Salmoneus saotomensis, Anker, 2020

Anker, Arthur, 2020, Two new species and new records in the alpheid shrimp genera Salmoneus Holthuis 1955 and Deioneus Dworschak, Anker & Abed-Navandi, 2000 in theAtlantic Ocean (Malacostraca: Decapoda), Zootaxa 4786 (3), pp. 345-368 : 357-362

Salmoneus saotomensis sp. nov.

Figs. 8–10

Type material. Holotype, ovigerous specimen (cl 3.8 mm), MZUSP 34071 , Gulf of Guinea, São Tomé and Príncipe, São Tomé Island, near São Tomé’s old fortress, small shallow bay with sand-mud bottom and scattered large rocks, under large rock, depth at low tide: 0.5–1 m, leg. A. Anker, 04.02.2006 [fcn 06-149].

Description. Small-sized (cl 3.8 mm) alpheid shrimp with not particularly slender or compressed body. Carapace glabrous, not setose. Rostrum well developed, broadly subtriangular, about as long as broad at base, acute distally, overreaching distal margin of first article of antennular peduncle, lateral margins feebly concave; rostral carina present, faint, extending posteriorly well beyond bases of eyes ( Fig. 8a, b ). Orbital teeth well developed, sharp distally, pointing slightly mesially in dorsal view, anteriorly in lateral view ( Fig. 8a, b ). Pterygostomial region broadly rounded; anterolateral suture present ( Fig. 8b ); cardiac notch well developed. Each epistomial sclerite with strong acute process.

Pleon with first to fourth pleura broadly rounded to slightly angular; fifth pleuron with posteroventral margin produced into posteriorly directed, acute tooth; sixth pleonite with distinct suture at posteroventral angle, but without complete articulated flap, posterior margin produced into sharp tooth flanking telson ( Fig. 8c ); preanal plate rounded. Telson moderately slender, subrectangular, tapering distally, about 2.8 times as long as maximal (proximal) width; dorsal surface with two pairs of stout cuspidate setae both inserted at some distance from lateral margin, first pair slightly anterior to telson mid-length, second pair at about 0.7 of telson length; posterior margin with shallow rounded notch flanked by two pairs of short plumose setae and with two pairs of slender spiniform setae, lateral slightly stouter and about 1.3 times longer than mesial ( Fig. 8d, e ).

Eyes almost completely concealed in dorsal view, partly visible in lateral view; cornea well developed; anteromesial margin of eyestalk not protruding anteriorly and without tubercle ( Fig. 8a, b ).

Antennular peduncle stout; stylocerite long, rather robust, with sharp tip falling short of distal margin of second article; ventromesial carina with small anteriorly directed tooth; second article square-shaped in dorsal view, as long as wide; lateral antennular flagellum with very short fused portion, consisting of two discernable subdivisions, and well-developed secondary ramus, latter with at least three groups of aesthetascs; mesial antennular flagellum as stout as lateral ( Fig. 8a, b, e ). Antenna with basicerite stout, bearing subacute tooth on its distoventral margin; scaphocerite ovate in general shape, not reaching end of antennular peduncle, with straight lateral margin and broad blade, latter convex anteriorly and overreaching slender sharp distolateral tooth; carpocerite short, cylindrical, barely reaching mid-length of scaphocerite ( Fig. 8a, b ).

Mouthparts not dissected, typical for genus in external observation. Third maxilliped slender, pediform; coxa with rounded lateral plate; antepenultimate article slightly flattened ventrolaterally; penultimate article about three times as long as wide; ultimate article with numerous rows of short serrulate setae and some longer simple setae, tip with blunt corneous point and one small subapical spiniform seta; arthrobranch well developed ( Fig. 8f, g ).

First pereiopods (chelipeds) very asymmetrical in shape and dissimilar in size, carried flexed when not in use. Major cheliped enlarged, relatively slender; ischium slightly flattened ventrolaterally, unarmed; merus moderately slender, more than five times as long as proximal width, not noticeably widening distally, smooth, distodorsal and distomesial margins rounded, ventrolateral surface depressed distally; carpus short, cup-shaped, distal margin with blunt process mesially and subacutely projecting process ventromesially; chela subcylindrical, flattened on ven- tromesial surface, with palm smooth, noticeably longer than fingers; fingers not gaping when closed, subequal, strongly crossing distally, not twisted, with evenly serrated cutting edges; both dactylus and pollex with about 14 rounded to subtriangular teeth on cutting edge, extending for most of finger length, except for distal-most portion ( Fig. 9 a–c). Minor cheliped much smaller and more slender than major cheliped; ischium armed with stout cuspidate seta on ventrolateral surface; merus as long as ischium, not swollen or widening distally, smooth, unarmed; carpus about 0.6 times length of merus, cylindrical, widening distally, distal margin unarmed; chela 1.5 times length of carpus, simple, with palm smooth, longer than fingers; fingers slightly gaping when closed, subequal in length, crossing distally, cutting edges armed with six or seven low rounded teeth ( Fig. 9d, e ).

Second pereiopod slender; ischium with one cuspidate seta on ventrolateral surface, located in proximal third; merus slightly shorter than ischium; carpus with five subdivisions, first subdivision about as long as other four combined, with ratio approximately equal to 4.5/1.0/0.9/1.1/1.3; chela longer than distal-most carpal joint, simple ( Fig. 8h ). Third pereiopod slender; ischium with two cuspidate setae on ventrolateral surface; merus about 6.2 times as long as wide, unarmed; carpus equal to merus in length, noticeably more slender, with one spiniform seta on distoventral margin; propodus shorter than carpus, with three widely spaced spiniform setae on ventral margin, in addition to one pair of spiniform setae (one of them much longer) near dactylar base; dactylus about 0.4 length of propodus, slender, conical, simple, smoothly curving distally ( Fig. 8i, j ). Fourth pereiopod generally similar to third pereiopod, more slender; ischium unarmed on ventrolateral surface; merus about eight times as long as wide; carpus 0.8 times length of merus, slenderer than merus, with small spiniform seta on distoventral margin; propodus noticeably longer than carpus, with two spiniform setae on ventral surface, in addition to one pair of longer spiniform setae near dactylar base; dactylus almost half-length of propodus, similar to that of third pereiopod ( Fig. 8k ). Fifth pereiopod as slender as fourth pereiopod; ischium unarmed; merus about nine times as long as wide, unarmed; carpus as slender and as long as merus, unarmed distoventrally; propodus elongate, slender, 1.2 times as long as carpus, with numerous rows of progressively longer serrulate setae forming cleaning brush on distal ventrolateral surface, ventral margin with two slender spiniform setae subdistally, in addition to one pair of long spiniform setae adjacent to dactylar base; dactylus about 0.3 times length of propodus, similar to that of third and fourth pereiopods ( Fig. 8l, m ).

Second pleopod with appendix masculina as long as appendix interna, furnished with at least six longer and shorter stiff setae, as illustrated ( Fig. 8n ). Uropod with lateral lobe of protopod ending in subacute tooth; exopod broadly oval-shaped with small distolateral tooth and fairly long distolateral spiniform seta; diaeresis sinuous, with broad subtriangular tooth mesial to spiniform seta; endopod as long as exopod, oval-shaped without specific features ( Fig. 8o ).

Gill formula typical for genus.

Colouration. Semitransparent-whitish; ovaries or fresh eggs yellow ( Fig. 10 ).

Type locality. São Tomé Island, São Tomé & Príncipe .

Distribution. Eastern Atlantic: presently known only from the type locality, São Tomé Island in the Gulf of Guinea.

Ecology. Shallow subtidal sandy flats with scattered rocks, depth less than 1 m at low tide; dwelling deep under rocks.

Etymology. Named after the type locality, the island of São Tomé.

Remarks. Salmoneus saotomensis sp. nov. is characterised by the presence of a moderately enlarged minor cheliped, with the chela palm slightly swollen and the chela fingers armed with small teeth. Among the Atlantic species of Salmoneus , this type of minor cheliped is found only in S. camaroncito from the western Atlantic ( Anker 2010a; see above). However, S. saotomensis sp. nov. may be separated from S. camaroncito by the orbital teeth slenderer and directed less mesially than in S. camaroncito ; the position of the cuspidate setae on the dorsal surface of the telson, with the anterior pair situated well anterior to the telson mid-length (vs. with both pairs situated in the posterior half of the telson in S. camaroncito ); the comparatively better developed cornea of the eyestalks (vs. noticeably reduced in S. camaroncito ); the comparatively longer second article of the antennular peduncle, being as long as wide (vs. much wider than long in S. camaroncito ); the major cheliped ischium unarmed (vs. armed with a cuspidate seta in S. camaroncito ); the major cheliped carpus relatively short, cup-shaped, with a stout distal process ventromesially (vs. more elongate, cylindrical, unarmed distally in S. camaroncito ); the major chela fingers armed with 14 teeth on the cutting edges (vs. armed with at most seven teeth in S. camaroncito ); and the slenderer second pereiopod, e.g., with the first carpal subdivision about seven times as long as wide (vs. at most five times in S. camaroncito ).

The presence of a moderately developed minor cheliped immediately separates S. saotomensis sp. nov. from three eastern Atlantic species, in which the minor cheliped is conspicuously enlarged and/or elongated, viz. S. sketi Fransen, 1991 , S. erasimorum Dworschak, Anker & Abed-Navandi, 2000 , both from the Adriatic Sea, and S. caboverdensis Dworschak, Anker & Abed-Navandi, 2000 from Cape Verde, but also from the only eastern Atlantic species, in which the minor cheliped is not enlarged at all, i.e. S. kekovae Grippa, 2004 from Turkey (cf. Fransen 1991; Dworschak et al. 2000; Grippa 2004).

The difference in the general shape and armature of the minor cheliped between S. saotomensis sp. nov. and S. sketi , S. caboverdensis and S. erasimorum is rather substantial (cf. Fransen 1991: fig. 14; Dworschak et al. 2000: figs. 30, 31, 44, 45). This difference alone would be sufficient to separate the new species from the latter three taxa, but there are also several other, quite obvious differences between them. For instance, S. saotomensis sp. differs specifically from S. sketi by the general shape of the frontal margin of the carapace, including the length of the rostrum and shape of the orbital teeth, and the proportions of the telson, including the position of the dorsal cuspidate setae (cf. Fransen 1991: figs. 1–3); and from S. caboverdensis and S. erasimorum by the better developed, sharper orbital teeth, and the major cheliped ischium unarmed (vs. armed with one or two cuspidate seta(e) in S. caboverdensis and S. erasimorum , respectively) (cf. Dworschak et al. 2000: figs. 28, 29, 43, 46). In addition, S. saotomensis sp. nov. is ecologically very different from S. sketi , S. caboverdensis and S. erasimorum , the first being a marine cave dweller ( Fransen 1991) and the latter two symbiotic inhabitants of callianassid shrimp burrows ( Dworschak et al. 2000).

Salmoneus saotomensis sp. nov. differs from S. kekovae not only by the stronger minor cheliped, with the fingers armed with small teeth on their cutting edges (vs. weaker and with the fingers completely unarmed in S. kekovae ), but also by the much shallower median notch on the posterior margin of the telson (which is very deep in S. kekovae ); the major cheliped carpus with a stout distal process ventromesially (vs. unarmed distally in S. kekovae ); the general shape of the major chela, with a relatively elongate palm (vs. short, swollen palm in S. kekovae ); the ischium of the minor cheliped and the second pereiopod each armed with one stout cuspidate seta (vs. both ischia unarmed in S. kekovae ) (cf. Grippa 2004). The two species also differ in the colouration, which is whitish in S. saotomensis sp. nov. ( Fig. 10 ) and “pink-orange” in S. kekovae , according to Grippa (2004). Noteworthy, the striking similarity (both in morphology and colouration) between S. kekovae and S. serratidigitus (Coutière, 1897) from the Indo-West Pacific (including the Red Sea, see Banner & Banner 1981a) calls for a reinvestigation of the taxonomic status of the former species. In fact, it cannot be excluded that S. serratidigitus is yet another Lessepsian migrant that has established a population in southern Turkey. However, such a reinvestigation would require a recollection of S. kekovae , which apparently has not been found since its original description [for instance, Ateș et al. (2010) in their checklist of the decapod crustaceans of Turkey only listed the species’ original record], and through morphological and molecular comparisons with S. serratidigitus and other closely related Indo-West Pacific species ( Ďuriš & Horká 2016).

The only remaining species of Salmoneus in the eastern Atlantic is S. jarli ( Holthuis, 1951) , known with certainty only from the holotype collected off the coast of Nigeria ( Holthuis 1951). In S. jarli , the minor cheliped is moderately enlarged, but the chela fingers are unarmed, unlike in S. saotomensis sp. nov. and S. camaroncito (see above). Additionally, the new species can be easily separated from S. jarli by the rostral carina feebly marked, disappearing posterior to the level of the eyes (vs. well-marked, extending to the mid-length of the carapace in S. jarli ); the major chela palm not swollen, rather elongate (vs. swollen, short, almost ovoid in S. jarli , but see below); the major chela fingers armed with teeth on the cutting edges (vs. unarmed in S. jarli , but see below); the minor cheliped ischium armed with one cuspidate seta (vs. unarmed in S. jarli ); the minor cheliped fingers armed with teeth (vs. unarmed in S. jarli ); the second pereiopod ischium armed with one cuspidate seta (vs. unarmed in S. jarli ); the third pereiopod ischium armed with two cuspidate setae (vs. unarmed in S. jarli ); and the third to fifth pereiopod dactyli moderately slender, not elongate, with the third pereiopod dactylus about 0.4 length of propodus (vs. extremely elongate, with the third pereiopod dactylus almost 0.7 length of propodus, in S. jarli ) (cf. Holthuis 1951: fig. 20). However, it must be noted that the major cheliped of the holotype of S. jarli (ZMUC Cru-6934) is very soft on touch and appears to have been regenerated (A. Anker, pers. obs.). The only other record of S. jarli is that of Holthuis & Gottlieb (1958), who tentatively identified a heavily damaged specimen from Israel, lacking all of its pereiopods (including both chelipeds), as “ Salmoneus ? jarli ”. Therefore, a direct comparison of the major chelipeds between S. saotomensis sp. nov. (or any other species) and S. jarli is currently problematical.

The presence of a stout process on the distal margin of the major cheliped carpus, in ventromesial position, may represent a phylogenetically important feature within the genus Salmoneus . This process is present in S. inconspicuus sp. nov., S. teres , S. saotomensis sp. nov., and S. caboverdensis , but is absent in S. camaroncito , S. erasimorum and S. sketi , and all other Atlantic species of the genus. The two West African species, S. saotomensis sp. nov., and S. caboverdensis may be in fact more closely related, despite their numerous morphological differences and their ecological separation. Similarly, the two Adriatic taxa, S. sketi and S. erasimorum , which share a number of morphological features, e.g. in the configuration of the frontal margin of the carapace and in the armature of the major cheliped fingers, may be closest phylogenetically, despite being ecologically rather very different (see above). The remarkable evolutionary plasticity of Salmoneus and alpheid shrimps in general ( Anker 2003; Anker et al. 2006) seems to result in numerous homoplasies that obscure the true relationships between the species.

Figures

FIGURE 8. Salmoneus saotomensis sp. nov.: holotype, ovigerous specimen (cl 3.8 mm) from São Tomé (MZUSP 34071); a—frontal region, dorsal view; b—same, lateral view; c—posterior pleonites, lateral view; d—telson, dorsal view; e—first article of antennular peduncle, tooth on mesioventral carina, lateral view; f—third maxilliped, lateral view; g—same, tip of ultimate article, dorsolateral view; h—second pereiopod, lateral view; i—third pereiopod, lateral view; j—same, distal portion of propodus and dactylus, mesial view; k—fourth pereiopod, lateral view; l—fifth pereiopod, lateral view; m—same, propodus and dactylus, mesial view; n—second pleopod, appendix interna and appendix masculina, lateral view; o—uropod, dorsal view.

FIGURE 9. Salmoneus saotomensis sp. nov.: holotype, ovigerous specimen (cl 3.8 mm) from São Tomé (MZUSP 34071); a—major cheliped, mesial view; b—same, lateral view; c—same, chela and carpus, mesial view; d—minor cheliped, lateral view; e—same, carpus and chela, mesial view.

FIGURE 10. Salmoneus saotomensis sp. nov.: holotype, ovigerous specimen (cl 3.8 mm) from São Tomé (MZUSP 34071), living shrimp in dorsal [a] and lateral [b] views. Photographs by the author.