Revision of Alpheus euphrosyne De Man, 1897 and A. microrhynchus De Man, 1897, with description of three new species and taxonomic remarks on several other morphologically and ecologically similar snapping shrimps (Malacostraca: Decapoda: Alpheidae) Author Anker, Arthur text Zootaxa 2023 2023-05-09 5282 1 1 115 http://dx.doi.org/10.11646/zootaxa.5282.1.1 journal article 54693 10.11646/zootaxa.5282.1.1 7912c179-a542-47d7-9b44-6af1c9185a23 1175-5326 7912292 DF418763-8F0E-44DD-97C4-B123A81A8DB4 Alpheus nipa Banner & Banner, 1985 ( Figs. 44 , 45 , 52D ) Alpheus nipa Banner & Banner 1985: 21 , fig. 2. Type material . Paratypes , 5 males (cl 6.2–7.5 mm , tl 16.0 –20.0 mm, all missing chelipeds, but detached major and minor chelipeds present in the vial), 1 ov. female (cl 9.5 mm , tl 23.5 mm , chl 12.0 mm), ZMUC CRU-7526 , Indonesia , Strait of Malacca off Sumatra , vicinity of Medan , Galathea Expedition sta. 325, 4°20’N 98°53’E , palm fronds floating on water surface (depth at collection site: 40 m ), 10.05.1951 . Description . See Banner & Banner (1985) for detailed description and illustrations; complementary illustrations of one of the paratypes are provided in Figs. 44 , 45 . FIGURE 44 . Alpheus nipa Banner & Banner, 1985 : paratypes, males (cl 6.2–7.5 mm) from off Medan, Sumatra, Indonesia (ZMUC CRU-7526), detached chelipeds; A—major (right) cheliped, lateral view; B—same, mesial view; C—minor (right) cheliped, lateral view; D—same, dorsolateral view; E—same, mesial view. Colour pattern . Unknown. Type locality . Off Sumatra , Indonesia . Distribution . Indo-West Pacific: presently known only from the type locality in the Straits of Malacca off Sumatra , western Indonesia ( Fig. 52D ). Common name proposed . Nipa palm snapping shrimp. FIGURE 45 . Alpheus nipa Banner & Banner, 1985 : paratype, male (cl indet., range: 6.2–7.5 mm) from off Medan, Sumatra, Indonesia (ZMUC CRU-7526); A—rostro-orbital region of carapace, dorsal view; B—frontal region, lateral view; C— ventromesial carina of first article of antennular peduncle, lateral view; D—antennal scaphocerite, dorsal view; E—third maxilliped, lateral view [arthrobranch not drawn]; F—same, detail of branchial structures on exopod, mesial view; G—major (right) cheliped, chela, mesial view; H—same, distal part of chela, fingers open, lateral view; I—second pleopod, appendices masculina and interna; J—right uropod, detail of distolateral angle, dorsal view. Ecology and biology . All known specimens of A. nipa were found on floating fronds of nipa palm ( Nypa fructicans Wurmb , Arecaceae ), suggesting that they may inhabit estuarine muddy banks fringed by nipa palms, a habitat that is both difficult to access and dangerous to sample due to the presence of saltwater crocodiles [ Crocodylus porosus (Schneider) ]. Taxonomic remarks . Banner & Banner (1985) provided a reasonably detailed description of A. nipa , accompanied by illustrations of all major diagnostic features. Two important features of A. nipa not mentioned nor illustrated by Banner & Banner (1985) are the unarmed antennal basicerite ( Fig. 45B ) and the presence of a faint mesial subdistal ridge on the major cheliped pollex ( Figs. 44B , 45G ), which may link this species to the A. euphrosyne — A. microrhynchus complex. Another previously unknown feature of A. nipa is the presence of three small, gill-like leaflets at the base of the third maxilliped exopod; this feature was observed on two dissected third maxillipeds and one maxilliped still in situ . This gill-like structure does not appear to be homologous to the “rudimentary pleurobranch at the base of the third maxilliped” in A. pontederiae ( Christoffersen 1984 ) and “une petite pleurobranchie de forme très spéciale sur le 3 e mxp.” in several other species of Alpheus , including A. euphrosyne , A. microrhynchus and A. macrodactylus (see discussion in Coutière 1899: 279–281 ). As noted by Banner & Banner (1985) , A. nipa can be separated from A. euphrosyne , A. richardsoni , A. paludicola and A. microrhynchus by the dactyli of the third and fourth pereiopods being short and conical rather than spatulate (in the first three species) or trigonal-subspatulate (in the latter species). This distinguishing character is also valid for A. eurydactylus , A. nomurai sp. nov. , A. mangalis sp. nov. , A. takla sp. nov. and A. songkla , all of which with spatulate dactyli on the ambulatory pereiopods. In addition, A. nipa differs from A. microrhynchus by the markedly different ratio of the first two carpal subarticles of the second pereiopod (1: 0.8 in A. nipa vs . 1: 0.3 in A. microrhynchus ); from both A. microrhynchus and A. cyanoteles by the much stronger sculpture of the male minor chela, with both dorsal and ventral transverse grooves well pronounced and bordered by shoulders ( vs . feebly delineated, if it all, and without shoulders, in A. microrhynchus and A. cyanoteles ); and the scaphocerite blade much shorter than the distolateral tooth ( vs . reaching slightly or far beyond the distolateral tooth in A. microrhynchus and A. cyanoteles ). Another diagnostic character of A. nipa is the presence of several long erect setae on the rostrum ( Fig. 45A, B ; see also Banner & Banner 1985 : fig. 2a, b); these setae are absent in the other species being dealt with in this study (or if present, not nearly as conspicuous as in A. nipa ). Banner & Banner (1985) suggested that A. nipa “is derived from one of these euryhaline mud-or soft sedimentdwelling species, possibly from the most common and widespread A. euphrosyne * and has left the mud and silt where the other three species [ A. euphrosyne * , A. richardsoni , A. paludicola ] dwell and has invaded a unique habitat, the nipa palms. In so doing, it has lost the spatulate dactyli on the walking legs, so necessary for digging in soft sediments” [*note: A. euphrosyne not sensu De Man (1897) ]. This is indeed an interesting hypothesis to be tested in the future, and to be contrasted to an alternative hypothesis of A. nipa not being closely related to the A. euphrosyne — A. microrhynchus complex and being derived, for instance, from the morphologically similar A. lobidens complex, in which the walking leg dactyli are also conical. Whatever the case may be, the origin and phylogenetic affinites of A. nipa are difficult to ascertain without a comprehensive phylogenetic analysis of the entire A. edwardsii group, with inclusion of as many members as possible of the A. euphrosyne — A. microrhynchus and A. lobidens complexes.