Octomana hadromischa, 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 : 2345-2350

Octomana hadromischa sp. nov.

(figures 18, 19)

Type material

H  : adult W, 9.5 mm, (appendages on one slide), CMNC 2002-0014 , Sta. 1118, Cup# 3, 34°50.2∞N, 123°05.11∞W, 4050 m, 16 March 1992 . A  : adult X, 10 mm, (appendages on one slide), CMNC 2002-0015 , Sta. 327, Cup# C, 34°47.18∞N, 123°04.18∞W, 4000 m, 27 August 1990 . P    : X, CMNC 2002-0016 , same data as allotype; X, ZMUC-CRU-3723, Sta. 208, Cup# 2, 34°46.59∞N, 123°04.04∞W, 4000 m, 22 November 1989 ; X, USNM 1004364 , Sta. 2305, Cup# 5, 34°53.98∞N, 123°11.10∞W, 3450 m, 23 November 1994 ; X, CMNC 2002-0017 , Sta. 1014, Cup# 5, 34°53.22∞N, 123°02.13∞W, 4050 m, 4 December 1991 ; X, juvenile W, CMNC 2002- 0018 , Sta. 621, Cup# 10, 34°50.88∞N, 122°58.68∞W, 4050 m, 26 May 1991 ; X, CMNC 2002-0019 , Sta. 1216, Cup# 3, 34°47.94∞N, 123°03.80∞W, 3450 m, 15 July 1992 ; W, (broken), CMNC 2002-0020 , Sta. 439, Cup# 2, 34°50.97∞N, 122°59.79∞W, 4000 m, 7 July 1990 ; X, (broken), CMNC 2002-0021 , Sta. 1822, Cup# 6, 34°49.22∞N, 123°05.50∞W, 4050 m, 9 February 1994 ; juvenile X, (broken), CMNC 2002-0022 , Sta. 725, Cup# 3, 34°53.07∞N, 122°59.05∞W, 3500 m, 16 July 1991 ; X, (broken), CMNC 2002-0023 , Sta. 439, Cup# 2, 34°50.97∞N, 122°59.79∞W, 4050 m, 7 July 1990 ; W, CMNC 2002-0024 , Sta. 3034, Cup# 13, 34°55.97∞N, 123°13.89∞W, 3500 m, 3 October 1996 .

Other material examined. W, 8.5 mm (slide mount only), IOS Sta. 91–12, Tow 3,

Net 13, 47°56.25∞N, 129°05.76∞W, B.C., Off Vancouver Island, over Endeavour Ridge, 1985– 1787 m.

Description

H  , male, CMNC 2002-0014.

Head: slightly longer than deep; eyes absent; rostrum slender, about 0.25×head length; midcephalic margin of head produced into a sharp process about level with lateral cephalic lobe; lateral cephalic lobe broad, apically rounded; antenna 2 sinus absent. Antenna 1: elongate, exceeding body length, peduncular article 1 long, about 1.75×head length, lanceolate, apical process reaching 0.7×along peduncular article 3, peduncular article 2 long, length 1.2×article 3, with apicolateral and medial setae, peduncular article 3 short, length 0.8×article 2; accessory flagellum blade-like, long, length 2.8×peduncular article 3, overreaching article 1 of primary flagellum, onearticulate; primary flagellum about 38-articulate, callynophore strong, length about 0.6×peduncles, with strong aesthetascs medially, calceoli absent. Antenna 2: elongate, slightly longer than antenna 1, peduncular article 4 slightly expanded proximally, short, length about 0.6×article 5; flagellum about 47-articulate, calceoli absent.

Peraeon and pleon: smooth. Coxae 1–4: small, wider than deep, not overlapping. Urosomite 2: with a slender, dorsal tooth.

Upper lip: slightly produced, rounded, slightly separated from midcephalic margin, ventral margin very weakly incised, asymmetric. Lower lip: outer lobes broad, mandibular lobes narrow; inner lobes large. Mandible: incisors symmetric, very broad with straight margins, anteroventral corner with a large tooth; left lacinia mobilis present as a stout, peg-like spine; right lacinia absent; accessory spine row with two stout spines and proximal row of stiff setae; molar absent; palp strong, three-articulate, article 1 short, article 2 strongly bent, setose, article 3 pseudofalcate, length 0.8×article 2, margins lined with long setae, with two to three long apical setae. Maxilla 1: inner plate ovate with one subapical, plumose seta; outer plate rectangular with eight spine-teeth; palp longer than outer plate, slightly broadening distally, two-articulate, with eight apical spines and two subapical setae, medial margin with five setae. Maxilla 2: inner plate slightly wider than outer, with five to six plumose setae medially and two apical setae; outer plate narrower, with three apical, plumose setae. Maxilliped: inner plate short, reaching about 0.3×along article 3, with two stiff, apical setae; outer plate narrow, reaching distal end of the basal article of the palp, with two stout, apical spines, medial margin with setae and one spine; palp short, four-articulate, article 1 with lateral setae, articles 2–3 with lateral and medial marginal setae, article 3 ovate, with mediofacial setae, dactylus shorter than article 3.

Gnathopod 1: coxa narrowly rounded anteriorly; basis with plumose setae on anterior margin, ischium and merus short, ventral margin of merus with scattered setae; carpus subrectangular, non-lobate, length 0.8×propodus, dorsal margin with long setae, ventral margin with short setae, with mediofacial setae; propodus stout, ovate, subchelate, lateral, medial and distal margins with many clusters of strong setae, palm margin with about six rows of short, comb-like, pectinate setae increasing in length distally, proximally with long, slender setae; dactylus long, about equal to ventral margin, anterior margin with six setules, posterior margin finely denticulate. Gnathopod 2: coxa broadly rounded anteriorly; basis slightly stouter, but similar to gnathopod 1 basis; merus with long setae on ventral margin, carpus with shallow, broadly rounded lobe, length 1.4×depth, dorsal margin with setae, ventral margin with setae and stout spines; propodus similar to gnathopod 1 but slightly larger; dactylus, length 0.8×ventral margin, otherwise similar to above.

Peraeopod 3: coxa and basis like gnathopod 2 except anterior and posterior margins of basis more setose; ischium short, length 0.5×width; merus strongly expanded, length 1.4×width, posterior margin setose; carpus broad, ovate, as wide as long, anterior and posterior margins setose, posterior margin with two spines; propodus similar to others but slightly smaller; dactylus nearly as long as ventral margin, posterior margin finely denticulate. Peraeopod 4: coxa wider than deep, anterior margin rounded; basis stouter and shorter than peraeopod 3, with setose margins; ischium short, length 0.4×width; merus strongly expanded, longer and wider than merus of peraeopod 3, anterodistal and posterior margins strongly setose; carpus narrowly ovate, length 1.3×width, anterior margin weakly and posterior margin strongly setose, posterior margin with one spine; propodus narrower but similar to others; dactylus as above. Peraeopod 5: coxa shallow, anteroventral corner with cluster of setae; basis rectangular, very deep, depth 3×width; merus, carpus and propodus in ratio of 16:12:24, merus expanded, anterior margin lined with long setae; margins of carpus and propodus spinose; dactylus long, slender, length 0.8×propodus. Peraeopod 6: long, slightly shorter than body; basis deep, depth twice width; merus, carpus and propodus in ratio of 15:32:51, with spinose margins; dactylus long, slender, length 0.4×propodus. Peraeopod 7: longer than peraeopod 5, shorter than 6; basis deep, depth 1.9×width; merus, carpus and propodus in ratio of 14:29:35, carpus and propodus with spinose margins; dactylus as above.

Gills: found on peraeopods 2–7. Pleopods: strong, rami long. Epimeron 3: posteroventral corner subquadrate.

Uropod 1: peduncle length 1.3×inner ramus, dorsolateral and dorsomedial margins strongly setose; rami lanceolate, margins strongly spinose, outer shorter, length 0.8×inner. Uropod 2: as above except, peduncle length 1.1×inner ramus; outer ramus short, length 0.6×inner ramus. Uropod 3: peduncle short, length 0.2×outer ramus, with one apicolateral spine and medial plumose setae; rami elongate, margins lined with plumose setae, length 4.6×peduncle, outer slightly longer, outer ramus two-articulate, article 2 minute, about 0.1×ramus. Telson: long, length 3.4×width, lobes slender, narrowing distally, cleft nearly to base, tips acute, with two penicillate setae.

A  , adult female, 10 mm. Similar to adult male, except the following. Antenna 1: peduncular article 1 long, about 1.75×head length, lanceolate, apical process reaching 0.5×along peduncular article 3, peduncular article 2 short, length 0.7×peduncular article 3, peduncular article 3 long, length 1.4×article 2; accessory flagellum dagger-like, short, length 0.5×peduncular article 3, one-articulate; primary flagellum about 42-articulate, lacking callynophore. Antenna 2: peduncular article 4 very slightly expanded proximally, short, length about 0.6×article 5, peduncular article 5 narrower; flagellum about 45-articulate. Peraeopods 5–7: dactyls shorter. Peraeopod 7: carpus longer and propodus shorter than in male. Brood plates: linear, narrow, with long brood setae, found on peraeopods 2–5. Urosomite 2: posterodorsal tooth absent.

Etymology

The species name is from the Greek hadros (well developed, stout, strong, great) and mischos (stalk, petiole, peduncle), referring to the immense first peduncular article of antenna 1.

Condition

Male with all appendages present. The left uropod 1 was removed instead of the right. The right uropod 1 has the outer ramus partially broken. Female with all appendages and setose brood plates, but not ovigerous. The left peraeopods 5–7

were dissected instead of the right. The right peraeopods 6 and 7 are broken off along the carpus.

Variation

Female. Slight differences in the lengths of antenna 1 and 2 were noted, most likely due to the loss of some terminal articles. These articles are very slender and fine and it is difficult to ascertain whether or not the flagella have been broken near the tips.

Juvenile. Similar to adults, but have fewer flagellar articles on the antenna, less setose peraeopods and weaker setation on the uropod 3 rami.

Remarks

The immense, apical process of the first peduncular article of antenna 1 and the unusual, strongly prehensile, paddle-like structure of the gnathopods and peraeopods 3 and 4 are unique in the pardaliscids. The morphology of the first antennae is noteworthy. When the first antennae are brought together in front of the head, the first peduncular articles form a strong, V-shaped keel. The resultant structure may form an effective shape for swimming by cutting resistance through the water, much like the bow of a boat. In addition, peduncular articles 2 and 3 of antenna 1 can be brought forward and folded backward under a lateral overhang on peduncular article 1, further decreasing resistance and increasing swimming efficiency.

The very complex, strong setation of the gnathopods and peraeopods 3 and 4 may be used for removing fine debris from the antennae or other appendages, while the powerfully subchelate propodi may be used in capturing and holding prey.

According to Bousfield and Shih (1994), most members of the Pardaliscoidea are specialized as pelagic predators. The morphology of the mouthparts, gnathopods and peraeopods 3 and 4 (specialized as gnathopods) of O. hadromischa support this view.

Distribution

North-east Pacific, off Point Conception , California and off British Columbia in 1787–4000 m depth .