Two new mite species of the genus Zygoseius Berlese from Mexico (Acari, Mesostigmata)

Abstract Two new species of mites of the genus Zygoseius Berlese, Zygoseius papaver sp. n. and Zygoseius lindquisti sp. n., collected from moss and flood debris, respectively, in a creek in Chiapas State, Mexico, are described herein.


Introduction
The genus Zygoseius Berlese, 1916 is a moderately small genus of mesostigmatic mites, with 13 described species currently. It was first defined by Berlese (1916) as a subgenus of Lasioseius Berlese, 1916, with description of the species Z. furciger, collected from ants' nests in Argentina. The genus was variously reviewed by Halliday (1997), Karg (1998) and Karg and Schorlemmer (2009). Zygoseius species are found in soil, leaf litter, moss, compost, cow and chicken dung, and ants' nests (Halliday 1997, Karg 1998, Karg and Schorlemmer 2009. Some species were found in association with insects, namely dung beetles (e.g. Z. furciger (Costa 1963) and Z. sarcinulus Halliday, 1997 was measured from the anterior margin of stigmata to the anterior end of peritreme. Length and width of anal opening were measured excluding the raised band of cuticle surrounding the anus. Idiosomal notation for setae used in this paper follows that of Lindquist and Evans (1965). The notations for leg and palp setae follow those of Evans (1963aEvans ( , 1963b. Idiosomal and peritrematal shield notations for pore-like structures (gland pores and poroids/lyrifissures) follow the systems of Athias-Henriot (1971) for ventral idiosoma and Athias-Henriot (1975) for dorsal idiosoma. The notations of spermathecal structures are based on Athias-Henriot (1968) and Evans and Purvis (1987).
Gnathosoma. Epistome as in female, with two projections, 19 long, distance between bases of projections 5. Corniculi (26 long) and deutosternum as in female. Lengths of hypostomal setae: h1 39, h2 14, h3 24, pc 19. Chelicera and spermatodactyl not avail- Chaetotaxy of legs I-IV similar to that of female, except that the femur II has one conical spine-like projection ventrodistally (Fig. 14). Setae pd1-2 on femur I thickened as in female, pd1 14-15, pd2 10-12. Sigillae locations similar to those of female. Etymology. The specific name refers to the shape of the spermatheca of the new species, which resembles the ca psule of opium (Papaver somniferum L., 1753). It is considered as a noun in apposition.
Remarks. The spermathecal apparatus of Z. papaver sp. n. is distinct from that of any other Zygoseius species for which it was described: the spermetheca is globular and larger than any other sclerotized part of the apparatus, and ends in a flower-like pattern.
The new species can also be distinguished by its long J1-2 setae relative to the distance between J1 and J2 setae (ratio setal length/distance = 0.90 ± 0.06 st.dev., range 0.75-1.0). Based on their illustrations, a few species described from South America have long J1-2 setae relative to the distance between them, such as Z. alveolaris Karg, 1998 and Z. triramuli Karg & Schorlemmer, 2009(Karg 1998, Karg and Schorlemmer 2009), but these have a different arrangement of setae of the j-J series, including the presence of J3.
The epistome of Zygoseius papaver sp. n. is unique among described species, with relatively short but thick projections that are conspicuously barbed apically. The epistome of Z. laticuspidis Karg, 1998 is similar; however, it is even more swollen apically, and is slightly denticulate on the basal margin in-between the projections. Zygoseius laticuspidis also has J5 setae inserted mesad of Z5 (note, however, that the relative position of J5 and Z5 can vary, depending on how flattened is the dorsal shield on the slide). The new species can further be distinguished from Z. laticuspidis by its shorter dorsal setae (all are <30 long; most are 30-60 long in Z. laticuspidis), J4 setae separated by 1.4-1.9× the distance between J1 setae (J4-J4 distance over twice that between J1-J1 in Z. laticuspidis), and by the presence of nine pairs of setae on the opisthogastric soft cuticle (six pairs in Z. laticuspidis). Other Zygoseius species can be distinguished from Z. papaver sp. n. by some of the same characters mentioned above, as well as by (1) its epistome; (2) the length and width (and their ratios) of the dorsal, sternal and ventrianal shields; (3) relative length of dorsal setae, especially Z5; (4) the ornamentation of the dorsal and sternal shields; and (5) long JV1-2 setae, 1.5-2× as long as other pre-anal setae on the ventrianal shield, and as long as about 2/3 of distance between JV1 and JV2. Zygoseius ampullus Halliday, 1997 and Z. foramenis Karg, 1998 also have longer JV1-2 setae but clearly differ by their epistomes, and by shorter J1 -2 setae and a ventrianal shield as long as wide. In the key to species of Karg and Schorlemmer (2009), Z. papaver sp. n. would reach couplet 3 (12), and can be distinguished from species in (3) and (12) by the characters mentioned above.
Another distinguishing feature of Z. papaver sp. n. is the distinctly serrated lateral margins of the dorsal shield. This also characterizes Z. ovatus Karg, 1998. The margins of the dorsal shield of other species may appear somewhat serrated (e.g. Z. ampullus, Z. metoecus Halliday, 1997 andZ. separatoporus Karg, 1998), although the serration matches with the insertion of setae in marginal positions (mostly r and S setae), whereas in the new species and at least in Z. ovatus, most serration are independent of setal insertions. Such serrated margins of the dorsal shield are reminiscent of the dorsal shield of many Zerconidae (Ujvári 2010(Ujvári , 2011 and some species of Pachyseius Berlese (Pachylaelapidae) (Mašán 2007, Ahadiyat et al. 2016. Note that the serration of dorsal shields in zerconid and Pachyseius species is largely correlated, although not entirely, with the insertion of marginal setae.
Zygoseius papaver sp. n. also differs from other Zygoseius species by its reduced chaetotaxy on genu II, lacking seta av, and genu III, lacking seta pv, instead of the usual complement of two ventral setae, including both av and pv as noted in the genus diagnosis of Halliday (1997). His diagnosis was based on four species (Z. furciger, Z. ampullus, Z. metoecus, Z. sarcinulus), so we can predict that other described (with unstudied leg chaetotaxy) and undescribed species have such genual chaetotaxy. However, because at least another species of Zygoseius, newly described herein (see below), sometimes lacks pv on genu III, we can suspect that other species also lacks such seta. Members of other non-parasitic dermanyssine families lack both of these setae (e.g. Phytoseiidae; Evans 1963a), or lacks either av on genu II (some Pseudolaelaps species, Pseudolaelapidae; Mašán 2014) or more commonly pv on genu III (e.g. some Eviphididae, Pachylaelapidae, Macrochelidae, Ascoidea, Blattisociidae; Evans 1963a, Lindquist and Evans 1965, Moraza and Johnston 1990, Mašán 2007, Mašán and Halliday 2010, showing plasticity of the development of those setae. Based on the studied chaetotaxy of Z. furciger and of other dermanyssines (Evans and Till 1965, Lindquist and Evans 1965, Halliday 1997, when present in the adults, ventral setae of genua II-III appear at the deutonymphal stage. Therefore, they are theoretically not as stable as (i.e. less likely to be retained in the adult stage than) setae appearing at an earlier developmental stage (Evans 1963a, Lindquist and Evans 1965, Rowell et al. 1978.
Male and immature stages. Unknown. Etymology. The species is named in honor of Evert E. Lindquist, for his invaluable endeavors on the systematics of Mesostigmata over the years. The specimens of this new species were collected by him.
Remarks. The dorsal seta of trochanter I in Z. papaver and Z. lindquisti is inserted in a posterior position. We herein call this seta d (Figs 10, 23), although in the chaeto-  tactic formula, we indicated it as posterodorsal, given its clear posterior position, as in Halliday (1997). Evans (1963a, fig. 1i) indicated 'ad' for this dorsal seta, as illustrated for Pergamasus (Parasitidae). In the text, however, he called it 'd', for Pergamasus and  In his diagnosis of the genus Zygoseius, Halliday (1997) indicated one pv and one pl setae on trochanter IV, whereas Evans (1963a) indicated two pv and no pl (as we did, herein). Indeed, pv1 is inserted much more posteriorly than pv2 (although not necessarily posterolaterally), and this situation is similar to that of pv1-2 of trochanters II-III (Evans 1963a;Figs 11-13, 24-26).
In addition to poroid idR3, between setae R3 and R4, the soft opisthogastric cuticle has a sclerotized complex of two pore-like structures, posterolaterad the peritre- matal-metapodal shield. These structures may be two openings of the same underlying gland complex; alternatively, they may be a gland opening and an associated poroid (note that both of these structures are sometimes visible in lateral view when the soft cuticle is folded, instead of the normal ventral view). It is unclear whether this gland opening is homologous to the one (gp) typically found in the poststigmatic region of peritrematal shields in many Mesostigmata (e.g. Lindquist and Moraza 2016). This double pore-like structure also occurs in Z. papaver sp. n., as well as in Z. ampullus and Z. metoecus (Halliday 1997), and Z. sarcinulus (AA, personal observations).

Discussion
The record of a "Zygoseius sp." by Palacios-Vargas (1983) probably represents from the first mention of the genus in Mexico. Among the now 15 described species, 12 are found in South America, including one (Z. furciger) that is also found elsewhere (USA, Africa, Israel); two (described herein) occur in Mexico, and one (Z. sarcinulus) is widespread in Australia.
Some morphological characters are of particular interest for the diagnosis of Zygoseius species and possibly also for classifying them into species groups. Perhaps the most useful character to distinguish Zygoseius species is the spermatheca itself varying in size relative to the rest of the apparatus, and the sperm reservoir varying in shape, ranging from oval to globular (Halliday 1997, Karg 1998. More detailed studies of the spermathecal apparatus will probably help further the systematics of Zygoseius, analogously as to its use for other Mesostigmata, such as the Phytoseiidae McMurtry 1994, Beard 2001) and Pachylaelapidae (Mašán 2007).
The dorsal idiosomal chaetotaxy is moderately useful, with some setae varying markedly in position between species, such as J5 relative to Z5, and with the atypical presence of seta J3 in some species (in Z. triramuli and Z. alveolaris; Karg 1998). Although Halliday (1997) stressed the difficulty in using shield ornamentation (e.g. sternal shield) for species discrimination because of intraspecific variation, it is useful in some cases, including for the dorsal, sternal and ventrianal shields (compare Z. papaver and Z. lindquisti, Figs 1-2, 28-29, 15-16, 32-33;Halliday 1997).
The epistome and the male chelicerae appear as the most studied (or most often illustrated) gnathosomal characters in Zygoseius. There is some interspecific variation in the epistome, including the number (usually 2, rarely 3 or 4) and length of projections, and the extent of barbs on the margins. These variations are overall only moderate, although overall represent useful diagnostic features. Male chelicerae may be useful, with some apparent variation in dentition and in the lengths of spermatodactyls (e.g. Z. furciger has a longer spermatodactyl relative to cheliceral digits; Halliday 1997, Karg 1998, Karg and Schorlemmer 2009. The dentition of the female chelicerae has been illustrated for a few species only (Z. incisus, Z. alveolaris, Z. furciger (in Halliday 1997), Z. papaver sp. n.), and may differ in some species (e.g. Z. incisus has stronger teeth). The deutosternum has a variable numbers of transversal rows of denticles; e.g. that of Z. papaver, Z. lindquisti and Z. furciger have 7, 6-7 and 8 rows of denticles, respectively. The relative lengths of hypostomal setae (h1-h3, pc) also vary significantly, with some species having a particularly long h1 seta (e.g. in Z. papaver sp. n.), whereas in other species (e.g. Z. lindquisti sp. n., Z. furciger), h3 tends to be the longest.