Alpheus amblyonyx Chace, 1972

Soledade, Guidomar O., Scioli, Justin A., Terossi, Mariana, Mantelatto, Fernando L. & Almeida, Alexandre O., 2019, Congruence between morphology and molecular data supports the distinction between the snapping shrimps Alpheus macrocheles and A. amblyonyx (Caridea, Alpheidae), Zootaxa 4624 (1), pp. 1-22 : 9-15

Alpheus amblyonyx Chace, 1972

( Figs. 4–6 )

Alpheus amblyonyx Chace, 1972: 59 ; fig. 16. [Near center of Arrecife Nicchehabin, Baía de la Ascensión, Territorio de Quintana Roo, Mexico]; Christoffersen 1979: 302, fig. 1 (in part); Abele & Kim 1986: 197, 208, 209, figs. b–d; Martínez-Iglesias et al. 1997: 403, fig. 2; 356; Coelho Filho 2006: 7 ; Serejo et al. 2007: 198; Alves et al. 2008: 48; Souza et al. 2011: 46; Soledade & Almeida 2013: 94 (in part); Anker et al. 2016: 14, fig. 2.

Type material. 1 OVF, Mexico, Quintana Roo, Bahía de la Ascención, #52–60, USNM 135356 (Not examined) .

Material examined. WEST ATLANTIC— Mexico. 1 NI, Quintana Roo, southwest of the Chinchorro Reef, 28.VIII.1990 , CNCR 21271 (topotype, genetic voucher); 1 NI, Gulf of Mexico, 34–36 m, R/ V Pelican, Box Dredge 14.XI.2005 , 022°6.78’N 91°26.43’W, ULLZ 6615 (genetic voucher) ; Belize. 1 OVF, Stann Creek, Carrie Bow Cay , 16.80251°N 88.081747°W, 3–4 m, 28.IV.2015 , ULLZ 16584 (genetic voucher); 1 M, same locality, 04.IV.2007 , ULLZ17432 ; 1 OVF, same locality, 21.IV.2015 , ULLZ16509 , Guadeloupe. 1 M, KARUBENTHOS, #GB20, 16 m, 18.V.2012 , MNHN 12112 ; 1 OVF, KARUBENTHOS, #GB24, 16 m, 18.v.2012 , MNHN 12026 (genetic voucher) ; Saint Martin. 1 OVF, Chicot, windward side of Tintamarre Island , 12–20 m, 23.IV.2012 , UF 32400 (genetic voucher) ; Brazil. 1 OVF, Espírito Santo, REVIZEE Benthos #34, 20°24’10”S 39°55’35”W, R/ V Astro Garoupa, 50 m, dredge, 15.VII.2001 , MNRJ 17471 ; 1 OVF, Trindade Island, Ilha da Racha , 20°30’26.5”S 29°20’40.0”W, 32 m, under rocks, 30.I.2012 , MZUSP 30317 ; 1 OVF, Trindade Island, Ilha da Racha , 20°30’26.5”S 29°20’40.0”W, 25 m, under rocks, 12.XI.2014 , MZUSP 30262 ; 1 OVF, off Rio de Janeiro, REVIZEE Benthos #Y1, R/ V Astro Garoupa, 60 m, dredge, 11. VI.2002, MNRJ 17467 .

Type locality. WEST ATLANTIC—Mexico, Quintana Roo , Bahía de la Ascensión ( Chace 1972) .

Distribution. WESTERN ATLANTIC–Gulf of Mexico, Yucatan Peninsula, Florida, Caribbean Sea, Brazil (Ceará to Espírito Santo, North Chain Seamounts, Fernando de Noronha, Atol das Rocas, Vitória-Trindade Seamount Chain, Trindade & Martin Vaz Archipelago) ( Chace 1972; Abele & Kim 1986; Christoffersen 1979; Martínez-Iglesias et al. 1997; Soledade & Almeida 2013 and references therein; Anker et al. 2016; present study).

Diagnosis. Rostrum almost reaching distal margin of first article of antennular peduncle; scaphocerite blade reaching half length of second article of antennular peduncle; distal tooth reaching distal limit of antennular peduncle. Minor cheliped with ischium armed with 4 spiniform setae; ventromesial margin of merus with 6 spiniform setae similar in size and shape, spaced almost equidistantly along length of mesial surface of merus; dactylus without crest on extensor margin. Major cheliped with ischium armed with 3 spiniform setae; ventromesial margin of merus with 6 spiniform setae similar in size and shape, spaced almost equidistantly along length of mesial surface of merus; dactylus flattened, laterally twisted, dorsally convex and strongly bulbous distally; plunger developed, with anterior surface distinctly angular. Second pereiopod elongated, slender; ischium slightly longer than merus; carpus subdivided in 5 articles with ratio approximately equal to 3: 2: 1: 1.3: 1.5. Distolateral margin of uropodal exopod with 1 mesial and 1 lateral teeth adjacent to spiniform setae.

Morphological characterization (bold characters represent the main differences regarding A. macrocheles ). Carapace smooth, frontal margin with strong rostrum, ocular hoods with well-developed teeth originating from anterior margin of hoods; rostrum slightly flat in dorsal view, distinctly longer than broad, distally tapering and ending in sharp point, without setae, almost reaching distal margin of first article of antennular peduncle; margin between orbital teeth and rostrum V-shaped ( Fig. 4A, B ); orbital process present. Pterygostomial angle rounded, not anteriorly protruding ( Fig. 4B ); cardiac notch deep. Pleonal segments with posteroventral margins broadly rounded, those of fifth segment slightly angular; sixth segment without articulated plate in posterolateral margin.

Eyes with well-developed corneas; ocellar beak projecting anteriorly, acute, visible in lateral view. Antennular peduncle moderately slender; stylocerite with acute tip reaching distal limit of first article of antennular peduncle; ventromesial carina well-developed, triangular in shape, with small pointed tooth ( Fig. 4C ); second article of antennular peduncle much longer than visible part of first article, about 2 times longer than broad ( Fig. 4A ); lateral flagellum with groups of aesthetascs extending to article 10. Antennal basicerite with acute lateral tooth; carpocerite slightly exceeding distal end of scaphocerite and antennular peduncle; lateral margin of scaphocerite slightly concave, ending in strong lateral tooth overpassing distal margin of blade ( Fig. 4A ); blade reaching half length of second article of antennular peduncle; distal tooth reaching distal limit of antennular peduncle. Mouthparts as illustrated by Chace (1972). Third maxilliped slender; coxa with lateral plate slightly truncated distally; exopod reaching beyond distal limit of antepenultimate article when extended; antepenultimate article somewhat flattened, approximately 4 times longer than broad, ventral surface sparsely setose; penultimate article approximately 3 times longer than broad, slightly broadened distally and densely setose; ultimate article unarmed, distally tapering, with dense rows of long setae ( Fig. 4I ).

Minor cheliped with short and stout ischium; distomesial margin broad, sub-triangular in cross-section, armed with 4 spiniform setae; ventrolateral surface unarmed; ventromesial margin of merus slightly convex, ending in small acute tooth, with 6 spiniform setae similar in size and shape, spaced almost equidistantly along length of mesial surface of merus; carpus cup-shaped; chelae strongly compressed, palm with grooves and notches from distal half of lateral surface; mesial surface convex and devoid of depressions or grooves; lateral surface with low crest starting at about middle of palm and ending in acute distolateral tooth; ventral surface smooth, ending in welldefined notch; dorsal margin also smooth, with sub-cylindrical elevation ending distally in small adhesive disk; distomesial surface with high ridge ending in strong sharp tooth; fingers as long as palm; pollex lightly excavated on cutting edge; dactylus slightly flattened and twisted laterally, without crest on extensor margin, with small adhesive disk proximally ( Fig. 5C, D ).

Major cheliped with ischium short and robust, ventromesial surface with 3 small spiniform setae; merus robust, not elongated, about 2 times longer than wide, sub-triangular in cross section; ventrolateral margin unarmed; ventromesial margin straight, with 6 small spiniform setae, ending in robust and sharp tooth; carpus very short, cupshaped, slightly compressed; lateral surface with low crest starting at approximately 0.6 of length of palm, ending in distolateral sharp tooth, slightly directed laterally; linea impressa well-marked; mesial surface convex, devoid of sculptures and grooves; ventral surface with rounded smooth shoulder slightly projecting into adjacent deep notch; notch extending transversely to groove on mesial surface; dorsal margin with sub-cylindrical elevation ending distally in large adhesive disk; distomesial surface with deep transversally notched crest ending in sharp tooth; distal third of ventral margin of palm with strong and long setae extending to distomesial margin of palm; pollex shorter than dactylus, strongly curved laterally, cutting edge slightly excavated and with small rounded tooth in proximal portion; dactylus flattened, laterally twisted, dorsally convex and strongly bulbous distally; plunger developed, with anterior surface distinctly angular ( Fig. 5A, B ).

Second pereiopod elongated, slender; ischium slightly longer than merus; carpus with 5 articles with ratio approximately equal to 3: 2: 1: 1.3: 1.5; chelae not sculptured, fingers as long as palm, with small tufts of setae ( Fig. 6A ). Third pereiopod with ischium armed with strong spiniform setae on ventrolateral surface; merus 4 times longer than broad, without tooth at distoventral angle; carpus slender, about half length of merus; propodus about 1.5 times longer than carpus, with about 9 robust spiniform setae along ventral margin and 1 pair of spiniform setae near to articulation with dactylus; dactylus slightly shorter than half length of propodus, conical, slightly curved, ending in sharp tip; extensor margin with 1 sub-terminal denticle ( Fig. 6B ). Fourth pereiopod similar to third in shape and proportion of articles, but slightly less robust; ischium armed with strong spiniform setae on ventrolateral surface; propodus with about 7 robust spiniform setae along ventral margin and 1 pair of spiniform setae near to articulation with dactylus ( Fig. 6C ). Fifth pereiopod slenderer than third and fourth ( Fig. 6D ); merus slightly longer than carpus; ischium with 1 spiniform setae; propodus with about 8 spiniform setae along ventral margin and 10 well-developed distolateral setal brushes. Pleopods with sparse setae on lateral margin of protopod; endopods and exopods with edges densely setose; first pleopod very reduced, distal margin of endopod with setae; second pleopod in male with appendix masculina subequal in length to appendix interna, not reaching distal margin of endopod, with numerous rigid setae at distal end; uropod with lateral lobe of protopod ending in strong and sharp tooth; diaeresis sinuous, ending in 1 mesial and 1 lateral teeth adjacent to spiniform setae; endopod with row of small spiniform setae along distal margin ( Fig. 4I ). Telson subretangular, tapering to posterior margin; proximal margin 2.0 times broader than distal margin; lateral margins slightly convex; dorsal surface with 2 pairs of spiniform setae, first pair located at half-length of telson, second pair located approximately 0.7 of length of telson; posterior margin broadly convex, with 2 pairs of spiniform setae, mesial pair about 3 times size of lateral pair ( Fig. 4J ); anal tubercles well-developed.

Morphological variation. Little morphological variation has been observed (see Table 2 ). No significant differences between sexes have been observed.

Comparative material analyzed. Alpheus crockeri . EAST ATLANTIC— Cape Verde. 1 NI, São Vicente Island , 01.X.2013 , OUMNH 2014-01 - 0030 (genetic voucher) .

Alpheus pouang . WEST ATLANTIC— Brazil. 1 M (Holotype), off São Paulo, R/ V Wladimir Besnard #1019, 23°39’S 43°37’W, 120–121 m, mud and sand, 27.V.1970 , MZUSP 4543 ; 1 F, 1 M, off Rio Grande do Sul , GEDIP I #330 , 34°35’S 52°00’W, sand, 30. VI.1968 , MNRJ 4388 .

Alpheus puapeba : WEST ATLANTIC— Brazil. 1 OVF (Paratype), off Rio de Janeiro, R/ V Wladimir Besnard #1632, 23°33’S 44°11’W, 72 m, 17.XII.1971 , MZUSP 31525 ; 1 OVF, off Rio de Janeiro , HAB 2 #66, 23°11’15.741”S 41°37’17.184”W, trawl, continental shelf of the Campos Basin , 26.IV.2008 , MNRJ 21836 ; 1 M, Rio de Janeiro, Ilha Grande , #302, 49 m, 16.II.1968 , MNRJ 4387 ; 1 F, 1 M , HAB 1 , # 66 , trawl, 98.7 m, 26.IV.2008 , MNRJ 21836 (genetic voucher); 4 F, 10 M, off Santa Catarina , #61 — CB102 , 27°07’S 42°03’W, 100 m, 01. VI.1987, MZUSP 31900 .

Alpheus platydactylus : WEST ATLANTIC— Azores. 1 OVF, 1 NI, # 5.010, 26.V.1981 , RMNH. Crus. D.51229; 2 OVF, # 5.129, 06.VI.1981, RMNH. Crus. D.51237; Canary Islands. 1 OVF, 1 M, # 4.07, 20.I.1980 , RMNH. Crus. D.51238; 2 F (1 OV), # 4.17, 09.I.1980 , RMNH. Crus. D.51239; Cape Verde. 2 F (1 OV), 1 M, “Tydeman” Cancap- VII, # 7.122, 01.IX.1986 , RMNH. Crus. D.51240 .

Molecular analysis. A total of 10 new 16S rRNA gene sequences were obtained from species of the A. macrocheles species complex (see Table 1 ). The substitution model that best fit the data was the TPM3uf + I (= K81) assuming the nucleotide frequencies A = 0.2812, C = 0.1185, G = 0.2601, T = 0.3402, replacement rates AC = 0.1431, AG = 4.6735, AT = 1, CG = 0.1431, CT = 4.6735, GT = 1, and invariable sites = 0.54.

The topology generated from the Bayesian Inference Analysis shows the presence of two main clades, clearly separating the specimens of A. macrocheles and A. amblyonyx ( Fig. 8 ). In the first clade A. crockeri ( Cape Verde) is placed as a sister group of A. puapeba ( Brazil) + A. macrocheles (Azores and Canary Islands), in the second clade are the specimens of A. amblyonyx , including the topotypic material (Quintana Roo, Mexico). In both clades the groupings are well supported by the posterior probability values ( Fig. 8 ).

The values of interspecific genetic distance (K81 model) ranged from 14 ( A. macrocheles X A. puapeba ) to 29% ( A. amblyonyx X A. crockeri ). There was no genetic intraspecific divergence among specimens of A. macrocheles or A. amblyonyx . The two species of interest ( A. macrocheles and A. amblyonyx ) had a genetic distance of 19%.

Figures

FIGURE 4. Alpheus amblyonyx Chace, 1972, male specimen from Quintana Roo, Mexico, CNCR 21271. (A) Carapace and cephalic appendages, dorsal view (setae omitted); (B) same, lateral view; (C) ventromesial carina of the antennular peduncle; (D) third maxilliped, lateral view; (E) telson and uropods, dorsal view (setae omitted); (F) uropod, detail of the distal margin of endopod, setae ommited. Scale bars: A, B, D, E, F, 1 mm; C, 0.5 mm.

FIGURE 5. Alpheus amblyonyx Chace, 1972, ovigerous female specimen from Guadeloupe, MNHN 12112. (A) major cheliped, lateral view; (B) same, mesial view; (C) minor cheliped, lateral view; (D) same, mesial view; (E, F) detail of the spiniform setae in the ischium and propodus of the major and minor chelae, respectively; (G) dactylus of the major chelae, mesial in mesial view, detail on the plunger. Scale bars: A–E, 1 mm; F, G, 0.5 mm.

FIGURE 6. Alpheus amblyonyx Chace, 1972, ovigerous female specimen from Guadeloupe, MNHN 12112. (A) second pereiopod, lateral view; (B) third pereiopod, lateral view; (C) fourth pereiopod, lateral view; (D) fifth pereiopod, lateral view; (E–G) third–fifth pereiopods, detail of the propodus; (H, I) third and fourth pereiopods in lateral view, detail of the dactylus. Scale bars: A–D, 1 mm; E–I, 0.5 mm.

FIGURE 8. Bayesian Inference Tree of 16S gene among specimens of Alpheus macrocheles (Hailstone, 1835b) and Alpheus amblyonyx Chace, 1972 and other snapping shrimp of the genus Alpheus Fabricius, 1798 and Synalpheus Spence Bate, 1888. CNCR: Colección Nacional de Crustáceos, Mexico; MNHN: Muséum national d’Histoire naturelle, France; RMNH: Netherlands Centre for Biodiversity Naturalis; OUMNH: Oxford University Museum of Natural History; UF: Florida Museum of Natural History; ULLZ: University of Louisiana at Lafayette Zoological Collection. Numbers close to nodes represent posterior probabilities.