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Takeda, 1977

Description of holotype: Carapace quadrilateral with protruded frontal region, its dorsum being uneven, indistinctly rugose or reticulated; protogastric regions markedly convex, high and more or less reticulated with irregular ridge-like elevations; median gastric region low, but medially traversed by a short ridge with indistinct two tubercles; cardiac region deeply separated from median gastric region, and only weakly convex, with reticulation and microscopical pits; a small tubercle at some distance from lateral end of cardiac region, and a similar but slightly larger one obliquely behind the said tubercle and cardiac region; intestinal region not demarcated, but only sunken; hepatic region nearly smooth, and widely and deeply sunken; a prominent protuberance with reticulation at anterior branchial region; antero-inner part of anterior branchial region prolonged toward posterior part of protogastric protuberance as an indistinct ridge; posterior branchial region irregularly reticulated, with three low protuberances which are obliquely separated by smooth shallow furrows.
Front strongly developed as two convexities. Anterior part of lateral border of carapace thin, weakly curved upward and armed with four lobes behind a weak concavity next to external orbital angle; these lobes contact with each other, only leaving three narrow slits; border of each lobe again subdivided into three conical teeth, median one of which is the largest. Posterior part of lateral border remarkably expanded as a thin lobe, its upper surface, or outer surfaces of posterior branchial protuberances, curving downward and its lower surface being deeply excavated for reception of ambulatory legs; on a close examination three equidistant closed sutures traced.
Both chelipeds stout and equal in size. Merus smooth and concealed beneath carapace; its upper border nearly truncated throughout its length, and thus two weak ridges formed; its outer lower border bears two subdistal conical teeth, border between them being concave to receive in natural position first tooth of lower border of palm. Carpus enlarged, smooth on its inner surface, and roughly and irregularly reticulated or eroded on its outer surface; its inner angle sharply angulated. Palm high, roughly reticulated or eroded with some long longitudinal and many short transverse ridges; several small tubercles on longitudinal ridges; upper border sharp and armed with two conical teeth, and its distal end also produced to a similar tooth; lower border thin and cut into three conical teeth. Immovable finger broad and ornamented with two longitudinal ridges, its lower border being cut into three low teeth. Movable finger rather slender, and its proximal end of upper border angulated. Cutting edges of both fingers regularly toothed with several conical teeth throughout their length.
Ambulatory legs distinctly depressed and reduced their length from first to fourth. Merus smooth for its most part, but places near crests on posterior upper and lower borders ornamented with pits of various size; a remarkable thin crest developed on anterior border, being reinforced by several transverse ridges; margin of crest nearly entire, but in first two pairs their proximal halves more or less irregular each with two or three setae. Upper surface of carpus pitted and divided into two by a longitudinal ridge; anterior part of upper surface markedly roughened and more or less reticulated; anterior border sharp, and its distal end produced into a conical tooth. Both borders of propodus sharp and ornamented with pits of various size; in first two pairs each upper border cut into three teeth including distal one, and proximal part of posterior border with a tooth-like expansion, while last two pairs with these features of weak development; upper surface markedly uneven with about three longitudinal ridges. Both borders of dactylus also thin with two prominent teeth on anterior border and one on posterior border; upper surface ornamented with two ridges, viz., dentate anterior one with three or four teeth and non-dentate posterior one; posterior ridge ill-developed in last pair, but anterior dentate ridge always strong; terminal horny claw very small.
In life, the holotype was entirely creamy white. (Takeda, 1977a)

Type locality: Ogasawara-shoto, Japan.
Range: Japan - Ogasawara-shoto (Takeda, 1977a).

Osachila expansa