Oedicerina denticulata, 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 : 2359-2364

Oedicerina denticulata sp. nov. (figures 22, 23)

Type material

H  : X, 7.2 mm, (appendages on one slide), CMNC 2002-0025 , Sta. 208, Cup# 1, 34°46.59∞N, 123°04.04∞W, 4050 m, 23 October 1989. A  : adult W, 5.6 mm, (appendages on one slide), CMNC 2002-0026 , Sta. 2030, Cup# 12, 34°53.80∞N, 123°10.31∞W, 4050 m, 23 October 1994; P    : X, CMNC 2002- 0027 , Sta. 2624, Cup# 6, 34°55.80∞N, 123°09.88∞W, 4050 m, 17 October 1995; juvenile W, CMNC 2002-0028 , (same data as previous station, except Cup# 12) .

Diagnosis

Rostrum strongly deflexed, apex acute, as long as peduncular article 1; maxilla 1, lateral margin of palp article 2 with small spines; gnathopods 1–2, carpal lobes massive, triangular, carpal lobe of gnathopod 2 narrowly rounded ventrally, directed anteriorly, propodus triangular, expanded distally, palm strongly convex, margin crenate, dactylus not reaching end of palm; peraeopod 5, dactylus length 1.1×propodus; pleonites 2–3 and urosomite 3 (male with urosomite 1 also) with a posterodorsal tooth; telson, cleft 40%, apices of lobes acute, with subapical notch.

Description

H  , female, CMNC 2002-0025.

Head: about as long as peraeonites 1–3, midcephalic margin of head obliquely angled; rostrum strongly deflexed, narrowing to an acute apex, reaching end of penduncular article 1; eye absent; lateral cephalic lobe broad, margin truncated. Antenna 1: short, length about 0.25×body; peduncular articles 1:2: 3 in ratio of 17:15:8, peduncular article 1 with a distolateral cusp, with long, plumose setae distally and medially, peduncular article 2 long, with plumose setae distally and medially, peduncular article 3 short, length 0.5×article 2; accessory flagellum short, length 0.2×peduncle 3, conical, one-articulate, with two short and one long setule distally; primary flagellum eight-articulate, slightly shorter than peduncles, terminal article tipped with an aesthetasc and a long seta, calceoli absent. Antenna 2: slightly longer than antenna 1; peduncular article 4 stout, long, length 1.7×peduncular article 5, article 4 strongly setose, peduncular article 5 short, setose; flagellum very short, length 0.2×peduncles, six-articulate, with setae on distal margins, with a few aesthetascs distally, calceoli absent.

Peraeon: smooth. Pleonites 2–3: with a posterodorsal tooth, that of 2 the larger. Urosomite 3: with an acute, posterodorsal and laterodorsal tooth.

Upper lip: broad, separate from midcephalic margin, ventral margin flattened, with fine setules laterally and medially. Lower lip: outer lobes broadly rounded, mandibular lobes narrow; inner lobes large, separate. Mandible. incisor margins with five teeth; left lacinia mobilis five-cusped; right lacinia mobilis narrower with six to seven cusps; accessory spine rows with four to five slender, pectinate spines; molar strongly triturative, columnar, lateral margin of right molar denticulate, medial margin smooth, with a plumose seta; palp three-articulate, long, length 1.6×mandible body, article 1 short, length 0.8×width, article 2 equal in length to article 3, slightly tapering distally, with 11 posterodistal setae, article 3 slender, slightly tapering distally, anterior margin with two setae, posterior margin with six setae, with three apical setae. Maxilla 1: inner plate oval, with three plumose, apical setae; outer plate with nine multi-cusped spine-teeth (three with bifurcate tips); palp two-articulate, longer than outer plate, slender, rounded apically, article 1 short, length 0.25×article 2, article 2 with eight apical/subapical setae, three medial and two long, lateral setae, lateral margin with 10 small spines. Maxilla 2: plates subequal, inner plate slightly tapering distally, width about 1.3×outer, with setae and spines apically and subapically; outer plate rounded with apical spines and setae, with two apicolateral setae. Maxilliped: inner plate subrectangular, reaching about 0.3×basal article of palp, apical margin with eight slender spines, with four to five small setae, with a stout spine on apicolateral face; outer plate slender and curved, long, reaching about 0.3×length of palp article 2, apical and medial margins with setae and small spines, base of outer plate with cluster of minute, triangular scales; palp fourarticulate, strong, mediolateral margins of articles 1–2 with minute, triangular scales, article 2 triangular, widest at the midpoint, with strong medial setae, article 3 produced distomedially, with mediofacial, distomedial and lateral setae, dactylus strong, slightly curved, length 1.5×article 3.

Gnathopod 1: coxa broadly triangular, anteroventral corner bluntly rounded, anterior margin with scattered setae, ventral margin straight, lined with curled setae, posteroventral corner right angled; basis, distal half of anterior margin with long setae, posterior margin with long setae; merus with a small, ventral lobe, ventral margin with setae; carpus about equal to propodus, with 15 long submarginal, plumose setae on dorsal margin, with a huge, broadly triangular ventral lobe, ventral margin lined with setae; propodus subchelate, triangular, strongly widening distally, dorsal margin with long, plumose setae, palm convex, margin crenate, with fine denticulations, with medial spines and lateral row of submarginal setules, palm slightly longer than ventral margin; dactylus robust, length about equal to palm, with minute scales proximally, dactylus inserted slightly distal to dorsal margin. Gnathopod 2: similar to gnathopod 1, slightly longer and narrower, less setose; coxa narrow, depth 1.9×width, ventral margin lined with setae; basis longer, with a circular patch of strong setae anterodistally; carpus very slightly longer, with 10 dorsal setae, ventral lobe exceeding palm of propodus, directed slightly anteriorly, strongly narrowing ventrally, ventral margin lined with setae; dactylus slightly shorter than palm, lacking minute scales proximally.

Peraeopod 3: short, coxa wider than coxa 2, ventral margin less setose; basis short, length 3.3×width, anterior and posterior margins with setae; merus with setae anterodistally and posteriorly; carpus length 1.3×merus, expanded posteriorly, posterior margin strongly setose; propodus length 0.7×carpus, with setae anterodistally and posterodistally; dactylus spatulate-shaped, robust, length 1.2×propodus. Peraeopod 4: as above except; coxa large, wide, width 1.3×depth, with a huge, blunt, posteroventral lobe, posterior margin deeply excavated; carpus short, length 0.9×merus; propodus length 0.9×carpus; dactylus, length 1.4×propodus. Peraeopod 5: subequal to peraeopod 6 and about 0.5×peraeopod 7; coxa bilobate, posterior lobe strongly produced ventrally, lobe broadly triangular, deep, depth about 0.8×width; basis narrow, rectangular, with anterodistal and posterior marginal setae; merus slightly shorter than basis, margins setose; propodus long, length 1.7×carpus, with cluster of setae anterodistally, with eight rows of setae on posterior margin; dactylus robust, spatulate-shaped, length 1.1×propodus. Peraeopod 6: similar to peraeopod 5 except; posterior lobe of coxa broadly rounded, deep. Peraeopod 7: long, length about twice peraeopods 5–6; basis ovate, slightly tapering distally, expanded posteriorly, anterior margin convex, setose, posterior margin with long, plumose, submarginal setae; merus, carpus and propodus in ratio of 43:44:27, merus and carpus with clusters of setae and spines on margins; propodus with clusters of setae on margins; dactylus straight, slender, length about 0.5×propodus, with long setae apically.

Gills: on peraeopods 3–6. Brood plates: on peraeopods 2–5, small, not fully developed, lacking brood setae. Pleopods: powerful, peduncles and rami long. Epimeron 2: deep, deeper than epimeron 1 and 3, anteroventral corner produced, rounded, ventral margin convex, posteroventral corner subquadrate. Epimeron 3: anteroventral corner rounded, posterior margin convex and extending on to the surface of pleonite 3.

Uropod 1: peduncle length 1.2×inner ramus, dorsolateral margin strongly spinose, dorsomedial margin with long, slender spines; rami lanceolate; outer ramus short, length 0.7×inner, lateral margin spinose, medial margin without spines; inner ramus with margins spinose. Uropod 2: similar to above except; peduncle length 0.7×inner ramus. Uropod 3: peduncle length 0.4×inner ramus, with one dorsolateral and one dorsomedial spine; outer slightly longer than inner, margins with long, plumose setae. Telson: short, length 1.4×width, cleft 40%, lobes acute, widely diverging, notched subapically, with terminal penicillate setae, with a pair of dorsolateral penicillate setae.

A  , male, 5.6 mm. Similar to female, except the following. Lateral cephalic lobe: broad, margin slightly emarginate. Antenna 1: peduncular articles 1:2: 3 in ratio of 23:17.5:10; accessory flagellum, length 0.25×peduncle 3, conical, one-articulate, with one short and three long setules distally; primary flagellum 11-articulate, article 1 long, length 1.2×peduncular article 3, proximal articles enlarged, forming a weak callynophore. Maxilla 1: palp article 2 with eight to nine small spines on lateral margin. Gnathopods 1–2: dactylus more strongly curved. Peraeopod 7: basis narrower, posterior margin with fewer long, plumose setae. Urosomite 1: with a small, posterodorsal tooth, flanked by two setules. Uropod 2: outer ramus short, length 0.6×inner.

P    , juvenile male, 5.0 mm. Similar to adult male, except the following: Antenna 1: proximal articles of primary flagellum weakly broadened, starting to form a weak callynophore. Antenna 2: peduncular article 4, lateral and medial margins less setose. Gnathopod 2: ventral lobe of carpus is slightly narrower; propodus, palm with fewer spines; dactylus straighter.

Etymology

The species name is from the Latin denticulatus (with small teeth), referring to the dorsal teeth on the second and third pleonites and urosomite 3.

Condition

Female with all appendages and small, non-setose brood plates. The left uropods are damaged and bent. Male with all appendages intact. The left peraeopod 7 is broken off at the end of the merus. Juvenile male has damaged uropods.

Variation

Paratype female. The propodus and ventral lobe of the carpus of gnathopods 1 and 2 are narrower.

Remarks

Oedicerina denticulata is the first species described from complete specimens and the first record of the genus in the Pacific. This is also the first recorded male specimen and represents a new depth record. The other two species, O. ingolfi Stephensen, 1931 (type of genus) and O. megalopoda Ledoyer, 1986 , were both described from incomplete female specimens, the former without even gnathopods. Oedicerina ingolfi was collected at a depth of 1802 m between the Faroes and Jan Mayen (66°23∞N, 7°25∞W) and O. megalopoda was taken off Madagascar in 200–500 m depth.

The genus is distinctive and easily recognized by the following combination of characters: the immense, posteroventral lobe of coxa 4; strong rostrum; peduncular article 1 of antenna 1 with a distal tooth; strongly subchelate gnathopods with very large, broad, carpal lobes; strongly posterolobate coxae 5 and 6; the triangular shape of the maxilliped palp article 2; the distomedial process of the maxilliped palp article 3, and the strongly triturative, mandibular molar. Additional characters of O. denticulata which cannot be compared with the other species include: the very short flagellum of antenna 2; the small, posterodorsal teeth on the margins of pleonites 2 and 3, urosomites 1 (male only) and 3; peraeopod 6, coxa deeply posterolobate, basis narrow, rectangular; outer ramus of uropods 1 and 2 strongly shortened and the telson, which is cleft quite deeply for an oedicerotid, about 40%.

The type female specimen of O. megalopoda ( MNHN, Am. 4182) was borrowed and compared to the new species. An interesting discrepancy exists between this specimen and Ledoyer’s description. He notes that his specimen is lacking ventral marginal setae on coxae 1 and 2, and uses this character as one to differentiate his species from O. ingolfi . Upon careful examination, insertion points of setae were observed lining the ventral margin of coxae 1–3 and he did illustrate one seta on the margin of coxa 1 (Ledoyer, 1986: 833, figure 326). It is apparent that the specimen has lost all the marginal setae and does not differ from O. ingolfi or O. denticulata in this character.

Oedicerina denticulata can be differentiated from O. ingolfi and O. megalopoda as seen in the key.