ILYOCRYPTUS PARANAENSIS INARMATUS SUBSP. NOV. FROM TABASCO, MEXICO (CLADOCERA, ANOMOPODA) BY ALEXEY A. KOTOV 1,3 /, MANUEL ELÍAS-GUTIÉRREZ 2,4 / and MARTHA GUTIÉRREZ-AGUIRRE 2,5 / 1 / A. N. Severtsov Institute of Ecology and Evolution, Leninsky Prospect 33, Moscow 117071, Russia 2 / El Colegio de la Frontera Sur, Km 2 Carretera Chetumal-Bacalar, Zona Industrial #2, Chetumal, Quintana Roo 77000, Mexico
ABSTRACT Ilyocryptus paranaensis Paggi, 1989 is found at four localities in the basin of the Usumacinta River, Tabasco, southern Mexico. A new subspecies I. paranaensis inarmatus subsp. nov. is established for Mexican populations of this species. Probably, this subspecies is an endemic with a distribution restricted to the Usumacinta basin. The differences between the new subspecies and the nominate form are discussed.
RÉSUMÉ Ilyocryptus paranaensis Paggi, 1989 a été trouvé dans quatre localités de bassin de l’Usumacinta, Tabasco, au sud du Mexique. Une nouvelle sous-espèce, I. paranaensis inarmatus subsp. nov. a été établie pour les populations mexicaines de cette espèce. Cette sous-espèce est probablement endémique, avec une répartition limitée au bassin de l’Usumacinta. Les différences entre la nouvelle sous-espèce et la forme nominale sont discutées.
INTRODUCTION
Studies on the Cladocera of Mexico have rendered numerous discoveries of biogeographical interest, as a mixture of Nearctic and Neotropical fauna is found in this country (Elías-Gutiérrez et al., 1997; Elías-Gutiérrez et al., 1999). Also, several new species have been described (cf. Ciros-Pérez et al., 1996; Ciros-Pérez 3 / Present address: El Colegio de la Frontera Sur, Km 2 Carretera Chetumal-Bacalar, Zona Industrial
#2, Chetumal, Quintana Roo 77000, Mexico; e-mail:
[email protected] 4 / Author for correspondence; e-mail:
[email protected] 5 / e-mail:
[email protected] c Koninklijke Brill NV, Leiden, 2001 °
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& Elías-Gutiérrez, 1997a), including a new genus (Ciros-Pérez & Elías-Gutiérrez, 1997b), and many new records have otherwise been added as well (e.g., ElíasGutiérrez et al., 2001a). Among ilyocryptids, the list of species known includes only Ilyocryptus agilis Kurz, 1878, I. spinifer Herrick, 1882, and I. nevadensis Cervantes-Martínez, Gutiérrez-Aguirre & Elías-Gutiérrez, 2000. In this paper, we describe a new subspecies of Ilyocryptus paranaensis Paggi, 1989, a taxon related with the South American form that was described from the Paraná River (Argentina). This species is well-characterized by a complete moulting and the presence of horn-like protuberances on each valve, among other features.
MATERIAL AND METHODS
Material for this study was collected on 31.i.1999 by M. Gutiérrez-Aguirre, A. Cervantes-Martínez, A. García-Morales, and C. Quintal-Lizama from four permanent pools (locally called Pulsar, Popalillo, Leona Vicario, and Guanal), all of which are located in the basin of the Usumacinta River. The location is situated near Balancan, a small town in Tabasco State, near the Guatemala border. The main physical and chemical variables of each pond are summarized in table I. Sampling was carried out with a hand-held net of 50 ¹m mesh. Water was ltered directly from the system, including sites with submerged and/or oating vegetation. In case of the presence of the water hyacinth (Eichhornia sp.), i.e., in Pulsar and Guanal, roots were squeezed through the net. All animals from the type-locality were isolated from the sample, washed in distilled water, and used for morphometric investigations. The following measurements were made with the aid of a Nikon Alphaphot microscope (for parthenogenetic females): body length (BL), height (BH), and width (BW); head length (HL) and
TABLE I Geographic coordinates and main physical and chemical variables from each locality were Ilyocryptus paranaensis inarmatus subsp. nov. was found; in all cases, the date of collection was 31 January, 1999 Locality
N
W
Depth Secchi Water Dissolved pH Apparent (m) disk temp. oxygen colour (m) (± C) (mg/l)
Pulsar pool Popalillo pool Guanal pool Leona Vicario lagoon
17± 390 1000 17± 470 5700 17± 450 1000 17± 420 5400
91± 330 2300 91± 320 0600 91± 310 1900 91± 320 5300
0.67 1.25 2.79 2.5
0.30 0.41 0.42 0.88
28.8 26.2 28.6 29.9
1.6 1.3 1.6 1.6
6.5 8 8 7
grayish brown dark green green brown
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width (HW); eye diameter (ED); valve length (VL); number of marginal elements (NE); number of setae in antero-ventral bunch (NB); number of setae with single basal spines (NS); maximal length of a seta on postero-ventral valve portion (PV); postabdomen length (from base of claws to base of postabdominal setae) (PL) and height (PH); anus length (AN); length of preanal part of postabdomen (PR); number of preanal teeth (NT) and large, paired spines on distal part (NP); number of large (NL), medium-sized (NM), rudimentary (NR) lateral setae, length of the largest spine (SP) and the largest lateral seta (LA) on postanal part of postabdomen; postabdominal claw length (CL); length of more distal (DS) and more basal spine (BS) on base of claw; number of distal denticles on claw (DD); rudimentary, additional denticles on middle part of claw (AD); postabdominal (“natatorial”) seta length (SN); length of the basal segment of postabdominal seta (BA); antennule length (AL) and maximal diameter (DA), and its proximal segment length (PS); length of second antenna (without apical setae) (SL); length of exopod (EX) and its apical spine (AS), length of endopod (EN) and its apical spine (AP); length of third exopod segment (TH) and of spine on its second segment (SE); maximal length of apical swimming seta (SW) of second antenna, length of proximal lateral swimming seta on antennal exopod (PX).
This outline is in accordance with Kotov & Dumont (2000). After that, some relative values were calculated for each animal. Three specimens from the typelocality were placed on slides in a glycerol-formaldehyde mixture, and then dissected under a stereoscopic microscope for the study of their appendages and postabdomen. Drawings were prepared using a camera lucida attached to an Alphaphot compound microscope.
TAXONOMY
Ilyocryptus paranaensis paranaensis Paggi, 1989 Ilyocryptus paranaensis Paggi, 1989: 240-245, gs. 1-39. Holotype. — Adult parthenogenetic female, preserved in glycerol-formalin mixture (9/1), deposited in the collection of the Instituto Nacional de Limnologia, Santo Tomé, Argentina. Paratypes. — Three adult parthenogenetic females in the same collection. Type-locality. — Unnamed, weedy oxbow at Island Los Sapos, in the lower course of the River Salado near Santo Tomé, Paraná River basin, Province of Santa Fe, Argentina.
Distribution. — Paraná River basin, Argentina (Paggi, 1989), Orinoco River basin, Venezuela and Paraguay (Štifter, pers. comm.). The complete distribution of this form in South America is as yet unclear. Re-worked species diagnosis. — Adult parthenogenetic female: Body high and wide, with lateral horns. Depression between head and valves from very shallow to distinct. Postero-dorsal angle expressed, low dorsal keel present. Moulting complete. Reticulation not visible, instead of this, there are numerous small pits on whole valve surface. Head in dorsal view narrow, triangular-ovoid. Valves large, ovoid, brood pouch strongly in ated. With 51-61 setae along free valve margin, four anterior ones sparsely located. Next 4-5 setae assembled in a bunch, these setae more or less longer than following setae of ventral margin. Each seta of
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posterior edge with a single stout spine at base. Postabdomen with dorsal margin bilobed. Maximal height in the middle. Length of preanal part of postabdomen more or less equal to that of postanal one. Ten to twelve preanal single teeth of subequal size, located at approximately right angle to postabdomen margin. Denticles on postabdomen base present or greatly reduced. Postanal part with 5-7 large lateral setae on it. This row never reaching preanal margin. Postabdominal claws slightly and regularly bent, distally with 1 or 2 denticles. Claw armed with 2 basal spines on dorsal side, with distalmost thicker and shorter than proximal one. Additional row of denticles in middle portion of claw. A group of short setules ventrally on claw base. First antennae medium sized. Proximal segment with nger-like projection and more or less developed system of hillocks. Distal segment with slightly expressed transverse ridges, or without those, but without any denticles. The longest aesthetasc longer than half the distal segment. Distal sensory seta on basal segment of second antenna long, distal burrowing spine reaching distal end of basal segment. Antennal branches short and massive. Spines on apical segments long, of subequal size. Length of a spine on second segment of exopod approximately half the length of the third segment. Apical swimming setae short, armed with short setules. Lateral seta on rst endopod segment shorter than the one on the second segment. Both lateral setae asymmetrically plumose, without hooks on tips. Limb I without large seta near bases of ejector hooks. Limb VI with six dense bunches of setules. Size up to 925 ¹m. Ilyocryptus paranaensis inarmatus subsp. nov. Holotype. — Adult parthenogenetic female (total length 760 ¹m), preserved in alcohol 70%, deposited in The Natural History Museum, London (BMNH 2001.6634). Label of holotype: “Ilyocryptus paranaensis inarmatus subsp. n., Pulsar pond, 17± 390 1000 N 91± 330 2300 W, Tabasco, Mexico, 1 parth. , 760 ¹m, HOLOTYPE”. Paratypes. — Six females, preserved in alcohol 70%, deposited in The Natural History Museum, London (BMNH 2001.6635-6640); six females, preserved in 70% alcohol, deposited in El Colegio de la Frontera Sur (ECOSUR), Chetumal, ECO-CH-ZOO-01162; six females, preserved in the same medium, deposited in the Zoological Museum of Moscow University (Ml-19). Additional material. — Two parthenogenetic females from Popalillo lagoon; one from Leona Vicario pond, and two from Guanal pond, all of these in alcohol 70%, and deposited in El Colegio de la Frontera Sur, Chetumal, ECO-CH-ZOO-01163-65. Original samples are also in this collection.
Etymology. — The name “inarmatus” means “un-armed” in Latin; it was given due to the slight expression or absence of denticles on the base of the postabdomen, and the complete absence of spinules on the inner face of the carapace margin. Subspecies diagnosis. — Depression between head and valves distinct. Surface of valves smooth; instead of with wavy lines, entirely covered by small pits. In adults, the setae in the antero-ventral bunch are only slightly longer than following setae. Spinules at valve margin absent on inner surface. Denticles on base of
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postabdomen completely absent, or at least greatly reduced. Basal segment of antennule with system of hillocks, distal segment without transverse ridges. Spine of second segment of antennular exopod bisegmented, with pointed, setulate distal segment. Description Parthenogenetic female. — General: in lateral view, body more or less ovoid, more elongated in juveniles (BH/BL D 0.66-0.73), and high in adults (BH/BL D 0.77-0.85), maximum height of body in its middle or middle-posterior portion ( gs. 1, 3, 7, 10). Depression between head and rest of body well expressed, as a result dorsal margin not forming regular arch, postero-dorsal angle expressed, although not clearly visible. Animal thick (BW/BL D 0.55-0.65), maximum width of body in the middle or mid-dorsal portion of valves ( gs. 2, 4, 8). In anterior view, body ovoid or heart-shaped in juveniles ( gs. 5-6), and rhomboid-ovoid in large adults ( g. 9); maximum width of body in middle part, due to the fact that brood pouch is greatly in ated laterally here. Dorsal keel sharp in smaller females, and thick in larger adults. Moulting complete, valves and head shield mono-layered. Body transparent, although carapace covered by detritus particles. Reticulation not visible, numerous small pits on whole valve surface. Lateral horns of different relative length (up to 21% of body length in large adults) slightly anterior to centre of valves ( gs. 7-12). Head long for a representative of the genus (in large females HL/BL D 0.280.33). In lateral view, head triangular-rounded, ventral margin slightly convex, with an especially prominent base of antennules in posterior head portion. A special fold surrounds the base of the labrum. In ventral and dorsal view, head narrow (HW/BL D 0.33-0.36), triangular-ovoid, without any concentric lines. Fornices greatly prominent ( g. 11). Border between head and valves not clear in dorsal view. No dorsal head pore or projection for this opening were found. No reticulation on head. Compound eye (ED D 33-39 ¹m) in middle of distance between anteriormost point and base of antennule, located closely to ventral margin of head. Very small ocellus (2-3 times smaller than eye) near base of antennule. Labrum ( gs. 13-14) wide, subrectangular in ventral view, on each anterior corner there is a blunt lateral projection. Two rows of setules are present in distal portion. In lateral view, labrum seems robust, rectangular, with slightly expressed projection at antero-ventral angle. Labral plate boot-shaped in lateral view. Valves large (VL/BL D 0.71-0.82), widely ovoid. Dorsal part of valves in ated greatly in adults, forming a voluminous egg chamber; as a result the dorsal margin is convex. Anterior, ventral, and posterior margins form a continuous, strongly
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Figs. 1-10. Ilyocryptus paranaensis inarmatus subsp. nov., general view of females from Pulsar pond, Tabasco, Mexico. 1-2, juvenile female I in lateral and ventral view; 3-4, juvenile female in lateral and dorsal view; 5-6, anterior view, and dorsum of other female of similar size; 7-9, holotype, adult female in lateral, dorsal, and anterior view; 10, adult female of maximal size. Scale bars 100 ¹m.
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arched free edge of valve without any angles, armed with a row of marginal setae (NE D 52-61). Four anteriormost setae short, with setulation similar to posterior elements. Posterior to these, a bunch of closely located elements (NB D 4-5), each with in ated base ( gs. 15-17), the largest are only somewhat longer than the more posterior setae of ventral margin (AV/BL D 0.12-0.17); 1-2 anteriormost elements of this bunch directed posteriorly. Next 22-27 setae of approximately equal length, plumose, regularly distributed along ventral edge. Postero-ventral bunch of setules not expressed, although setae here are the longest among all elements of the free margin (PV/BL D 0.15-0.19). Each of next marginal setae on posterior edge with an in ated basal part, armed with a stout, pointed spine (NS D 21-27). Distal part of these setae feathered by sparsely distributed setules ( gs. 18-19). Only last 1-2 setae lacking spines ( g. 20). Thorax long, without external traces of segmentation, with six pairs of limbs. Abdomen ( gs. 21-22) with a very long horn-like abdominal projection on the rst (anteriormost) somite, and the cross rows of setules on the dorsum. Postabdomen large (PL/BL D 0.47-0.52), strongly compressed laterally, height maximal in middle portion (PH/PL D 0.47-0.53). Ventral margin straight, with cross series of small-sized setules in distal portion ( gs. 21-22). Dorsal margin generally convex, but markedly interrupted by anal depression. Anus (AN/PL D 0.13-0.16) opens slightly closer to distal extremity than the base of the postabdomen, or at middle of distance between these structures, no spinules on its internal walls. Preanal margin (PR/PL D 0.50-0.55) of medium size, slightly convex, with special, small base for postabdominal setae posteriorly, followed by a single row of teeth, approximately at right angle with dorsal margin (NT D 10-12), size of teeth subequal. Sparse groups of small lateral spinules present near some of preanal teeth. In the majority of specimens studied there were no spinules on lateral face of postabdomen base, only in three of the largest females, 1-2 denticles could be seen on each side. Postanal margin regularly arched, with a row of spines on each side (NP D 7-9), this row continues on the anal margin, but never reaches the preanal margin. Middle-distal elements slightly longer than the rest. Large lateral setae not numerous (NL D 6-7), proximal and distal ones are slightly shorter than those in the middle (LA/PL D 0.16-0.18). The proximalmost lateral seta located on anal or postanal margin. On the distal part of the postabdomen ( g. 23), the row of lateral setae gradually turns into a bunch of smaller setae (NM D 2-3), the latter, more distally, into two series of rudimentary setae (NR D 7-13). A row of long setules is present at the base of each single lateral seta, also there are smaller setules near spines on anal margin. Postabdominal claws long (CL/PL D 0.41-0.44), narrow, slightly but regularly bent. On the lateral side, three successive series of thin setules along dorsal margin.
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Figs. 11-24. Ilyocryptus paranaensis inarmatus subsp. nov., adults from Pulsar pond. 11, head and anterior part of valves in ventral view; 12, lateral horn on valve of other specimen of similar size; 13-14, labrum in lateral and ventral view; 15-17, setae at anterior portion of valve margin in three different adults; 18-19, setae at posterior valve margin; 20, setae at postero-dorsal part of valve; 21-22, postabdomens of two adults; 23, distal portion of postabdomen; 24, armature of postabdominal seta. Scale bars 100 ¹m.
One or two denticles are present in the ventral distal part of the claw (DD D 1-2). Also, some series of smaller, additional denticles (AD D 1-3) are on the middle of this part. Two relatively large basal spines are located ventrally on the base of each claw, the distal one shorter in the majority of animals than the proximal one (but always thicker) (DS/BS D 0.93-1.02). A group of relatively short setules ventrally on claw basal border (length markedly less than claw diameter at base).
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Postabdominal (‘natatorial’) setae relatively short compared with those of other Ilyocryptus species, shorter than the body, but longer than postabdomen (SN/PL D 1.50-1.65). Basal segment shorter than distal one (BA/SN D 0.37-0.42). In contrast with the majority of the representatives of the genus, distal segment armed with relatively dense and short hairs ( g. 24). First antenna two-segmented, middle-sized for an Ilyocryptus (AL/BL D 0.160.19 in largest females) and thin (DA/AL D 0.14-0.16), almost straight in transversal plane ( g. 25). Bases of antennules not pressed against each other ( g. 11). Proximal segment short (PS/AL D 0.14-0.16), with elongated, nger-like projection and system of low hillocks on anterior face ( gs. 26-27). Distal segment long, slightly extended in the middle part, without transverse ridges or denticles. Nine aesthetascs of unequal length, two of them remarkably larger that the rest ( g. 28), shorter than the distal segment, but much longer than half its length. One of the longest aesthetascs located rather far from the rest. No spines on distal end of antennule. Second antennae ( gs. 29-30) stout, short for a species of this genus (SL/BL D 0.31-0.39). Coxal part folded, with hairs on posterior side of these folds. In the middle part of “concertina”, two densely setulated sensory setae of different lengths, their length differing more than twofold ( g. 31). Basal segment robust, bearing sparse rows of denticles. Distal sensory seta relatively long, armed with dense setules ( g. 32), located on inner (posterior) face of basal segment closely to its distal end. Distal burrowing spine armed with long, sparse setules, located on outer (anterior) surface far from end of basal segment ( g. 33). Tip of this spine reaching distal border of basal segment. Antennal branches relatively short and massive, on all segments there are denticles around distal segment ends, and several transverse rows of similar denticles. Endopod (EN/BL D 0.11-0.14) with two short basal and one elongated distal segments. Exopod longer than endopod (EX/BL D 0.13-0.15), its basal segment the longest, and its third segment the shortest one. Swimming setae 0-0-0-3/1-1-3, spines 0-1-0-1/0-0-1. All apical swimming setae short (SW/BL D 0.29-0.39), armed with short setules on both sides ( gs. 34-36). Lateral swimming setae of unequal size (PX/BL D 0.28-0.37; DI/BL D 0.22-0.29), both plumose by short setules along one side, and long, sparsely located setules along other side ( g. 37), without hooks on tips. Spines of apical segments long, slightly curved, of subequal length ( gs. 38-41) (AS/BL D 0.08-0.09; AP/BL D 0.07-0.09). Spine on second segment of exopod approximately half of length of third segment (SE/TH D 0.44-0.55), pointed, with short, sparse setules on distal segment ( gs. 42-44). Mandibles robust, relatively thick, with heads slightly dilated. Maxillae I (maxillulae) as a small hillock bearing three long and one short seta ( g. 45). Maxillae II absent.
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Figs. 25-44. First and second antennae of Ilyocryptus paranaensis inarmatus subsp. nov. from Pulsar pond. 25, rst antenna in lateral view; 26-27, proximal portion of rst antenna, and variability of form of nger-like projection; 28, rst antenna in distal view; 29-30, second antenna in anterior and lateral view; 31, sensory setae on coxal portion; 32-33, distal sensory seta and distal burrowing spine of basal segment; 34-35, smallest and largest apical swimming seta of endopod; 36, latter in transversal section; 37, lateral swimming seta of endopod; 38-41, apical spines of exopod (38, 40) and endopod (39, 41) in two adults; 42-44, spine on second segment of exopod in three females. Scale bars 100 ¹m.
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Limb I ( gs. 46-47) with epipodite globular, without a distal projection. Inner portion of limb corm elongated and covered by long setules. The cylindrical outer distal lobe bears a large, setulated seta, plumose more sparsely and unilaterally in basal portion, and densely and bilaterally in distal part. Second seta of outer distal lobe small, bilaterally setulate in its distal portion. Relatively large, bilaterally setulate seta near base of outer distal lobe. Two ejector hooks of different size on anterior face of limb. On the inner edge of limb four setae, armed in different ways. The fth, rudimentary seta, characteristic for the majority of the species of the genus (Kotov, 1999, 2000) was not found. Relatively large element (sensillum?) anteriorly between bases of ventralmost large setae, a very small receptor in the middle of the distance between ejector hooks and ventralmost large seta. Remainder of gnathobase I as setulated hillock on limb base. Limb II ( gs. 48-50) with epipodite as a hillock. Quadrangular distal lobe with two long setae, somewhat different in length and bilaterally setulated from base to top in similar manner, and a small bud-like element. Along inner margin of limb, four plumose setae, size of which gradually decrease in inner direction. Small elements (sensilla) near bases of the second and third setae of row. Inner portion of limb strongly projected, but not in ated as in Ilyocryptus tuberculatus Brehm, 1913 according to Kotov (2000). A curved sensillum at the base of this projection. A single, bisegmented beating seta, armed with short setules in distal part, near gnathobase. Distal armature of gnathobase with four elements: two small setae with fused bases, one longer and feathered, the other a single, naked, bent element. Series of bunches of long setules on gnathobase, too. Filter plate with eight bisegmented setae, identically feathered from base to top. Limb III ( g. 51) with slightly projected pre-epipodite, and subovoid epipodite. Exopodite with ve terminal, differently armed, and three lateral, soft setae, proximalmost of lateral group much larger than the rest and bent backwards. Distal portion of inner limb part forms a lobe, or distal endite. At inner margin three long setae, bilaterally setulated from base to top, middle one markedly larger that the rest. On distal extremity, two smaller and nely plumose setae of similar length. In addition, on distal endite there are one small element near base of the largest seta, and a series of setules. Basal endite with a row of four uniform, soft setae, that continues as a row of soft setae on distal endite. Somewhat posteriorly, a curved element. No beating seta was found. No distinct border between gnathobase (coxal endite) and basal endite. Four bisegmented, differently armed setae in distal armature of gnathobase. Filter plate with 8 elements, and a bunch of long setules inserted basally to it. Limb IV ( gs. 52-54) with large, setulate pre-epipodite and smaller ovoid epipodite. Large subovoid exopodite with 8 feathered setae and groups of setules along its margin. The distalmost seta is the shortest. Distal portion of inner limb
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Figs. 45-57. First maxilla and thoracic limbs of Ilyocryptus paranaensis inarmatus subsp. nov. from Pulsar pond. 45, rst maxilla; 46-47, limb I and its outer distal lobe; 48-50, limb II, its middle portion and distal armature of gnathobase; 51, limb III; 52-54, limb IV, sensillum on distal portion of inner lobe and distal armature of gnathobase; 55-56, limb V, and distal armature of its gnathobase; 57, limb VI. Scale bars 100 ¹m.
part in the form of a at lobe, with ve long and thin setae, bilaterally feathered from base to top on posterior limb face. In inner-distal portion, the row of the other four, rarely setulate setae of similar size, and relatively short, curved sensillum. Near gnathobase a large projection with ne, dense setulation. Distal armature of gnathobase with four elements: a very thick and long seta, fringed bilaterally with
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speci c hyaline fold in its distal part, a long seta, armed asymmetrically in its distal portion, and two bisegmented spines. Filter plate with 8 setae, border between lter plate and row of setae on posterior face of inner limb portion is not clear. Limb V ( gs. 55-56) with relatively small pre-epipodite, epipodite as in limb IV. Large subovoid exopodite armed with seven setae, medium ones shorter than the rest. No setules between two basalmost setae. Inner limb portion as a large, at lobe, its inner margin subdivided into three lobes by small incisions. Row of setules along distal margin continues on posterior surface. Two setulate setae on posterior face of limb. No distinct border between basal endite and gnathobase. Distal armature of gnathobase with 4 elements: a very long, fully setulated, and a short, unilaterally feathered, seta, with short spines near their bases. Filter plate with 4 setae, gradually decreasing in size, and group of robust setules. Limb VI ( g. 57) a trapezium-shaped plate with slightly convex inner margin. Six bunches of setules along that margin, each bunch supported by a very low projection of limb margin, setules in basalmost bunch particularly robust. Ephippial female and male unknown. Size. — Parthenogenetic females 405-925 ¹m (N D 24). Ecology. — All systems where the species was found were shallow, permanent, small water bodies with abundant submerged vegetation and high temperature, but with clear water. Pulsar pond, the locality that yielded most specimens, is an arti cial cow-drinking reservoir. Animals were found in littoral samples, taken across vegetation and muddy bottom.
DISCUSSION
Ilyocryptus paranaensis was known from only tree localities in the Paraná basin (Paggi, 1989). Recently, Štifter (in litt.) found this species in material from Paraguay and Venezuela. The rst description was quite detailed, so we immediately identi ed this species in our material, and it was unexpected to see this taxon far north from the type locality. After detailed examination we found a series of discriminative features of the Mexican specimens (table II). Unfortunately, some features of I. paranaensis s. str. from Argentina (i.e., armature of the postabdominal setae) were not completely described by Paggi (1989), so we are unable to discuss possible differences on this point. Also, it may be that he missed the fourth seta of gnathobase V. So far, no species of Ilyocryptus with less than 4 setae in lter plate V is known. The majority of them has 4 setae (Kotov, 1999; Kotov & Dumont, 2000). Possibly, the second seta of IDL I is also setulate in the typical paranaensis form, but Paggi (1989) gured it as naked.
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TABLE II Differences between the two known subspecies of Ilyocryptus paranaensis Paggi, 1989 Feature
I. paranaensis s. str.
Relative length of lateral horns Up to 0.14 in adults Depression between head and Very shallow valves Setae in antero-ventral bunch Markedly longer than following setae Small spinules on inner side of Present valve Denticles on sides of postab- Present in all specimens domen base Distal segment of postabdomi- ? nal setae feathered with Basal segment of antennule Relatively smooth Distal antennular segment With a few weak transversal ridges in distal portion Spine on 2nd segment of anten- Not segmented, with rounded nal exopod tip, without setules Small seta on IDL I Naked Number of setae in lter plate V 3 (?)
I. paranaensis inarmatus subsp. nov. Up to 0.21 in adults Distinct Only slightly longer Absent Absent in the majority of females, rarely 1-2 denticles Relatively short and densely located setules With system of hillocks Without ridges Bisegmented, with pointed, rarely setulated distal segment Setulated in distal part 4
The systematics of Ilyocryptus have become of interest recently, and its aspects have been restudied, revealing many previously unknown details (Štifter, 1988; Kotov & Dumont, 2000). Because of that, we were able to nd some omissions in Paggi’s (1989) description, although this is one of the best for an ilyocryptid that exists to date (Kotov & Timms, 1998). In spite of these facts, some other features of Mexican populations are of speci c nature and the differences between Mexican and Argentinian populations relate at least to subspecies level, according to the morphology and discontinuity of these populations. The reduction of the slanting row of denticles on the postabdomen base seems to be important for ilyocryptid systematics, because sometimes this is a distinctive trait at species level (Kotov et al., 2001). Also, the Usumacinta river populations lack spinules on the inner side of the valve, but the presence of these in I. paranaensis s. str. seems to be a unique trait for this form within the genus. Presence (or absence) of transverse ridges on the antennules was regarded as a very important feature earlier (Smirnov, 1976), but this feature is not too helpful in the case of an intermediate situation (weak expression of these ridges, as in I. paranaensis s. str.). The distribution of I. paranaensis inarmatus subsp. nov. seems to be restricted to a small part of the basin of the Usumacinta River. It was found in only a few samples from this region, although we studied several other samples from the lower
ILYOCRYPTUS PARANAENSIS INARMATUS NOV.
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Usumacinta. In about 50 samples from the surroundings of this river, I. paranaensis was found only in the localities mentioned above, and always in low numbers. Also, no I. paranaensis populations were found in more than 200 samples from other southern states of Mexico: Yucatan, Quintana Roo, Campeche, and Chiapas. Perhaps, I. paranaensis inarmatus is an endemic of a small region. Most probably, this taxon could be found in the Guatemalan part of the Usumacinta basin in the future. In southern Mexico there are other anomopods, like macrothricids and chydorids, closely related to South American forms. For example, the macrothricids M. mexicanus Ciros-Pérez, Silva-Briano & Elías-Gutiérrez, 1996 and M. smirnovi Ciros-Pérez & Elías-Gutiérrez, 1997, restricted to the highlands of Mexico, are related to the South American M. superaculeata Smirnov, 1982. Interesting South American representatives found in the Mexican southeast are, among others Camptocercus dadayi Stingelin, 1913, Chydorus eurynotus Sars, 1901, Onchobunops tuberculatus Fryer & Paggi, 1972, Alonella brasiliensis Bergamin, 1935, Leydigipopsis brevirostris Brehm, 1938 (cf. Elías-Gutiérrez et al., 2001b). These authors considered about 9% of the Mexican cladoceran fauna to comprise taxa that formerly were exclusively South American. In case of ilyocryptids, the limited fauna known for North America can be further elucidated following recent investigations in Europe (Štifter, 1988; Kotov, 1999), Australia (Kotov & Timms, 1998; Kotov & Dumont, 2000), and South America (Paggi, 1989, 1992; Kotov & Dumont, 2000). This paper, together with others already published (Williams, 1978; Elías-Gutiérrez, 1995; CervantesMartínez et al., 2000; Kotov & Williams, 2000) will contribute to establish the identity of the American ilyocryptid fauna, in many aspects quite different from that of other continents.
ACKNOWLEDGEMENTS
A. A. Kotov thanks the Consejo Nacional de Ciencia y Tecnología (CONACYT) for supporting his stay in Mexico, through the Catedras Patrimoniales program. A. Cervantes-Martínez, A. Morales-García, and C. Quintal-Lizama participated in the collection of material.
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First received 11 April 2001. Final version accepted 22 May 2001.
