Triquetramana brevipalpa, Hendrycks & Conlan, 2003

Hendrycks, EA & Conlan, KE, 2003, New and unusual abyssal gammaridean Amphipoda from the north-east Pacific, Journal of Natural History 37, pp. 2303-2368 : 2353-2359

Triquetramana brevipalpa sp. nov.

(figures 20, 21)

Type material

H  : adult X, (broken into three parts), ~ 11.5 mm, (appendages on one slide), CMNC 2002-0039 , Sta. 1912, Cup# 7, 34°52.46∞N, 123°06.98∞W, 3500 m, 20 June 1994 .

Description

H  , female, CMNC 2002-0039.

Head: slightly shorter than peraeonites 1 and 2 combined, midcephalic margin concave; rostrum short, broad; eye absent; lateral cephalic lobe broad, margin truncated. Antenna 1: about 0.5×body length, peduncular articles 1:2: 3 in ratio of 11:9:3, distally with a few setae, peduncular article 3 with a cluster of fine, distomedial spines; accessory flagellum short, length 0.5×peduncle 3, conical, one-articulate, with a short and a long spine distally; primary flagellum about 15-articulate, proximal articles with long, fine aesthetascs and slender spines distally, terminal article with a fine seta apically, calceoli absent. Antenna 2: slightly longer than antenna 1, peduncular article 4 slightly broadened proximally, peduncular article 5 long, length 1.6×article 4, with cluster of plumose setae distally; flagellum short, length 0.6×peduncles, nine-articulate, terminal article with a long, fine seta apically, calceoli absent.

Peraeon and pleon: smooth. Coxae 1–4: unequal in size and form. Coxae 5–7: shallow, decreasing in size posteriorly.

Upper lip: slightly produced, rounded, separated from midcephalic margin, ventral margin rounded, with fine setae. Lower lip: outer lobes broadly rounded, mandibular lobes narrow; inner lobes very weak. Mandible: incisors asymmetric, margins broad, left with two teeth at anterodorsal corner, margin smoothly concave, right with two teeth at anterodorsal corner, margin straight and slightly denticulate; left lacinia mobilis broad, 0.65×incisor, eight-cusped; right lacinia mobilis narrower with denticulate margin; accessory spine row with two to three stout, pectinate teeth and three to four slender spines; molar strongly triturative, margin sharply ridged on one side and smooth on the other, with two medial, plumose setae; palp threearticulate, very short, length 0.8×mandible body, article 1 about as long as wide, article 2 long, nearly twice length of article 3, with eight setae, article 3 short, length 0.5×article 2, slender, with one lateral, one medial and three apical setae, posterior marginal setae absent. Maxilla 1: inner plate tall, narrow, reaching distomedial margin of outer plate, with a tiny, setule subapically; outer plate with nine multicusped spine-teeth; palp two-articulate, longer than outer plate, slender, article 1 long, length 0.6×article 2, article 2 with five apical, five subapical and two lateral setae. Maxilla 2: inner plate wide, 1.8×outer plate, ovate, medial half of apical margin with nine short setae, with nine short setae apicomedially; outer plate longer than inner, with apical spines and setae. Maxilliped: inner plate reaching about 0.5×basal article of palp, apical margin with five slender spines, with two stout spines at apicomedial corner, with two subapical and one medial seta; outer plate subovate, lateral, apical and medial margins with setae; palp four-articulate, strong, article 2 long, length 1.2×article 3, with distomedial row of setae, article 3 with mediofacial and distomedial setae, dactylus strong, slightly longer than article 3, medial margin lined with short, slender spines.

Gnathopods: equal in size and shape, subchelate. Gnathopod 1: coxa, anterior margin slightly concave, widening slightly distally, posterior margin with a spine and three mediofacial spines; anterior and posterior margins of basis with long, plumose setae; merus, length 3×width; carpus elongate, length 6.7×width, nonlobate, with scattered setae on dorsal and ventral margins; propodus of eusirid-like structure, attached on a very narrow point, triangular, length about 0.5×carpus, palm smoothly convex, with medial and lateral row of submarginal setules, palm corner defined by two long and two short spines, palm slightly longer than ventral margin; dactylus long, slender, exceeding palm. Gnathopod 2: coxa depth about 1.3×width, posterior margin with one spine; basis slightly longer than gnathopod 1 basis, carpus longer and slightly wider, length 6.2×width, propodus as above.

Peraeopod 3: coxa larger than coxa 4, hatchet-shaped, with a broad, posteroventral lobe, posterior margin shallowly excavate with one spine; basis slender, length 9.7×width, anterior margin with proximal and distal plumose setae, with four clusters of long setae on posterior margin; merus slender, length 8.3×width, with one long, anterodistal and one posterodistal seta; carpus short, length 0.6×merus; propodus, length 1.4×carpus, anterior margin with seven setae, posterior margin with two setae; dactylus long, slender, length 1.25×propodus, anterior margin with two setae. Peraeopod 4: coxa small, about as wide as deep, with a small, rounded posteroventral lobe, posterior margin shallowly excavate; basis slightly shorter than peraeopod 3, with four long setae on posterior margin, with posterodistal cluster of plumose setae; merus slender, length 10.4×width, with one long, anterodistal seta; carpus as above; propodus length 1.5×carpus, anterior margin with nine setae, posterior margin with five setae; dactylus as above. Peraeopod 5: subequal to peraeopod 6 and about 1.2×peraeopod 7; coxa equilobate, shallow, depth about 0.3×length; basis nearly round, expanded, posterior margin smoothly convex, lacking posteroventral lobe; merus strongly expanded proximally, narrowing distally, anterior margin with short spines, posterior margin with setae and spines proximally; carpus longer than merus, anterior and posterior margins spinose; propodus long, length 18.5×width and 1.7×carpus, anterior margin with spines, posterior margin with six to seven long, plumose setae; dactylus straight, slender, length 0.4×propodus. Peraeopod 6: very similar to above; merus slightly narrower; carpus slightly longer than merus; propodus long, length 15×width and 1.9×carpus, posterior margin with spines and six long, plumose setae; dactylus as above. Peraeopod 7: basis ovate, expanded, depth 1.25×width, anterior margin spinose, posterior margin smoothly convex, posteroventral lobe round, reaching distal margin of ischium; merus slightly expanded in the middle, margins spinose; carpus length 1.2×merus, anterior and posterior margins spinose; propodus, length 12.5×width and 1.4×carpus, anterior and posterior margins with spines; dactylus as above.

Gills: on peraeopods 2–7. Brood plates: narrow, with short brood setae, on peraeopods 2–5. Pleopods: powerful, peduncles and rami long. Epimeron 2: posteroventral corner with a slight tooth. Epimeron 3: posterior margin convex, posteroventral corner with a very weak tooth.

Uropod 1: peduncle length 1.1×inner ramus, dorsolateral and dorsomedial margins strongly spinose; rami broadly lanceolate, outer ramus length 0.8×inner, margins spinose; inner ramus with margins spinose. Uropod 2: same as above, except peduncle length 0.7×inner ramus. Uropod 3: peduncle length 0.6×inner ramus, with two lateral, two dorsolateral, one apicodorsal, three dorsomedial and two apicomedial spines; rami broadly lanceolate; outer slightly shorter than inner, length 3.6×width, with ten lateral and 16 distomedial spines; inner ramus length 3.8×width, with six distolateral, 14 distomedial spines and one plumose seta. Telson: long, length 3×width, with five to six dorsolateral spines, cleft 61%, lobes narrowing distally, acute apically. Male unknown.

Etymology

The species name is from the Latin brevis (short) plus palpo (touch, feel, stroke), referring to the short mandibular palp.

Condition

All appendages are present. The left peraeopod 7 was dissected instead of the right. The left antenna 1 is broken off at the end of peduncle 1, but is with the body. Peraeopod 3 of the left side is broken off at the end of the merus, with the distal segments missing.

Remarks

The combination of the triangular, equal sized gnathopods, elongated non-lobate carpus of the gnathopods, the feeble mandibular palp and the proximally expanded merus of peraeopods 5–7 differentiate Triquetramana brevipalpa from all other eusirid species.

The gnathopods of this species are of a peculiar form, with the attachment point of the propodus to the carpus being on a very small point of the propodus. The gnathopods then hang downward, much like a pendulum. The propodus of the gnathopods are of an equilateral triangular shape, with the dorsal and ventral margins nearly straight. In other eusirid species, especially members of the genus Eusirus , the ventral margin of the propodus is strongly curved, fitting into a matching, carpal lobe when the propodus is moved posteriorly. This gives the propodus essentially four distinct margins, not three, as is the case in T. brevipalpa . The unusual, gnathopod structure may afford T. brevipalpa great flexibility and would assist this predator in the capture of prey items, grooming and fighting.

Distribution North-east Pacific off Point Conception, California in 3500 m depth.