Pseudechiniscus mascarenensis sp. nov. Kiosya, Voncina & Gasiorek

Kiosya, Yevgen, Voncina, Katarzyna & Gasiorek, Piotr, 2021, Echiniscidae in the Mascarenes: the wonders of Mauritius, Evolutionary Systematics 5 (1), pp. 93-120 : 93

Pseudechiniscus mascarenensis sp. nov. Kiosya, Voncina & Gasiorek Figures 12 , 13 , 14 , 15 , 16 , 17 , Tables 9, 10, 11, 12

Pseudechiniscus sp. 5 in Gąsiorek et al. (2021)

Locus typicus and type material.

ca. 20°22'S, 57°29'E, 580 m asl; Sophie Nature Walk, vicinity of Mare aux Vacoas (Plaines Wilhems, Mauritius, Mascarene Archipelago, Western Indian Ocean); mosses from tree trunks. Holotype (mature female on slide MU.001.04), allotype (mature male on slide MU.001.05), sixty paratypic females, seven paratypic males, ten juveniles, and six larvae (slides MU.001.01-21). Single hologenophore on slide MU.001.22. All deposited in the Department of Invertebrate Evolution.

Etymology.

The name indicates the Mascarenes, terra typica of the new species. Adjective in the nominative singular.

Description.

Mature females (i.e. from the third instar onwards; measurements in Table 9 ). Body yellow to orange, with minute, round black eyes absent after mounting (Fig. 12A ). Elongated (dactyloid) cephalic papillae (secondary clavae) and elongated (primary) clavae (Figs 12A , 13 , 15 , 16 ); peribuccal cirri with poorly developed cirrophores. Cirrus A short, with cirrophore.

Dorsal plates are both poorly sclerotised and demarcated from each other, with the Pseudechiniscus -type sculpturing, i.e. endocuticular pillars protruding through the epicuticle and visible as dark dots in PCM (Fig. 12A ). Striae present, but not visible in SEM (Figs 15A , 16 ). Epicuticular ornamentation absent. The cephalic plate pentapartite, with the anterior bi-halved portion and three posterior portions, roughly equal in size. The cervical (neck) plate absent. The scapular plate with sutures, separating wide anterior portion and four rectangular posterior portions. Three median plates: m1 and m3 unipartite, the latter indistinctly merged with the anterior margin of the pseudosegmental plate IV’ (Fig. 12A ), clearly delimited in SEM (Fig. 15A ); m2 bipartite and large. Four pairs of lateral intersegmental platelets flanking the boarders of m1-2 (Figs 12A , 16 ). Two pairs of large segmental plates. The pseudosegmental plate IV’ undivided by a median longitudinal suture; the posterior margin of the plate sinusoid and smooth. The caudal (terminal) plate with short, very poorly marked incisions (Figs 15A , 16 ).

Ventral cuticle with a pronounced species-specific pattern reaching the lateroventral sides of the body (Figs 12A , 13 , 14 , 15B ), being a typical reticulum composed of belts of pillars. The pattern is relatively stable and well developed in the majority of individuals. The subcephalic zone with a wide belt of pillars. No epicuticular thickenings. Sexpartite gonopore located anterior to legs IV and a trilobed anus between legs IV.

Pedal plates and dentate collar IV absent; instead large patches of pillars are present centrally on each leg (Fig. 12A ). Pulvini faint. Papilla on leg I absent (Figs 12A , 13 , 16 ) and papilla on leg IV present (Figs 12A , 16 , 17D ). Claws I-IV of similar heights. External claws on all legs smooth. Internal claws with spurs positioned at ca. 1/5 of the claw height and directed downwards (Fig. 17 ).

Mature males (i.e. from the second or third instar onwards; measurements in Table 10 ). Clearly smaller than females (compare Tables 9 , 10 ). The posterior margin of the pseudosegmental plate IV’ bears two weakly developed lobes joined at their bases (Fig. 12B, C ). Gonopore circular.

Juveniles (i.e. from the second instar onwards; measurements in Table 11 ). Morphometric gap exists between adult females and juveniles. Qualitatively similar to adults. Gonopore absent.

Larvae (i.e. the first instar; measurements in Table 12 ). Morphometric gap exists between juveniles and larvae. Gonopore and anus absent.

Eggs. One egg per exuviae was found in few examined exuviae.

DNA sequences and phylogenetic position.

Single haplotypes in 18S rRNA (MW031972), 28S rRNA (MW032061), and ITS-1 (MW032151) were found. Pseudechiniscus mascarenensis sp. nov. has no close relatives according to the phylogeny presented in Gąsiorek et al. (2020) (see fig. 2 therein), constituting a separate evolutionary lineage within the subgenus Pseudechiniscus Meridioniscus .

Phenotypic differential diagnosis.

The species must be compared to other members of Meridioniscus with no projections on the pseudosegmental plate IV’ or with rudimentarily developed projections. Pseudechiniscus mascarenensis sp. nov. is differentiated from:

P. angelusalasRoszkowska et al., 2020, described from Madagascar, by the body length (151-177 μm in females of P. mascarenensis sp. nov. vs 113-143 μm in females of P. angelusalas), the cirrus A/body length ratio (9-13% in females of P. mascarenensis sp. nov. vs 19-22% in females of P. angelusalas), and by the division of the pseudosegmental plate IV’ (undivided in P. mascarenensis sp. nov. vs with median longitudinal suture in P. angelusalas);

P. dastychiRoszkowska et al., 2020, described from the Argentine Islands (maritime Antarctic), by the presence of males (present in P. mascarenensis sp. nov. vs absent in P. dastychi), and by the division of the pseudosegmental plate IV’ (undivided in P. mascarenensis sp. nov. vs with median longitudinal suture in P. dastychi);

P. indistinctusRoszkowska et al., 2020, described from Norway, by the division of the pseudosegmental plate IV’ (undivided in P. mascarenensis sp. nov. vs with median longitudinal suture in P. indistinctus), and by the presence of males (present in P. mascarenensis sp. nov. vs absent in P. indistinctus);

P. santomensisFontoura et al., 2010, considered endemic to the island São Tomé (Gulf of Guinea), by the presence of males (present in P. mascarenensis sp. nov. vs absent in P. santomensis), and the morphology of the posterior margin of pseudosegmental plate IV’ in females (smooth in P. mascarenensis sp. nov. vs with two projections in P. santomensis, as in males of P. mascarenensis sp. nov.); overall, these two species are most similar within the genus.

Moreover, only the ventral sculpturing pattern of P. santomensis resembles that of P. mascarenensis sp. nov.; the remaining species have a very different ventral arrangement of pillars. Pseudechiniscus juanitae de Barros, 1939 should be treated as unidentifiable due to the lack of knowledge on its morphology ( Grobys et al. 2020), although one attempt was made to characterise this species based on individuals from Central America ( Pilato and Lisi 2006; Tumanov 2020), whereas its locus typicus lies in Brazil. Consequently, it is not included within the differential diagnosis.

Figures

Figure 12. Habitus of Pseudechiniscus mascarenensis sp. nov. (PCM): A female, dorsolateral view, B, C males, dorsal view. Scale bars in μm.

Figure 13. Ventral sculpturing pattern of female of Pseudechiniscus mascarenensis sp. nov. (PCM). Scale bar in μm.

Figure 14. Schematic ventral sculpturing pattern of female of Pseudechiniscus mascarenensis sp. nov.

Figure 15. Habitus of females of Pseudechiniscus mascarenensis sp. nov. (SEM): A dorsal view, B ventral view. Scale bars in μm.

Figure 16. Habitus of females of Pseudechiniscus mascarenensis sp. nov. (SEM) in lateral view. Scale bars in μm.

Figure 17. Claws of Pseudechiniscus mascarenensis sp. nov.: A claws I (PCM), B claws II (SEM), C claws III (PCM), D claws IV with papilla (SEM). Scale bars in μm.