Synalpheus gloriosus, Anker, 2025

Anker, Arthur, 2025, Three new species of the shrimp family Alpheidae from the south-western Indian Ocean (Decapoda: Caridea), Zootaxa 5659 (1), pp. 51-68 : 57-60

Synalpheus gloriosus sp. nov.

( Fig. 4 )

Type material. Holotype: female (cl 4.3 mm), MNHN-IU-2019-5917, Mozambique Channel , Îles Glorieuses, BIOMAGLO sta. CP4796, 11°26’30.5”S 47°20’33.1”E (11.441816 47.342533), depth 80–147 m, beam trawl, leg. MNHN team, 23.01.2017.

Description. Small-sized alpheid shrimp (holotype:cl 4.3 mm).Body moderately stout.Carapace subcylindrical, smooth, not setose. Rostrum short, acuminate, subtriangular, about 1.5 times as long as wide at base, with some erect setae distally; tip not reaching distal margin of first article of antennular peduncle ( Fig. 4A, B ). Orbital hoods somewhat angular anteriorly, without produced teeth; mesial margin noticeably oblique, forming a 90° angle with rostrum ( Fig. 4A, B ). Rostro-orbital process well developed, bulging ventrally between eyes. Pterygostomial angle rounded, slightly protruding ( Fig. 4B ). Cardiac notch moderately developed.

Pleon smooth, cylindrical, glabrous; first to fourth pleonites with pleura posteroventrally rounded, second pleura enlarged; fifth pleuron posteroventrally somewhat angular; sixth pleonite with blunt posterolateral angle. Telson relatively broad, gradually tapering posteriorly, with slightly convex lateral margins, 1.8 times as long as greatest width; dorsal surface with two pairs of slender spiniform setae inserted submarginally, first just anterior to mid-length, second at about 0.7 of length; posterior margin about third as long as anterior margin, slightly rounded in its centre, with one pair of slender spiniform setae at each posterolateral angle, mesial spiniform setae more than twice as long as lateral ones, and four long plumose setae between mesial spiniform setae ( Fig. 4C ).

Cornea of eye moderate in size, normally pigmented, completely concealed in dorsal view, only anterior-most portion visible in lateral view ( Fig. 4A, B ). Antennular peduncle stout; visible portion of first article short; stylocerite subacute distally, slightly overreaching distal margin of first article; second article square-shaped, about as long as wide; third article shortest; dorsolateral flagellum with short accessory ramus and four groups of aesthetascs along ventral surface, fused portion composed of at least three subdivisions ( Fig. 4A, B ). Antenna with basicerite moderately stout, armed with large, acute tooth on distolateral margin; scaphocerite not overreaching distal end of antennular peduncle, blade relatively broad, distolateral tooth prominent, reaching beyond distal margin of blade and separated from blade by deep cleft, lateral margin straight; carpocerite long, subcylindrical, reaching well beyond scaphocerite and end of antennular peduncle; flagellum slender in comparison to dorsolateral flagellum of antennule ( Fig. 4A, B ).

Mouthparts not dissected, appearing typical for genus in external view. Third maxilliped slender; coxa with distally subcute lateral (coxal) plate and subacute ventral process; antepenultimate article about 6.5 times as long as wide, moderately setose along ventral margin; penultimate article short, about 1.7 times as long as proximal width, slightly widening distally, distodorsal margin armed with two stout spiniform setae; ultimate article about 0.6 times as long as antepenultimate article, gently tapering distally, mesial surface with dense transverse rows of microserrulate setae, apex armed with crown of at least five slender corneous spiniform setae; exopod slender, not reaching distal margin of antepenultimate article; arthrobranch small ( Fig. 4D ).

Major cheliped of moderate size compared to body in female; ischium very short, with blunt dorsal lobe; merus not particularly swollen, about 3.2 times as long as greatest width, with acutely produced distodorsal angle; carpus cup-shaped, with blunt ventral lobe; palm subcylindrical, somewhat elongate, about three times as long as wide, with single, subacute, obliquely upwards directed, distodorsal tooth; fingers unequal in length, with dactylus tip noticeably exceeding pollex tip, 0.33 (dactylus) – 0.28 (pollex) times length of palm; dactylus rounded distally, slightly off-set mesially from main chela + pollex axis ( Fig. 4E–H ) [Note: the dactylar plunger was not observed due to a very firm closure of the chela fingers and an increased risk of breaking the dactylo-propodal articulation while attempting to open them].

Minor cheliped comparatively large, although more slender than major cheliped and with much smaller and shorter chela; coxa and basis unarmed; ischium short; merus slender, somewhat widening distally, about four times as long as greatest width, with acutely produced distodorsal angle; carpus vase-shaped; palm subcylindrical, somewhat compressed, about 1.5 times as long as wide; fingers subequal in length, slightly longer than palm, gently twisted laterally, with bidentate corneous tips; dorsal surface of dactylus with several rows of gambarelloid setae in distal half, appearing as dense brush ( Fig. 4I, J ).

Second pereiopod moderately slender, short; coxa and basis unarmed; ischium distinctly shorter than merus; carpus as long as merus, with five subarticles, first about as long as remaining four combined; chela simple, slightly longer than first carpal subarticle, with several tufts of stiff setae distally ( Fig. 4K ). Third pereiopod moderately slender; coxa with stout spiniform seta on ventral margin; ischium slightly widening distally, less than half-length of merus; merus 4.5 times as long as wide, not swollen; carpus about 0.4 length of merus, much more slender, with small distoventral spinule; propodus as long as merus, more slender than carpus, distally narrowing, with seven spiniform setae along ventral margin and two spiniform setae (one lateral and one mesial) on distoventral margin near propodo-dactylar articulation; dactylus stout, gently curved, less than 0.2 length of propodus, biunguiculate, secondary unguis subparallel to main (terminal) unguis, flexor margin between two ungui broadly U-shaped ( Fig. 4L, M ). Fourth pereiopod generally similar to third, slightly more slender. Fifth pereiopod much more slender than third and fourth; propodus with five spiniform setae along ventral margin and about nine rows of microserrulate setae forming grooming brush on distolateral surface.

Second to fifth pleopods with appendix interna. Uropod with lateral portion of protopod acutely produced; exopod with strong distolateral tooth flanked mesially by slender spiniform seta, latter not reaching distal margin of exopod; diaeresis somewhat uneven, complete, with acute lateral tooth adjacent to spiniform seta; endopod ovate, as long as exopod, without specific features ( Fig. 4N ).

Gill/exopod formula typical for genus ( Coutière 1899; Chace 1988).

Colour pattern. Unknown.

Etymology. The specific epithet gloriosus (Latin for glorious, famous, outstanding, etc.) derives from the type locality, Îles Glorieuses, also referring to the new species’ morphological distinctiveness; used as an adjective.

Type locality. Îles Glorieuses ( Glorioso Islands ), French overseas territory in the northern Mozambique Channel .

Distribution. Western Indian Ocean: presently known only from the type locality in the Mozambique Channel.

Ecology. The holotype of S. gloriosus sp. nov. was dredged from a depth of 80– 147 m. The species appears to inhabit deep-water reefs and its morphology strongly suggests that it is probably associated with sponges. The social organisation of S. gloriosus sp. nov., i.e., whether the species is pair-living or eusocial, remains unknown.

Remarks. Synalpheus gloriosus sp. nov. belongs to a small and probably non-monophyletic group of Indo-West Pacific species of Synalpheus characterised by the minor chela bearing a more or less dense brush of distally curved setae, disposed in one or several rows along the dorsal surface of the dactylus, also known as gambarelloid setae ( Anker et al. 2012). The gambarelloid setae appear to have evolved convergently in some Indo-West Pacific species and in the largely Atlantic / eastern Pacific S. gambarelloides ( Nardo, 1847) species group ( Ríos & Duffy 2007; Hultgren et al. 2014; Ashrafi & Hultgren 2023). The recently shown non-monophyly of the S. gambarelloides species group ( Ashrafi & Hultgren 2023) provided an additional strong argument in favour of the retention of all members of this group within Synalpheus (see Anker & De Grave 2008 for discussion).

In the Indo-West Pacific, the species with a well-developed row of gambarelloid setae are: (1) S. haddoni Coutière, 1900 (northern Australia); (2) S. sladeni Coutière, 1908 ( Mauritius, Red Sea, see also below); (3) S. lophodactylus Coutière, 1908 (Chagos, Marshall Islands, Australia, South China Sea); (4) S. spongicola Banner & Banner, 1981 (Red Sea); (5) S. crosnieri Banner & Banner, 1983 ( Madagascar, Seychelles, Kenya); (6) S. sponjy Ashrafi & Hultgren, 2023 ( Madagascar); and (7) S. calypso Ashrafi, 2024 ( Seychelles) ( Coutière 1900, 1908, 1909, 1921; Banner & Banner 1975, 1981, 1983; Wang & Sha 2015; Ashrafi & Hultgren 2023; Ashrafi 2024). In addition, Banner & Banner (1983) reported a rather enigmatic species from Toliara, Madagascar, under the name S. gambarelloides (Mediterranean species), without providing a detailed description and/or illustrations. Ashrafi & Hultgren (2023) separated S. sponjy from S. gambarelloides sensu Banner & Banner (1983) by the presence/absence of the rostro-orbital process, respectively, but the taxonomic identity of the Toliara material remains unknown. It must be noted that the record of S. sladeni from north-western Madagascar in Ashrafi & Hultgren (2023: fig. 1, table 1) appears to be based on a misidentified specimen (pers. obs.).

Synalpheus gloriosus sp. nov. can be separated from S. sladeni , S. crosnieri , S. spongicola , S. sponjy and S. calypso , all five known from the western Indian Ocean, by the greatly reduced, bluntly angular orbital teeth, and the more slender, elongate, subcylindrical major chela; from S. sladeni , S. crosnieri , S. spongicola and S. sponjy by the dorsally blunt, non-projecting antennal basicerite; from S. sladeni by the absence of rostral carina and rostro-orbital depression, the much shorter carpus of the minor cheliped, and the third maxilliped with a normal-sized exopod, which is unusually elongate and expanded in S. sladeni ; from S. crosnieri by the longer stylocerite of the antennule, the presence of a well-developed blade on the antennal scaphocerite, the much more slender third pereiopod, the non-expanded minor chela dactylus, the latter also with much denser rows of gambarelloid setae, and the major chela palm with a more anterodorsally (not anteriorly, as in S. crosnieri ) directed distodorsal tooth; from S. spongicola by the much shorter distolateral tooth of the antennal basicerite, the telson distally more tapering and with a narrow posterior margin (which is rather broad in S. spongicola ), the dorsal spiniform setae of the telson located closer to the lateral margins (vs. located at some distance from the lateral margins in S. spongicola ), the noticeably broader blade of the antennal scaphocerite, and the more slender major chela; from S. sponjy by the noticeably longer minor cheliped carpus, the scaphocerite with a well-developed blade (vs. greatly reduced in S. sponjy ), and the distodorsal tooth of the major chela directed up (vs. directed forward in S. sponjy ); and from S. calypso by the stouter antennular peduncle, also with a shorter stylocerite, reaching distal margin of the first article (vs. greatly overreaching this margin in S. calypso ), and the more slender third pereiopod merus, with almost straight margins (vs. more swollen, with broadly convex margins in S. calypso ) (cf. Fig. 4 ; Banner & Banner 1981: figs. 11, 12; Banner & Banner 1983: fig. 11; Ashrafi & Hultgren 2023: figs. 2–4; Ashrafi 2024: figs. 1–3).

Furthermore, S. gloriosus sp. nov. can be easily separated from S. lophodactylus and S. haddoni by the reduced orbital teeth, which are well developed in the other two species, the much more slender major chela, and the general shape and armature (position and size of dorsal spiniform setae) of the telson; specifically from S. lophodactylus by the presence of a sharp distodorsal tooth on the minor cheliped merus (which is absent on S. lophodactylus ); and from S. haddoni by the unarmed dorsal margin of the basicerite (vs. armed with a prominent and sharp tooth in S. haddoni ) (cf. Fig. 4 ; Banner & Banner 1975: figs. 17, 20). It must be noted that the Australian material of S. lophodactylus reported by Banner & Banner (1975) likely contains more than one species, based on the illustrated variation in the shape of the orbital region and telson.

The minor chela dactylus of several other species, such as S. hastilicrassus Coutière, 1905 (species complex, widely distributed in the Indo-West Pacific) and S. dorae Banner, 1988 ( Australia), may have setae or tufts of setae organised in a row-type pattern ( Coutière 1905; Banner & Banner 1975; Bruce 1988), however, without forming a dense setal brush, as seen in S. gloriosus sp. nov.

Figures

FIGURE 4. Synalpheus gloriosus sp. nov., female holotype (cl 4.3 mm) from Îles Glorieuses, MNHN-IU-2019-5917:A, frontal region, dorsal; B, same, lateral; C, telson, dorsal; D, third maxilliped, lateral; E, major (left) cheliped, ischium to carpus, lateral; F, same, carpus and chela, lateral; G, carpus and chela, same, mesial; H, same, chela fingers, ventral; I, minor (right) cheliped, lateral; J, same, carpus and chela, lateral (with detail of gambarelloid setae); K, second pereiopod, lateral; L, third pereiopod, lateral; M, same, distal portion of propodus and dactylus, lateral; N, uropod, dorsal.