Alpheus margaritae, Salgado-Barragan, Jose, Ayon-Parente, Manuel & Zamora-Tavares, Pilar, 2017

Salgado-Barragan, Jose, Ayon-Parente, Manuel & Zamora-Tavares, Pilar, 2017, New records and description of two new species of carideans shrimps from Bahia Santa Maria-La Reforma lagoon, Gulf of California, Mexico (Crustacea, Caridea, Alpheidae and Processidae), ZooKeys 671, pp. 131-153 : 131-132

Alpheus margaritae sp. n. Figs 1, 2, 3, 4, 5

Material examined.

Holotype: Male (CL 4.6 mm), Costa Azul Island, Santa María-La Reforma, Sinaloa, Mexico, 25°5'56"N, 108°7'58"W, 0.1-0.3 m, mudflat with gravel at neap tide, March 30, 2015, (EMU- 10580). Paratypes: all same locality and data as holotype, 5 females (CL 3.0-5.7), 2 ovigerous females (CL 4.3-5.6 mm), 1 juvenile (CL 2.3 mm), (EMU-10581); paratypes, same locality and data as holotype, 1 male (CL 6.5 mm), 1 ovigerous female (CL 5.8 mm), (CNCR 32595).

Diagnosis.

Ocular hoods unarmed. Antepenultimate segment of third maxilliped broad. Scaphocerite with concave lateral margins, distolateral tooth overreaching the distal margin of the inner blade, inner blade almost reaching the distal end of antennular peduncle. Major cheliped markedly compressed, with grooves on both dorsal and ventral margins. Pereopods 3-5 with dactylus subspatulate; ischium of third and fourth pereopods with ventral spine.

Description.

Carapace glabrous (Fig. 2A, B), rostrum triangular, sharp, exceeding anterior margin of ocular hood, reaching 0.33 of visible portion of first antennular segment; rostral carina low and narrow, barely overpassing posterior end of eye; orbital hoods inflated dorsally and produced anteriorly, anterior margin convex, unarmed; orbitorostral groove shallow; pterygostomial margin slightly produced anteriorly below basis of basicerite. First antennular segment (Fig. 2A, B, E) bearing subtriangular carina on ventromesial margin, posterior margin of ventromesial carina convex, anterior margin concave, ventral margin with acute tip, directed anteriorly; second antennular segment approximately 2.0 times as long as wide, 1.5 times length of visible part of first segment, and 3.0 times as long as third segment; stylocerite almost reaching distal margin of first segment.

Antenna (Fig. 2A, B) with lateral margin of scaphocerite slightly concave; distolateral tooth reaching distal end of antennular peduncle; inner blade falling short of tip of distolateral tooth; cleft between inner blade and distolateral tooth arising from approximately 0.25 of scaphocerite; carpocerite overpassing distal end of antennular peduncle by 0.4 length of third antennular segment; basicerite with acute lateral tooth.

Third maxilliped (Fig. 2C, D) reaching distal margin of carpocerite; last segment tapering distally, mesial surface setose, almost twice as long as penultimate segment; penultimate segment approximately twice as long as broad; antepenultimate segment fairly enlarged and flattened, approximately 2.6 times as long as broad, longer than the sum of preceding two segments; lateral surface smooth, mesial surface with sinuous carina bearing long setae; exopod falling near to median part of penultimate segment in holotype and two female paratypes, shorter than penultimate segment in males and the rest of females; precoxa with one arthrobranch near distal end and small supplementary arthrobranch near proximal end.

Major cheliped of first pereopods (Fig. 3 A–D) narrow, 2.4 times as long as broad and with trace of fine granules at anterior half; fingers clearly narrower than palm, occupying the distal 0.4 of chela (0.35 in juveniles); movable finger with superior margin slightly arched at proximal two thirds and then right angled, tip narrow and acute; pollex acute at tip, inferior margin almost straight along proximal two thirds and convex along distal third; palm with superior and inferior transverse grooves; superior transverse groove broad and low, continuing to shallow elongated triangular depression on mesial face and continuing to shallow broad rectangular depression on lateral face; mesial superior depression continuing to proximal portion of palm; lateral superior depression continuing to linea impressa; linea impressa continuing with mesial upper longitudinal depression; inferior transverse groove fairly deep and broad with proximal shoulder slightly projecting, connecting to inverse V-shaped inferior lateral palmar depression; lateral palmar face with shallow depression below superior palmar depression and behind inferior palmar depression, and with median depression between the above two depressions and continuing to below proximal portion of dactylus; mesial palmar surface with elongate depression near inferior margin; a slightly depressed area between upper and lower longitudinal depressions and lower areas between and in front of upper and inferior transverse grooves; ventromesial margin of merus with trace of fine granules, bearing two minute movable teeth at proximal half, unarmed distal end; ventral surface with trace of fine granules in largest specimens.

Minor chela of first pereopods (Fig. 4A) elongate, 5.6 times as long as broad, with trace of fine granules inferiorly; fingers occupying 0.7 of chela ; cutting edges barely serrated, subparallel when closed, apex deflexed inward; movable finger longer than immovable finger in most specimens; tips of fingers blunt to acute. Palm lacking sculpturing, with trace of fine granules on mesial face, swollen laterally and thicker than fingers. Merus with ventromesial margin bearing short setae, with two small movable teeth at proximal half.

Second pereopod (Fig. 4B) reaching distal end of carpocerite beyond distal end of first segment of carpus. Chela shorter than the sum of three distal segments of carpus. Fingers of chela 1.4 times as long as palm. First segment of carpus 1.4 times as long as second; second segment 2.6 times as long as third; fourth segment almost as long as third; fifth segment 1.7 times as long as fourth.

Dactylus of third pereopod (Fig. 4C) subspatulate, 0.5 times as long as propodus; propodus 1.4 times as long as carpus, with inferior margin bearing six small spines along its extension. Merus 5.6 times as long as broad and 1.8 times as long as carpus; ischium with ventral spine.

Fourth pereopod (Fig. 4D) similar to third pereopod; ischium with ventral spine.

Ischium of fifth pereopod (Fig. 4E) unarmed; propodus setose distally, setae increasing in number distally; dactylus subspatulate.

Pleura of first to fourth abdominal somites rounded ventrally, not overlapping each other much on ventral regions, that of fifth somite subtriangular on posterior ventral margin (Fig. 2F). Abdominal sternite unarmed at midline. Appendix masculina (Fig. 2H, I) slightly shorter than appendix interna.

Telson (Fig. 2G) Approximately 1.5 times as long as broad at anterior end, armed with two pairs of dorsal spines and low longitudinal median depression on dorsal surface; posterior margin very convex, with two pairs of postero-lateral spines, inner spine stronger, twice as long as outer. Uropodal endopod with fairly distinct mesial depression at anterior half; uropodal exopod bearing movable spine outside of transverse suture, movable spine flanked laterally by short immovable tooth and internally by round lobe; suture forming almost two straight lobes.

Habitat.

Soft mud with gravel composed of shells and rocks, in intertidal.

Color in life.

Creamy-white with irregular sparse olive green to light brown patches on dorsal surface of carapace, abdomen and telson; uropodal endopodite and distal lobe of exopodite olive green to light brown, proximal lobe of exopodite creamy-white; patches on abdominal plates tend to be more dense towards the rear; first pereopod olive green. No clear differences were observed between sexes (Fig. 1).

Distribution.

Only known from Bahía Santa María-La Reforma coastal lagoon, Sinaloa, Mexico.

Etymology.

The species is named after Dr. Margarita Hermoso Salazar in recognition of her contributions to the knowledge of Mexican carideans.

Variations.

Body structures in Alpheus margaritae sp. n. are similar between sexes; sculpture in major cheliped becomes deeper in larger specimens. Disparities among the specimens are:

In nine of the twelve specimens the antepenultimate segment of the third maxilliped is approximately 2.5 times as long as broad, with a sinuous carina on the inner surface bearing long setae and the exopod not reaching the distal end of the antepenultimate segment (Fig. 2D), in three females the shape of that appendage is quite different; the antepenultimate segment of the third maxilliped is slender, without a well-defined inner carina and sparse long setae; the exopod is longer, reaching the middle of the penultimate segment (Fig. 2C); all specimens, with exception of the largest female, bear two spines on proximal half of inferior inner margin of merus of both major and minor chelae and no distal spines are present. In the largest female those proximal spines are absent, although there are some marks in the place where the spines should be located, that likely indicates that spines were lost; relative length of fingers in minor first pereopod increases with the size of the specimens; ranging from 64% in the smallest juvenile to 72% in one of the largest females, with exception of one female (CL = 5.0 mm) whose fingers occupied only 45% of minor chela length. The latter chela does not seem to be damaged and does not appear to represents a case of regeneration.

Remarks.

Alpheus margaritae sp. n. is morphologically similar to A. antepaenultimus , A. mazatlanicus , and A. chacei . These species share the absence of teeth on the ocular hoods, the antepenultimate segment of the third maxilliped being broad, the major cheliped markedly compressed with grooves on both dorsal and ventral margins, and pereopods 3-5 with subspatulate dactylus.

The new species and A. antepaenultimus have the inferior inner margin of merus with spines, while in A. chacei the merus lacks these spines. Alpheus margaritae sp. n. can be differentiated from A. antepaenultimus as in the former the scaphocerite has concave lateral margins, the distolateral tooth overreaches the distal margin of the inner blade, and the inner blade almost reaches the distal end of the antennular peduncle, whereas in A. antepaenultimus the lateral margins of the scaphocerite are almost straight, the distal spine almost reaches the distal margin of the inner blade, and the inner blade overpasses the distal end of antennular peduncle. In large specimens of the new species (CL> 5.0 mm) the superior transverse groove of the major cheliped is deeper and the sculpture is more conspicuous than in A. antepaenultimus . The proximodorsal margin of the movable finger of A. margaritae sp. n. is almost straight and the tip is narrow and acute, while in A. antepaenultimus the dorsal margin of the movable finger is arched along all its longitude and bluntly rounded at tip. Also, the number of spines on inferior inner margin of merus of major first pereopods in A. antepaenultimus is greater than in the new species (3 or 4 vs. 1 or 2).

Alpheus margaritae sp. n. can be differentiated from A. mazatlanicus as in the new species the second antennular segment is proportionally much shorter than wide (2 times vs. 4 times) and the lateral margin of the scaphocerite is slightly concave instead of straight; A. margaritae has a hook-like carina on the ventromesial face of the first article of antennular peduncle whereas in A. mazatlanicus this carina is broadly triangular; besides, A. margaritae has the inner margin of merus of the first pereopod with movable spines on proximal half while in A. mazatlanicus such spines are absent; and the ratio of the fingers in relation to the palm in the minor chela is shorter (60%) in A. mazatlanicus than in the new species (approximately 70%).

Alpheus margaritae is more related to A. antepaenultimus B. The latter is part of a species complex from the Eastern Pacific which include A. floridanus specimens from Eastern Pacific sensu Williams et al. 2001 and A. hephaesthus (Braken-Grissom et al. 2014). A. antepaenultimus A, A. antepaenultimus B, and A. chacei form a clade consistent with the morphological traits previously described. This clade could be the result of an ecological radiation, probably associated to the species flexibility to inhabit in tropical and subtropical conditions (Williams et al. 2001). The position of A. margaritae within the A. antepaenultimus complex suggests that this group of species, and probably A. mazatlanicus , could have been subject to such ecological radiation.

Phylogenetics relationships.

The COI matrix of Alpheus molecular data consisted of 668 characters. The ML phylogenetic hypothesis shows that Alpheus margaritae sp. n. is more related to A. antepaenultimus B with a bootstrap support of 63. On the other hand, A. margaritae sp. n. shows an important mutational distance that differentiates it from A. antepaenultimus B. This pair of species is grouped together in the clade formed by A. chacei and A. antepaenultimus (Fig. 5). COI matrix of Alpheus shows that A. margaritae sp. n. belongs to the species complex formed by A. antepaenultimus A, B, and A. chacei . This complex corresponds to the mangrove group (type a) of the clade I proposed by Williams et al. (2001). The A. antepaenultimus complex is characterized by the combination of: 1) the absence of spines on the occular hoods, 2) the antepenultimate segment of the third maxilliped is broadened, 3) major cheliped compressed, with transverse groove on superior and inferior margins proximal to fingers, 4) immovable finger of minor chela never balaeniceps, and fingers occupying more than 0.6 of chela , 5) pereopod 3-5 with subspatulate dactylus, 6) ischium of pereopods 3-4 with spine on the ischium, 7) uropodal spines not colored.