Mayaweckelia troglomorpha Angyal

Angyal, Dorottya, Solis, Efrain Chavez, Magana, Benjamin, Balazs, Gergely & Simoes, Nuno, 2018, Mayaweckeliatroglomorpha, a new subterranean amphipod species from Yucatan state, Mexico (Amphipoda, Hadziidae), ZooKeys 735, pp. 1-25 : 5-14

Mayaweckelia troglomorpha Angyal sp. n. Figs 2, 3, 4, 5, 6, 7, 8, 9

Material examined.

Holotype ♂, 10 mm, Nr. 00046, 14 May 2016, Dzonbakal, 20.669819°N, 89.778869°W, San Antonio Mulix, Umán, Yucatán state, México, collected by D. Angyal, R. Acosta, J. Baduy & S. Reyes in cave part, 26.7 m depth in fresh water; dissected and mounted on slide. Collection ID: CNR 34392 (UNAM, Institute of Biology, National Crustacean Collection, México City.)

Allotype ♀, 10 mm, Nr. 00113, 11 June 2016, Cenote Kankirixché, 20.37225°N, 89.632892°W, Mucuyché, Abalá, Yucatán state, México, collected by D. Angyal & E.M. Chávez Solís in cavern part, 20.4 m depth in fresh water; dissected and mounted on slide. Collection ID: HNHM Amphipoda -4094 (Hungarian Natural History Museum, Collection of Crustaceans, Budapest).

Paratypes ♀, 7 mm, Nr. 00056, 14 May 2016, Dzonbakal, 20.669819°N, 89.778869°W, San Antonio Mulix, Umán, Yucatán state, México, collected by D. Angyal, R. Acosta, J. Baduy & S. Reyes in cave part, 26.3 m depth in fresh water; sputter-coated by gold-palladium. Collection ID: HNHM Amphipoda -4095 (Hungarian Natural History Museum, Collection of Crustaceans, Budapest).

♂, 8 mm, Nr. 00043, 4 June 2016, Cenote Kanún, 20.745599°N, 89.244638°W, Homún, Homún, Yucatán state, México, collected by D. Angyal, R. Acosta, J. Baduy, B. Magaña & S. Reyes in cave part, 24.3 m depth in fresh water; not dissected. Collection ID: CNR 34393 (UNAM, Institute of Biology, National Crustacean Collection, México City).

Juvenile, 3 mm, Nr. 00095, 9 June 2016, Cenote Xaan, 20.727571°N, 89.256834°W, Homún, Homún, Yucatán state, México, collected by D. Angyal & E.M. Chávez Solís in cave part, 25.4 m depth in fresh water; not dissected. Collection ID: YUC-CC-255-11-003922 (UNAM, Academic Multidisciplinary Unit of Teaching and Research, Yucatán Crustacea Collection, Sisal).

Juvenile, 5 mm, Nr. 00110, 11 June 2016, Cenote Kankirixché, 20.37225°N, 89.632892°W, Mucuyché, Abalá, Yucatán state, México, collected by D. Angyal & E.M. Chávez Solís in cave part, 33.3 m depth in fresh water; dissected and mounted on slide. Collection ID: HNHM Amphipoda -4096 (Hungarian Natural History Museum, Collection of Crustaceans, Budapest).

Diagnosis.

Medium-sized, eyeless hadziid with conspicuous troglomorphic traits. The first antenna almost twice as long as body and three times as long as the second antenna; gnathopod I propodus palm armed with distally notched spine teeth, carpus more than 1.5 times as long as corresponding propodus, merus as broad as but shorter than carpus, ventrally produced lobe with three long sensory setae; gnathopod II propodus twice as long as propodus I, palm armed with unnotched spine teeth, carpus slightly shorter than propodus on males. Dactylus, propodus. and carpus of pereopods VI-VII extremely long; therefore, pereopods VI and VII are 1.3 times as long as body length; epimeral plates I-III ventro-posterior corner tiny but distinct, ventral margin without robust setae, posterior margins concave; surfaces of uropods I-III pubescent; telson lobes each possess five-six robust setae and one-three slender setae on outer margin and six-seven robust setae on inner margin. Largest males and females both measured 10 mm.

Description.

(10 mm ♂, 8 mm ♂, 8 mm ♀, 7 mm ♀, 5 mm juvenile, 3 mm juvenile.) Antenna 1 (Figures 2, 3) 1.75 times as long as body; three times long as antenna II; primary flagellum with more than 60 articles; aesthetacs were not visible as distal half of the flagellum was missing from each animal (examination of the antennae was possible only using the photos of the living specimens); accessory flagellum with three articles. Antenna II (Figures 2, 3): flagellum with more than 20 articles. Mandibles (Figure 3) subequal; both molar with seta; setal row with four or five serrated setae; palp lacking. Maxilla I (Figure 3): inner plate with approximately 15 apical setae; outer plate with eight apical, pluri-toothed robust setae; second palpal article with five apical robust setae. Maxilla II (Figure 3): inner plate with 15-23 obliquely placed setae on inner margin. Maxilliped (Figure 3): inner plate with four or five cone shaped, thick robust setae and several coarse setae apically; outer plate with stiff setae apically. Lower lip (Figure 3): outer lobes narrowly rounded; lateral process prominent; inner lobes rather small.

Gnathopod I (Figure 4, 5): dactyl thick, single seta present on anterior margin, inner margin without seta, unguis (nail) length 35% of total dactylus length. Propodus small, longer than broad; palm short, slightly convex, in palmar corner double row of four-five distally notched spine teeth always present, additional notched spine teeth and spine-like setae sometimes present on palm, close to the base of dactylus; posterior margin of propodus slightly concave, surface near margin covered with pubescent setae; anterior margin with five-seven rows of long, plumose setae (sometimes singly inserted); antero-distal group with six-eight long plumose and simple setae; four singly inserted helical medial setae always present, sometimes additional singly or doubly inserted medial setae present. Carpus narrow, 1.5-1.7 times longer than propodus. Merus: as broad as but shorter than carpus, ventrally produced into pubescence, conspicuous lobe with three long sensory setae. Sensory papillae visible on one of the setae. Coxal plate I large, deep, longer than broad, broadly rounded ventrally, margin with three-four robust setae and seven-eight slender setae on females and six robust setae and three-eight slender setae on males.

Gnathopod II (Figure 4, 6): dactylus thick, along anterior margin (close to antero-distal corner) a single seta present, inner margin with three-five setae. Propodus twice as long as gnathopod I propodus, narrow, subrectangular; palm length is more than 50% of propodus length on males and less than 50% of propodus length on females; palm armed with double row of five-six unnotched spine teeth which are sometimes accompanied by long, pearl row-like setae; surface near margin covered with pubescent setae; helical seta sometimes present below (proximal to) spine teeth; posterior margin with four-five, anterior margin with six-nine sets of plumose setae; three-four medial plumose setae. Carpus slightly shorter than propodus on males and slightly longer than propodus on females, armed with seven-eight rows of comb-like plumose setae on posterior margin. Merus as broad as but more than two times shorter than carpus; not produced ventrally into conspicuous lobe. Coxal plate II kidney-shaped, margin with three-four robust setae and eight slender setae.

Coxal plate III (Figure 7) rather small and shallow, margin with two fine setae. Coxal plate IV (Figure 7) more than twice as broad as coxal plate III; posterior margin concave, ventral margin with four short stiff setae; dactylus length 28% of propodus; single robust seta and one long slender seta at the base of the unguis. Pereopod V (Figure 7) basis 1.7 times longer than broad, margins convex; pereopods VI (Figure 7) and VII (Figure 7) bases twice as long as broad, margins of pereopod VI slightly convex, posterior margin of pereopod VII straight; dactylus of pereopod V 40% length of corresponding propodus; outer margin with two slender setae; pereopod VI and VII extremely long (especially dactylus, propodus and carpus), 1.3 times as long as body; pereopod VI slightly longer than pereopod VII; pereopod VII dactylus with some short, slender setae at the base of the unguis. Coxal gills (Figure 4) large, almond shaped, pedicellate, present on pereon segments II-VI; oostegites (Figure 4) long, slender. Pleopods (Figs 7, 9) I-III with two-hooked retinaculae.

Epimeral plates I-III (Figure 8) ventro-posterior corner tiny but distinct with one slender seta at the corner; ventral margin without robust setae; posterior margin slightly concave on epimeral plate I, concave on epimeral plate II and strongly concave on epimeral plate III. Urosomites (Figure 8): urosomite I with one strong robust seta at the base of uropod I; urosomite II without robust and slender setae; urosomite III with one robust seta mid-dorsally.

Uropod I (Figures 8, 9) surface of rami and peduncle covered with pubescent setae; outer ramus 10-15% longer than inner ramus, outer ramus 20-33% shorter than peduncle; peduncle with five-eight spine-like robust setae; outer ramus with four-six robust setae (plus five apical robust setae), inner ramus with five-six robust setae (plus five apical robust setae). Uropod II (Figures 8, 9) surface of rami and peduncle covered with pubescent setae; outer ramus 13-22% longer than inner ramus on the studied males and 25-35% longer than inner ramus on females; outer ramus 5-15% longer than peduncle; peduncle with six spine-like robust setae; inner ramus with three-four robust setae (plus five apical robust setae); outer ramus with four-five robust setae (plus five apical robust setae). Uropod III (Figures 8, 9) surface of rami and distal end of peduncle covered with pubescent setae; uropod III 20% as long as body; inner ramus slightly longer than outer ramus, margins with long, singly-inserted plumose and pappose setae and some short robust setae, apex with two short spine-like robust setae; outer ramus with long, plumose setae on inner margin and short robust setae on outer margin toward distal end, apex with three robust setae and sometimes additional with long spine-like seta; peduncle with two-four robust setae.

Telson (Figure 8) cleft to base, each half 2.65 times longer than broad; lobes each with five-six robust setae and one-three slender setae on outer margin and six-seven robust setae on inner margin.

Variability.

Sexes very similar in size and appearance, except a few traits. Propodus I more oblong in males than in females. Coxal plate I margin with six robust setae and three-eight slender setae in males, and with three or four robust setae and seven-eight slender setae in females. Palm length of gnathopod II is more than 50 % of propodus length on males and less than 50 % of propodus length on females. Carpus of gnathopod II slightly shorter than propodus on males and slightly longer than propodus on females. Sexually mature females have long and narrow oostegites. Left and right side gnathopod I and II are unequal in length in both sexes. Outer ramus of uropod II 13-22 % longer than inner ramus on males and 25-35 % longer than inner ramus on females, however this character should be further analysed on an elevated number of individuals of both sexes.

Etymology.

The name troglomorpha refers to the highly adaptive troglomorphic features of the new species, particularly the elongation of appendages, the increased number of sensory setae and papillae, and general appearance of fragility. Gender feminine.

Distribution and remarks on ecology.

The new species is known from four cenotes in the state of Yucatán, covering a distribution distance of 52 km (distance between the farthest cenotes Dzonbakal and Xaan). All the individuals were found in fresh water habitat, in most cases far from the cenote entrances, deeper in the associated cave passages, where sunlight does not penetrate. Water temperature was between 26 and 27 °C. Specimens were collected between 20 and 33 meters depth; in cenote Kankirixché some individuals were observed below 45 meters depth. The new species was represented in all four localities with low abundance, though it proved to be more common and more abundant than M. cenoticola , of which a single specimen was found in only one (Ayun-Nah) of the 14 visited cenotes, during an underwater waste collecting activity, hidden in a plastic soft drink bottle. In the type locality and in cenotes Xaan and Kankirixché the new species co-occurred with the hadziid amphipod Tuluweckelia cernua . Other co-occurring stygobiont macro-crustaceans (in the four cenotes) were the mysid Antromysis cenotensis Creaser, 1936, the stygiomysid Stygiomysis cf. holthuisi (Gordon, 1958), the isopods Creaseriella anops (Creaser, 1936) and Yucatalana robustispina Botosaneanu & Iliffe, 1999, and the decapods Typhlatya mitchelli Hobbs & Hobbs, 1976, Typhlatya pearsei Creaser, 1936, and Creaseria morleyi (Creaser, 1936).

Remarks and affinities to related species and genera.

Holsinger (1990) noted that his original description of M. yucatanensis ( Holsinger 1977) 'was based on what appear to be submature specimens, therefore raising the strong possibility that the differences noted between the two species of Mayaweckelia are due primarily to age’, and the two species probably should be synonymized. However, the synonymisation has not been published until now. Mayaweckelia troglomorpha sp. n. differs from M. yucatanensis by i) three times larger body size; ii) significantly increased number of flagellum articles in both antennae (three times more articles on primary flagellum); iii) gnathopod I carpus 1.5-1.7 times longer than propodus (vs. same length); iv) proportionally longer and differently ornamented propodus of gnathopod II (palm armed with unnotched spine teeth and pearl row-like setae); v) pereopods VI and VII 130 % of body length (vs. 60 % of body length) vi) more distinct ventro-posterior corner of epimeral plates. M. troglomorpha sp. n. differs from M. cenoticola by i) its two times larger body size; ii) elevated number of flagellum articles in both antennae; iii); less narrow and differently ornamented propodus of gnathopod I (palm armed with distally notched spine teeth); iv) gnathopod I carpus 1.5-1.7 times longer than propodus (vs. 0.7 times longer); v) longer and differently ornamented propodus of gnathopod II; vi) pereopods VI and VII 130 % of body length (vs. approximately 60 % of body length); and vii) more distinct ventro-posterior corner of epimeral plates. Scanning electron microscopy has revealed that uropods I–III are covered with pubescent setae (not mentioned in the description of M. yucatanensis and M. cenoticola ), this character should also be checked on these species using SEM studies, as this trait is not visible using light microscopy.

The new species corresponds with the diagnostic characters of the genus Mayaweckelia . It differs from the related Tuluweckelia in the following traits: i) anterior body region does not bend markedly downward; ii) maxilla I outer lobe with seven-nine setae; iii); gnathopod II sexually dimorphic; iv) epimeral plates ventro-posterior corners less produced. Mayaweckelia differs from Bahadzia by i) the absense of palp from both mandibles; and ii) outer ramus of uropod III with one article ( Holsinger and Yager 1985, Holsinger 1992). Mexiweckelia Holsinger & Minckley, 1971 and Paramexiweckelia Holsinger, 1982 are subterranean genera of the ‘weckeliid’ group known from north of México (e.g., Holsinger and Minckley 1971, Holsinger 1982). Mayaweckelia differs from them in some important ways: i) accessory flagellum of first antenna three-articulated (vs. single or vestigial); ii) presence of robust setae on inner margin of maxilliped outer lobe; iii) presence of large, ventrally produced lobe on gnathopod I merus; iii) sexually dimorphic gnathopod II (of Paramexiweckelia is not dimorphic); iv) pereopod VI little longer than pereopod VII; and v) completely separated telson halves (vs. deeply incised but fused in the other two genera).