longer than broad, with 1 or 2 long granulate transverse ridges on mediolateral and anterolateral part and some short ridges in between, anterior margin thin with minute row of tubercles, mesial angle round with 1 or 2 prominent denticles and rest of the margin separated by 1 incision and with 1 prominent denticle, no spine laterally. Lateral angle with a prominent projection and lateral margin concave anteriorly. Article 3 of antennule devoid of spinule.
Antennal peduncle short, freely accessible to orbit; article 1 broadest with blunt spine, accompanied by few spinules at anterodistal angle; article 2 with sharp spine at mid-anterior margin with few scattered granules on both sides; article 3 distinctly shorter than articles 1 and 2; article 4 shortest (Fig. 3B).
Mxp3 with coxa bearing longitudinal ridge distally on ventral side. Basis triangular, fused with ischium. Ischium broad, subovate, lateral surface with oblique ridges; dorsal margin with longitudinal ridges. Merus with rounded lobe on ventral margin, fringed with few short setae on base of lateral margin, reaching about 1/3 of merus; flagellum well developed (Fig. 3D).
P1 subequal in size, similar, flattened; dorsal surface slightly convex. Merus almost 1/2 length of carpus, inner lobe spineless, ventral border ends distally in slight angulation. Carpus length about 2.5 times as long as broad, anterior and posterior borders straight, subparallel, anterior border unarmed, posterior border with 1 distal and 1 subdistal spine, dorsal surface flat and with oblique striations posteriorly. Chela in male subequal; major chela robust, fingers shorter than that of minor chela, fingers about 0.6–0.7 length of carpus; palm 2.2–2.3 times as long as broad, fixed finger about 1/3 to 1/4 of total length of entire propodus; dactylus subequal to fixed finger; fingers with dense pubescence from the base of both fingers to the base of hooked tips; both fingers have uniformly serrated cutting edge; fingertips curved (Fig. 2C). Female chela less robust, equal or subequal, ventral margin serrated distally with pubescence (Fig. 2 B, D).
Walking legs decreasing in size posteriorly from P2 to P4, smooth both dorsally and ventrally. Merus of P2 unarmed or with 1 vestigial tooth on distal lateroventral margin (Fig. 3E); merus of P3 and P4 unarmed. Meri to carpi ratio of P2–P4 gradually decreases from 1.7 to 1.5; P2–P4 propodus slightly longer than respective carpus, with 5 or 6 movable corneous spines ventrally, 3 or 4 medially aligned evenly, 1 pair on distal margin near angulation with dactylus; P2–P4 dactylus 0.5–0.6 times length of extensor margin of respective propodus, each terminating with 4–5 corneous slender spines increasing in size towards claw. Distal part of carpus, propodus, and dactylus of P5 with dense, sickle-shaped serrate setae.
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Pleon subrectangular, dorsal surface smooth, lateral margins with dense row of setae. Female pleopods well developed on somite 4 and 5. Uropods reaching distal margin of telson. Telson smooth on external surface, as long as broad, subdivided into 7 plates (Fig. 4C).
Colouration. Dorsal carapace slate-brown with light brown patches. Prominent mid-dorsal line made up of patches (Fig. 2A). Cheliped and walking legs overall slate-brown, with irregular brown patches ventrally. Mxp2 endopod cobalt blue, with long orange setae (Fig. 3C). A small orange spot at the base of dactylus of cheliped.
Etymology. This new species is named after our Teacher, Dr. Tanmay Bhattacharya, former Professor of Zoology, Vidyasagar University for his notable taxonomic contribution and for his constant guidance and support to us. The species name is a noun in the genitive singular.
Remarks. Morphologically, P. tanmayi sp. nov. is close to P. kranjiensis and P. cinctipes, which are not found in India. Petrolisthes tanmayi and P. kranjiensis resemble each other in general shape, structure and sculpturing of the carapace and chelipeds. In both species, the carapace is rectangular with similar length to width ratio and is marked with broken transverse lines. The chelipeds are large, flattened and subequal; the anterior and posterior margins of carpus are straight and almost parallel and the posterior margin terminates in a distal and a subdistal spine. Petrolisthes tanmayi, however, can easily be distinguished from P. kranjiensis by the absence of sub-basal tooth on anterior margin of the carpus of cheliped, absence of a distal large tooth at the ventrolateral margin of P2 merus, as seen in P. kranjiensis, in colouration of P2–P4; in the absence of spine on lateral margin of article 1 and in the absence of spinule on article 3 of antennular peduncle. Additionally, P. tanmayi shows sexual dimorphism in the palm of the cheliped, which is not recorded in P. kranjiensis. Petrolisthes tanmayi is similar to P. cinctipes in length to width ratio of the carapace, which lacks an epibranchial spine and in the absence of distinct tooth on the anterior margin of the carpus of the cheliped. Petrolisthes tanmayi, however, can be distinguished from P. cinctipes in the shape and colouration of the carapace and by the number of distal spines on the posterior border of P1. Petrolisthes tanmayi and P. cinctipes differ also in colouration of P2–P4. The former has slate-brown and light bands and the latter has yellow median banding on the propodus and narrow brown bands on the dactylus.
A comparison of the morphological characters of P. tanmayi sp. nov. with similar species of Petrolisthes is given in Table 1. Petrolisthes tanmayi sp. nov. differs from all these species in the absence of an acute tooth or lobe in the anterior margin of the P1 carpus. Petrolisthes tanmayi sp. nov., however, doesn’t bear any spine on the anterior margin of carpus of P1, a character that distinguishes it from the 10 species of Petrolisthes recorded so far from India.
Molecular evidence and phylogeny. DNA fragments of 652 bp were amplified using mitochondrial COI gene. The sequences generated from the current study were published in NCBI GenBank and the accession number are provided in Table 2. The sequences were subjected to a NCBI BLAST search to find highlight close relatives of the new species. The BLAST search of COI gene sequences shows 90% identity with an unidentified porcellanid species (MN69000.1).
The neighbor-joining tree using COI gene (Fig. 5) shows that the three haplotypes of P. tanmayi sp. nov. were clustered together in a separate clade compared to COI sequences of other species of Petrolisthes. No COI sequences of P. kranjiensis are available in GenBank. The COI sequence of P. cinctipes shows 79% similarity and forms a distant clade separate from P. tanmayi. sp. nov. Instead, P. ornatus and P. armatus show 85% and 84–85% similarity in their COI sequences, respectively.
description: Published as part of Pahari, Priti Ranjan, Das, Shubhrajyoti, Das, Mitali & Maiti, Subhadeep, 2025, Petrolisthes tanmayi sp. nov., a new species of the porcelain crab (Decapoda: Anomura: Porcellanidae) from G-Plot Island, Sundarbans, India, pp. 369-379 in Zootaxa 5631 (2) on pages 371-377, DOI: 10.11646/zootaxa.5631.2.9, http://zenodo.org/record/15370736