Alpheus agilis , Anker, Arthur, Hurt, Carla & Knowlton, Nancy, 2009
Anker, Arthur, Hurt, Carla & Knowlton, Nancy, 2009, Description of cryptic taxa within the Alpheus bouvieri A. Milne-Edwards, 1878 and A. hebes Kim and Abele, 1988 species complexes (Crustacea: Decapoda: Alpheidae), Zootaxa 2153, pp. 1-23: 12-16
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Alpheus agilis n. sp.
Type material. São Tomé. Holotype: 1 male (CL 5.0), USNM 1123865, ST 3, 200 m west of Lagoa Azul, rocky intertidal with coralline algae, from rock crevices and under rocks, coll. A. Anker and N. Knowlton, 31 Jan 2006 [fcn 06-067]. Paratypes: 1 male (CL 4.6), 2 ovig. females (CL 4.4, 4.7), USNM 1123866, same collection data as for holotype [06-068 (male), 06-069, 06-071 (females)]; 1 male (CL 5.9), USNM 1123867, ST 8, near Porto Alegre, rocky intertidal with cemented basaltic rocks and coralline algae, depth about 30 cm, under rocks on coarse sand, coll. A. Anker, 5 Feb 2006 [fcn 06- 152, specimen dissected]; 1 male (CL 4.4), 2 ovig. females (CL 4.5, 4.7), MNHN-Na 17185, ST 8 A, near Porto Alegre, rocky intertidal with cemented basaltic rocks and coralline algae, depth about 30 cm, under rocks on coarse sand, coll. A. Anker, 14 Feb 2006 [fcn 06- 221]; 1 ovig. female (CL 5.5), FLMNH UF Arthropoda 16556, ST 4, 2 km west of Lagoa Azul, near ship wreck, rocky cliffs, under rocks in tide pool, coll. N. Knowlton and A. Anker, 1 February 2006 [fcn 06- 114].
Additional material examined. Cape Verde. 2 males (CL 4.6, 6.7), 4 juveniles (CL not measured), USNM 1123868, São Vicente, between Baia das Gatas and Praia Grande, coll. N. Knowlton et al., 25 Mar 1998; 6 juvenile specimens (CL not measured), USNM 1123869, São Vicente, Calhau, in tide pools, coll. N. Knowlton et al., 26 Mar 1998; 1 specimen (CL not measured) of unknown sex (chelipeds and abdomen missing), not deposited, Santiago, Praia, beach near Club Nautics, coll. N. Knowlton et al., 5 April 1998. Brazil: 4 males (CL 5.8, 6.2, 7.2, 7.3), 2 ovig. females (CL 7.2, 8.0), 2 immature females (CL 4.0, 4.1), MNRJ 20845, Atol das Rocas, Ilha do Cemitério, in tide pools, coll. P.S.Young, P.C. Paiva and A.A. Aguiar, 13 Oct 2000.
Diagnosis. Species of Alpheus leviusculus group (Clade L). Frontal margin of carapace with short, subtriangular rostrum; rostral carina not delimited, postrostral area flattened; orbital hoods unarmed, rounded, swollen, markedly but not steeply sloping into shallow orbitorostral grooves. Antennule with second peduncular segment less than twice as long as wide; stylocerite with acute tip, reaching or slightly overreaching distal margin of first segment. Antenna with basicerite armed with sharp distoventral tooth; scaphocerite with strong distolateral tooth extending only slightly beyond broad blade, not reaching end of antennular peduncle; carpocerite greatly overreaching both scaphocerite and end of antennular peduncle. Third maxilliped not particularly broadened, unarmed. Major cheliped with merus lacking sharp distomesial tooth; chela somewhat compressed, dorsal groove relatively broad and deep, extending mesially as contrasting rounded depression and laterally as well defined, posteriorly extending groove; dorsal shoulder rounded, not overhanging; ventral groove broad and deep, adjacent shoulder rounded, not protruding; adhesive disks small; fingers slightly less than half-length of palm; plunger of dactylus well developed. Minor cheliped sexually dimorphic; palm with very shallow dorsal groove; fingers somewhat broadened and balaeniceps in males, subconical and non-balaeniceps in females. Second pereiopod with first carpal segment nearly twice as long as second. Third pereiopod with ischium armed with small ventrolateral spine, merus and carpus unarmed; propodus with row of stout spines, most paired; dactylus stout, simple, conical. Male second pleopod with typical appendices masculina and interna. Uropod with protopod laterally projecting as acute tooth; exopod with distolateral spine bordered laterally by sharp distolateral tooth; transverse suture sinuous, consisting of two rounded lobes and subtriangular tooth adjacent to distolateral spine; both exopod and endopod furnished with row of spinules distally. Telson broad, tapering distally, with two pairs of dorsal spines; posterior margin convex, with two pairs of spines at each posterolateral angle and row of spinules in-between.
Description. Carapace smooth, not setose, laterally not compressed. Rostrum short slender, subtriangular, slightly descendant, distally subacute ( Fig. 4View FIGURE 4 A, B), not reaching half length of first segment of antennular peduncle; postrostral area flattened, broadening posteriorly to level of posterior margin of corneas ( Fig. 4View FIGURE 4 A); adrostral grooves shallow, not abruptly delimited from either orbital hoods or postrostral area; orbito-rostral process feebly developed. Orbital hoods inflated, distally rounded, unarmed ( Fig. 4View FIGURE 4 A); anterior margin between rostrum and orbital hoods feebly concave. Pterygostomian angle rounded ( Fig. 4View FIGURE 4 B). Eyes completely concealed in dorsal and lateral views, partly visible in frontal view, with small subacute tooth on anteromesial margin; cornea well developed. Ocellar beak conspicuously protruding between eyes.
Antennular peduncles rather stout, second segment only slightly longer than broad; stylocerite with acute tip, slightly overreaching distal margin of first segment in dorsal view ( Fig. 4View FIGURE 4 A, C); mesioventral carina of first segment with blunt, broadly subtriangular tooth ( Fig. 4View FIGURE 4 E); lateral flagellum with numerous tufts of aesthetascs approximately on 8 th to 16 th segments, secondary ramus rudimentary ( Fig. 4View FIGURE 4 D). Antenna with basicerite bearing strong, acute ventrolateral tooth ( Fig. 4View FIGURE 4 B); carpocerite stout, reaching far beyond distolateral tooth of scaphocerite ( Fig. 4View FIGURE 4 A); scaphocerite with nearly straight lateral margin, reaching distal margin of antennular peduncle; distolateral tooth of scaphocerite moderately strong, reaching distinctly beyond blade; cleft between blade and distolateral tooth relatively deep ( Fig. 4View FIGURE 4 A).
Mouthparts typical for Alpheus in external view. Third maxilliped moderately stout ( Fig. 4View FIGURE 4 F); lateral plate with subacute point; antepenultimate segment subtriangular in cross-section; penultimate segment slender, more than twice as long as wide; ultimate segment distally tapering ( Fig. 4View FIGURE 4 F).
Male major cheliped with short ischium and stout merus; ventromesial margin of merus straight, ending bluntly distally; distodorsal margin also blunt; carpus short, cup-shaped; chela ( Fig. 4View FIGURE 4 G, H) laterally somewhat compressed; dorsal and ventral margins of palm with broad transversal grooves; dorsal groove extending to mesial face in form of well delimited, rounded depression, latter not extending posteriorly; same dorsal groove continuing to lateral face as well marked rounded depression, however, extending from here posteriorly to linea impressa ( Fig. 4View FIGURE 4 H); dorsal shoulder rounded, gently sloping, not overhanging groove ( Fig. 4View FIGURE 4 G); ventral groove broad, deep, oblique, extending to both mesial and lateral face; ventral shoulder rounded, not protruding ( Fig. 4View FIGURE 4 G, H); linea impressa well marked; adhesive disks small; fingers about half-length of palm; proximal margin of pollex forming large, nearly 90 ° angle on mesial face ( Fig. 4View FIGURE 4 G); dactylus reaching slightly beyond pollex, with small transverse ridge near base of plunger; plunger well developed, stout ( Fig. 4View FIGURE 4 G, H). Female major cheliped generally similar to male major cheliped; chela usually smaller, more slender, and with somewhat different proportions.
Male minor cheliped with short ischium and stout merus; ventromesial margin of merus straight, unarmed distally; carpus short, cup-shaped; chela ( Fig. 4View FIGURE 4 I) subcylindrical, without sculpture; palm slightly longer than fingers; dactylus slightly expanded, with rows of balaeniceps setae ( Fig. 4View FIGURE 4 I), cutting edges sharp, blade-like; pollex proximally with row of setae. Female minor cheliped similar in general proportions, but chela ( Fig. 4View FIGURE 4 J) without row of balaeniceps setae on fingers.
Second pereiopod ( Fig. 4View FIGURE 4 K) slender; ischium subequal to merus; carpus five-segmented, first segment longest, ratio of carpal segments (from proximal to distal) approximately 4: 2.5: 1: 1: 2; chela longer than second segment, simple, with fingers subequal to palm. Third and fourth pereiopods similar in shape and length; third pereiopod ( Fig. 4View FIGURE 4 L) with ischium armed with small ventrolateral spine; merus unarmed, about five times as long as wide; carpus unarmed, distinctly slenderer than merus; propodus with about six slender ventral spines, often in pairs, and two distoventral spines ( Fig. 4View FIGURE 4 L); dactylus simple, conical, gradually curved, with acute tip, 0.4 length of propodus. Fifth pereiopod smaller and slenderer than third and fourth pereiopods; ischium unarmed ventrally; propodus with six-seven ventral spines (including distoventral spine); distolateral margin with about six rows of grooming setae; dactylus simple, conical, similar to that of third or fourth pereiopods.
Abdominal somites (pleurites) broadly rounded posteroventrally; sixth pleuron without articulated flap. Male second pleopod with appendix masculina subequal to appendix interna, furnished with slender setae on tip and along margins ( Fig. 4View FIGURE 4 M). Uropod with protopod armed with two large acute distal teeth; exopodal diaeresis with two broad rounded lobes ( Fig. 4View FIGURE 4 N, O); distolateral spine long, slender; distal margin of endopod and exopod with row of spinules ( Fig. 4View FIGURE 4 O). Telson relatively broad ( Fig. 4View FIGURE 4 P), subrectangular, tapering posteriorly; dorsal surface with two pairs of moderately strong spines, situated at some distance from lateral margins, first pair slightly anterior to mid-length, second pair well posterior to telson mid-length ( Fig. 4View FIGURE 4 P); posterior margin broadly rounded, with two pairs of posterolateral spines, mesial much longer than lateral, apparently without row of spinules between mesial spines ( Fig. 4View FIGURE 4 P); anal tubercles moderately developed. Gill/exopod formula typical for Alpheus .
Size. Eastern Atlantic: largest male from Cape Verde at CL 6.7 mm and TL 17.3 mm; largest ovigerous female from São Tomé at CL 5.5 mm and TL 16.5 mm; western Atlantic (Atol das Rocas, Brazil): largest male at CL 7.3 mm and TL 24.1 mm; largest ovigerous female at CL 8.0 mm and TL 22.2 mm; egg size: about 1.1 x 1.2 mm (average from 3 eggs from a 4.7 mm CL ovigerous female from São Tomé).
Etymology. The species’ name refers to shrimp’s agility ( agilis, Latin for agile, quick), which makes them somewhat hard to collect, even at low tide.
Type locality. São Tomé Island in the Gulf of Guinea.
Distribution. Eastern Atlantic: presently known only from São Tomé and Cape Verde.
Ecology. Mid-intertidal, under rocks on sand; usually in male-female pairs. The shrimps are very agile and almost restless, crawling quickly over the bottom both in or out of water.
Remarks. Alpheus agilis n. sp. is most closely related to the eastern Pacific A. hebes . The main difference between these two species lies in the stylocerite, which is sharp and exceeding the distal margin of the first segment of the antennular peduncle in A. agilis n. sp. ( Fig. 4View FIGURE 4 A –C) and usually blunt (sometimes subacute) and not exceeding this margin in A. hebes ( Fig. 3View FIGURE 3 A, B). Further, possibly consistent but even more subtle differences, are the ratio of the carpal segments in the second pereiopod, e.g., the relatively longer second segment in A. agilis n. sp. (compare Figs. 4View FIGURE 4 K and 3 F), the relative width of the flattened postrostral area (compare Figs. 4View FIGURE 4 A and 3 A), and the width of the dorsal notch of the major chela (compare Figs. 4View FIGURE 4 G, H and 3 C, D). Remarkably, the color patterns of A. agilis n. sp. and A. hebes are quasi-identical (compare Figs. 5View FIGURE 5 F, E). The western Atlantic (Atol das Rocas) specimens are also quasi-identical with the eastern Atlantic specimens. In the field, e.g., in Brazil or in West Africa, A. agilis n. sp. may be confused with A. bouvieri , differing from the latter species by the presence of a spine on the ischium of the third and fourth pereiopods.
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