Hyposternus, Joharchi & Halliday, 2021

Joharchi, Omid & Halliday, Bruce, 2021, A new genus and species of Laelapidae Canestrini from Sri Lanka (Acari: Mesostigmata), Zootaxa 5048 (3), pp. 391-406 : 392

Genus Hyposternus gen. nov.

Type species: Hyposternus ceylonicus sp. nov.

Diagnosis (adult female). The genus can be readily distinguished from other Laelapidae by the shape of the sternal shield of the female. The shield is strongly desclerotised, except for narrow lateral and anterior ridges, which are fused with endopodal plates I/II and II/III. The pre-sternal platelets are apparently fused with the sternal shield, the epistome projects anteriorly, and the movable digit of the chelicera tapers apically. Caudal seta Z5 is longer and thicker than other setae on the dorsal shield; and the anal shield is long and narrow, and flanked by a few pairs of long thick opisthogastric setae. Femora II–IV bear elongate dorsal setae ad1.

Description. Adult Female.

Dorsal idiosoma ( Figs 1 , 8, 10 ). Dorsal shield covering idiosoma, oval-shaped, slightly extending onto ventrolateral aspect of idiosoma, bearing 38 pairs of setae, 21 pairs of podonotal setae, z3 absent, 17 pairs of opisthonotal setae, including two pairs of Zx setae.

Ventral idiosoma ( Figs 2 , 9, 11–14 ). Separate pre-sternal platelets absent, apparently fused with sternal shield; sternal shield markedly reduced to lateral and anterior ridges ( Fig. 12 ), anterolateral edges fused to endopodal elements to form arms projecting between coxae I–II, bearing three pairs of smooth setae ( Figs 2 ). Metasternal setae st4 and associated poroids (iv3) located on soft integument.

Gnathosoma ( Figs 3–7 , 15–16 ). Epistome projecting anteriorly (more than usual), anterior margin truncate, irregularly denticulate ( Fig. 6 ). Hypostomal groove with six transverse multidenticulate rows of denticles, with smooth anterior and posterior transverse lines, groove greatly widened anteriorly. Movable digit of chelicera narrowing and tapered apically.

Legs ( Figs 18–21 ). Leg I & IV moderately long, leg I approximately as long as idiosoma, leg IV longer than idiosoma; all legs with well-developed paired subequal claws and rounded pulvilli borne on ambulacral stalk. Many setae on tarsi II–IV thickened or spine-like, especially ventral setae, macrosetae (ad1) present on femora II–IV ( Figs 19–21 ).

Male ( Figs 22–23 ). As for female except sternal, genital, endopodal, ventral and anal shields fused into holoventral shield, with ten pairs of smooth setae; movable digit of chelicera with one tooth, spermatodactyl stout, with truncate tip, free portion of spermatodactyl about as long as movable digit ( Fig. 23 ).

Etymology. The name Hyposternus refers to the distinctive reduction of the sternal shield. Gender masculine.

Figures

FIGURES 1–7. Hyposternus ceylonicus gen. nov, sp. nov., female. 1, dorsal idiosoma; 2, ventral idiosoma; 3, subcapitulum; 4, palp; 5, supralabral process; 6, epistome; 7, chelicera.

FIGURES 8–11. DIC micrographs of Hyposternus ceylonicus gen. nov, sp. nov., female. 8, general view dorsally; 9, general view ventrally; 10, idiosoma in dorsal view; 11, idiosoma in ventral view.

FIGURES 12–17. DIC micrographs of Hyposternus ceylonicus gen. nov, sp. nov., female. 12, sternal shield; 13, genital shield; 14, anal shield and portion of opisthogaster; 15, subcapitulum; 16, chelicera (note that the movable digit of left chelicera has been moved from its natural position). Male: 17, idiosoma in ventral view.

FIGURES 18–21. Hyposternus ceylonicus gen. nov, sp. nov., female.18, leg I (trochanter-tibia); 19, leg II; 20, leg III; 21, leg IV.

FIGURES 22–23. Hyposternus ceylonicus gen. nov, sp. nov., male. 22, ventral idiosoma; 23, chelicera.