Synalpheus sponjy, Ashrafi & Hultgren, 2023

Ashrafi, Hossein & Hultgren, Kristin M., 2023, Eusociality unveiled: discovery and documentation of two new eusocial shrimp species (Caridea: Alpheidae) from the Western Indian Ocean, Arthropod Systematics & amp; Phylogeny 81, pp. 1103-1120 : 1103

3.2.1. Synalpheus sponjy sp. nov.

Figures 2 , 3 , 4

Etymology.

The new species derives its name from the Malagasy word ‘sponjy’, which translates to ‘sponge’. The term is used as a noun in opposition.

Material examined.

Holotype: MADAGASCAR • 1 male (CL 3.6 mm); Nosy Be ; 13°25 ’9.7” S, 48°15 ’37.94” E; 17 May 2008; Bakary G, Bruggermann H, Michonneau F, Paulay G, Werner T leg.; 6-9 m, from cryptic sponge; FLMNH-UF-14409 . - Paratypes: MADAGASCAR • 19 males (CL ranging from 1.99 to 3.6 mm); Nosy Vorona ; 15 May 2008; Paulay G leg.; 4 m, from cryptic sponge; FLMNH-UF-14256 • 2 males (CL 3.1-3.2 mm); same data as for preceding; FLMNH-UF-14228 • 1 male (CL 3.35 mm); same data as for preceding; Anker A, Bakary G, Boissin E, Bruggemann H, Horeau T, Michonneau F, Paulay G, Werner T leg.; FLMNH-UF-14313 • 1 male (CL 3.23 mm); same data as for preceding; FLMNH-UF-14316 .

Description.

Small-sized species of Synalpheus . Carapace (Fig. 2A, B ) glabrous, unarmed; frontal margin between rostrum and orbital teeth relatively deep, U-shaped, with moderately developed rostrum; rostrum triangular in dorsal view, subacute at tip, about twice as long as wide, reaching to about proximal third of visible part of first antennular article, slightly shorter than orbital teeth, orbitorostral process present; orbital teeth relatively stout, subtriangular, distally subacute, as long as wide, about three times as broad as rostrum at base; pterygostomial angle bluntly protruding; cardiac notch deep.

Male pleon (Fig. 2C ) with first pleuron bearing small ventrally-pointing hook-shaped projection posteroventrally; third pleuron rounded anteroventrally and angled posteroventrally; fourth pleuron rounded anteroventrally and subrounded posteroventrally; fifth pleuron rounded antero- and posteroventrally; sixth pleuron with blunt projection on posterolateral margin.

Telson (Fig. 2D ) subrectangular, tapering distally, slightly shorter than endopod, flat, without depression on mid-line; dorsal margin with two pairs of relatively strong spiniform setae located at 0.3 and 0.6 telson length, respectively; posterolateral angle with no projection; posterior margin broad, slightly convex, furnished with about 10 setae, with two pairs of spiniform setae, mesial spiniform setae slightly longer than lateral ones.

Antennula (Fig. 2A, B ) with peduncle relatively stout; first antennular article almost twice as long as broad; stylocerite relatively short, subacute, falling short of distal margin of first antennular article; second antennular article slightly shorter than first one, slightly longer than broad; third antennular article slightly longer than second one, subequal to first one, slightly longer than broad; lateral flagellum biramous, fused portion consisting of five subdivisions, secondary ramus with three subdivisions, aesthetascs extending from third subdivision of fused portion to end of secondary ramus.

Antenna (Fig. 2A, B ) with inferior tooth of basicerite subacute, slightly overreaching first antennular article, superior tooth small, subacute; scaphocerite relatively slender, lateral tooth overreaching end of second antennular article, lateral margin straight, blade fully absent; carpocerite somewhat slender, extending beyond antennular peduncle.

Mouthparts not dissected. Third maxilliped (Fig. 2E ) pediform; lateral plate with small acute hooked-shaped projection pointing laterally; antepenultimate article about 4 times as long as widest part, mesial margin furnished with setae; penultimate article short, about a sixth of antepenultimate length; ultimate article relatively stout, about 0.6 times as long as antepenultimate article, slightly tapering distally, with crown of six spiniform setae at tip; exopod slender, reaching to about 0.8 of antepenultimate article length.

Major cheliped (Fig. 3A-D ) with coxa bearing small spiniform seta on dorsodistal margin; basis and ischium short; merus robust, dorsal margin convex, about twice as long as broadest part, dorsodistal margin with blunt projection; carpus short, cup-shaped; palm swollen, ovoid, about 1.5 times as long as wide, dorsodistal margin with subrounded, prominent tubercle; fingers 0.4 times as long as palm, pollex subequal to dactylus. Minor cheliped (Fig. 3E, F ) with coxa bearing small spiniform seta on dorsodistal margin; basis and ischium short; merus relatively robust, ventral margin concave, about 3 times as long as broadest part; carpus vase-shaped; palm ovoid, nearly 0.7 times as long as merus, about 0.7 times as long as wide; fingers subequal, about 0.8 times as long as palm; pollex with several tufts of setae situated on lateral side, simple at tip; dactylus bearing densely-situated tufts of distally-curved setae (known as gambarelloides setae), simple at tip.

Second pereiopod (Fig. 4A ) with coxa bearing small spiniform seta dorso-distally; basis short; ischium relatively robust, approximately 3.5 times as long as broad; merus relatively robust, 3.5 times as long as broad, about 1.3 times as long as ischium; carpus slightly longer than merus, composed of five articles, proximal article longest, as long as sum of three medial articles, second to fourth articles subequal, distal article twice as long as fourth one; palm subequal to fingers.

Third pereiopod (Fig. 4B, C ) robust, coxa with small spiniform setae on dorsodistal margin; ischium vase-shaped, 1.5 times as long as broadest part; merus robust, about 3 times as long as broad, about 2.8 times as long as ischium, distal half of ventral margin concave, mesial margin of concavity furnished with thick setae and lateral margin widened; carpus slightly widening distally, slightly longer than ischium, with spiniform seta on distoventral margin; propodus with five spiniform setae on ventral margin in addition to distal pair, about 1.7 times as long as carpus; dactylus biunguiculate, inferior unguis slightly wider at base than superior one, latter one slightly longer than former. Fourth pereiopod (Fig. 4D ) generally similar to third pereiopod, less robust; coxa lacking spiniform setae on dorso-distal margin; merus concavity less prominent and mesial margin lacking thick setae. Fifth pereiopod (Fig. 4E ) generally similar to third pereiopod, less robust; merus without concavity; carpus about 0.7 times as long as merus, without spiniform setae on distoventral margin; propodus subequal to merus, bearing four transverse rows of microserrulate setae on distal half.

Uropods (Fig. 2D ) with protopods bearing two subacute teeth; exopod with small distolateral tooth; diaeresis inconspicuous except for lateral margin terminating to small tooth; distolateral spiniform setae next to diaresis stout, not overreaching posterior margin of exopod.

Type locality.

North of Madagascar: Nosy Be and Nosy Vorona.

Ecology.

All the specimens were collected from cryptic sponges situated among dead coral and coral rubbles.

Remarks.

The new species exhibits similarities to several rare species found in the Indo-West Pacific region, characterized by a dense brush of setae on the dactylus of the minor cheliped, known as gambarelloides setae. These species include S. sladeni Coutière, 1908; S. spongicola Banner and Banner, 1981; S. crosnieri Banner and Banner, 1983; and S. gambarelloides (Nardo, 1847) [as reported in Banner and Banner (1983)]. Originally described from Cargados Carajos Shoals (Mauritius) and reported in the Gulf of Aqaba [ Banner and Banner (1981)], S. sladeni , each time based on a single specimen, can be distinguished from the new species by several notable characteristics: slender orbital teeth, presence of a scaphocerite blade, less prominent inferior tooth and more prominent superior tooth of the basicerite, highly robust exopods of the second and third maxillipeds, a subacute tooth on the dorso-distal margin of the major chela palm, and complete presence of diaeresis.

According to Banner and Banner (1983), 45 males and 6 females, suggesting a potential communal lifestyle for the species, from Tuléar, Madagascar were reported and identified as S. gambarelloides , (for further details, see Banner and Banner 1983: page 97). However, no descriptions or illustrations were provided for these specimens, except for one distinguishing characteristic of S. gambarelloides , namely the absence of an orbitorostral process. This particular trait can be utilized to differentiate the new species from S. gambarelloides .

Synalpheus sponjy sp. nov. is closely related to the other two species, S. crosnieri and S. spongicola , both of which have not been reported since their original descriptions. The new species can be distinguished from S. crosnieri (found northwest of Madagascar) by the overall shape of the major cheliped fingers. In S. sponjy sp. nov., the major cheliped is normal and straight, whereas in S. crosnieri , it appears twisted when viewed dorsally. Additionally, the shape of the meri in the third and fourth pereiopods sets the new species apart. In the new species, these meri are concave on the distal half, and the third pereiopod merus bears a row of stiff setae along the mesial margin of the concavity. However, caution should be exercised when using the latter characteristic as the drawings provided by Banner and Banner (1983) are schematic, and the description lacks precise information regarding the exact shape of the meri in the third and fourth pereiopods.

One of the authors (HA) had the opportunity to examine the type series of S. spongicola deposited in the Naturalis Biodiversity Center, Leiden, Netherlands. As mentioned by Banner and Banner (1981), S. spongicola is a relatively large species of Synalpheus . In addition to differences in size, S. sponjy sp. nov. can be distinguished from S. spongicola based on the following characters: 1) the stylocerite falls short of reaching the end of the first antennular article in the new species, whereas in S. spongicola , it extends to the end; 2) the blade of the scaphocerite is absent in the new species, while it is complete in S. spongicola ; 3) the palm of the major cheliped terminates in an obtuse, robust tubercle that points forward on the dorso-distal margin in S. sponjy sp. nov., whereas in S. spongicola , it ends in an upturned subacute tooth; 4) the last three pereiopods are more robust in the new species, and the meri of the third and fourth pereiopods are ventrally concave (lacking concavity in S. spongicola ); and 5) in the new species, the diaeresis is confined to the lateral tooth, whereas in S. spongicola , the diaeresis is complete. Unfortunately, as these types were very old (date), they could not be included in the phylogenetic tree. Limited information is available regarding the ecology of S. spongicola , as it has been recorded only once with 9 females and 1 male from a single collection, suggesting a potential communal lifestyle for the species.

In the phylogenetic tree (Fig. 1 ), S. sponjy sp. nov. forms a clade with S. aff. somalia (Banner and Banner, 1979) and S. thai (Banner and Banner, 1966), along with S. sladeni . The new species can be easily distinguished from both S. somalia and S. thai by the densely-located ( Synalpheus gambarelloides ) setae on the dactylus of the minor cheliped. Additionally, S. thai stands out within the entire genus due to its distinctive shape of the telson (see Banner and Banner 1966: fig. 19L). Synalpheus somalia can be further differentiated from the new species by the dactylus of the major cheliped being much longer than the pollex ( Banner and Banner 1979: fig. 3c, e).

Figures

Figure 1. Phylogenetic tree constructed for the members of the genus Synalpheus using the Bayesian Inference approach based on a concatenation of four genes: 16 S, COI, PEPCK, and 18 S. Bayesian posterior probabilities are provided above each branch. Taxa are shown as Synalpheus species plus unique identifier (see supplementary table S 1). Eusocial species are indicated with an arrow (red, WA = West Atlantic; blue, IWP = Indo-West Pacific).

Figure 2. Synalpheus sponjy sp. nov., holotype (FLMNH-UF- 14409). A anterior region, dorsal view B same, lateral view, C pleon, D telson and uropods, E third maxilliped.

Figure 3. Synalpheus sponjy sp. nov., holotype (FLMNH-UF- 14409). A major cheliped, B same, chela, C lateral view same, D mesial view same, E fingers minor cheliped, F mesial view same, lateral view.

Figure 4. Synalpheus sponjy sp. nov., holotype (FLMNH-UF- 14409). A second pereiopod, B third pereiopod, C lateral view same, mesial view, D fourth pereiopod, mesial view, E fifth pereiopod, lateral view.