Hemieuryale

Genus Hemieuryale von Martens, 1867

Hemieuryale von Martens 1867: 484.― Lütken 1869: 47.― Lyman 1882: 249.― Verrill 1899b: 363 –364.― H.L. Clark 1915: 192.

Sigsbeia (not Sigsbeia Lyman, 1878).― Barboza & Borges 2012: 5.

Type-species. Hemieuryale pustulata von Martens 1867.

Diagnosis. Swollen radial primary plates, numerous flat overlapping scales in center of dorsal disc. A mosaic of small plates on dorsal arm. Accessory dorsal arm plate swollen and rounded, much enlarged on first free arm segment. Lateral arm plate large with tuberculous stereom. Small triangular extraoral plate, present on all or only some jaws. Short bursal slits lateral to oral shields. Two short arm spines, about half the length of an arm segment, with a crown of thorns at tip.

Remarks. In the original description of the genus, von Martens (1867) provides the following diagnostic characters, some of which need to be modified according to the new findings (in parentheses): arms simple, sides of arms provided with a series of large bumps (= swollen accessory plates), without differentiated madreporic plate (in SEM identifiable by hydropore), bursal slit located on inferior and lateral parts of oral shields, a row of oral papillae, teeth absent (clearly present). According to Lyman (1878), Hemieuryale and Sigsbeia form a peculiar group, in which both genera are differentiated from each other by the shape of the dorsal arm plate, forming a mosaic of small pieces in the first genus, and being an entire plate in the second. A detailed study of Sigsbeia is needed to decide if they indeed are a monophyletic taxon.