Leptalpheus mexicanus Ríos & Carvacho, 1983

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 : 51-52

Leptalpheus mexicanus Ríos & Carvacho, 1983

Leptalpheus mexicanus Ríos & Carvacho, 1983: 306 , figs. 1–3.— Ríos, 1992: 7; Campos et al., 1995: 176.— Ramos, 1995: 131, fig. 1.— Robles, 2005: chapter 3, table 1.— Lazarus-Agudelo & Cantera-Kintz, 2007: 228.— Salgado-Barragán et al., 2014: 580 , fig. 6.

Leptalpheus cf. mexicanus .— Salgado-Barragán et al., 2017: 149 .

Leptalpheus bicristatus Anker, 2011: 19 , figs. 15–17. [New synonymy]

Material examined. Panama: 1 male (cl 4.3 mm), MNHN-IU-2011-5243 [holotype of L. bicristatus ], Pacific Coast, Chame Bay, estuarine mudflat with fringing mangroves, low tide, in perforated mangrove wood with Upogebia spp. , coll. A. Anker & J.A. Vera Caripe, 07.11.2006. Mexico: 2 males (cl 5.7, 6.0 mm), ULLZ 5177 [ USNM 1540786], Pacific coast, Baja California Sur, Puerto San Carlos, sandy beach with Neotrypaea and Upogebia burrows, coll. R. Robles & J.A. Cuesta, 03.12.2001; 2 males (cl 3.5, 4.3 mm), 1 female (cl 2.7 mm), ULLZ 5178 [ USNM 1540787], same locality as previous, coll. R. Robles & J.A. Cuesta, 04.12.2001. Nicaragua: 1 female (cl 4.2 mm), ULLZ 18228 [ USNM 1706494], Pacific coast, León, Las Peñitas, coll. D.L. Felder & R. Robles, 14.08.2001.

Description. See Ríos & Carvacho (1983) for the description of a small, possibly juvenile specimen. For the description of a larger specimen, see the description of Leptalpheus bicristatus by Anker (2011).

Color in life. Semitransparent with faint bluish tinge; red-purple chromatophores present throughout antennal and antennular peduncles, uropods, telson, major cheliped, dorsal surface of carapace, and anterior margins of abdominal somites where they are organized in transverse bands; walking legs semitransparent, without chromatophores (see Anker 2011: fig. 17).

Type locality. Estero Mulegé , Baja California Sur, Mexico .

Distribution. Tropical eastern Pacific region: Baja California Sur and Sinaloa, Mexico ( Ríos & Carvacho 1983; Ríos 1992; Campos et al. 1995; Salgado-Barragán et al. 2014; 2017; present study), Nicaragua (present study), Panama ( Anker 2011; present study), and Colombia ( Ramos 1995; Lazarus-Agudelo & Cantera-Kintz 2007).

Ecology. Obligate burrow cohabitant of axiidean and gebiidean mud and ghost shrimps: associated with Upogebia dawsoni Williams, 1986 in Baja California Sur ( Ríos 1992; Campos et al. 1995), Upogebia macraryae Williams, 1986 and Upogebia veleronis Williams, 1986 in Panama ( Anker 2011), and with Neotrypaea tabogensis ( Sakai, 2005) in Sinaloa ( Salgado-Barragán et al. 2017).

Remarks. This species was described based on relatively small-bodied specimens (cl 2.9–3.5 mm) from Baja California Sur, Mexico ( Ríos & Carvacho 1983). A morphologically similar species, L. bicristatus , was later described from a somewhat larger specimen (cl 4.3 mm) ( Anker 2011). Leptalpheus bicristatus was distinguished from L. mexicanus based on five morphological characters: (1) the presence of crests on the dorsal surface of the carapace above the eyes in L. bicristatus (vs. absent in L. mexicanus ), (2) the shape of the lateral lobe of the uropodal protopod, which is more acute in L. mexicanus , (3) the less produced rostral projection of L. bicristatus , (4) the relative proportion of the first carpal article of the second pereopod, which is longer in L. bicristatus , and (5) the relative proportions of the major cheliped, which is stouter in L. bicristatus . A reexamination of the type specimens of L. mexicanus by the third author determined that they did in fact possess minute crests on the dorsal surface of the carapace, which were not illustrated or mentioned in the original description (see Salgado-Barragán et al. 2014: fig. 6E, F). Specimens of L. mexicanus from Sinaloa reported by Salgado-Barragán et al. (2014) both possess these crests and have uropodal protopods more closely resembling the description of L. bicristatus than L. mexicanus , thus invalidating characters 1 and 2 and bringing the validity of L. bicristatus into question. Salgado-Barragán et al. (2014) also questioned the utility of characters 3–5 in distinguishing species, as they may represent intraspecific variation. Despite these conclusions, they declined to synonymize L. bicristatus with L. mexicanus , instead suggesting molecular data would be necessary to resolve this question.

The specimens reported above from Baja California included both individuals with and without crests on the dorsal margin of the carapace. The specimen reported above from Nicaragua lacked these crests. The margin of the lateral lobe uropodal protopod varied among specimens from Mexico, with some having a broader, “U” shaped margin as illustrated in the description of L. bicristatus and others having a more acute, “V” shaped margin as illustrated in the description of L. mexicanus . With respect to the other characters, specimens herein reported as L. mexicanus more closely matched the description of L. bicristatus than the description of L. mexicanus . One possible explanation for this is that the type specimens of L. mexicanus may be juveniles or subadults, and therefore some anatomical proportions differ from larger individuals.

As discussed above, a 16S sequence amplified from the holotype of L. bicristatus was minimally divergent from those of specimens of L. mexicanus from Mexico. Due to this result, in conjunction with the morphological trends outlined, we synonymize L. bicristatus with L. mexicanus .

All specimens of L. mexicanus listed herein have projections on the ventromesial margin of the ischum of the major cheliped, differing from the type description of this species, which stated that the ischium of the major cheliped is unarmed. Some of these projections were compressed and subacute, like in other members of the L. forceps species group, such as L. ankeri n. sp., L. degravei n. sp., and L. forceps . Others more closely resembled a large tubercle, as was described in L. bicristatus (see Anker 2011: fig. 16D). The absence of this structure in the original description may be the result of it being damaged or possibly overlooked. This character is present in all other members of the L. forceps species group, to which L. mexicanus belongs.