Echiniscus insularis sp. nov. Gasiorek , Voncina & Kiosya

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

publication ID	https://dx.doi.org/10.3897/evolsyst.5.59997
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scientific name	Echiniscus insularis sp. nov. Gasiorek , Voncina & Kiosya
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Echiniscus insularis sp. nov. Gasiorek, Voncina & Kiosya Figures 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 View Figure 6 , 7 View Figure 7 , 8 View Figure 8 , Tables 3, 4, 5

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.002.04), allotype (mature male on slide MU.002.02), seven paratypic females, fourteen paratypic males, and five juveniles (slides MU.001.01-3, MU.002.01-6). One hologenophore on slide MU.001.24, and three hologenophores the slide MU.002.07. All deposited in the Department of Invertebrate Evolution.

Etymology.

From Latin insula = island. The name refers to locus typicus. Adjective in the nominative singular.

Description.

Mature females (i.e. from the third instar onwards; measurements in Table 3 View Table 3 ). Body small and plump (Figs 1 View Figure 1 , 3 View Figure 3 , 6A View Figure 6 ), yellow to orange, with minute red eyes absent after mounting. Ordinary primary and secondary (cephalic papillae) clavae of the Echiniscus -type; peribuccal cirri with well-developed cirrophores. Cirrus A very short (<25% of the body length), with cirrophore. Body appendage configuration A -(B)- C - Cd - D - Dd - E, with the majority of appendages developed as spicules, slightly longer spines can occur only in the positions Cd, Dd, and E (Figs 1 View Figure 1 , 3B View Figure 3 , 6A View Figure 6 ). Asymmetries frequent, but only rarely are more appendages absent (Fig. 3A View Figure 3 ). Additionally, supernumerary spicules occur along the margins of all dorsal plates and sometimes on their surface (Fig. 6A View Figure 6 ), particularly frequent (up to five) along the caudal incisions (Fig. 6D, E View Figure 6 ). Spines and spicules are always smooth and simple, not ramified.

Dorsal plates strongly sclerotised and well-demarcated from each other, with the Echiniscus spinulosus type sculpturing, i.e. only pores are present (Figs 1 View Figure 1 , 3 View Figure 3 , 6A View Figure 6 ). Pores are densely arranged and may be of various size: from medium (Figs 1B, C View Figure 1 , 3B View Figure 3 , 6A View Figure 6 ) to large (Fig. 1A View Figure 1 ), even merging into groups of two/three pores (Fig. 3A View Figure 3 ). Dark endocuticular rings usually absent (Figs 1 View Figure 1 , 3B View Figure 3 , 6A View Figure 6 ), or present, but only in the largest pores (Fig. 3A View Figure 3 ). Only in one female are pores absent and irregular dark epicuticular swellings are developed, most visible on the scapular plate (Fig. 4A View Figure 4 ). The cephalic plate consists of two halves, with an anterior chalice-like incision (Figs 1A View Figure 1 , 3A View Figure 3 ). The cervical (neck) plate is in the form of a narrow grey belt, weakly delineated anterior to the scapular plate (Figs 1A View Figure 1 , 3 View Figure 3 ). The scapular plate non-facetted, with the usual lateral sutures delineating small rectangular portions (Figs 1 View Figure 1 , 3 View Figure 3 ). Three median plates: m1, m3 unipartite, the latter reduced to a narrow stripe, and m2 bipartite (Figs 3A View Figure 3 , 6A View Figure 6 ); sculpture well-developed in all portions of the median plates with the exception of the anterior portion of m2, where it is reduced (Figs 1B, C View Figure 1 , 3 View Figure 3 , 6A View Figure 6 ). Two pairs of large segmental plates, their narrower anterior portions with two thin belts devoid of sculpture (Figs 1B View Figure 1 , 3 View Figure 3 , 6A View Figure 6 ) or with only one belt (Fig. 3B View Figure 3 ). The caudal (terminal) plate with evident incisions (Figs 1 View Figure 1 , 3 View Figure 3 ) and may be facetted (Figs 3B View Figure 3 , 6A View Figure 6 ).

Ventral cuticle smooth. Sexpartite gonopore located anteriorly of legs IV and a trilobed anus between legs IV. Pedal plates absent, but dim pulvini present (Figs 1B View Figure 1 , 3A View Figure 3 ). Spine I thin and minute (Figs 1 View Figure 1 , 3A View Figure 3 ). Dentate collar IV composed of numerous acute teeth (Fig. 7D View Figure 7 ). Papilla on leg IV present (Figs 1 View Figure 1 , 3 View Figure 3 , 6A View Figure 6 ). Claws I-IV of similar heights. External claws on all legs smooth. Internal claws with proportionally large spurs positioned at ca. 1/4-1/3 of the claw height, spurs IV slightly heteromorphic since they are more divergent from the branches than spurs I-III (compare Fig. 7A-C, D View Figure 7 ).

Mature males (i.e. from the third instar onwards; measurements in Table 4 View Table 4 ). Body slender (Fig. 2 View Figure 2 ). Only one male has rudimentary developed pores (Fig. 4B View Figure 4 ). Males have often comparatively better developed supernumerary spicules than females (Fig. 2B View Figure 2 ). Clavae enlarged, more prominent than in females (Figs 2 View Figure 2 , 6B View Figure 6 ). Subcephalic region with a pair of weakly developed oval swellings (probably rudimentary subcephalic plates). Gonopore circular, with a U-shaped slit; semicircular bulge resembling a genital plate with a cracked surface present anterior to the gonopore (Fig. 6C View Figure 6 ).

Juveniles (i.e. from the second instar onwards; measurements in Table 5 View Table 5 ). No morphometric gap between adults and juveniles (likely a result of general miniaturisation of the species). Qualitatively similar to adults (Fig. 5 View Figure 5 ). Gonopore absent.

Larvae. Unknown.

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

DNA sequences and phylogenetic position.

Two haplotypes in all markers were found, corresponding with the populations MU.001 and MU.002: 18S rRNA (MW180887, MW180888), 28S rRNA (MW180879, MW180880), ITS-1 (MW180910, MW180911), ITS-2 (MW180898, MW180899), and in COI (MW178242, MW178243). p -distance in COI between the two populations is 4.9%. Echiniscus insularis sp. nov. belongs in the Echiniscus spinulosus complex, being a sister species to the clade composed of E. manuelae da Cunha & do Nascimento Ribeiro, 1962 + E. tristis Gąsiorek & Kristensen, 2018 (Fig. 8 View Figure 8 ).

Remarks.

The species is easily recognisable because of the additional supernumerary dorsal spicules along margins of all plates and sometimes on the plates, making it an unusual member of the Echiniscus spinulosus group and of the entire genus. Besides, it is one of the smallest representatives of Echiniscus with the average adult body length at ca. 150 μm, whereas adults of Echiniscus spp. usually reach 200-250 μm at least. There is one species resembling specimens of E. insularis sp. nov. with a lower number of spicules - E. tropicalis Binda & Pilato, 1995 described from the Seychelles. For the purpose of the comparison E. insularis sp. nov. - E. tropicalis , we present updated description of the latter species below.

Due to the fact that E. manuelae and E. tristis currently emerge as species closest phylogenetically to E. insularis sp. nov., we compare them with the new species accordingly:

E. manuelae has larger and more sparsely distributed pores in dorsal plates (see fig. 3 in da Cunha & do Nascimento Ribeiro (1962) and fig. 5 in Gąsiorek and Kristensen (2018)), and appendages C d + D d are long and serrated (smooth and short in E. insularis sp. nov.);

E. tristis is a larger species (adult females ≥ 180 μm in E. tristis vs <170 μm in E. insularis sp. nov.) and has larger claw spurs that are more divergent from branches than in E. insularis sp. nov.