Hirondellea guyoti Barnard & Ingram 1990

Hirondellea guyoti

ETYMOLOGY.—The species is named for the type locality, Hess Guyot.

DIAGNOSIS.—Dactyl of gnathopod 1 strongly overlapping palm in adult, scarcely toothed, with small inner setules and 1 cusp, palm narrow and deeply excavate. Pleonite 3 unproduced posterodorsally; epimeron 3 with strong recurved anteroventral tooth; epimeron 3 rounded behind; urosomite 1 with strong dorsal sinus followed by large rounded hump, urosomites 1 and 3 without dense dorsal prickles; spine row on peduncle of uropod 1 with basal gap; inner ramus of uropod 2 constricted; telson moderately cleft.

DESCRIPTION.—Holotype: Male “Gvp” 11.63 mm: Probably not as fully mature as male of H. glutonis. Rostrum vestigial, lateral cephalic lobe broadly mammilliform, with medium sinus for antenna 2, anteroventral corner sharp; eyes barely indicated by sigmoid outer stain and internal glandular tissue.

Article 3 of antenna 1 invaginated medially, primary flagellum ?-articulate (broken), ?longer than peduncle, basally conjoint, article 1 as long as peduncle, heavily armed with rows of aesthetascs; accessory flagellum conjoint basally, ?5-articulate on left. Antenna 2 ?slightly longer than antenna 1, gland cone large, articles 4–5 armed anteriorly with setular tufts, flagellum 23-articulate, shorter than peduncle, calceoli small.

Epistome dominating upper lip, with thin anterior keel, upper lip entire, with small distal lobule. Incisors with inner and outer notch and tooth, right lacinia mobilis apparently absent, left slender, curved, attached at edge of fossa; principal right and left rakers 3 and 3, remainder of raker row composed of numerous setae, molar large and strongly pubescent along one side, with strong sharp recurved apical point; palp thin, article 2 with line of apicomarginal setae, article 3 weakly falcate, setae =2A, 14D, 2E. Lower lip with small gape between outer lobes, mandibular lobes strong, blunt, inner lobes absent. Inner plate of maxilla 1 with typical giant falcate seta and one smaller seta, outer plate with 11 spines in sets of 7 and 4, heavily pubescent, palp article 2 with one inner notch, inner apex subsharp, apex with 8 thick and one slender spines. Apices of maxilla 2 beveled mediad, heavily setose, no facial setae. Inner plate of maxilliped with apicolateral notch marked laterally with 2 thin spines, medially with long apicomedial row of setae; outer plate enlarged, medial margin weakly crenulate, bearing line of weak facial spines; articles 3–4 thin, latter unguiform, with weak accessory spinule.

Coxa 1 reduced, broader than long, coxae 2–4 longer than broad, coxa 4 well excavate, coxa 5 much shorter than 4. Article 2 of gnathopod 1 densely setose anteriorly, article 6 slightly shorter than 5, tapering, palm narrow, excavate, armed with cusps on either side of excavation, defined by thick spine and slender spine, dactyl strongly overlapping palm, with 1 small inner tooth and several setules. Gnathopod 2 slender and elongate, article 6 much shorter than 5, strongly broadened, minutely chelate, palm broad and hemilunar, defined by short thick spine, bearing few palmate spines projecting from posterior margin but inner face of propodus densely covered with straw-like setules; dactyl failing full reach of palm, with inner wire-seta, subapex with 3–4 setules.

Pereopods ordinary and slender, with 2 locking spines, pereopod 4 smaller than 3; posteroventral margins of article 2 on pereopods 5–7 lobate, weakly beveled only on pereopod 7. Gills present on coxae 2–6, large, flat, weakly plaited, only gill 6 with small conical accessory lobe.

Epimera unarmed, first with anteroventral tooth, rounded behind, second with weak posteroventral protrusion, third rounded-quadrate. Pleopods 1–3 elongate, each with 2 coupling hooks, no peduncle setose laterally, rami about 1.6–1.7 times as long as peduncle, multiarticulate. Oostegites on coxae 2–5, thin, strap-shaped, well setose mostly behind.

Urosomite 1 with dorsal hump (of shape distinct from H. glutonis), urosomite 3 much longer than 2. Peduncles of uropods 1–2 each with lateral flange, spine row on dorsolateral margin of peduncle on uropod 1 with basal gap, rami extending subequally on both pairs, spinosity ordinary, apical nails not apparent, inner ramus of uropod 2 constricted. Uropod 3 ordinary, rami subequal, inner with 8 medial spines, outer 2-articulate, poorly spinose. Telson about as long as rami of uropod 3, cleft about 45 percent, each apex with 1 weak setule-notch, dorsolateral margins on each side with row of 2 spinules.

Other Material: Female “x” 15.70 mm: Much larger than male holotype; head and antennae like male (latter not mature), accessory flagellum 7-articulate; primary flagella broken; flagellum of antenna 2 with 22 articles, calceoli absent; oostegites strap-shaped, thin; spine row on peduncle of uropod 1 also with basal gap, on uropod 2 with 5 spines (versus 3 in male “y”), inner ramus dorsomedially with 9 spines (versus 8), same ramus on uropod 3 with 7 spines; telson like male, also with dorsal denticles.

Juvenile “w” 8.06 mm: Primary flagellum of antenna 1 with 10 articles, of antenna 2 with 14 articles, accessory flagellum broken, calceoli absent; peduncle of uropod 2 with 3 dorsolateral spines, inner ramus with 3 medial spines, same ramus of uropod 3 with 4 medial spines, basalmost spine on each side of telson weak.

ILLUSTRATIONS.—Mandibles like H. glutonis.

HOLOTYPE.—USNM 195196, male “v” 11.63 mm (illustrated).

TYPE LOCALITY.—SIO Cat. No. C5703, Acc. No. BI-68-45, Cruise STYX-7 MPE 68091 & 2, sta 5, Hess Guyot, 17°53′N, 174°14.8W, 1–2 Sep 1968, 1740 m, free vehicle trap, R/V Agassiz.

MATERIAL.—Type locality, female “x” 15.70 mm, juvenile “w” 8.06 mm, and 2 broken specimens.

RELATIONSHIP.—This is a very distinctive species of Hirondellea because of the strong anteroventral tooth on epimeron 1 and the greatly expanded propodus and hemilunar palm on gnathopod 2. Minor distinctions from H. glutonis include details on the inner and outer plates of the maxilliped, the slightly thicker article 3 of the mandibular palp, the gap in basal spination on the peduncle of uropod 1, the very narrow propodus and palm of gnathopod 1 with strongly overlapping dactyl, the fewer inner teeth on that dactyl, and the less strongly beveled article 2 on pereopod 7.

DISTRIBUTION—Hess Guyot, 1740 m.