(Fig. 54)

Description. FEMALE (holotype). Body, including gnathosoma, 380 long (370–395 in 8 paratypes), 175 wide (175–185). Propodonotal shield with widely rounded posterior margin, length 55 (55–60), maximum width 60 (60–65). Setae si 30 (30–35) about 1.6–2 times shorter than se, 52 long (50–55). Distance se–se 57 (55–60), about 5 times greater than si–si, 9 (8–9). Bursa copulatrix opening dorsal. Sternum about 22 long. Posterior projections of coxal fields I distinctly developed, about 9 long, 13 wide. Distance between distal ends of apodemes II about 30. Two pairs of distinct, slightly sclerotized folds present ventrally on propodosoma posterior to coxal fields II. Distance 4a–4a 33 (30–38), subequal or 1.5 times greater than ps3–ps3, 30 (20–30). Alveoli of setae h1 and h3 absent. Legs III and IV subequal in length, about 125 and 135 long, respectively (excluding pretarsus). Setae cG I–II microspines, about 2 long. Setal lengths: 1a 9 (9–13), c3 13 (11–16), cp 35 (31–38), h2 145 (140–150), vF I about 25, vF II about 27, mG I–II 24–27, gTI–II 2–3, ϕI–II 10– 11, solenidia ω 1 I–II about 9.

MALE (paratype). Body, including gnathosoma, 360 long, 170 wide. Propodonotum as in female. Propodonotal shield 54 long, 65 maximum wide. Setae si 25 long, 1.5 times shorter than se, 38 long. Distance se– se 57, about 4.5 times greater than si–si, 12. Sternum about 15 long. Posterior projections of coxal fields I very short and wide, about 9 long, 12 wide. Distance between distal ends of apodemes II about 35. Two pairs of distinct folds present ventrally on propodosoma posterior to coxal fields II. Aedeagus about 40 long, its posterior end situated at level of setae g. Length and width ratio of postgenital shield subequal, about 30 long. Distance g–g 17, about 1.3 times greater than ps3–ps3, 13. Alveoli of setae h1 and h3 absent. Legs III and IV subequal in length, about 125 and 140 long, respectively (excluding pretarsus). Setae cG I–II microspines, about 2 long. Setal lengths: 1a 8, c3 9, cp 25, h2 135, vF I–II about 22, mG I–II about 17, gT I–II about 2, solenidia ϕI–II about 10, ω 1 I–II about 8.

Type material examined. Female holotype (BMOC 92-1400 - 014) ex Apomys sp. C (sensu Heany et al. 1998) (Muridae) (FMNH 146895), PHILIPPINES: Romblon Prov., Sibuyan Is., 4.5km S, 4km E Magdiwang, 325m, 12º30'N, 122º31'E, 17 February 1992, coll. S.M. Goodman (SMG 4937); female and tritonymph paratype (BMOC 92-1400 - 033) ex Apomys sp. C (Muridae) (FMNH 146900), same locality, 20 February 1992, coll. S.M. Goodman (SMG 4982); 7 female and 1 male paratypes (BMOC 92-1400 - 012) ex Apomys sp. C (FMNH 146893), same locality, 16 February 1992, coll. S.M. Goodman (SCG 4928).

Type deposition. Holotype and paratypes are deposited in FMNH, other paratypes in NMP, UMMZ and ZISP.

Host range and distribution. This species is known only from the type host, an undescribed species of Apomys referred to as “sp. C” by Heaney et al. (1998), from the Philippines.

Etymology. The species name is derived from the generic name of the host and is a noun in apposition.

Remarks. This new species is most similar to Y. muris. In both species, setae si are distinctly shorter than se, the distance si–si is short, about 3–6 times shorter than se–se, setae cG I–II are microspines, about 2 long. It differs from Y.muris by the following characters. In females of Y. apomys, setae si and se are 30–35 and 50–55 long, respectively, the bursa copulatrix opens dorsally, the propodosoma bears two pairs of distinctly developed and slightly sclerotized folds ventrally. In females of Y. muris, setae si and se are 13–15 and 27–30 long, respectively, the bursa copulatrix opens terminally, and the propodosoma bears two or more pairs of weakly developed folds ventrally.