Ischnomesidae Hansen, 1916

Merrin, K. L. & Poore, G. C. B., 2003, Four new species of Ischnomesidae (Crustacea: Isopoda: Asellota) from off south-eastern Australia, Memoirs of Museum Victoria 60 (2), pp. 285-307 : 285

Ischnomesidae Hansen

Ischnomesini Hansen, 1916: 54.— Wolff, 1956: 86. Ischnomesidae .— Gurjanova, 1932: 40.— Menzies, 1962: 111.—

Wolff, 1962: 71–73.— Birstein, 1971: 198–199.— Menzies and

George, 1972: 971.— Chardy, 1974: 1537.— Kussakin, 1988: 418.

Diagnosis. Body elongate, subcylindrical and narrow. Pereonites 4–5 elongate, pereonite 5 longest, at least twice as long as wide, pereonite 4 widest anteriorly, 5 widest posteriorly. Head fused to and embedded in pereonite 1. Pereonites 1 (posterior margin) to 4 free and articulating. Pleon with maximum of 2 free pleonites plus pleotelson. Anus separated from branchial chamber. Eyes absent. Antenna 1 terminating with simple setae, article 1 squat and globular, article 2 elongate, at least twice as long as article 1. Antenna 2 length more than half body length, without squama. Maxilla 2 inferior margin with 2 medial pectinate setae. Pereopod 1 robust, strongly subchelate and haptorial; pereopods 2–7 ambulatory; dactylus with single unguis and 2 simple setae. Pleopod 3 endopod with 3 distal plumose setae, exopod tapering, shorter than endopod, with long distal plumose seta. Pleopod 4 unadorned, simple lobe, exopod absent; pleopod 5 absent. Uropod uniramous, terminal. In females, operculum wider at midpoint than proximally.

Remarks. This family is unique amongst the asellotes in having the fifth pereonite at least twice as long as wide and the head completely fused to the first pereonite, with only a slight indentation between the somites, and medial pectinate setae on the inferior margin of maxilla 2. This paper acknowledges the often overlooked generic synonymies of Kussakin (1988).