Description of two new epigean species of the genus Hyalella S.I. Smith, 1874 (Crustacea: Amphipoda: Hyalellidae) from Jalisco, Mexico

Abstract Two new species of Hyalella S.I. Smith, 1874 are described from state of Jalisco, Mexico. Hyalella marysolae sp. nov. can be identified by the presence of small projections or carinae on pleonites 1−2, with the first antenna being composed of 12 articles and the second antenna being composed of 15 articles. The first maxilla bearing 2−3 distal pappose setae, and the propodus in male first gnathopod is hammer-shaped. Conversely, in H. morronei sp. nov., dorsal projections or carinae are absent on pleonites 1−2, with the first antenna being composed of 10 articles and the second antenna of 14 articles. The first maxilla always bears two distal pappose setae, and the propodus in male first gnathopod is hatchet-shaped. Both species are distinguishable from other Hyalella species found in Mexico by the second antenna. In these two species, the second antenna is approximately half as long as the total body length, and the peduncle comprises 14 −15 articles; whereas, in other Mexican species, it is shorter and composed of maximum 12 articles. Here, we add two species to the four previously described in Mexico as it is necessary to increase the knowledge of the alpha taxonomy of this group of crustaceans and compensate for the biodiversity of the genus being underestimated.


INTRODUCTION
Studies on freshwater amphipods in Mexico are scarce, with most of them focusing on subterranean environments (Marrón-Becerra et al., 2014).Nevertheless, Hyalella S.I. Smith, 1874 is a ubiquitous element of the epigean freshwater communities in Mexico, and other parts of the Americas.The genus Hyalella comprises a widespread group of freshwater endemic amphipods from the Americas, with distribution from Alaska, United States, all the way to Patagonia, Argentina (Bousfield, 1996;Gonzalez and Watling, 2002).More than 90 species have been formally described, most of which inhabit South America, especially Brazil with 37 species (Rangel et al., 2022).Because of their abundance in several water bodies, those amphipods are a key link in the nutrient and matter cycling, transferring energy from microorganisms, or primary producers, to higher trophic levels, such as birds, fish, reptiles, and macroinvertebrates (Brown and Fredickson, 1986;González and Watling, 2003;Gonzalez et al., 2006;Rogers et al., 2010;Wellborn and Cothran, 2004).Due to their ubiquity, crucial role in the trophic web, and close relation with sediment, most studies on these organisms focus on ecotoxicological experiments concerned with heavy metals and chemicals, including medicine or pesticides effects (Novoa-Luna et al., 2016;Poynton et al., 2018).Meanwhile, the alpha taxonomy of the group is still largely unknown, and its real biodiversity underestimated.

Study area
During a recent population study of crayfish of the genus Cambarellus Ortmann, 1905 in Jalisco, two previously undescribed species of Hyalella were collected from the El Tajo and Teuchitlán streams which empty into La Vega Dam, a RAMSAR site since 2010 (SEMADET, 2014) (Fig. 1).
The El Tajo stream is a narrow and shallow stream near the town of Teuchitlán, in the middle of corn and sugarcane fields with macrophytes in the surrounding littoral zone.In contrast, the Teuchitlán stream is located in the middle of the town and is somewhat wider (6 m) and deeper (1.3 m) with floating vegetation, such as Lemna sp. or Pistia stratiotes L., 1753.

Sampling
The material examined was collected using a 50 cm diameter net with 0.50 cm mesh size at 30 cm depth, near the roots of macrophytes.Then organisms were stored in 90% ethanol.The temperature (°C), dissolved oxygen = DO (mg/l), salinity (‰), and pH were measured with a YSI 556 multiparameter instrument with a precision of 0.01 units.

Identification
The total body length of the amphipods was measured following the dorsal outline of the body, from the base of the first antenna to the base of the telson, using an ocular micrometer, calibration slide, and segmented tool line in ImageJ software (following Gonzales and Watling, 2002;James and McClintock, 2017).The appendages were dissected and mounted on semi-permanent glycerol slides and permanent Entellan® slides to be described, drawn, and measured with an ocular micrometer.For the identification of morphological characteristics, the same pattern as the previous descriptions of Hyalella from Mexico was used.Descriptions were based on the holotypes, considering the variations within the paratypes.Namely, the following characteristics were analyzed; the relative length of appendages, number, shape, and arrangement of the setae of the mouthparts, antennae, gnathopods, pereopods, uropods, and telson following Gonzales and Watling (2002), Marrón-Becerra et al. (2014), Soucek et al. (2015), Marrón-Becerra et al. (2018), andMarrón-Becerra et al. (2020).The whole specimens were examined under a Leica M125 stereomicroscope equipped with a camera lucida.Mouthparts and appendages were examined under a Leica DM100 compound microscope also equipped with a camera lucida.The terminology used for the setae follows Zimmer et al. (2009).Illustrations were digitized in Adobe Illustrator 24.0.The morphological variation observed among specimens of each species is reported.The type material is deposited in the Colección Nacional de Crustáceos (CNCR), at the Instituto de Biología, on the Universidad Nacional Autónoma de México (UNAM).The distribution map was made using QGIS 3.16 (QGIS, 2021) software.Etymology.This species is named in honor of Montserrat Marysol Ayón, the beloved daughter of the third author.
Head typically gammaridean (Fig. 2A), with smooth surface, total length less than the combined length of the first 2 pereonites, reaching half of second pereonite, rostrum absent.Eyes pigmented, medium, rounded, and black, located between the insertions of antennae 1 and 2.
Antenna 2 (Fig. 2A, C) almost 1.4 times longer than antenna 1, almost half of total body length, almost reaching seventh pereonite; peduncle almost reaching middle of third pereonite, articles gradually increasing in length and decreasing in width, article 5 longer than article 4 (about 1.5 times); flagellum with 15 articles, longer than peduncle (about 1.5 times); flagellum without aesthetascs.Mouthparts: upper lip (Fig. 3A) distal margin rounded, with numerous setules, being longer and more distant towards lateral end.Lower lip (Fig. 3B) subquadrate, outer lobes without notches or excavations; mandibular projection of outer lobes rounded; without inner lobes.
Left and right mandibles (Fig. 3C, D) without palp, asymmetric.Incisor with 6 teeth.Left lacinia mobilis similar to incisor process, with 5 teeth; setal row on left mandible with 3 main pappose setae plus accessory setae.Right lacinia mobilis more reduced than left, with 2 pairs of asymmetric L-shaped teeth, fused at base, proximal pair longer than distal, inner margin denticulate; near lacinia mobilis base with setules on inner margin; setal row on right mandible with 2 main pappose setae plus accessory setae and with setulae near molar process.Molar process large, cylindrical, and triturative; accessory pappose setae present in both molars.
Maxilla 1 (Fig. 3E, F) palp short, vestigial, uniarticulated, longer than wide, distally pointed with 1 short stout distal seta, reaching less than half of palp length, palp length less than half distance between base of palp and base of seta on outer plate; inner plate slender, shorter than outer plate, with 2−3 pappose apical setae; outer plate with 9 apical stout serrate setae and with setules.
Maxilla 2 (Fig. 3G) plates subequal in length, width, and shape; inner plate shorter and slightly slender, with 2 pappose setae on mid-distal margin, and with 5 long serrulate setae on distal margin; outer and inner plates with large simple distal setae (type A2) and abundant setules on both distal surfaces and margins.
Maxilliped (Fig. 3H) inner plate lobe longer than outer plate lobe; distal margin slightly convex; inner plate distal margin with 3 cuspidate setae of equal size and with plumose setae, inner margin with several pappose setae; outer plate, inner and distal margins with numerous simple setae.Palp composed of 4 articles subequal in maximum length; first article with 3−4 simple setae at inner distal end and 2 setae at outer distal end; second article with numerous simple setae on inner margin and 2−3 at outer distal end; third article with several setae on distal margin, distal end on outer margin with 4−7 simple setae and comb scales, inner margin with at least 8 setae and 6 at distal end; fourth article unguiform, slightly longer than nail, with comb scales, inner margin with 4 setae near distal half, outer margin with 1 seta near nail base; nail overreaching two-thirds of fourth article in length, with serration on distal half.Gnathopod 1 (Fig. 4A) subchelate, propodus hammer-shaped, shorter than gnathopod 2. Basis elongated, maximum length 3−3.5 times longer than maximum width; medial seta absent, posterior distal end with cluster of 2 setae.Ischium short, subquadrate, longer than wide, length almost same as maximum width of basis and maximum length of merus; distal posterior end with 1 cluster of 2 setae.Merus longer than wide, almost at midway of posterior margin with comb scales; almost at distal margin with 3−8 setae.Carpus longer than wide, slightly longer and wider than propodus, with strong, short, and wide posterior lobe forming 1 scoop-like structure open to inside; mesial surface of lobe with 2−5 serrate setae, outer surface on distal half of lobe, near margin, with comb scales and serrate setae (10), anterior distal end with 7−9 simple setae.Propodus maximum length almost 1.5 times longer than wide; inner surface near distal margin with 3−5 serrate setae in 1 row; distal anterior end with 2 clusters of approximately 5 setae; distal half of anterior and posterior surfaces with comb scales; posterior margin with 1 medial seta; palm transverse, Marrón-Becerra et al.
posterior distal end with 1 robust seta and cup for dactyl.Dactyl claw-like; nail present; anterior surface near proximal third with 1 plumose seta, with comb scales on anterior surface.
Gnathopod 2 (Fig. 4B) subchelate.Basis elongate, 4 times longer than wide; posterior margin with 1 slender seta.Ischium short, subquadrate, as long as merus.Merus short; distal end of posterior margin with 4 simple setae, medial setae absent; distal end with comb scales.Carpus shorter than propodus, length similar to merus maximum length, slightly exceeding 1.5 times the width of merus; anterodistal end with 1−3 simple setae; posterior lobe scoop-like, elongate, almost 1.5 times width of merus, with several submarginal pappose setae and comb scales.Propodus robust, ovate, 1.5 times longer than maximum width; palm oblique, shorter than posterior margin; slope slightly irregular, with several long simple setae, few short and medium setae; distal margin of palm with 1 truncated process near insertion of dactyl and with presence of 1 wide posterior excavation at base; palm posterior distal end with 2 robust setae, comb scales, and cup for dactyl.Cup for dactyl as long as space between the inner end of cup and truncated process.Dactyl claw−like, congruent with palm, occupying less than half of cup of dactyl without comb scales; outer margin proximal third with 1 plumose seta; inner margin slightly crenulated with separated setules.
Pereopod 3 (Fig. 5A), basis elongate; posterior margin with 1 simple seta; anterodistal and posterodistal ending with simple setae.Ischium subquadrate; posterodistal end with one pair of setae.Merus longer than ischium (almost 2.5 times maximum length); anterior margin with 1 robust seta; posterior margin with 5 slender simple setae (2 clusters of 2 setae plus 1 separated seta); anterodistal and posterodistal ends with 1 cluster of 4 slender setae, anterodistal end with 1 robust seta.Carpus shorter and more slender than merus; posterior margin with 4−5 stout setae plus accessory setae; posterodistal end with at least 2 slender setae; anterodistal end with at least 2−3 setae.Propodus shorter than anterior margin of merus, more slender than carpus; posterior margin with 5−6 stout setae plus accessory seta; anterodistal end with 3−5 simple setae.Dactyl claw-like, length more than half of propodus; nail present; first proximal third of anterior margin with 1 plumose seta; anterior and posterior margins with 1 simple seta near base of nail.
Pereopod 7 (Fig. 5F) basis lobe widely expanded posteriorly, overreaching ischium distal margin; wider than lobes of pereopods 5 and 6; basis lobe, width almost 2.2 times as wide as basis (measured at cleft between basis and basis lobe); posterior margin with 10−11 serrations, each with 1 setule, without stout seta on distal margin; anterior margin with 3 stout setae and 1 at distal end.Dactyl length less than half of propodus.
Uropod 3 (Fig. 6C) slightly longer than peduncle of uropod 2; peduncle subrectangular, wider than ramus with 4 robust distal cuspidate setae of variable length (1 with accessory seta, type B6); inner ramus absent, outer ramus uni-articulate, slender, slightly longer than peduncle, about 2 times length of the larger seta of peduncle, basal width about 2 times apex width of ramus, with 3−7 slender apical simple setae and 1 connate seta.Telson (Fig. 6D) entire, as long as wide or wider than long, distal margin rounded or truncated with 2 long simple setae widely separated; dorsal surface bearing 2 clusters of 3 plumose setae near middle distal portion, near lateral margin, symmetrically distributed.
Description of paratypes females.Females mean body size 4.8 ± 0.6 mm, cephalothorax length 0.55 ± 0.12 mm.Gnathopod 1 (Fig. 4C), carpus with 5 setae on inner face lobe; propodus with a row of 5 setae on inner face.Gnathopod 2 (Fig. 4D) smaller than male gnathopod 2, parachelate; palm reverse oblique.Basis posterior margin with 1 seta.Propodus 2.6 longer than maximum width; outer face with 2 setae in 1 row and 2 large setae near palm, with 3 medial setae on mid-posterior surface; anterior and posterior distal half with comb scales.Pereonite 2 with 1 anterior excavation or notch for amplexus.Pereopod 7 lobe with 11 serrations and setules, without stout setae on distal margin.Oostegites subtriangular, with curled setae on margins, almost reaching half of length of merus.Telson similar in shape to male.
Intraspecific variation.The number of articles in the flagellum of antennae 1−2 is variable, increasing proportionally with body size.The length of antenna 2 can posteriorly reach one-third of the sixth pereonite or almost reach the seventh.The length of the flagellum of antenna 2 varies from 1.3 to 1.5 times as long as the peduncle.The palp of maxilla 1 can be different between individuals or even between right and left side on the same individual, from one third to more than half of the length from the base of palp to the base of setae on the outer plate.Also, the number of setae on the inner plate of maxilla 1 can be 2−3.The number of setae in the first and third article of maxilliped is variable.The basis of the first gnathopod can be 3−3.5 times as long as wide.Some individuals bear an extra robust medial cuspidate seta on the peduncle of uropod 3, like in Hyalella wakulla wakulla (Drumm and Knight-Gray, 2019).Moreover, the distal margin of the telson varies from rounded to truncated.
Remarks.Hyalella marysolae sp.nov.exhibits two short dorsal projections or carinae on pleonites 1−2, barely visible, this characteristic is also in H. azteca, H. cenotensis, H. maya, H. tepehuana, and H. wakulla from North America, and it is not in the species from South America but, unlike H. marysolae sp.nov., in the species from North America the projections or carinae are evident.The presence or absence of projections or carinae was long considered a crucial feature to distinguish the species of the genus.The most morphologically similar species to H. marysolae sp.nov. is H. morronei sp.nov., despite the absence of projections or carinae in this last species (described below).Both species share characters, such as: the number of articles in the antennae 2 (more than 13), the relative length of antennae 2 and the body, and the form of the eyes that distinguish them from the other species from Mexico (Tab.1).Nevertheless, several differences can be observed between both species, for example: H. marysolae sp.nov., the palp of maxilla 1 presents setules; the length of the head relative to the second pereonite is smaller in H. marysolae sp.nov.than in H. morronei sp.nov.; H. marysolae sp.nov.has one pair of aesthetascs on the articles 4−11 of the flagellum of antenna 1, while H. morronei sp.nov.has one aesthetasc on articles 1, 5, 8, 9 and one pair on articles 6−7; in H. marysolae sp.nov., the propodus of the gnathopod 1 is hammer-shaped, while in H. morronei sp.nov. it is hatchet-shaped; the propodus maximum length relative to the width of gnathopod 1 is greater in H. marysolae sp.nov.than in H. morronei sp.nov.(1.5× vs. 1.25×, respectively); and the telson is wider than long in H. marysolae sp.nov.and longer than wider in H. morronei sp.nov.(Tab.1).
Habitat and conservation.This species was collected near the sediment and in the roots of macrophytes in the littoral zone.It is important to mention that the habitat of this species is threatened by anthropogenic activities.Water is regularly extracted from the El Tajo stream to maintain surrounding crops of corn and sugarcane.This process generates runoff of herbicides and chemicals (urea) into the stream (M.A.-P., pers.observation).
Diagnosis.Pleonites 1−2 without dorsoposterior carina.Coxa 4 excavated posteriorly.Eyes pigmented, black.Antenna 1 shorter than antenna 2, without accessory flagellum.Antenna 2 less than half of body length, almost reaching the seventh pereonite.Maxilla 1 palp short, reaching less than half of length between base of palp and tip of setae of outer plate, with 1 short stout distal seta and without setules; inner plate slender with 2 strong pappose apical setae.Maxilla 2 inner plate with 2 strong pappose setae on inner margin and serrate setae on distal margin.Gnathopod 1 propodus hatchet-shaped, palm with transverse slope, inner face with 4 serrate setae, comb scales on distoposterior and distoanterior border, carpus inner face lobe with 2 serrate setae.Gnathopod 2, basis hind margin with 1 slender seta, merus without medial seta, palm with wide excavation.Uropod 1 male inner ramus without curved setae.Uropod 3, ramus longer than peduncle, styliform and with 5 cuspidate setae.Telson as long as wide, or longer, distal margin rounded or truncated with 2 long simple setae widely separated.Sternal gills on segments 3−7.Table 1.

Comparison between the closest Mexican species of the genus
Hyalella.

Cont.
Head typically gammaridean (Fig. 7A), with smooth surface, total length less than the combined length of first two pereonites, reaching two-thirds of second pereonite, rostrum absent.Eyes pigmented, medium, subquadrate, and black, located between the insertions of antennae 1 and 2.
Antenna 2 (Fig. 7A, C) almost 1.4 times longer than antenna 1, almost half of total body length, almost reaching seventh pereonite; peduncle reaching third pereonite, articles gradually increasing in length and decreasing in width, article 5 longer than article 4 (about 1.3 times); flagellum with 14 articles, longer than peduncle (about 1.8 times); flagellum without aesthetascs.Mouthparts: upper lip (Fig. 8A) distal margin rounded with numerous setules, being longer and more distant towards lateral end.Lower lip (Fig. 8B) subquadrate, outer lobes without notches or excavations; mandibular projection of outer lobes widely rounded; without inner lobes.
Left and right mandibles (Fig. 8E, F) without palp, asymmetric.Incisor with 6 teeth.Left lacinia mobilis similar to incisor process, with 5 teeth; setal row on left mandible with 3 main pappose setae plus accessory setae.Right lacinia mobilis more reduced than left, with 2 pairs of asymmetric L-shaped teeth, fused at base, proximal pair subequal to distal, inner margin denticulate; near lacinia mobilis base with setules on inner margin; setal row on right mandible with 2 main pappose setae plus accessory setae and with setulae near molar process.Molar process large, cylindrical, and triturative, accessory pappose setae in both molars.
Maxilla 1 (Fig. 8C) palp short, vestigial, uniarticulated, longer than wide, distally pointed with 1 short stout distal seta, reaching less than half of palp length, setules absent; palp length less than half distance between base of palp and base of seta on outer plate; inner plate slender, shorter than outer plate, with 2 pappose apical setae; outer plate with 9 apical stout serrate setae and with setules.
Maxilla 2 (Fig. 8D) plates subequal in length, width, and shape; inner plate shorter and slender, with 2 pappose setae on mid-distal margin, and with simple setae and 5 long serrulate setae on distal margin; outer and inner plates with large simple distal setae (type A2) and few setules on both distal surfaces and margins.
Maxilliped (Fig. 8F) inner plate lobe longer than outer plate lobe; distal margin slightly convex; inner plate distal margin with 3 cuspidate setae of equal size and with plumose setae, inner margin with several pappose setae; outer plate, inner and distal margins with numerous simple setae.Palp composed of 4 articles subequal in maximum length; first article with 2−4 simple setae at inner distal end and 2 setae at outer distal end; second article with numerous simple setae on inner margin and 2−3 at outer distal end; third article with several setae on distal margin, distal end on outer margin with 7 simple setae and comb scales, inner margin with at least 8 setae and 6 at distal end; fourth article unguiform, longer than nail, with comb scales, inner margin with 5 setae near distal half, outer margin with 1−2 setae near nail base; nail almost half length of fourth article, with serration on distal half.
Gnathopod 1 (Fig. 9A) subchelate, propodus hatchet-shaped, shorter than gnathopod 2. Basis elongated, maximum length almost 3.3 times longer than maximum width; medial seta absent, posterior distal end with cluster of 2 setae.Ischium short, subquadrate, longer than wide, length longer than maximum width of basis, and as long as maximum length of merus; distal posterior end with 1 cluster of 2 setae.Merus longer than wide, at one-third of the posterior margin with comb scales; almost at distal margin with 3−6 setae.Carpus longer than wide, longer and slightly wider than propodus, with strong, short, and wide posterior lobe forming one scooplike structure open to inside; mesial surface of lobe with 2 serrate setae, outer surface with comb scales and serrate setae (10−12), anteriodistal end with 5 simple setae.Propodus maximum length 1.25 times longer than wide; inner surface near distal margin with 4 serrate setae in 1 row; distal anterior end with 2 clusters of approximately 5 setae; distal half of anterior and posterior surfaces with comb scales; palm transverse, posterior distal end with 1 robust seta and cup for dactyl; posterior surface, near distal third with 1 long, simple seta.Dactyl claw-like; nail present; anterior surface near proximal third with 1 plumose seta, with comb scales on anterior surface.
Gnathopod 2 (Fig. 9B) subchelate.Basis elongate, more than 3 times longer than wide; posterior margin with 1 slender seta.Ischium short, subquadrate, as long as merus.Merus short; distal end of posterior margin with 4 simple setae, medial setae absent; distal quarter of posterior inner and outer surfaces with comb scales.Carpus shorter than propodus, length similar to merus maximum length, slightly exceeding 1.5 times width of merus; anterodistal end with 2 simple setae; posterior lobe scoop-like, elongate, almost 1.5 times width of merus, with several submarginal pappose setae and comb scales.Propodus robust, subrectangular, 1.5 times longer than maximum width; palm oblique, as long as posterior margin; slope slightly irregular, with several long simple setae, few short and medium setae; distal margin of palm with 1 truncated process near insertion of dactyl and with 1 wide posterior Marrón-Becerra et al.

Two new species of Hyalella from Jalisco, Mexico
Nauplius, 31: e2023010 excavation at base; palm posterior distal end with 2 robust setae, comb scales, and cup for dactyl.Cup for dactyl as long as the space between it and the truncated process.Dactyl claw-like, congruent with palm, occupying less than half of cup of dactyl, without comb scales; proximal third of outer margin with 1 plumose seta; inner margin slightly crenulated with separated setules.Pereopods 3−7 (Fig. 10A, E) simple, gradually expanding posteriorly.Pereopod 5 shorter than 4 and 6.
Pereopod 3 (Fig. 10A) basis elongate; posterior margin with 1 simple seta; anterodistal and posterodistal ends with simple setae.Ischium subquadrate; posterodistal end with 1 pair of setae.Merus longer than ischium (almost 2.5 times the maximum length); anterior margin without robust seta; posterior margin with 4 clusters of slender simple setae (3 clusters of 2 setae plus 1 single separated seta); anterodistal and posterodistal ends with 1 cluster of 3−4 slender setae, anterodistal end with 1 robust seta.Carpus shorter and more slender than merus; posterior margin with 4 stout setae plus accessory setae; posterodistal end with at least 4 slender setae; anterodistal end with at least 2 setae.Propodus shorter than anterior margin of merus, more slender than carpus; posterior margin with 7 stout setae plus accessory seta; anterodistal end with 6 simple setae.
Dactyl claw-like, length less than half of propodus; nail present; first proximal third of anterior margin with 1 plumose seta; anterior and posterior margins with 1 simple seta near base of nail.

Two new species of Hyalella from Jalisco, Mexico
Nauplius, 31: e2023010 Uropod 2 (Fig. 11B) longer than peduncle of uropod 1; peduncle as long as rami or slightly shorter, with 2 dorsal cuspidate setae (with accessory seta) on distal half and 1 cuspidate seta at distal end; rami subequal, inner ramus slightly longer with 2 dorsal cuspidate setae with accessory seta and 5 cuspidate distal setae with accessory seta, outer ramus with 2 dorsal cuspidate setae with accessory seta and up to 4 distal cuspidate setae, the 3rd cuspidate seta is shorter with accessory seta.
Telson (Fig. 11D) entire, as long as wide, distal margin rounded with 2 long simple setae widely separated; dorsal surface bearing 2 clusters of 3 plumose setae near middle distal portion, near margin, symmetrically distributed.
Intraspecific variation.The peduncle of antenna 1 in some individuals of this species is as long as or even longer than the head (reaching half of the first pereonite).In maxilla 1, the palp nearly reaches or overreaches half of the distance between the base of the palp and the base of serrate seta on the outer plate.The telson can be as long as wide or longer.Remarks.One notable morphological feature of H. morronei sp.nov. is the hatchet-shaped propodus of gnathopod 1, which is 1.25× as long as wide (less than twice the maximum width), which distinguishes this species from the other species from Mexico (Tab.1).This morphology of gnathopods has been observed in hyalellids species from South America, including e.g.hyalellids from Chile (Gonzalez, 2003); therefore, H. morronei sp.nov.constitutes the first North American species to exhibit this morphology.
Hyalella morronei sp.nov.can be easily distinguished by the length of the flagellum of the antenna 2, it is almost twice the length of the peduncle, in other species from Mexico it is 1.1×−1.5×(Tab.1).The most morphologically similar species to H. marysolae sp.nov. is H. morronei sp.nov.and the differences are described above.H. morronei sp.nov.and H. marysolae sp.nov.have more articles in the flagellum of antenna 2 (14 and 15 articles, respectively) and the antenna reaches the seventh pereonite; in contrast, in other species from Mexico, the flagellum is shorter and has 8-12 articles (Tab.1).Additionally, the form of the eyes in H. morronei sp.nov.and H. marysolae sp.nov.are subquadrate, whereas in H. azteca are rounded, in H. maya and H. tepehuana are subtriangular, and in H. cenotensis are absent (Tab.1).
H. cheyennis Bueno, Oliveira and Wellborn, 2019 from Oklahoma, USA, as H. morronei sp.nov., lacks projections or carinae on pleonites 1−2; in addition, both species have serrated setae on maxilla 2, and in the male gnathopod 2, the palm of propodus is as long as the posterior margin.However, these two species are separated from each other by the shape of the propodus of gnathopod 1: in H. morronei sp.nov. it is hatchet-shaped and in H. cheyennis is hammer-shaped.Moreover, H. morronei sp.nov.has one slender seta on the posterior margin of the basis of pereopods 3−4, while H. cheyennis has two setae; H. morronei sp.nov.lacks distal robust setae on the lobe of pereopod 7, and H. cheyennis has three robust setae; H. morronei sp.nov.has less robust setae on peduncles of uropods 1−2 (three and two robust setae, respectively), and H. cheyennis has six on uropod 1 and five cuspidate setae on uropod 2; and the ramus of uropod 3 is longer than the peduncle in H. morronei sp.nov., which is shorter in H. cheyennis.Type locality.Teuchitlán stream (Fig. 1A, D), La Vega reservoir, Teuchitlán, state of Jalisco,Mexico (20°41'11.15"N 103°50'36.43"W).
Habitat and conservation.This species was collected from the water column, associated with the roots of Lemna sp., although the predominant vegetation was water lettuce Pistia stratiotes L., 1753.As in the case of H. marysolae sp.nov., the habitat of this species is also threatened by anthropogenic activities.The Teuchitlán stream is impacted by caustic soda waste, molasses, cane bagasse, domestic plastics, and sewage discharge generated by the Teuchitlán people, in addition to nitrogen fertilizers from sugarcane crops (RAMSAR, 2018).Documenting the diversity of species of highly impacted freshwater environments such as the Teuchitlán stream, is a crucial task as increased anthropogenic activity may threaten the biodiversity of these habitats.
In summary, the new species in the state of Jalisco described in this paper, H. marysolae sp.nov.and H. morronei sp.nov., can be distinguished from all other Hyalella species present in Mexico by several morphological characters, including the length of the antenna 2 being approximately half as long as the body length, composed of 14-15 articles, and the relative length of the ramus in the uropod 3, which is longer than the peduncle.The length of the antenna 2 distinguishes these species from those found in North America, except for Hyalella longicornis Bousfield, 1996, which has less than 16 articles in the flagellum of antennae 2, and more than 5 setae on the posterior margin of the basis of both gnathopods.In contrast, H. marysolae sp.nov.and H. morronei sp.nov.have only one simple seta.
The findings concerning these two species contribute to highlighting the hidden diversity of the genus by showing that the biodiversity in the group is underestimated and increases to six the total number of species from Mexico.It is important to emphasize the need for further studies within this group of freshwater amphipods due to their importance in environmental and toxicological research, and secondly to record the unknown species before their habitat is lost.It is important to underline that we could preserve the unknown biodiversity of the group by enhancing the policies to protect freshwater bodies and raising awareness of water issues in the local communities. zoobank.org/urn:lsid:zoobank.org:act:68D260B8-6FD1-4440-9156-1CBB0BE15FF0

Figure 1 .
Figure 1.Type localities.(A) Location of streams El Tajo and Teuchitlán, La Vega system.Teuchitlán, state of Jalisco, Mexico; (B) El Tajo stream, arrow shows the sample site; (C) La Vega dam; (D) Teuchitlán stream, arrow shows the sample site.