Leptalpheus sibo, Scioli & Robles & Felder, 2024

Scioli, Justin A., Robles, Rafael & Felder, Darryl L., 2024, New species and records of the symbiotic shrimp genus Leptalpheus Williams, 1965, with notes on Fenneralpheus Felder & Manning, 1986, and preliminary molecular analysis of phylogenetic relationships (Crustacea: Decapoda: Alpheidae), Zootaxa 5466 (1), pp. 1-72 : 58-63

publication ID	https://doi.org/ 10.11646/zootaxa.5466.1.1
publication LSID	lsid:zoobank.org:pub:B43F7FDA-5E3B-4153-A991-E2A96E582A3B
persistent identifier	https://treatment.plazi.org/id/03DF87CE-FF84-FF97-8CC4-FEA64CE6EA3A
treatment provided by	Plazi
scientific name	Leptalpheus sibo
status	sp. nov.

Treatment

Leptalpheus sibo n. sp.

( Figs. 31–34 View FIGURE 31 View FIGURE 32 View FIGURE 33 View FIGURE 34 )

Leptalpheus sp. 2 .— Robles, 2005: chapter 3, table 1.

Leptalpheus sp. 6 aff. mexicanus .— Anker et al., 2006b: table 1.

“ Leptalpheus ” nov. sp. D.— Felder et al., 2003: table 3.

Type material. Holotype: female (cl 5.4 mm) [major cheliped morphotype B], ULLZ 18270 View Materials [ USNM 1705351 View Materials ], Nicaragua, Pacific coast, León, Las Peñitas, coll. D.L. Felder & R. Robles, 27.09.2000 . Paratypes: 1 male (cl 7.6 mm) [major cheliped morphotype B], ULLZ 18238 View Materials [ USNM 1705350 View Materials ], same locality as holotype, coll. D.L. Felder & R. Robles, 27.09.2000 ; 1 male (cl 6.6 mm) [major cheliped morphotype B], ULLZ 18284 View Materials [ USNM 1705352 View Materials ], same locality as previous, coll. D.L. Felder & R. Robles, 27.09.2000 ; 1 male (cl 5.7 mm) [major cheliped morphotype B], ULLZ 5175 View Materials [ USNM 1540784 View Materials ], same locality as previous, with Lepidophthalmus natesi (host catalog no. ULLZ 5174 View Materials [ USNM 1540783 View Materials ), coll. D.L. Felder & R. Robles, 27.09.2000 ; 1 male (cl 7.4 mm) [major cheliped morphotype B], ULLZ 18219 View Materials [ USNM 1705349 View Materials ], Pacific coast, León, Puerto Sandino, Playa La Garita , Salinas Grandes estuary, with Lepidophthalmus sp. , coll. J.A. Cuesta, R. Robles & I.T. Rodriguez.

Additional material. Nicaragua: 1 female (cl 8.4 mm) [major cheliped morphotype A], ULLZ 18227 View Materials [ USNM 1706493 View Materials ], Pacific coast, León, Las Peñitas, coll. D.L. Felder & R. Robles, 14.08.2001 ; 1 male (cl 7.7 mm) [major cheliped morphotype A], ULLZ 18269 View Materials [ USNM 1706508 View Materials ], same locality as previous, coll. D.L. Felder & R. Robles, 27.09.2000 ; 2 ovigerous females (cl 7.6, 8.4 mm) [major cheliped morphotype A], ULLZ 18283 View Materials [ USNM 1706519 View Materials ], same locality as previous, coll. D.L. Felder & R. Robles, 27.09.2000 .

Description. Frontal margin of carapace broadly rounded, without rostral projection or orbital crests ( Fig. 31a, b View FIGURE 31 ). Carapace glabrous; branchiostegal margin with narrow folded lip; lip broadest posteriorly and gradually tapering in breadth anteriorly; pterygostomian angle rounded, very shallowly projecting anteriorly. Telson 1.5–2 times as long as basal breadth, gradually tapering in breadth through length; distal margin shallowly arcuate, 0.4–0.6 times as broad as basal margin; dorsal surface bearing two pairs of spiniform setae; anterior pair inserted at 0.25–0.35 of length of telson from base; posterior pair inserted at 0.55–0.7 of length of telson from base; posterolateral margins with two pairs of spiniform setae; mesial pair 4–5 times length of lateral pair ( Fig. 31c View FIGURE 31 ).

Antennular peduncles moderately stout; stylocerite somewhat appressed against first article, with subacute tip not reaching distal margin of first antennular article; ventromesial carina bearing subacute, anteriorly directed ventral tooth; second antennular article 2.5–3.5 as long as broad; secondary ramus of lateral flagellum furnished with aesthetascs beginning on article 7–8 ( Fig. 31a–c View FIGURE 31 ). Antennal peduncles subequal in length to antennular peduncles; basicerite bearing broad, subacute ventrolateral tooth, tip of latter distally distally reaching or nearly reaching distal margin of stylocerite; scaphocerite broad, oval-shaped, 2.5–3 times as long as widest breadth, bearing small, subacute distolateral tooth; carpocerite somewhat broad, 3.5–5 times as long as widest breadth, distally overreaching scaphocerite ( Fig. 31a, b View FIGURE 31 ).

Mouthparts somewhat typical for genus. Mandible with 2-segmented palp; molar process small, bearing rows of minute, stiff setae; incisor process bearing 6 teeth ( Fig. 31e View FIGURE 31 ). Maxillule with bilobed palp ( Fig. 31f View FIGURE 31 ). Maxilla with dorsal endite bearing deep groove; scaphognathite somewhat broad, palp present ( Fig. 31g View FIGURE 31 ). First maxilliped with small palp; exopod with expanded caridean lobe; epipod bilobed ( Fig. 31h View FIGURE 31 ). Second maxilliped with broad, roughly oval-shaped epipod ( Fig. 31i View FIGURE 31 ). Third maxilliped with developed arthrobranch; lateral plate slender, elongate, distally reaching or nearly reaching half-length of antepenultimate article, with subacute tip; exopod long, reaching distal margin of or overreaching antepenultimate article; ultimate article shorter than antepenultimate article, bearing transverse rows of setae on mesial face, with blunt tip ( Fig. 31j View FIGURE 31 ).

Major cheliped slender; ischium bearing subacute subtriangular projection on ventromesial margin; merus very slender, 6.5–7.5 times as long as maximum breadth, with ventral margin concave to accommodate chela when folded; ventrolateral, ventromesial and dorsal margins of merus all lined with minute tubercles throughout length; carpus short, cup-shaped, with two subtriangular projections on distoventral margins; chela slender, tapering in breadth distally, bearing numerous minute tubercles throughout ventral half; adhesive disks absent; fingers 0.25– 0.35 palm length; dactylus and pollex both curving ventrolaterally throughout length, each bearing 16–19 small, rounded teeth on cutting margins; teeth on margins gradually decreasing in size distally through length; fingers not gaping when closed ( Fig. 33 View FIGURE 33 ).

Minor cheliped distinctly smaller than major cheliped; ischium unarmed; merus relatively slender, 5.5–8 times as long as maximum breadth, with concave ventral face to accommodate chela when folded; ventrolateral, ventromesial and dorsal margins smooth; carpus short, cup-shaped; chela slender, 5–5.5 times as long as maximum height; fingers subequal in length to palm; ventral margin slightly concave at base of fingers; dactylus and pollex with with raised cutting margins bearing minute, subacute medial projections; tips distally crossing when closed ( Fig. 32a, b View FIGURE 32 ).

Second pereopod slender, with merus slightly longer than ischium; carpus subdivided into five articles, with article ratio approximately 13: 2: 3: 2: 5; fingers of chela subequal in length to palm, bearing sparce setal tufts ( Fig. 32c View FIGURE 32 ). Third pereopod laterally compressed; ischium unarmed; merus unarmed, 4–5.5 times as long as maximum height; carpus 0.35–0.45 length of merus, bearing distoventral spiniform seta, with distodorsal margin projecting over carpo-propodal articulation; propodus bearing 3 spiniform setae along ventral margin; dactylus taping in breadth to acute, simple tip ( Fig. 32d View FIGURE 32 ). Fourth pereopod similar to third, but slightly slenderer ( Fig. 32e View FIGURE 32 ). Fifth pereopod slender, not compressed; ischium short, unarmed; merus slender, 4.5–5.5 times as long as maximum height; carpus slender; propodus bearing 4–5 transverse rows of grooming setae on lateral face and minute spiniform seta in middle of ventromesial margin; dactylus simple, with acute tip ( Fig. 32f, g View FIGURE 32 ).

Male second pleopod with long, slender appendix masculina, latter 1.5–2 length of appendix interna, bearing apical setae ( Fig. 32h View FIGURE 32 ). Uropod with bilobed protopod; lateral lobe of protopod with shallow concavity on distal margin; uropodal exopod with truncate distal margin; uropodal endopod bearing distal caudal appendix composed of 1–8 articles ( Fig. 31k View FIGURE 31 ).

Variation. Similarly to L. ankeri n. sp., two distinct major cheliped morphotypes were present among specimens of L. sibo n. sp. The type specimens exhibited the armature of the dactylus and pollex described above, which resembled morphotype B of L. ankeri n. sp. (major cheliped morphotype B). Specimens listed above as additional material exhibited a form similar to L. ankeri n. sp. morphotype A: dactylus with 1–3 small, obtuse proximal teeth, a deep, large, plunger-like medial tooth, and 3–5 minute, obtuse subapical teeth; pollex distally overreaching dactylus, bearing proximal, rounded tooth, medial large, subtriangular to subrectangular projection, and 3–4 rounded, minute subapical teeth; tip of pollex strongly curving laterally (major cheliped morphotype A) ( Fig. 34 View FIGURE 34 ).

Color in life. Not recorded.

Etymology. The specific name is in reference to Sibö (also referred to as Sibú), the god of wisdom and creator of the Earth in the mythology of several Central American indigenous groups, including the Chorotega people, who are indigenous to Pacific Nicaragua, Honduras, and Costa Rica; used as noun in apposition.

Type locality. Las Peñitas , León, Pacific coast, Nicaragua .

Distribution. Known only from the Pacific coast of Nicaragua.

Ecology. Obligate burrow cohabitant of the callichirid ghost shrimp Lepidophthalmus natesi Felder & Robles, 2015 .

Remarks. Leptalpheus sibo n. sp. morphologically closely resembles the western Atlantic L. ankeri n. sp., and it is likely that these two species represent transisthmian sister species. As was the case in L. ankeri n. sp., we found two distinct major cheliped morphotypes among specimens of L. sibo n. sp. without any intermediate forms, and specimens exhibiting the two morphotypes did not otherwise morphologically differ. Major cheliped morphotype did not correspond to sex, as we report both males and females of each morphotype. Unlike L. ankeri n. sp., specimens of morphotype A of L. sibo n. sp. reported herein were larger-bodied than specimens of morphotype B (cl 7.7–8.4 mm for morphotype A vs. cl 4.6–7.6 mm for morphotype B). However, as we were only able to examine eleven total specimens of L. sibo n. sp., we cannot confidently speculate on whether the two forms truly correspond to body size.

We were able to generate few genetic data for L. sibo n. sp., as we only obtained 16S and COI sequences from a single paratype with major cheliped morphotype B. The 16S sequences with the smallest pairwise distances from this species were those of L. ankeri n. sp. from the Caribbean Sea (1.1–1.6% divergence), supporting the hypothesis that these two species form a transisthmian sister species pair. However, COI pairwise distances between L. sibo n. sp. and L. ankeri n. sp. (9.3–9.7% divergence) were overlapping with distances between L. sibo n. sp. and L. degravei n. sp. (8.8–9.6%). As a result, our phylogenetic analysis failed to confirm the sister species relationship, as it did not confidently place this sequence beyond being within the L. forceps species group ( Fig. 1 View FIGURE 1 ). Unlike the case L. ankeri n. sp., we were not able to compare genetic data from the two morphotypes of L. sibo n. sp. However, given the lack of genetic differentiation between the two morphotypes in the western Atlantic species, we conclude that it is likely that the two forms of L. sibo n. sp. represent a single, polymorphic species. As in the case of L. ankeri n. sp., we conservatively restrict the type series of L. sibo n. sp. to specimens of a single morphotype in case later evidence supports the specific delimitation of the two forms. As we have more specimens of morphotype B and a genetic sequence for this form, specimens of this morphotype constitute the type series, while specimens of morphotype A are listed as additional material.

Leptalpheus sibo n. sp. is a member of the L. forceps species group, which also contains L. forceps , L. marginalis , L. mexicanus , L. ankeri n. sp. and L. degravei n. sp. It can be morphologically distinguished from all species of Leptalpheus and related genera outside of this group except for L. melendezensis , by the combination of the following characters: (1) the absence of adhesive disks on the major cheliped, (2) the elongate lateral plate of the third maxilliped, and (3) the presence of a distinct subtriangular projection on the ventromesial margin of the ischium of the major cheliped.

Both morphotypes of L. sibo n. sp. can be distinguished from L. forceps and the morphologically similar L. degravei n. sp. by the armature of the fingers of the major cheliped, which bear a series of small, subacute teeth in the proximal half and are gaping in the distal half in the latter two species.

Leptalpheus melendezensis , which is presently only known from the Gulf of California, differs from L. sibo n. sp. in the stouter proportions of the antennular peduncle (second article approximately 1.5 times as long as broad in L. melendezensis vs. 2.5–3.5 times as long as broad in L. sibo n. sp.) as well as the dentition of the cutting edges of the minor chela (bearing 4 or 5 irregularly spaced acute teeth in L. melendezensis vs. bearing only a small, subacute median projection in L. sibo n. sp.). The major cheliped of L. melendezensis somewhat resembles morphotype A of L. sibo n. sp., but differs in the absence of both small, rounded proximal teeth on the margin of the dactylus and subapical teeth on the margins of the dactylus and pollex (compare Fig. 34 View FIGURE 34 vs. Salgado-Barragán et al. 2017: fig. 7A–D).

The western Atlantic L. marginalis closely resembles specimens of L. sibo n. sp. morphotype B but can be distinguished based on the presence of dorsal processes on the proximal articles of the antennal flagella (which are absent in L. sibo n. sp.). Also, specimens of L. marginalis from Colombia and some specimens from Brazil possess dorsal crests on the carapace, which are not present in any specimens of L. sibo n. sp.

The eastern pacific L. mexicanus can be easily distinguished from both morphotypes of L. sibo n. sp. by its unique major cheliped morphology, which exhibits strongly curved fingers that very broadly gape distally (see Ríos & Carvacho 1983: fig. 2).

The most morphologically similar species to L. sibo n. sp. is the western Atlantic L. ankeri n. sp., for reasons discussed above. We were only able to detect small differences in the dentition of both cheliped morphotypes of these two species. Morphotype A of L. sibo n. sp. possesses 1–3 small proximal rounded teeth on the cutting margin of the dactylus, whereas morphotype A of L. ankeri n. sp. always only possesses one small proximal tooth (compare Fig. 34d–f View FIGURE 34 vs. Figs. 5d View FIGURE 5 , 11f View FIGURE 11 ). The cutting margins of the fingers of the major cheliped in morphotype B of L. sibo n. sp. consistently had more teeth than in morphotype B of L. ankeri n. sp. (16–19 teeth in L. sibo n. sp. vs. 8–15 teeth in L. ankeri n. sp.). It is entirely possible that additional collections will yield specimens that expand these ranges of variation, revealing that these subtle distinctions are invalid, and that the eastern Pacific and western Atlantic species are morphologically indistinguishable.