Commented and illustrated key for identification of Agaue chevreuxi (Trouessart, 1889) and A. panopae (Lohmann, 1893) (Acari, Halacaridae)

The Mediterranean gives home to three named Agaue species, two of them are at a quick glance very similar, namely Agaue chevreuxi and A. panopae , their idiosoma and legs have almost the same size and shape. The idiosoma, gnathosoma, legs, and details of these are illustrated and distinguishing characters described. Characters of a third Mediterranean species, Agaue adriatica , are outlined .

In the two species, the majority of the specimens studied have uniformly porose ventral plates, but in two individuals of A. chevreuxi, from the south-western coast of Spain (Cadiz), the ornamentation of the cerotegument gives the surface of the plates a foveate aspect. Except for the genital plates, there are almost no differences between females and males, the shape and setation of AE and PE (Figs 1E, 2E) is almost the same. The GA of females of A. chevreuxi and A. panopae is ovate, the number of pgs of A. chevreuxi is smaller than that of A. panopae (13-17 versus 16-21 pgs) (Viets 1928;Mari & Morselli 1990;Bartsch 1998), in A. chevreuxi there are two (rarely three) setae on either side of the antero-lateral margin, in A. panopae three to five setae (Fig. 1F, 2F). Moreover, there is a difference in length of the ovipositor in relation to the anterior margin of GA. In A. chevreuxi the ovipositor extends to or slightly beyond the anterior margin of GA, in A. panopae beyond the GA by almost the length of the GO. The GA of males is wider than that of females. Differences between the species are in the number of pgs, about 81-90 in A. chevreuxi and 100-110 in A. panopae (Figs 1G. 2G, Mari & Morselli 1990;Bartsch 1998). In A. chevreuxi, the spermatopositor extends to (Fig. 1G), but also somewhat beyond the anterior margin of the genital plate, in A. panopae, in the single male studied, it extends somewhat beyond that margin (Fig. 2G).  (Trouessart, 1889). A -gnathosoma, ventral, female. B -tip of palps, dorsal, female. Capical part of palp, chelicera and rostrum, lateral, male. Figure 4. Agaue panopae (Lohmann, 1893). A -gnathosoma, ventral, female. B -tip of palp, dorsolateral, female. Capical part of palp and rostrum, lateral, male. Scale = 50 µm. (arrows indicate differences in character states; fs, furcate seta; mxs-1, basal pair of maxillary setae; pa, porose areola; s, seta; so, solenidion; pa, porose areola; rs, rostral seta). (Trouessart, 1889). A -leg I, medial, female. B -tip of tarsus II, medial, female (lateral eupathidia in broken line, lateral claw and fossary seta omitted). C -leg II, medial, female. D -tip of tarsus III, lateral, female (medial claw and setae omitted). E -leg III, medial, female. F -claw of tarsus IV, medial, female. Figure 6. Agaue panopae (Lohmann, 1893). A -leg I, medial, female. B -tip of tarsus II, medial, female (lateral eupathidia in broken line, lateral claw and fossary seta omitted). C -leg II, medial, female. D -tip of tarsus III, medial, female (lateral claw and setae omitted). E -leg III, medial, female. F -claw of tarsus IV, medial, female. Scale = 50 µm.

Figure 5. Agaue chevreuxi
(arrows indicate differences in character states; acp, accessory process; ce, cerotegument; so, solenidion) Gnathosoma. The gnathosoma is slender in both species, its length more than 2.0 times the width (Lohmann 1893;Bartsch 1998) (Figs 3A, 4A). The cerotegumental cover on the gnathosomal base is thin in A. chevreuxi, inconspicuous in A. panopae. Within a ring-like area, interrupted only by the pharyngeal field, the integument of the gnathosomal base is porose. The tectum is scaliform. The rostrum of A. chevreuxi and A. panopae is slender, extends beyond the middle of P-4, in both species it is about twice as long as the gnathosomal base (1.8-2.1 times) (Bartsch 1998). In A. chevreuxi the length of the mxs-2 is less than one quarter of that of the mxs-1 (Fig. 3A) whereas in A. panopae (Fig. 4A) it is about half of that of the mxs-1 (mxs-2, 50-60 µm, mxs-1, 100-105 µm). The apical rostral setae are short, divaricate. The palps are slender. P-2 and P-3 bear one dorsomedial seta each. The seta on P-2 is slender in A. chevreuxi (Fig. 3B), in females about 24 µm long, but in females of A. panopae it is scaliform and furcate, 12 µm long (Fig. 4B). Males of both species have a slender seta on P-2, 20-25 µm long (Figs 3C,4C). In females and males of A. chevreuxi the dorsal seta on P-3 is distinct, similar though somewhat shorter than that on P-2 (16-20 µm), in females of A. panopae that seta is spiniform, its length 11-12 µm. The P-4 bears three setae in the basal whorl, a long dorsolateral solenidion and apically one slender setula and two short eupathid setae.
Legs. Both species have club-shaped tibiae and at a first glance the shape of legs is similar but the cerotegumental lamellae of A. chevreuxi are larger than in A. panopae (Figs 5A, C, E, 6A, C, E). The height of the dorsal lamellae on telofemur I of A. chevreuxi equals at least one third of the segment's height, that of A. panopae is one fifth or less. In A. chevreuxi the telofemora I to III are 3.1-3.2, 2.4-2.5 and 2.2-2.4 times longer than high, in A. panopae 2.9, 2.3 and 2.2-2.3 times, respectively. In both species tibiae I and II are somewhat shorter, but tibiae III and IV somewhat longer than the legs' telofemora. In A. chevreuxi the number of setae on the legs, from trochanter to tarsus (solenidia included) is: leg I, 1,2,5,5,11,23;leg II,1,2,5,5,11,11;leg III,2,2,3,4,8,5;leg IV,[0][1]2,3,3,8,5;in A. panopae: leg I,1,2,5,5,11,20;leg II,1,2,5,4,10,9; leg III, 2, 2, 3, 3, 7, 5; leg IV 0, 2, 3, 3, 7, 5. The genua I to IV of A. chevreuxi bear 3/2, 3/2, 3/1, 2/1 dorsal/ventral setae, those of A. panopae 3/2, 2/2, 2/1, 2/1; one of the dorsal setae of both genu II and III is lacking in that latter species. On tibiae I to IV of A. chevreuxi 6/5, 6/5, 4/4, and 4/4 dorsal/ventral setae are found, respectively, on those of A. panopae 6/5, 6/4, 3/4, and 3/4 setae. Of the five ventral setae on tibia II of A. chevreuxi two are ventromedial and three ventrolateral in position, of the four ventral setae on tibia II of A. panopae two are ventromedial and two ventrolateral in position. The tarsi have large fossa membranes. Tarsi I of A. chevreuxi and A. panopae each bear three dorsal setae, a solenidion on the lateral fossa membrane and one ventromedial seta in about the middle of the segment; the species differ in the number of eupathidia, in A. chevreuxi there are about 18 (pas included), in A. panopae only 15 eupathid setae. Tarsus II of A. chevreuxi bears three dorsal setae and on the inside of the medial fossa membrane a 10 µm long solenidion, at the tarsal tip three ventromedial and four ventrolateral eupathidia (doubled pas included) (Fig.  5B). The tarsal II chaetotaxy of A. panopae is similar except for the lower number of eupathidia on the tip of the tarsus, namely a single ventral seta and a pair of doubled eupathidia (Fig. 6B). Tarsi III and IV have three dorsal setae and a pair of filiform pas (Figs 5D, 6D). The claws differ in shape and number of tines. Most A. chevreuxi have 16-18 tines arranged along the concave flank of the claws (Fig. 5B, D, F) and distinctly raised accessory processes, each with six tines. In A. panopae the pectines, with 7-8 tines each, are restricted to the middle part of the concave flank (Fig. 6B, D, F), the accessory process is slightly raised and includes three to four tines.

Discussion and Conclusion
As demonstrated, A. chevreuxi and A. panopae can be separated on the basis of several morphological characters, though at present the number of specimens studied is small and the range of the character states not known. With more material at hand, variants, as well as intermediate and anomalous character states may be found. According to the descriptions above, the difference in length and ornamentation of the ds-2, ds-3 and ds-4 seems to be distinct but Boyaci & Durucan (2013: fig 3) illustrated a male of A. chevreuxi (from the Marmara Sea) with unusual long setae. In general the size of the cerotegumental cover will certainly vary from individual to individual (beside that it may be destroyed when clearing and mounting the mites). One of the distinguishing characters of A. chevreuxi is the foveate ornamentation on the PD, but at least in an individual from Morocco (Tanger) that sculpturing is very faint. The length ratio of the ovipositor with reference to the anterior margin of the GA is expected to vary, this may partly be the result of different orientation of the mite on the slide. Variants are often found in respect to the number of setae on the telofemora and tibiae, as e.g. demonstrated in the related species Agaue galatea (Bartsch 2015), such differences are often restricted to one side. Different character states will certainly also be found in A. chevreuxi and A. panopae. The paired claws of A. chevreuxi each have a prominent accessory process and its pectines numerous tines, these are arranged along the ventral flank of the claw, whereas in A. panopae the accessory process is only slightly raised and the few tines of the pectines are typically restricted to the middle part of the claw. In contrast to this, Mari & Morselli (1990: fig. 1a) found an A. panopae with 'tipo chevreuxi' claws (with raised accessory process and numerous tines), and a female and male taken on the south-western coast of Spain (Cadiz) and identified as A. chevreuxi had only slightly raised accessory processes. An example of an anomaly is that presented by a female of A. adriatica from Spain (Cadiz), beside the ds-2 to ds-4 an additional similar sized seta arises from the middle of the right OC.
A few anomalous variants may cause problems but in general A. chevreuxi can be separated from A. panopae. because of: (1) the larger cerotegumental lamellae, especially on the legs; (2) the short ds-2, ds-3 and ds-4, embedded in cerotegument; (3) the lower number of perigenital setae on the female GA, especially in the anterior part of the plate; (4) the slightly lower number of setae on the GA of males; (5) the very short second pair of maxillary setae; (6) the slender dorsal seta on P-2, only slightly longer than that on P-3 and absence of sexual dimorphism; (7) the higher number of setae on the genua and tibiae II; (8) the higher number of setae on the genua and tibiae III; (9) the higher number of ventral setae on the tips of tarsi I and II; (10) the conspicuous accessory process and the higher number of tines on the claws. A third named Agaue species known from the Mediterranean is Agaue adriatica. The idiosoma of females is 440-539 µm long, that of males 442-510 µm (Viets 1940;Morselli & Mari 1993;unpublished data). Agaue adriatica can be separated from A. chevreuxi and A. panopae on the basis of the wide cerotegumental lamellae on idiosoma and legs with their honey comb-like ornamentation. On the AD, the two cerotegumental lamellae are fused anteriorly, forming an inverted 'V'. The opposing margins of the AD and PD are ovate (Fig. 7A), not truncate; the PD is foveate, at least in its middle part. The marginal parts of AE and PE have a cerotegumental cover. The ovipositor extends to the anterior margin of GA, and in males the genital opening is surrounded by 70-90 perigenital setae (according to Mari & Morselli 1990) or almost 100 (according to a male collected off Marseille). The rostrum is 1.1-1.2 times longer than the gnathosomal base. The difference in length of the two pairs of maxillary setae is small (Fig. 7B). The seta on P-2 is slender in both female and male, somewhat longer than the length of P-3. The seta on P-3 is small, 3-4 µm long (Fig.  7C) (not recognizable in the holotype and paratypes because of the thickness of the mounting medium). Telofemora I to IV are about 3.3-3.6, 2.7-3.0, 2.4-2.8, and 2.7-2.8 times longer than high, both the dorsal and ventral flank is embedded within an ornamented cerotegumental cover. On telofemur I the height of this cerotegument is slightly less than the height of the segment (Fig. 7D). The chaetotaxy formula of trochanters to tibiae I to IV is: leg I, 1, 2, 5, 5, 10; leg II,1,2,5,5,9;leg III,2,2,3,4,7;leg IV,0,2,3,3,7. Tarsus I bears one ventromedial seta, in about the middle of the segment, and 15 apical eupathidia (parambulacral setae included), tarsus II two small ventral eupathidia and the pair of doubled pas. Each of the tarsi III and IV has a pair of pas singlets but no further ventral setae. The claws are slender, the accessory processes minute, 5-9 tines can be seen in the basal part of the concave flank (Fig. 7E), these tines are small in the type series but coarse in a specimen from Spain (Cadiz).
In addition to the three above mentioned at least a fourth species lives in the Mediterranean. Its idiosomal length equals that of A. chevreuxi. The species can easily be separated from the other three because of its long and slender idiosoma, gnathosoma and legs.