Megaesthesius yokoyai

Sakai, 1939

The carapace is subquadrate and strongly arcuated antero-posteriorly, but nearly level from side to side; the surface is rather ill-defined only with the submedial longitudinal furrows and roughened by somewhat scaly minute granules and by rugosities; near the orbits, front and lateral borders the scaly granules are rather prominent. The frontal region is well demarcated and strongly convex dorsally, being sulcated in the middle, but in the female the frontal region is not so strongly produced as in the male. The supraorbital border is turned downwards, and its free margin is almost invisible from above; the dorsal part of the border in dorsal view is almost transverse, slightly retreating backwards near the corner which is obtusely angulated.
The lateral borders of the carapace is parallel to each other; each of them is provided with three or four notches, of which that in front of the posterior corner is not deep but in reality only a depression. The lobes or teeth thus formed by the notches or depressions are granulated and not strongly protruded from the general contour of the border; of the lobes the last two are armed with spiniform granules, of which one or two of the middle are sometimes much larger than the others. The lateral extremity of the posterior border is prolonged laterally and downwards and armed with several curved spinules; the prolongation is more or less in the appearance of the lobule and visible from above just at the outside of the last two lobes of the lateral border.
The supraorbital and infraorbital borders are granulated and leave a narrow gape near the lateral corner, though they are rather widely separated near the front. The greater part of the long eyestalk is tightly embedded in the orbital gape, but the lateral part, about one-third or less the length of the orbit, is folded below the antero-lateral border of the carapace; that exposed part is also immovable in spite of the absence of the fossa; the cornea is well defined and rounded without pigments.
The antennule is enormously stout and fringed with very long silky hairs; in the male it is especially so and much more stouter than those of the female; there is no antennular fossa, so that it is wholly visible from above except for the basal segment. The antennal basal segment is only slightly shorter but stouter than the second segment; just outside of the basal segment is a subacute small tubercle of the inner extremity of the infraorbital border; the flagellum is long ans slightly exceeds the level of the antero-lateral border of the carapace, being tipped with two longish silky hairs; the female flagellum is, however, much shorter and ends far from the level of the antero-lateral border, when it is applied to the orbital gape. The pterygostomial region is granulated and swollen, but near the proximal part of the buccal cavity it is rather sunken. The buccal cavity is narrower in front. The third maxillipeds are wide and leave only a very narrow median gape. The ischium is wide, while the merus is only slightly narrower and somewhat triangular with acute anterior angle; the palp is very short.
The chelipeds are equal and not much stout ih both sexes. The segments are covered with long fine plumose hairs, and unarmed except for minute granules. However, the outer surface of the carpus is almost smooth and devoid of hairs, and the palm is covered with thick granules and sparse hairs. The outer angle of the carpus is articulated with the low tubercle at the proximal middle part of the palm. The inner angle of the carpus is more or less angulated in the male, and armed with a spinule in the female. The chela is compressed, especially the immovable finger is conspicuously so. The lower border of the chela is prominently crested and almost serrated with a row of spiniform granules. The movable finger is about twice the length of the upper border of the palm and also bears a row of sharp granules along the outer upper border, but not compressed.
The ambulatory legs are long and comparatively slender. The merus is fringed with a distinct row of long, fine plumose hairs, and in addition, bordered with a row of spinules. The carpus bears a fringe of long plumose hairs along the whole length and some spinules near the distal end. The propodus and dactylus are covered with fine hairs of various lengths mixed each with some stout, movable longish setae or hairs that are mostly implanted along the posterior border.
The male abdomen is composed of five pieces; the third to fifth segments are fixed and immovable, though the sutures are not entirely obliterated; in reality that between the fourth and fifth segments is possibly observable, and in the inner view those segments are all distinctly traceable. (Takeda & Miyake, 1969d: 460)

Type locality: Bungo Strait.
Range: Japan - Bungo Strait and Sata-misaki (Yokoya, 1933), Tsushima Strait (Takeda, 1973c); East China Sea (Takeda & Miyake, 1969d, Takeda & Miyake, 1972c).

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