Synalpheus calypso, Ashrafi, 2024

Synalpheus calypso sp. nov.

( Figs. 1 3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

Type material. Holotype: ovigerous female (cl 8.5 mm), MNHN-IU-2014-1371 , Aldabra , Seychelles, 23 May 1954, leg. Calypso crew . Paratypes: 2 males (cl 5.8 and 7.3 mm), MNHN-IU-20215304 , same data as for holotype

Description. Carapace ( Fig. 1A–C View FIGURE 1 ) glabrous, dorsally unarmed; frontal margin between rostrum and orbital teeth deep, V-shaped, with moderately developed rostrum; rostrum triangular in dorsal view, subacute at tip, about 1.5 times as long as wide, reaching to about proximal third of visible part of first antennular article, slightly longer than orbital teeth, orbitorostral process present; orbital teeth relatively stout, subtriangular, distally subacute, slightly wider than long, about 1.7 times as broad as rostrum at base; pterygostomial angle bluntly protruding; cardiac notch deep.

Pleon ( Fig. 1C, E View FIGURE 1 ) with slight sexual dimorphism at posteroventral angle of first pleura; female first pleuron ( Fig. 1C View FIGURE 1 ) with fully rounded posteroventral angle; male first pleura ( Fig. 1E View FIGURE 1 ) subrounded or slightly angled. Pleura of second to fifth pleonites rounded anteroventrally and posteroventrally; sixth pleuron with blunt projection on posterolateral margin.

Telson ( Fig. 1D View FIGURE 1 ) subrectangular, tapering distally, shorter than endopod, without depression on mid-line; dorsal margin with two pairs of spiniform setae located at 0.6 and 0.8 of telson length, respectively; posterolateral angle with small projection; posterior margin broad, convex, with two pairs of spiniform setae, mesial pair slightly more than twice as long as lateral pair and approximately as long as spiniform setae on dorsal surface.

Antennula ( Fig. 1A, B View FIGURE 1 ) with peduncle relatively stout; first antennular article about 1.5 times as long as broad; stylocerite relatively slender, subacute at tip, reaching to about proximal third of second antennular article; second antennular article subequal to first, about 1.5 times as long as proximal width; third antennular article about 0.7 times as long as second, slightly longer than broad; lateral antennular flagellum biramous, fused portion with six subdivisions, shorter ramus well developed.

Antenna ( Fig. 1A, B View FIGURE 1 ) with inferior tooth of basicerite subacute, reaching to extremity of first antennular article, superior tooth blunt; scaphocerite with lateral tooth reaching to about end of antennular peduncle, lateral margin straight, blade well-developed, broad, slightly shorter than lateral tooth; carpocerite somewhat slender, distinctly surpassing antennular peduncle and scaphocerite.

Third maxilliped ( Fig. 2A View FIGURE 2 ) pediform; lateral plate with small acute hooked-shaped projection pointing laterally; antepenultimate article stout, about five times as long as proximal width, mesial margin concave and furnished with long setae; penultimate article short, about 0.2 times as long as antepenultimate article, distolateral margin armed with three to five slender spiniform setae; ultimate article slender, slightly tapering distally, about 0.8 as long as antepenultimate article, with crown of seven or eight spiniform setae at tip; exopod somehow slender, falling short of extremity of antepenultimate article; arthrobranch of usual size for genus.

Major cheliped showing no sexual dimorphism. Holotype major cheliped ( Fig. 3A–D View FIGURE 3 ) with short basis and ischium; merus robust, dorsal margin convex, ventral margin slightly concave, about 2.8 times as long as wide, dorsodistal margin with small, subacute tooth; carpus short, cup-shaped; palm swollen, ovoid, almost twice as long as wide, dorsodistal margin with prominent, slightly up-turned tooth; fingers 0.3 times as long as palm; pollex without mesial protuberance, dactylus slightly longer than pollex. Minor cheliped ( Fig. 3E–G View FIGURE 3 ) with merus relatively robust, slightly widening towards distal margin, ventral margin concave, about 3.7 times as long as proximal width, dorsodistal margin armed with small triangular tooth; carpus vase-shaped; palm ovoid, about 1.5 times as long as wide; fingers subequal, as long as palm; pollex with simple tip; dactylus bearing densely-organised tufts of distally-curved setae on dorsomesial surface ( gambarelloides setae), simple at tip.

Second pereiopod ( Fig. 2A View FIGURE 2 ) with coxa bearing small spiniform seta ventrodistally; basis short; ischium relatively slender, approximately four times as long as wide; merus relatively slender, 4.5 times as long as wide, about 1.2 times as long as ischium; carpus slightly longer than merus, composed of five articles, proximal article longest, as long as three medial articles combined, second to fourth articles subequal, fifth article twice as long as fourth; palm and fingers typical for genus, subequal in length.

Third pereiopod ( Fig. 2B, C View FIGURE 2 ) relatively robust; coxa with prominent lobe on distoventral margin; basis short; ischium slightly widening towards distal margin, approximately 1.8 times as long as widest part; merus slightly inflated, about 3.5 times as long as wide, about 2.4 times as long as ischium; carpus slightly widening distally, approximately as long as ischium, distoventral margin with spiniform seta, dorsodistal margin with triangular projection; propodus with seven spiniform setae on ventral margin in addition to distal pair, almost twice as long as carpus; dactylus biunguiculate, flexor unguis slightly wider at base than extensor, extensor unguis distinctly longer than flexor one. Fourth pereiopod ( Fig. 2D View FIGURE 2 ) generally similar to third pereiopod, more slender; propodus with six spiniform setae on ventral margin in addition to distal pair. Fifth pereiopod ( Fig. 2E View FIGURE 2 ) generally similar to fourth pereiopod; carpus about 0.7 times as long as merus, without spiniform setae on distoventral margin; propodus slightly longer than merus, bearing eight transverse rows of microserrulate setae and five spiniform setae on distal half.

Uropod ( Fig. 1E View FIGURE 1 ) with protopod bearing one subacute tooth on each lobe; exopod with two small distolateral teeth and slender spiniform seta; diaeresis complete; endopod slightly longer than exopod, ovoid, without specific feature.

Etymology. The new species is named after Jacques Cousteau’s research vessel, Calypso, which was used during the expedition to Aldabra; used as a noun in apposition.

Type locality. Aldabra , Seychelles.

Ecology. Although specific information on the ecology of this species is lacking, several observations suggests that it potentially may be sponge-dwelling. Small pieces of sponge tissue were found in the tube containing the specimens, and sponge spicules were attached to the ventral side of the shrimp’s body, including the areas between the mouthparts, pereiopods, and pleopods. Additionally, the presence of gambarelloides setae on the dactylus of the minor cheliped is indicative of a sponge-dwelling habitat ( Ríos & Duffy 2007).

Remarks. The distinct minor cheliped of Synalpheus calypso sp. nov., i.e. furnished with gambarelloides setae, distinguishes it from many species inhabiting in the Indo-West Pacific. However, several species in this region do possess a similar minor cheliped, and interestingly, all of them have been described and reported from the Western Indian Ocean, except for S. haddoni Coutière, 1900 , for which the status remains to be confirmed (see below). These species include S. crosnieri Banner & Banner, 1983 , from the northwest of Madagascar, Kenya, and Seychelles; S. sladeni Coutière, 1908 , from Mauritius and the Gulf of Aqaba; S. spongicola Banner & Banner, 1981 , from the Gulf of Aqaba; and S. sponjy Ashrafi & Hultgren, 2023 , from the north of Madagascar.

The eusocial species S. crosnieri and S. sponjy share several characters that distinguish them from S. calypso sp. nov. In the former two species ( Banner & Banner 1983; Ashrafi & Hultgren 2023), the stylocerite is shorter and falls short of the extremity of the first antennular article, the scaphocerite lacks a blade, the superior margin of the basicerite bears a small subacute projection, major and minor cheliped meri bear no tooth on the dorsodistal margin, the major cheliped palm bears a prominent and straight subrounded tubercle on the dorsodistal margin, and the uropodal diaeresis is inconspicuous except for the lateral tooth. In contrast, S. calypso sp. nov., possesses a stylocerite overreaching the first antennular article, a wide and fully developed scaphocerite blade, a small tooth on the dorsodistal margin of the major cheliped and a small projection on the minor cheliped, a prominent up-turned tooth at the major cheliped palm above the dactylar articulation, a complete diaeresis, and a wider posterior margin of the telson.

Synalpheus sladeni is a unique and easily distinguishable species within the genus due to its enlarged exopods on all the maxillipeds ( Coutière 1908, 1921; Banner & Banner 1981). This distinctive characteristic clearly differentiates S. sladeni from S. calypso sp. nov. Additionally, the new species differs from S. sladeni in several other features, including the general shape of the anterior margin of the carapace (compare Fig. 1A, B View FIGURE 1 with Banner & Banner 1981: fig. 11a, b), a more slender stylocerite extending beyond the first antennular article (vs. reaching only to the mid-length of the first antennular article in S. sladeni ), and a more slender inferior tooth of the basicerite with a blunt superior tooth (vs. a strong superior tooth in S. sladeni ).

Synalpheus spongicola appears to be the closest species to S. calypso sp. nov. based on several shared characteristics (compare Figs 1 3 View FIGURE 1 View FIGURE 2 View FIGURE 3 with Banner & Banner 1983: fig. 12), including the overall shape and size of the rostrum and orbital teeth, the stylocerite overreaching the first antennular article, a complete scaphocerite blade, and the presence of a prominent upturned tooth on the major cheliped palm. However, S. calypso sp. nov. can be distinguished from S. spongicola by the following features: 1) the superior margin of the basicerite is blunt in S. calypso sp. nov., while it bears a small subacute tooth in S. spongicola ; 2) the dorsodistal margins of the meri of the major and minor chelipeds are armed with a tooth and a small projection, respectively, in S. calypso sp. nov., whereas the meri of both chelipeds are unarmed in S. spongicola ; 3) the first pleuron in male specimens of S. calypso sp. nov. has a slightly angulate posteroventral margin, while in S. spongicola a well-developed hook-shaped projection is present; and 4) the spiniform setae on the dorsal surface of the telson are positioned at 0.6 and 0.8 of the telson length in the new species, while in S. spongicola , they are positioned at 0.4 and 0.6.

Banner & Banner (1983) examined 113 specimens from Toliara, Madagascar, and identified them as the Atlanto-Mediterranean species S. gambarelloides (Nardo, 1847) . Although no illustrations were provided for these specimens, several characteristics of S. gambarelloides were discussed in their study, which can be used to differentiate their material from S. calypso sp. nov. First, the S. gambarelloides specimens reported from Madagascar lack an orbitorostral process ( Banner & Banner 1983, in the discussion section of S. crosnieri ), in contrast to the new species. Second, Banner & Banner (1983) noted that the scaphocerite blade in their specimens varies from greatly reduced to fully reduced, whereas the scaphocerite blade is well-developed in S. calypso sp. nov. These two characteristics strongly suggest that the specimens reported as S. gambarelloides by Banner & Banner (1983) are different from the new species. However, whether these specimens are indeed the same species as the Atlanto-Mediterranean S. gambarelloides remains to be confirmed in future studies.

Among the Synalpheus species reported from the Indo-West Pacific, S. haddoni may also possess gambarelloides setae ( Coutière 1900; Banner & Banner 1975). This species was originally described from the Torres Strait as a subspecies of S. gambarelloides , i.e. S. laevimanus haddoni . The original designation as a subspecies of S. gambarelloides suggests that S. haddoni likely possesses this type of setae. However, Coutière did not describe the minor cheliped nor provide any illustrations of it. Re-examination of the type material is necessary to confirm the presence or absence of such setae on the minor cheliped dactylus. Nonetheless, the distinct shape of the telson readily separates S. haddoni from S. calypso sp. nov. Additionally, the scaphocerite lacks a blade in S. haddoni , whereas a fully developed blade is present in S. calypso sp. nov.; the superior tooth of the basicerite is quite strong in S. haddoni , while it is blunt in the new species; and the major cheliped palm in S. haddoni bears a prominent straight tooth, whereas it is up-turned in S. calypso sp. nov..