Echiniscus tropicalis Binda & Pilato, 1995

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

Echiniscus tropicalis Binda & Pilato, 1995 Figures 8 , 9 , 10 , 11 , Tables 6, 7, 8

Material.

Together 402 adult females, 17 juveniles and 10 larvae mounted on slides.

Description.

Mature females (i.e. from the third instar onwards; measurements in Table 6 ). Body small and plump (Figs 9A , 11A ), 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 all appendages developed as spines or spicules, which are smooth or only sometimes spines E are serrated (Figs 9A , 10 , 11A ). Asymmetries frequent, especially in the lateral positions.

Dorsal plates strongly sclerotised and well-demarcated from each other, with the Echiniscus spinulosus type sculpturing, i.e. only pores are present (Figs 9A , 10 , 11 ). Pores are densely arranged and rather of uniform size. Dark endocuticular rings absent (Figs 10 , 11B, C ). The cephalic plate consists of two halves, with an anterior chalice-like incision. The cervical (neck) plate is in the form of a narrow grey belt, weakly delineated anterior to the scapular plate (Fig. 10 ). The scapular plate non-facetted, with the usual lateral sutures delineating small rectangular portions (Figs 9A , 10 ). Three median plates: m1, m3 unipartite, the latter reduced to a narrow stripe; m2 bipartite (Figs 9A , 10 , 11 ). Two pairs of large segmental plates, their narrower anterior portions with two thin belts devoid of sculpture (Fig. 10 ). The caudal (terminal) plate with evident incisions (Figs 9A , 10 ) and may be facetted (Fig. 11A ).

Ventral cuticle smooth or with densely arranged endocuticular pillars. Sexpartite gonopore located anteriorly of legs IV and a trilobed anus between legs IV. Pedal plates and pulvini present (Fig. 9A ). Spine I thin and minute (Fig. 9A ). Dentate collar IV composed of numerous acute teeth (Figs 9A , 11A ). Papilla on leg IV present (Fig. 9A ). Claws IV slightly higher than claws I-III. External claws on all legs smooth. Internal claws with heteromorphic spurs positioned at ca. 1/4-1/3 of the claw height.

Mature males. Absent.

Juveniles (i.e. from the second instar onwards; measurements in Table 7 ). No morphometric gap or qualitative differences between adult and juvenile females found. Gonopore absent.

Larvae (i.e. the first instar; measurements in Table 8 ). Clear morphometric gap between juveniles and larvae exists (compare Tables 7 , 8 ). Body appendage configuration A - Cd - Dd - E (Fig. 9B ). Anterior portions of paired segmental plates weakly sclerotised. Gonopore and anus absent.

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 ID.032 and ID.939: 18S rRNA (MW327546, MW327547), 28S rRNA (MW327542, MW327543), ITS-2 (MW327549, MW327550), with the exception of ITS-1, characterised by one haplotype (MW327551, MW327552). The sister species of E. tropicalis within the Echiniscus spinulosus complex is E. siticulosus (Fig. 8 ).

Phenotypic differential diagnosis.

Echiniscus tropicalis was originally described based on two adult females ( Binda and Pilato 1995). We compared the newly found Southeast Asian specimens with the microphotographs of the holotype that confirmed our suspicions after reading the description, i.e. the lack of sound morphological discrepancies between the type material from the Seychelles and abundant material from the Malay Archipelago and the Malay Peninsula. The only difference is the serration of spines E that may be well-developed in Asian populations (Fig. 10 ), whereas this trait was not reported by Binda and Pilato (1995). The original description mentions "primary and secondary points" in the paratype = a potential ramification. As there is a considerable intrapopulation variability regarding this trait, the Seychellois and Asian populations should be ascertained as conspecific unless DNA data from the Seychelles reject this hypothesis.

There is a plethora of differences between adult females of E. insularis sp. nov. and E. tropicalis after the description of the latter was supplemented with new data:

the presence of supernumerary spicules along the margins of dorsal plates and in the caudal incisions (present in E. insularis sp. nov. vs absent in E. tropicalis);

the presence of pedal plates (absent in E. insularis sp. nov. vs present in E. tropicalis);

the relative length of cirrus A (86.1- 106.2 in E. insularis sp. nov. vs 41.1- 79.3 in E. tropicalis);

the absolute lengths of lateral spines B- D (B 2.5-3.2 μm, C 2.0-5.2 μm, D 2.5-4.0 μm in E. insularis sp. nov. vs B 4.3-12.7 μm, C 6.5-14.7 μm, D 5.7-13.8 μm in E. tropicalis);

the presence of males (present in E. insularis sp. nov. vs absent in E. tropicalis);

additionally, the spine E is frequently serrated in E. tropicalis (smooth in E. insularis sp. nov.).

Figures

Figure 8. Phylogenetic position of Echiniscus insularis sp. nov. on the Maximum Likelihood consensus phylogenetic tree; the E. spinulosus complex is marked in green and Diploechiniscus oihonnae was used as an outgroup. ML bootstrap values are presented above the branches.

Figure 9. Habitus of Echiniscus tropicalis in dorsolateral view (PCM): A adult female (black arrowheads indicate pulvini, whereas white arrowheads - pedal plates), B larva. Scale bars in μm.

Figure 10. Dorsal plate sculpturing of Echiniscus tropicalis in close-up (PCM). Scale bar in μm.

Figure 11. Dorsal plate sculpturing of Echiniscus tropicalis (SEM): A adult female in dorsal view, B, C pores in close-up. Scale bars in μm.