(Figures 1–3)
Type material. Holotype, sex undetermined, 2.5 mm, NIWA 50185, Giggenbach submarine volcano, Kermadec Volcanic Arc, 30º02.2’S, 178º42.65’W, 160 m (KOK0505 /42), collected with the hydrothermal vent mussel Bathymodiolus sp. by submersible Pices V . Paratypes, 19 specimens, 1.8–3.0 mm, NIWA 48674, from the same locality.
Etymology. Named for the Kermadec Arc from where this material was collected.
Diagnosis. Antenna 1 peduncle with 3 distinct articles, article 3 long. Lateral cephalic lobes subquadrate, not downward-pointing. Eyes present. Pereopod 3 propodus largely expanded and strongly subchelate. Pereopod 7 basis posteroventral margin excavate.
Description of holotype. Antenna 1 subequal to antenna 2; peduncle with 3 distinct articles, articles 2–3 not telescoped; flagellum 7-articulate, article 1 slightly longer than article 2; accessory flagellum 3-articulate. Antenna 2 less than 40% of body length; flagellum 6-articulate. Calceoli absent. Eyes present, large, oblong. Lateral cephalic lobes subquadrate. Epistome and upper lip fused. Mandible incisor broad, smooth; lacinia mobilis absent from both mandibles; molar a setose flap; palp attached slightly proximally, article 3 slightly greater than half length of article 2. Maxilla 1 outer plate with setal-teeth in a modified 6/5 arrangement; palp present, 2 articulate. Maxilliped palp 4-articulate, article 4 well developed; outer plate poorly developed, not reaching palp article 3, apical margin weakly crenated; inner plate well developed, greater than half the length of outer plate.
Gnathopod 1 simple; coxa 1 large, about as long as coxa 2, slightly tapering posterodistally, rounded distally; ischium moderately elongate, about 1.8 × as long as broad; merus short; carpus very short, distinctly shorter than propodus; propodus margins tapering; dactylus without accessory tooth. Gnathopod 2 minutely chelate; carpus twice as long as propodus. Pereopod 3 highly distinctive of genus; propodus largely expanded, strongly subchelate. Coxa 4 with moderately developed posterior lobe; merus weakly expanded, subequal in length to carpus; carpus slender, slightly shorter than propodus; propodus slender; dactylus about half propodus length. Coxa 5 produced into an anterior lobe; basis about as long as broad, merus expanded posteriorly, subequal in length to carpus; carpus short, much shorter than propodus; dactylus about 0.4 × propodus length. Pereopod 6 basis distinctly longer than broad; merus expanded posteriorly. Pereopod 7 basis distinctly longer than broad, posteroventral margin excavate; posterodistal corner slightly produced, just reaching merus; merus slightly expanded posteriorly, slightly shorter than carpus; carpus slender, distinctly shorter than propodus; propodus slender; dactylus about 0.4 × propodus length. Gills on pereonites 2–6.
Epimeron 1 anterodistal corner broadly rounded. Epimeron 3 posterodistal corner quadrate. Urosomite 1 without distinct dorsal depression. Uropod 1 peduncle longer than rami; rami subequal in length. Uropod 2 peduncle subequal to rami; rami subequal in length, inner ramus without marginal constriction. Uropod 3 peduncle subequal to rami; outer ramus 2-articulate; inner ramus slightly shorter than outer ramus. Telson distinctly longer than broad, entire.
Length. 1.8–3.0 mm.
Distribution. New Zealand: Giggenbach submarine volcano, Kermadec Volcanic Arc; 160 m.
Ecology. A relatively shallow-water species associated with seamounts, possibly commensal on the vent mussel Bathymodiolus sp. (Mollusca, Bivalvia, Mytiloida).
Remarks. Ensayara kermadecensis sp. nov. is markedly similar to E. iara Lowry & Stoddart, 1983 (type locality: Snares Islands), differing only in the shape of the lateral cephalic lobes (subacute in E. iara, subquadrate in E. kermadecensis); the relative length of article 3 of the mandibular palp, which is more than half the length of article 2 in E. kermadecensis, but only about 0.35 × article 2 in E. iara; the maxillipedal palp, which is distinctly more slender, and article 4 of which bears an unguis in the new species that is not present in E. iara; and the relative length of the inner ramus to the outer ramus of uropod 3, which is proportionally longer in the E. kermadecensis.