Eurindicus, Grave & Arjun & Raghavan, 2018

Grave, Sammy De, Arjun, Charambilly Purushothaman & Raghavan, Rajeev, 2018, The discovery of Euryrhynchidae (Crustacea: Decapoda) in India, with the description of a new genus and species, Zootaxa 4462 (3), pp. 367-378 : 369

Eurindicus gen. nov.

Type species. Eurindicus bhugarbha sp. nov., by present designation and monotypy.

Differential diagnosis. RoStrum Smooth, non-dentate on both dorSal and Ventral marginS; diSto-meSial region of ocular peduncleS not anteriorly produced. Fourth thoracic Sternite (maleS) without tranSVerSal ridge or tooth; fifth thoracic Sternite with well-deVeloped tranSVerSal ridge. Upper antennular flagellum biramouS; fuSed portion compriSed of three diViSionS; acceSSory ramuS with four diViSionS; aeSthetaScS on Sub-diStal and diStal diViSion. Third maxilliped with two arthrobranchS. CarpuS of third and fourth pereiopod without cuSpidate Setae on diStoVentral margin; carpuS of third to fifth pereiopod without cuSpidate Setae on dorSal margin. Male Second pleopod with endopod Spatulate, not modified into gonopod, appendix maSculina preSent. Uropodal exopodS with Single cuSpidate Seta on diareSiS, protopod with weakly deVeloped lateral extenSion.

Etymology. Eurindicus iS an arbitrary combination of ‘ Eur- ’ the firSt three letterS of the family Euryrhynchidae , and ‘- indicus ’, from India, baSed on the geographic diStribution of the genuS, thiS being the firSt record of the family in India; gender maSculine.

Systematic remarks. A number of morphological featureS eaSily allow the new genuS to be placed within Euryrhynchidae . Notably, theSe are the Shape and form of the frontal region of the carapace, including the roStrum; the Shape of the eyeS; the form of the acceSSory ramuS of the upper antennular flagellum; the Shape and ornamentation of the telSon; the characteriStic tranSVerSe ridge on the fifth thoracic Sternite and the lower Surface of the palm and fixed finger of the firSt pereiopod with a well-deVeloped tuft of Serrate Setae. DeSpite the preSence of theSe putatiVe SynapomorphieS, Eurindicus gen. nov. occupieS an iSolated poSition within the family on account of the upper antennular flagellum and itS acceSSory ramuS being joined oVer three diViSionS (VS. one in all other genera), the preSence of a carpo-propodal bruSh, albeit reduced (VS. abSent in all other genera) and the welldeVeloped branchioStegal grooVe (VS. abSent or poorly deVeloped in all other genera). A further difference with all known genera iS the poorly deVeloped poStero-lateral expanSion on the protopod of the uropod (VS. well-deVeloped in all other genera). The new genuS alSo diSplayS a primitiVe gill formula with pleurobranchS on all ambulatory pereiopodS aS well aS two arthrobranchS on the third maxilliped, only Shared with the WeSt African Surface dwelling Euryrhynchoides (VS. fewer gillS in the other genera, See Pachelle & TaVareS 2018).

Due to the abSence of comprehenSiVe phylogenetic coVerage encompaSSing all genera, the exact SyStematic poSition of Eurindicus gen. nov. within Euryrhynchidae cannot herein be reSolVed. HoweVer, the morphological differenceS highlighted aboVe would indicate the genuS to be more likely to be baSal and perhapS moSt cloSely related to the WeSt African genuS Euryrhynchina with which it ShareS a number of potential SynapomorphieS (endopod of Second male pleopod Spatulate, low number of SpineS on uropodal diareSiS, abSence of Spiniform Setae on the dorSal margin of the dactyli of the third to fifth pereiopodS), although it differS SubStantially from that genuS in the branchial formula, the number of fuSed articleS, aS well aS the number and diSpoSition of the aeSthetaScS on the acceSSory ramuS of the antennular flagellum and the preSence of an appendix interna on the male firSt pleopod.

A number of preViouS StudieS haVe poStulated that the WeSt African freShwater family DeSmocarididae could be the SiSter-taxon to Euryrhynchidae , baSed on morphology (De GraVe 2007) aS well aS phylogeneticS ( Bracken et al. 2009; Kou et al. 2013; De GraVe et al. 2015a). The preSence of a well-deVeloped branchioStegal grooVe in Eurindicus gen. nov. iS howeVer reminiScent of the poSt-antennular Suture in Typhlocarididae , with a clear potential for homology. Although the acceSSory ramuS of the upper antennular flagellum in Eurindicus gen. nov. iS clearly homologouS with that obSerVed in the other euryrhynchid genera, the fact that it iS joined oVer three diViSionS with the flagellum may further Support a cloSe relationShip to Typhlocarididae .

Sankolli and Shenoy (1979) deScribed a new genuS and SpecieS of Subterranean Shrimp, Troglindicus phreaticus from a coaStal well in Ratnagiri, MaharaShtra State, which they aSSumed waS allied to the Cuban, Subterranean genuS Troglocubanus HolthuiS, 1949 and thuS placed in Palaemonidae . Pereira (1997) included thiS genuS in hiS cladiStic Study of Palaemonidae sensu lato and reSolVed the taxon to be cloSely related to Euryrhynchidae , albeit in a baSally unreSolVed clade which alSo contained Troglocubanus , Typhlocaris Calman, 1909 and Creaseria HolthuiS, 1950. No further StudieS haVe examined the SyStematic poSition of thiS genuS, which waS herein undertaken giVen the geographic proximity and Similar habitat to the type locality of Eurindicus gen. nov. BaSed on a direct examination of four paratypeS (RMNH D 35320) it iS eVident that T. phreaticus ShareS a number of putatiVe SynapomorphieS with Euryrhynchidae , notably the preSence of a well-deVeloped tranSVerSe ridge on the fifth thoracic Sternite, the well-deVeloped bruSh on the palm and fixed finger of the firSt pereiopod, a well-deVeloped poStero-lateral expanSion on the protopod of the uropod (leSS deVeloped in Eurindicus gen. nov.) and the Shape and ornamentation of the telSon, with itS typical euryrhynchid diStal margin. HoweVer, it iS noticeably different in the form of the acceSSory ramuS of the upper antennular flagellum, which conSiStS of 15 free, non-conical diViSionS with 2-3 pairS of aeSthetaScS on all diViSionS. Two further SimilaritieS Shared with Eurindicus gen. nov. are that the joined portion of the upper antennular flagellum conSiStS of three diViSionS and the preSence of a well-defined branchioStegal grooVe. It iS thuS SeemS eVident that Troglindicus iS phylogenetically cloSely allied to Euryrhynchidae . HoweVer, the genuS iS herein not formally tranSferred to that family, aS that would negate a further defining Synapomorphy of Euryrhynchidae , notably the unique Shape of the acceSSory ramuS of the upper antennular flagellum. NeVertheleSS, aS a preViouSly SuggeSted Synapomorphy, the Single jointed diViSion in the upper antennular flagellum, waS negated by the diScoVery of Eurindicus gen. nov., it iS unclear where the true circumScription of the family now lieS. GiVen the high leVel of morphological homoplaSieS at higher SyStematic leVelS within Caridea, thiS can only be fully reSolVed by a targeted molecular phylogenetic approach.