Leptalpheus melendezensis, 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 : 132-135

Leptalpheus melendezensis sp. n. Figs 6, 7, 8, 9

Material examined.

Holotype: Male (CL 4.1 mm), Meléndez Island, Santa María-La Reforma, Sinaloa, Mexico, 24°48'07"N, 108°03'22.3"W, sand, 0.2 m at low tide, January 18, 2015, (EMU-10582). Paratype: 1 male (CL 2.9 mm), same data as holotype, (EMU-10583).

Diagnosis.

Frontal margin of carapace broadly rounded, weakly produced, without dorsal crests. Antenna with carpocerite longer than scaphocerite, slightly shorter than antennular peduncle. Major cheliped slender; ischium armed with strong ventromesial spine directed upward; fingers slightly twisted laterally, not gaping when closed; without adhesive discs; dactylus with strong proximal tooth on cutting edge, tip acute, crossing distally with tip of pollex; propodus of pereopods 3 and 4 with two ventral spines; propodus of fifth pereopod with two distal rows of setae on ventral margin.

Description.

Frontal margin of carapace (Fig. 6A) broadly rounded, obtuse, weakly produced, carapace smooth, without dorsal crests or carina; eyestalks with anteromesial margin rounded.

Antennular peduncles (Fig. 6A) moderately stout, flattened dorsoventrally; second article longer than broad; stylocerite appressed, not reaching distal margin of first article of the antennular peduncle; ventromesial carina (Fig. 6C) terminating in an upward curving tooth projected beyond the carina; lateral flagellum with two articles.

Antenna (Fig. 6B) with stout basicerite bearing strong distoventral tooth. Scaphocerite (Fig. 6A, B) ovate, with acute distolateral tooth reaching beyond the anterior margin of blade, blade with mesial margin curved; carpocerite longer than scaphocerite, slightly shorter than antennular peduncle.

Mouthparts not dissected, typical for genus in external view. Third maxilliped (Fig. 6D) with lateral plate on coxa produced upward, not reaching the distal margin of the branchiae; ultimate article with rows of brush-like setae increasing in size distally; exopod longer than first article.

Major cheliped (Fig. 7 A–D) slender; ischium armed with strong ventromesial spine directed upward; merus slender, with concave depression along ventral margin, ventral margin minutely granulated; carpus short, cup-shaped, dorsally convex, with two distoventral processes, the external blunt and the mesial tooth-like; chela robust, longer than merus; palm 2.5 times as long as fingers, ventrally depressed, narrowing distally, ventral margin with sparse tubercles, dorsal margin smooth; without adhesive discs; fingers slightly twisted laterally, not gaping when closed; pollex with proximal half ventrally deflexed, outer cutting edge (Fig. 7C) armed with two teeth, distal stronger, mesial margin with proximoventral low tubercle and a shallowly excavated projection along proximal two thirds, tip acute, directed upward; dactylus noticeably curved, dorsum smooth, cutting edge with strong proximal tooth, tip acute, crossing distally with tip of pollex.

Minor cheliped (Fig. 7E, F) with segments unarmed; merus almost as long as chela ; carpus short; fingers pointing, slightly longer than palm, median portion of cutting edges armed with 4-5 small, irregularly spaced teeth, tips crossing distally.

Second pereopod (Fig. 8A) unarmed; ischium 0.75 as long as merus; merus shorter than carpus; carpus 5-articulated, articles ratio from proximal to distal approximately 6:2:2:1:4; distal portion of chela with long setae.

Third and fourth pereopods (Fig. 8B, C) similar, compressed; third pereopod slightly longer and stouter than fourth, merus slightly longer than combined length of carpus and propodus, ventrodistal margin of carpus with ventrodistal spine, propodus with 2 spines on median and distal ventral margin and sparse long setae along margins; dactylus curve, slender, acute distally, nearly half as long as propodus.

Fifth pereopod (Fig. 8D) slender, not compressed, ventral margin of propodus with 1 median spiniform seta and distal margin with two rows of setae, distalmost larger; dactylus acute, curved.

Male second pleopod (Fig. 6E) with slender appendix masculina, with two subterminal and four terminal setae; appendix interna 0.75 length of appendix masculina (Fig. 6F).

Telson (Fig. 6G) widest in proximal third, slightly tapering distally, dorsal surface with two pairs of strong spines inserted in deep pits close to lateral margins, posterior margin rounded, with two pairs of spiniform setae at posterolateral angles, lateral one much shorter than mesial one, posterior margin with 4 plumose setae.

Uropod (Fig. 6H) with lateral lobe of protopod ending in two small lobes; exopod with posterodistal margin straight, deeply incised, with a large spine near mesial margin.

Habitat.

Sandy beach, associated with burrows of N. tabogensis .

Distribution.

Known only from Meléndez Island, Bahía Santa María-La Reforma, Sinaloa, Mexico.

Etymology.

The name of the species is derived from Meléndez Island, the type locality.

Remarks.

Leptalpheus melendezensis sp. n. seemed to be related to L. mexicanus because the general plan of major cheliped of both species is similar; they both have a curved, slender merus, short carpus and ventrally depressed manus, narrowing distally, with sparse ventral tubercles and convex dactylus with a strong proximal tooth. However, a detailed analysis reveals differences between the species. The ischium of the major cheliped in L. melendezensis sp. n. bears a noticeable ventromesial spine, while in L. mexicanus it is absent; pollex and dactylus of the major cheliped do not gape in the new species but form a wide open gape in L. mexicanus ; the pollex of the major cheliped in L. mexicanus is ventrally convex and spoon-shaped at distal end, whereas in the new species it is ventrally concave, with a lateral projection along proximal two thirds and acute at its distal end. Other differences are that the carapace of L. mexicanus has an acute, carinate triangular rostrum and two small orbital crests above the eyes, whereas in L. melendezensis sp. n. the carapace has a blunt, scarcely projected rostrum without a median carina and without supraocular crests; the tooth on the antennular ventromesial carina is more anteriorly projected in the new species; the propodus of pereopods 3 and 4 of L. melendezensis sp. n. bears only two ventral spines as opposed to three in L. mexicanus ; and the fifth pereopod has two distal rows of setae instead of four as in L. mexicanus .

Leptalpheus melendezensis sp. n. is the eighth species assigned to the genus in the eastern Pacific and the fourth recorded from the Pacific coasts of Mexico, and is the only eastern Pacific species of Leptalpheus that presents a major cheliped without adhesive disks and isquium armed with a ventromesial spine.

Phylogenetic relationships.

The 16S matrix of Leptalpheus molecular data consisted of 688 characters. This relationship had a bootstrap support of 64 (Fig. 9). Also an insertion of five base pairs (TATTT) was identified which was not found in other Leptalpheus sequences.

The phylogenetic analysis presented here is a partial contribution to establish a phylogeny of the genus due to the almost total absence of genetic information from other species described in previous works, however this approach and morphological analysis provide sufficient information to recognize that L. melendezensis represent a species new to science.