(Figs 2, 3)
Type material. Holotype, male, 2.9 mm., ESFM-MAL/ 2010-2220, entrance of the Dardanelles in the Sea of Marmara, Turkey, 40 ° 26 ' 28 "N 27 °05'09"E, on coralligene bottom, April 2010. Paratypes, 76 males, 112 females, ESFM-MAL/ 2010-2221, dissected and figured paratype, 2.9 mm, ESFM-MAL/ 2010-2222, same data as holotype.
Type locality. Entrance of the Dardanelles in the Sea of Marmara.
Etymology. Named in honour of the carcinologist Prof. Dr. Tuncer Katagan, who always encourages young scientists.
Description. Based on male holotype 2.9 mm.
Head. Head ocular lobes strongly produced, rounded, sub-ocular margin strongly recessed. Eye subovoid to subreniform. Antennae missing (absent also in all paratypes). Mandible palp article 3 spatulate, shorter than article 2. Maxilla 1 inner plate without setae. Maxilla 2 inner plate with facial setal row. Maxilliped dactylus broad.
Pereon. Gnathopod 1 coxa subrectangular, not produced forward; basis elongate, slender; carpus subovoid, a little longer than propodus; propodus palm with rounded excavation, posterodistal margin produced, scalloped with about five equidistant robust setae; dactylus sub-straight, longer than propodus. Gnathopod 2 much larger than gnathopod 1, coxa subsquare; basis robust, about three times as long as broad, anterior margin concave, carpus shorter than propodus, subovoid; propodus about twice as long as broad, subovoid, palm weakly excavate with small, medial, rounded protrusion; dactylus about two thirds length of propodus, strongly overlapping palm. Pereopods 3–4 dactylus less than half length of propodus. Pereopods 5–7 in the length ratios 3: 4: 4; basis subovoid.
Pleon. Epimera 1–3 rounded. Uropod 1, peduncle with many marginal robust setae and with a short interramal spine; outer ramus shorter than inner ramus; inner ramus subequal in length with peduncle. Uropod 2 similar to uropod 1 but lacking an inter-ramal spine; Uropod 3 peduncle short; rami very unequal in length, inner ramus twice length of peduncle; outer ramus one and a half length of peduncle. Telson about as broad as long, each lateral crest with a single, long, robust seta.
Female sexually dimorphic characters (based on paratype 2.9 mm). Gnathopod 1 coxa subrectangular; basis robust, broadening distally, carpus distinctly longer than propodus; propodus palm oblique, evenly continuous. Gnathopod 2 only a little larger than gnathopod 1; carpus and propodus subequal in length; propodus palm oblique, evenly continuous.
Habitat. Coralligenous and sand-mud mixture at 15 m.
Remarks. Megamphopus katagani sp. nov. is most similar to M. cornutus Norman, 1869 and M. longidactylus Chevreux, 1926 in its subsquare coxa and subrectangular propodus on the male gnathopod 2. In M. longidactylus, however, the dactylus of the male gnathopod 2 is subequal in length with the propodus, and in M. cornutus it is very short. In M. longicornis Chevreux, 1911 and in M. brevidactylus Myers, 1976, the ocular lobes terminate in a sharp point whereas in M. katagani the lobes are rounded. It also differs from all other described species in the genus by the complexly scalloped posterodistal margin of the male gnathopod 1 propodus.
Distribution. Known only from the type locality.