Eurythenes thurstoni, Stoddart & Lowry, 2004

Stoddart, Helen E. & Lowry, James K., 2004, The deep-sea lysianassoid genus Eurythenes (Crustacea, Amphipoda, Eurytheneidae n. fam.), Zoosystema 26 (3), No. 3, pp. 425-468 : 451-460

Eurythenes thurstoni n. sp.

( Figs 16-20 )

Eurythenes gryllus –? Hurley 1957: 2 (in part). — J. L. Barnard 1961: 35 (in part), figs 6, 7 (material from South Pacific). — Lowry & Stoddart 1993: 72. — France & Kocher 1996a: 633 (in part).

Eurythenes cf. gryllus – Lowry & Stoddart 1994: 158 (in part).

Eurythenes sp. – France & Kocher 1996b: 306.

HOLOTYPE. — Australia, Tasman Sea , SE of Twofold Bay, New South Wales, FRV Kapala , stn K77-19-03, 37°24’S, 150°30’E- 37°28’S, 150°33’E, 550 m over bottom depth 3658 m, midwater trawl, 1.XI.1977, K. Graham, 33 mm, with 18 juveniles in brood pouch ( AM P62435).

PARATYPES. — Australia. Tasman Sea, SE of Twofold Bay, New South Wales, FRV Kapala , stn K77-19-03, 37°24’S, 150°30’E- 37°28’S, 150°33’E, 550 m over bottom depth 3658 m, midwater trawl, 1.XI.1977, K. Graham, 1 with calceoli, 29 mm ( AM P62436). — E of Flynn Reef, Queensland, RV Sunbird, SEAS, stn QLD-930, 16°37.81’S, 146°23.08’E, 1000 m, baited trap, bottom temperature 5.2°C, 6-7.VI.1993, J. K. Lowry, P. Freewater & W. Vader, 2 with non-setose oostegites, 30 mm; without calceoli, 21 mm ( AM P62420). — Same data, SEAS, stn QLD- 931, 1 with calceoli, 28 mm; 1 without calceoli, 20 mm; 3 immature specimens 16-19 mm ( AM P62421). — Between Norah Head and Port Stephens, NSW, FRV Kapala , stn K79-19-02, 33°03’S, 152°58’E- 32°59’S, 153°03’E, 640 m over bottom depth 2743 m, midwater trawl, 27.XI.1979, J. Paxton et al., 1 with non-setose oostegites, 24 mm ( AM P62422). — E of Botany Bay, NSW, HMAS Cook, stn JP 89-5, 33°44.5’S, 152°24.4’E- 34°8.9’S, 152°9.7’E, 0-1800 m over bottom depth 2994-3828 m, midwater trawl, 27-28.IV.1989, J. Paxton, 1 ovigerous 34 mm ( AM P62423). — Off Wollongong, NSW, MV Robin E, SEAS, stn NSW-788, 34°33.41’S, 151°21.35’E, 1000 m, baited trap, Globigerina ooze, bottom temperature 5.9°C, 6-7.V.1993, P. Freewater, S. Keable & W. Vader, 12 specimens ( AM P44370). — Same data, SEAS, stn NSW-789, 2 juveniles 8.5 and 9 mm ( AM P44380). — Same data, SEAS, stn NSW-808, 26 specimens ( AM P44388). — E of Nowra, NSW, RV Franklin, stn SLOPE 11, 34°57.60’S, 151°16.20’E, 1402 m, 5 m otter trawl, 16.VII.1986, M. F. Gomon et al., 1 with setose oostegites, 33 mm ( NMV J14605 ). — 52 km ESE of Nowra, NSW, RV Franklin, stn SLOPE 51, 34°56.10’S, 151°14.69’E, 3 m Isaacs-Kidd midwater trawl, 21.X.1988, G. C. B. Poore et al., 1 immature specimen 12 mm ( NMV J15790 ). — S of Point Hicks, Victoria, RV Franklin, stn SLOPE 23, 38°31.60’S, 149°23.80’E, 1960 m, 8 m rectangular midwater trawl, 21.VII.1986, M. F. Gomon et al., 25 specimens; 8 juveniles ( NMV J15784 ). — Same locality, RV Franklin, stn SLOPE 35, 38°20.30’S, 149°18.40’E, 400-500 m over bottom depth 800 m, 8 m rectangular midwater trawl, 23.VII.1986, G. C. B. Poore et al., 2 immature specimens 16 and 18 mm ( NMV J13717 ). — Same locality, RV Franklin, stn SLOPE 38, 38°39.23’S 149°15.00’E, 1500 m over bottom depth 2900-3200 m, 8 m rectangular midwater trawl, 24.VII.1986, M. F. Gomon et al., 22 specimens; 17 juveniles ( NMV J15785 ); 1 with short non-setose oostegites, 17 mm; 2 with calceoli, 18 and 22 mm; 2 immature specimens 15.5 and 16 mm ( NMV J13718 ). — 78 km S of Point Hicks, Victoria, RV Franklin, stn SLOPE 65, 38°30.13’S, 149°15.52’E, 3 m Isaacs-Kidd midwater trawl over bottom depth 1960-1990 m, 25.X.1988, G. C. B. Poore et al., 8 with non-setose oostegites, 24-29 mm; 3 with calceoli, 22-24 mm; 1 immature specimen 13 mm ( NMV J17158 ). — Off Freycinet Peninsula, Tasmania, RV Franklin, stn SLOPE 42, 42°03.3’S, 148°57.9’E- 42°07.0’S, 148°57.0’E, 900-1000 m over bottom depth 2100- 2300 m, 8 m rectangular midwater trawl, 26.VII.1986, M. F. Gomon & L. Hamond, 1 ovigerous 30 mm; 1 with setose oostegites, 31 mm; 2 with non-setose oostegites, 22 and 23 mm; 4 with calceoli, 19-24 mm; 1 immature specimen 17 mm ( NMV J13719 ). — Same locality, RV Franklin, stn SLOPE 44, 42°13.00’S, 148°46.10’E, 500-1000 m over bottom depth 1700 m, 8 m rectangular midwater trawl, 27.VII.1986, M. F. Gomon et al., 19 specimens ( NMV J15786 ). — 61 km ENE of Cape Tourville, Tasmania, RV Franklin, stn SLOPE 75, 41°58.49’S, 149°04.41’E, 3 m Isaacs-Kidd midwater trawl over bottom depth 1685-2524 m, 28.X.1988, G. C. B. Poore et al., 3 ovigerous 29- 36.5 mm; 3 with non-setose oostegites, 17- 15.5 mm; 1 with calceoli, 22 mm; 1 without calceoli, 20 mm ( NMV J17157 ). — 52 km ENE of Cape Tourville, Tasmania, RV Franklin, stn SLOPE 76, 42°02.39’S, 148°58.26’E, 3 m Isaacs-Kidd midwater trawl over bottom depth 1695-2029 m, 28.X.1988, G. C. B. Poore et al., 3 ovigerous 28- 30 mm; 5 with non-setose oostegites, 18-29 mm; 6 with calceoli, 21-25.5 mm; 7 immature specimens 8-20 mm ( NMV J17156 ). — Off St Patricks Head, Tasmania, FRV Soela, stn SO5/87/10, [c. 41°25’S, 148°43’E], 1000 m, 16.VII.1987, K. Graham, 1 with embryos, 30 mm; 3 with setose oostegites, 24-30 mm; 2 with non-setose oostegites, 18 and 20 mm; 7 with calceoli, 21- 25 mm ( AM P62424). — Same locality, FRV Soela, stn SO3/87/ gut #20, 800- 900 m, from orange roughy stomachs, IV-V.1987, 1 with setose oostegites, 29 mm ( AM P62425). — Same data, stn SO3/87/ gut #211, 1 ovigerous 29 mm ( AM P62426). — Same data, 800-1000 m, stn SO3/87/08 gut #368, 1 with non-setose oostegites, 22 mm ( AM P62427). — Same data, stn SO4/87/06, 900-1000 m, VI.1987, 1 with setose oostegites, 29 mm ( AM P62428). — Off Sandy Cape, Tasmania, FRV Soela, stn SO4/87/12 gut #447, [c. 41°13’S, 144°00’E], 840-940 m, from orange roughy stomachs, 9.VI.1987, 1 22 mm; 1 immature specimen 20 mm ( AM P62429). — Same data, stn SO4/87/12 gut #422, 1 with short non-setose oostegites, 22 mm ( AM P62430). — Same data, stn SO4/87/13 gut #466, 750- 840 m, VI.1987, 1 with juveniles, 31 mm ( AM P62431). — Same data, stn SO4/87/19 gut #579, 750- 820 m, 10.VI.1987, 1 22 mm ( AM P62432). — Same data, stn SO4/87/26, 100- 1000 m, 14.VI.1987, 2 with setose oostegites, 21 and 31 mm ( AM P62433). — South of Kangaroo Island, South Australia, FRV Soela, stn SO1/88/09 gut #13, [c. 37°00’S, 137°30’E], 700-1200 m, from orange roughy stomachs, I-II.1988, 1 with setose oostegites, 29 mm ( AM P62434).

OTHER MATERIAL EXAMINED. — Indonesia (recorded as Eurythenes gryllus by Lowry & Stoddart 1993). Tanimbar Island, KARUBAR, stn CC 57, 8°19’S, 131°53’E, 603-620 m, otter trawl, 31.X.1991, 1 with non-setose oostegites, 24 mm.

Western South Pacific Ocean (some recorded as Eurythenes cf. gryllus by Lowry & Stoddart 1994):

Loyalty Islands Basin. BIOGEOCAL, stn CP 265, 21°04.09’S, 166°00.40’E, 1760-1870 m, beam trawl, 18.IV.1987, 1 immature specimen 19 mm (MNHN- Am 4465).

Wallis and Futuna Islands. Combe Bank, MUSORSTOM 7, stn CP 550, 12°14.8’S, 177°28.0’W, 800-810 m, beam trawl, 18.V.1992, 1 with nonsetose oostegites, 40 mm (MNHN-Am 4778). — Bayonnaise Bank, MUSORSTOM 7, stn CP 627, 11°54.2’S, 179°31.4’W, 597-600 m, beam trawl, 29.V.1992, 3 with non-setose oostegites, 46, 39.5 and 33 mm ; 2 with calceoli, 36 and 34 mm; 1 immature specimen, 25 mm (MNHN-Am 4779). — Bayonnaise Bank , MUSORSTOM 7, stn CP 632, 11°54.0’S, 179°31.5’W, 595-600 m, beam trawl, 29.V.1992, 1 with calceoli, 34 mm ( MNHN- Am 4780) .

Tonga. [c. 20°S, 175°W], 617-747 m, trapped, M. King, 2 with non-setose oostegites, 42 and 40 mm ; 1 with calceoli, 30.5 mm ( AM P62439) .

Tasman Sea. RV Tangaroa, NORFANZ , stn TAN0308/111, 32°36.30’S 167°47.44’E, 1008- 1029 m, beam trawl, 29.V.2003, P. B. Berents, 1 with calceoli, 20.5 mm ( AM P66424). — Tasman Sea, RV Tangaroa, NORFANZ , stn TAN0308/129, 33°29.24’S, 170°00.71’E, 1158-1230 m, orange roughy trawl, 1.VI.2003, P. B. Berents, 1 immature 18.5 mm ( AM P66433). — Tasman Sea, RV Tangaroa, NORFANZ , stn TAN0308/166, 35°17.17’S, 169°33.63’E, 815-867 m, orange roughy trawl, 5.VI.2003, P. B. Berents, 1 with setose oostegites, 27.5 mm and 1 with calceoli, 23 mm ( AM P66447). Western North Atlantic Ocean: Gulf of Mexico. MARFIN- Geryon cruise, Area 1, [c. 29°N, 88°W], 370 fm [677 m], baited crab trap, 3.VIII.1987, 1 with long non-setose oostegites, 25.5 mm, 1 with calceoli, 30.5 mm ( GCRL 2050).

Caribbean Sea: French West Indies. Guadeloupe, Polka, ORSTOM-IRPM-SMCB, stn GC10, 16°19.15’N, 61°51.91’W, 1000 m, baited fish trap, IV.1993, 1 with long non-setose oostegites, 30 mm ( AM P67536).

Material identified by M. H. Thurston. Southern Ocean. Australia, S of Tasmania, Discovery, stn 1689, 48°09.9’S, 146°26.4’E, 750-1000 m over 2776 m, tow net N70V, 7.III.1936, 1 immature 27 mm. — SE of New Zealand, Discovery, stn 943, 45°28.4’S, 179°06.4’E, 0-128 m over 2552 m, tow net N100B, 1.IX.1932, 1 juvenile 13 mm.

ETYMOLOGY. — This species is named for Mike Thurston in recognition of his great contribution to our knowledge of deep-sea amphipods and Eurythenes in particular.

HABITAT. — Eurythenes thurstoni n. sp. has been taken in benthic trawls, midwater trawls and benthic baited traps. It is obviously an epibenthic scavenger, like E. gryllus , but its presence in relatively large numbers in midwater trawls suggests it also acts as a midwater predator or scavenger, as does E. obesus .

DISTRIBUTION. — Western South Pacific Ocean: Indonesia, eastern and southern Australia, New Zealand, Loyalty Islands Basin, Wallis and Futuna Islands, Tonga; 128-4670 m depth, up to 3000 m above bottom. Western North Atlantic Ocean: Gulf of Mexico, Bahamas, Caribbean Sea; 677-1000 m depth. DIAGNOSIS. — Anterodorsal margin of head forming an upturned ridge. Gnathopod 1 subchelate; basis length more than 3 times breadth; propodus margins subparallel. Pereopods 3 to 7 dactyli short. Pereopod 4 coxa deeper than wide. Pereopod 7 basis length of anterior margin about 1.5 times breadth; posteroventral margin straight but angled. Pleonite 3 without anterodorsal notch. Epimeron 3 posteroventral corner subquadrate. Urosomite 1 dorsodistally produced over urosomite 2. Uropod 3 peduncle, medial face with robust setae.

DESCRIPTION

Female

Based on holotype. Head much deeper than long, not extending much below insertion of antenna 2, anterodorsal margin forming an upturned ridge; lateral cephalic lobe small, subacute; rostrum absent; eyes not apparent. Antenna 1 short; peduncular article 1 short, length once breadth, distal margin without midmedial tooth; peduncular article 2 short, 0.2 times article 1; peduncular article 3 short, 0.13 times article 1; accessory flagellum 11-articulate, article 1 long, 4.8 times article 2; flagellum 21-articulate, with strong two-field callynophore, calceoli absent. Antenna 2 medium length, 1.7 times antenna 1; peduncle with brush setae; peduncular article 1 enlarged, not covering article 2 laterally; peduncular article 3 short, 0.9 times article 4; flagellum 53-articulate, calceoli absent.

Mouthpart bundle subquadrate. Epistome and upper lip separate, epistome produced, angular; upper lip not produced, slightly rounded. Mandible incisors large, symmetrical, with slightly convex smooth margins; lacinia mobilis a long slender distally-cuspidate robust seta; accessory setal row left and right with five short, slender, robust setae; intermediate setae pappose; molar large, setose, with vestigial distal triturating patch; palp attached midway; article 1 short, length 1.2 times breadth; article 2 slender, length 2.5 times breadth, subequal to article 3, with many submarginal posterodistal A2-setae, without D2- setae; article 3 falcate, long, length 3.5 times breadth, with one proximal A3-seta, with about 36 D3-setae along most of posterior margin, with two apical and four subapical E3-setae. Maxilla 1 inner plate narrow, with about 20 apical and subapical pappose setae; outer plate narrow, with 11 setal-teeth in 8/3 crown arrangement; ST1 to ST3 large, slender, three- to four-cuspidate, ST4 to ST6 large, slender, six- to nine-cuspidate, ST7 slightly displaced from ST6, elongate, slender, 12-cuspidate medially; STA large, broad, fourcuspidate; STB to STD large, broad, 11- to 13- cuspidate; palp large, two-articulate, with four apical long robust setae, four apicolateral short robust setae and one subapical slender seta, flag seta absent, distomedial margin smooth. Maxilla 2 inner and outer plates broad; inner plate length 0.7 times outer plate. Maxilliped inner plate large, subrectangular, with four apical nodular robust setae and three robust setae on lateral face; oblique setal row well developed, with at least 30 pappose setae; outer plate medium size, subovate, with 20 apical pappose setae and four apical robust setae, medial setae small, bead-shaped, submarginal setae short, simple; palp large, four- articulate, article 2 very broad, length 1.9 times breadth, 1.3 times article 3, article 3 long, slen- der, length 2.5 times breadth, dactylus well developed, with three subapical setae, unguis present.

Pereonites 1 to 7 dorsally smooth. Gnathopod 1 subchelate; coxa vestigial; basis long, slender, length 3.6 times breadth, anterior margin smooth, with tufts of slender setae; ischium short, length 1.2 times breadth; merus posterior margin lined with long slender setae; carpus wedge-shaped, not produced anteriorly, short, length 1.5 times breadth, shorter than (0.7 times) propodus, with long slender setae near posterodistal corner; propodus large, subrectangular, length 2.2 times breadth, not tapering distally, posterior margin subtly sinusoidal, smooth, with tufts of slender setae, palm slightly obtuse, margin straight, minutely serrate, posterodistal corner with one medial and one lateral robust seta; dactylus simple, without subapical spines or slen- der setae, reaching corner of palm. Gnathopod 2 minutely chelate; coxa small, shorter than coxa 3; ischium long, length 3.5 times breadth; carpus very long, length 5 times breadth, posterior margin straight; propodus subrectangular, long, length 3.3 times breadth, palm obtuse, with convex, minutely serrate margin, with three medial and four lateral robust setae; dactylus reaching corner of palm, posterior margin smooth. Pereopod 3 coxa large; merus weakly expanded anteriorly; propodus with four groups of slender setae along posterior margin and one posterodistal robust seta; dactylus short, stocky. Pereopod 4 coxa deeper than wide (length 1.25 times breadth), with large posteroventral lobe, anterior margin straight; merus weakly expanded anteriorly; propodus with four groups of slender setae along posterior margin and one posterodistal robust seta; dactylus short, stocky. Pereopod 5 coxa with anterior and posterior lobes subequal; basis expanded posteriorly, posterior margin minutely crenate; merus expanded posteriorly, with curved posterior margin; propodus with five groups of short robust setae along anterior margin and two anterodistal robust setae; dactylus short, slender. Pereopod 6 coxa small, not lobate posteriorly; basis expanded posteriorly, posterior margin minutely crenate; merus expanded posteriorly, with curved posterior margin; propodus with five groups of short robust setae along anterior margin and two anterodistal robust setae; dactylus short, slender. Pereopod 7 basis expand- ed posteriorly, anterior length 1.5 times breadth, posterior margin slightly rounded, minutely crenate, posteroventral corner rounded, posteroventral margin straight, strongly angled; merus expanded posteriorly, with curved posterior margin; propodus with five groups of four to eight short robust setae along anterior margin, two anterodistal robust setae and two pairs of robust setae along posterior margin; dactylus short, slender.

Oostegites present from gnathopod 2 to pereopod 5, long, setose. Gills present from gnathopod 2 to pereopod 7.

Pleonites 1 to 3 dorsally smooth. Pleonite 3 with a slight anterodorsal depression. Epimeron 1 anteroventral corner rounded with a few short slender setae. Epimeron 2 ventral margin lined with short fine setae; posteroventral corner produced into sharp spine. Epimeron 3 ventral margin lined with short fine setae; posteroventral corner subquadrate. Urosomite 1 with anterodorsal notch, posterodistally produced over urosomite 2. Uropod 1 peduncle with 38 dorsolateral, 15 dorsomedial and one apicomedial robust setae, without plumose setae; rami subequal in length; outer ramus with 14 lateral and five medial robust setae; inner ramus with seven lateral and 10 medial robust setae. Uropod 2 peduncle with 20 dorsolateral, one apicolateral, seven dorsomedial and one apicomedial robust setae; rami subequal in length; outer ramus with 11 lateral and eight medial robust setae; inner ramus with seven lateral and 10 medial robust setae. Uropod 3 peduncle short, length 1.4 times breadth, without dorsolateral flange, with three apicomedial, three midmedial and six distoventral robust setae, with lightly plumose setae on dorsomedial margin; rami paddle-like, subequal in length, inner ramus about 0.9 times outer ramus; outer ramus two-articulate, article 2 short, article 1 with six lateral and eight distomedial robust setae; inner ramus with four lateral and six distomedial robust setae; slender plumose setae present on both rami. Telson longer than broad, length 2.3 times breadth, deeply cleft (83%), with three very small dorsal robust setae on each lobe, distally tapered, with three very small apical robust setae and one short slender apical seta on each lobe.

Male

Apart from the presence of calceoli on the antennae there is very little sexual dimorphism. In the 29 mm paratype male ( AM P62436) antennae 1 and 2 are both slightly longer (24- and 59-articulate respectively) and there are slightly more (45) D3-setae on article 3 of the mandibular palp. Calceoli are present on the last 12 articles of antenna 1 and on all but the last two articles of antenna 2.

Colour

Relatively fresh material (preserved in formalin, not yet transferred to alcohol) from 1000 m depth, east of Coffs Harbour, New South Wales, was a fairly uniform reddish-orange colour over most of the body, with a narrow white edge to body segments and coxae; the mouthpart bundle, peduncle of antenna 1 and epistome/upper lip were a deep orange colour; areas of the cuticle normally covered by other parts (for example the anterior half of pereopod 5 basis) had very little colour, and were almost translucent; pleopods were white. The eye appeared as an irregular area of diffuse mauve to purple colour, without ommatidia; the eyes have completely disappeared from material stored in alcohol.

Size

Size ranges for E. thurstoni n. sp. from Eastern Australia and the Tasman Sea are: ovigerous females, 28-36 mm; females with setose oostegites, 24-33 mm; females with non-setose oostegites, 17-30 mm; males with calceoli, 18-29 mm; males without calceoli, 20-21 mm; juvenile (unsexable) specimens, to 19 mm. Material from other areas of the western South Pacific includes slightly larger specimens, with females ranging from 24 to 46 mm, males from 30 to 34 mm and juveniles from 19-25 mm.

Hatchling, from brood pouch of holotype

With a body length of about 6.5 mm, this hatchling is as large as the adults of many lysianassoid species. As well as the usual juvenile differences such as fewer setae on pereopods and uropods, it differs from adult E. thurstoni n. sp. in three significant characters: the anterodorsal margin of the head does not have the characteristic upturned ridge – it is smoothly produced, forming a slight rostrum; the posteroventral margin of pereopod 7 basis is curved, not strongly angled; and the anterodorsum of urosomite 1 has only a shallow depression, not a deep notch. In the smallest free-living specimens, about 8.5 to 9 mm length, these characters are the same as in adults.

REMARKS

Eurythenes thurstoni n. sp. is distinguished from both E. gryllus and E. obesus by: the recurved ridge around the anterior margin of the head; the subchelate gnathopod 1 with propodus not tapering distally; the greater length to breadth of gnathopod 1 basis; the strongly chelate gnathopod 2; the greater length to breadth of coxa 4; the narrower pereopod 7 basis with angled posteroventral margin; the absence of an anterodorsal notch on pleonite 3; and the dorsodistal projection of urosomite 1 over urosomite 2. It is further distinguished from E. gryllus by, but shares with E. obesus : the subquadrate posteroventral corner of epimeron 3 and the presence of robust setae on the medial face of uropod 3 peduncle. It is further distinguished from E. obesus by, but shares with E. gryllus : short dactyls on pereopods 3 to 7. Apart from the now resolved confusion of E. gryllus and E. obesus , the first suggestion that there could be more than one species in the E. gryllus complex was made by J. L. Barnard (1961) when reporting the material collected by the Danish Deep-Sea Expedition on the Galathea . Barnard (1961: 37) referred to his South Pacific material as “young specimens” though some of them were “obviously at sexual maturity” and commented that “The south Pacific material cited herein is only provisionally called E. gryllus ”. The principal difference Barnard cited was the “slightly chelate condition of both pairs of gnathopods”, but he also noted that the “third pleonal epimeron is quadrate in the juveniles but rounded in large adults” and “the dorsal notches of pleon segments 3 and 4 are beginning to develop on some of them”. These three characters, combined with the relatively small size of sexually mature specimens, the relative length to breadth of coxa 4, the shape of pereopod 7 basis and the posterodistally produced urosomite 1 (all evident in Barnard’s fig. 6, of a 23 mm female from the Kermadec Trench), identify this South Pacific material as Eurythenes thurstoni n. sp. Thurston & Bett (1995) acknowledged the existence of this species, based on their own observations and the account of J. L. Barnard (1961). From genetic studies, France & Kocher (1996b) also recognised south-east Australian material as separable from E. gryllus . The 24 mm female with young in the brood pouch, recorded by Hurley (1957) from Cook Strait, New Zealand, is probably also E. thurstoni n. sp., simply because of its small size; the 53 mm male from the same general area seems too large to be E. thurstoni n. sp. and probably is a true E. gryllus .

As well as the Australasian/south-west Pacific material, we include in this species material we have examined from the Gulf of Mexico and the Caribbean Sea. These specimens have all the distinguishing characters of the new species. France & Kocher (1996a) studied genetic patterns in populations of Eurythenes from the North Pacific Ocean, the western North Atlantic Ocean and the Arctic Ocean. The most divergent of the groupings they identified was a set of three specimens from the Northwest Channel, Bahamas, western North Atlantic Ocean. These specimens were much smaller than any others and France & Kocher (1996a) referred to this group as a “cryptic species”. France & Kocher (1996b) grouped these specimens with material from the continental slope of south-east Australia – material which we recognise as E. thurstoni n. sp.

France & Kocher (1996a) also reported other material of E. gryllus from Tongue of the Ocean, also in the Bahamas, which grouped with material from the Nares Abyssal Plain rather than with the Northwest Channel group. Bowman & Manning (1972) reported material of E. gryllus from Andros Island, Bahamas. Their illustrations of gnathopod 2 palm and the basis of pereopod 7 correspond to those of E. gryllus rather than E. thurstoni n. sp. These other records of Eurythenes from the Bahamas show that, as in eastern Australia and the south-west Pacific Ocean, E. gryllus and E. thurstoni n. sp. can occur in the same geographic area.

Figures

FIG. 16. — Eurythenes thurstoni n. sp., holotype 33 mm (AM P62435).

FIG. 17. — Eurythenes thurstoni n. sp., holotype 33 mm (AM P62435), paratype 29 mm (AM P62436). Abbreviations: A1, A2, antennae 1, 2; H, head; MD, mandible; MP, maxilliped; MX1, MX2, maxillae 1, 2; T, telson; U1-U3, uropods 1-3. Scale bars: 0.5 mm.

FIG. 18. — Eurythenes thurstoni n. sp., holotype 33 mm (AM P62435). Abbreviations: EP1-EP3, epimera 1-3; G1, G2, gnathopods 1, 2; P3-P7, pereopods 3-7. Scale bars: 1.0 mm.

FIG. 19. — Eurythenes thurstoni n. sp., hatchling, 6.5 mm, from brood pouch of holotype.

FIG. 20. — Recorded distribution of Eurythenes thurstoni n. sp.