Accepted by J. Mendoza: 14 Mar. 2018; published: 11 Jun. 2018 ZOOTAXA ISSN 1175-5326 (print edition) ISSN 1175-5334 (online edition) Copyright © 2018 Magnolia Press Zootaxa 4433 (1): 195–200 http://www.mapress.com/j/zt/ Article 195 https://doi.org/10.11646/zootaxa.4433.1.13 http://zoobank.org/urn:lsid:zoobank.org:pub:5D1E2ACB-C252-411E-B6AB-F447D1971164 A new pea crab species of the genus Arcotheres Manning, 1993 (Crustacea: Decapoda: Brachyura: Pinnotheridae) from India JIGNESHKUMAR N. TRIVEDI 1 , ERNESTO CAMPOS 2 & KAURESH D. VACHHRAJANI 3,4 1 Department of Life Sciences, Hemchandracharya North Gujarat University, Patan, Gujarat, India. E-mail:jntrivedi26@yahoo.co.in (JNT) 2 Facultad de Ciencias, Universidad Autónoma de Baja California, Km. 103 Carretera Tijuana – Ensenada, Ensenada, 22800 Baja California, Mexico. E-mail: ecampos@uabc.edu.mx (EC) 3 Marine Biodiversity and Ecology Laboratory, Department of Zoology, Faculty of Science, The Maharaja Sayajirao University of Bar- oda, Vadodara, Gujarat, India. E-mail: kauresh@gmail.com (KDV) 4 Corresponding author. E-mail: kauresh@gmail.com Abstract A new species of pinnotherid crab, Arcotheres shahi n. sp., is described on the basis of specimens collected during a crus- tacean survey along the coastal areas of Pamban fishing harbor in the Gulf of Mannar, Tamil Nadu state, east coast of India. The new species resembles A. pernicola (Bürger, 1895), A. winckworthi (Gordon, 1936) and A. rayi Ahyong & Ng, 2007, in having the dactyli of the longer fourth pereopod longer than that of fifth pereopod. Arcotheres shahi n. sp. differs from these three known species in the shape of female carapace, frontal region and chela, setal pattern on the dactyli of the fourth and fifth pereopods and relative length of the ambulatory pereiopods. Key words: Pinnotheridae, new species, dactylus length, Gulf of Mannar, India Introduction The genus Arcotheres Manning, 1993, contains 26 species, all characterized by a subquadrate to subhexagonal carapace, and pereopods 2–5 (P2–P5, ambulatory legs) which are asymmetrical in length, with the dactyli of P4 and P5 longer than those of P2 and P3 (Bürger 1895; Gordon 1936; Manning 1993; Campos 2001; Campos & Manning 2001; Ahyong & Ng 2007; Ng et al. 2008, 2017; Ng & Kumar 2015). On the basis of relative lengths of the dactyli of the longer P4 and P5, it is possible to recognize two subgroups within Arcotheres (Bürger1895; Hornell & Southwell 1909; Gordon 1936; Ahyong & Ng 2007; Ng et al. 2017). Species of the larger subgroup have the dactyl of the longer P5 longer than that of the P4 while the species of smaller subgroup have the dactyl of the longer P4 longer than that of the P5. A total of five species of Arcotheres are known from India (Ng & Kumar 2015, Ng et al. 2017). According to Ng & Kumar (2015) records of two more species, Arcotheres modiolicola (Bürger, 1895) and Arcotheres sinensis (Shen, 1932) (as Pinnotheres) by George & Nobel (1970) and Kannappan et al. (2012), respectively, are questionable and need reexamination of specimens in the view of study carried out by Ahyong & Ng (2007). The record of Arcotheres placunae (Hornell & Southwell, 1909) (as Pinnotheres) by Jose & Deepthi (2005) from the mytilid Perna viridis (Linnaeus, 1758) collected from the coastal areas of Kerala State also needs reexamination as the figure available in their paper is too small to record the diagnostic characters of the species (Ng & Kumar 2015). In this paper, we describe a new species of Arcotheres on the basis of specimens collected from the coastal areas of Tamil Nadu state located on east coast of India. The specimens are preserved in 70% alcohol and deposited in the Zoology Museum (ZL-AR-CR), Department of Zoology, The Maharaja Sayajirao University of Baroda, in Vadodara, Gujarat. The morphological terminology used in the description follows Manning (1993) and Ahyong & Ng (2007). The following abbreviations are used: CL = carapace length, measured along the vertical median line of the carapace; CW = carapace width, measured at the widest point; MXP3 = third maxilliped; G1 = male first