Cymadusa alyxis Hughes & Lowry, 2009

Hughes, L. E. & Lowry, J. K., 2009, Ampithoidae *, Zootaxa 2260 (1), pp. 153-219 : 171-174

Cymadusa alyxis Hughes & Lowry sp. nov.

( Figs 11 , 12 , Pl. 1D)

Type material. Holotype, male, 7.7 mm, 6 slides, AM P76245 ( QLD 1716 ) Picnic Beach , Palfrey Island , near Lizard Island (14°41.69’S 145°26.89’E), green alga Codium sp. , reef flat, 2 m, T. Krapp-Schickel, 27 February 2005 . Paratypes: female, 8.7 mm, 5 slides, AM P76246 ( QLD 1716 ) ; 7 unsexed, AM P71098 ( QLD 1716 ) .

Additional material examined. 1 dissected male ‘A’, 3 slides, AM 76247 ( QLD 1632); 1 dissected female ‘C’, 3 slides, AM P76248 ( QLD 1632); 1 dissected juvenile ‘B’, 4 slides, AM P76249 ( QLD 1632); 8 unsexed, AM P70166 ( QLD 1704); 2 unsexed, photo 4, AM P70949 ( QLD 1704); 6 unsexed, AM P71014 ( QLD 1705); 4 unsexed, AM P71265 ( QLD 1757); 2 unsexed, AM P71295 ( QLD 1769); 13 unsexed, AM P76250 ( SEL /LZI-5-2).

Type locality. Picnic Beach , Palfrey Island, near Lizard Island, Queensland, Australia (14°41.69’S 145°26.89’E), living on green alga Codium sp. , 2 m.

Etymology. From the Latin alyxis – ‘an escape’ – in reference to the history of the type locality, Lizard Island, where the early English explorer Captain Cook climbed to the top of the island and charted a passage out of the Great Barrier Reef.

Description. Based on holotype, male, 7.7 mm, AM P76245.

Head. Antenna 1 primary flagellum 20 articles, accessory flagellum with 1 article. Antenna 2 peduncle not densely setose on ventral margin, flagellum 24 articles. Upper lip lateral margins each with midlateral notch. Mandible molar well developed, triturating, accessory setal row with 8 serrate setae; palp 3–articulate, article 3 marginally setose; article 1 subequal in length to article 2; article 2 shorter than article 3; article 3 longer than article 1. Lower lip outer plates notched, lateral lobe distinctly longer than medial lobe; mandibular lobe with curved margins, rounded apically. Maxilla 1 inner plate with 4 setae. Maxilla 2 inner plate narrower than outer plate; palp article 2 broad. Maxilliped outer plate with row of large robust setae along medial margin.

Pereon. Coxae 1–4 deeper than broad. Gnathopod 1 smaller than gnathopod 2; coxa distinctly larger than coxa 2, produced, anterior margin straight, anteroventral corner rounded, with tuft of long slender setae in posteroventral corner; basis shorter than coxa, anterodistal lobe absent, without setae; merus posterodistal lobe subacute; carpus about 2 x as long as broad, subequal in length to propodus, anterior margin without setae, posterior margin straight; propodus broad, subrectangular; palm acute, straight, with obtuse posterodistal corner, with 1 robust seta defining palm; dactylus subequal to palm, inner margin crenate. Gnathopod 2 coxa with tuft of long slender setae in posteroventral corner; merus with short, acute anterodistal lobe; carpus much shorter than propodus, cup-shaped; propodus broad, less than 1.5 x as long as broad, subrectangular, not produced into an anterodistally setose lobe; palm acute, straight, without palm defining robust setae; dactylus slightly shorter than palm, tapering evenly, apically acute, inner margin crenate. Pereopods 3–4 basis narrow; merus subequal in length to carpus. Pereopods 5–7 weakly prehensile. Pereopod 5 basis with medial slender setae; distal articles slender; propodus not expanded distally, with 2 anterodistal striated robust setae. Pereopod 6 basis posterior margin rounded proximally, straight distally, with several marginal robust setae; distal articles slender; propodus not expanded distally, with 2 anterodistal striated robust setae. Pereopod 7 similar to pereopod 6.

Pleon. Epimera 2–3 with small acute cusp. Uropod 1 peduncle with 3–8 robust setae, with long fringe of slender setae (greater than 0.5 x length of peduncle), with large, acute distoventral spine; outer ramus length about 5–6 x as long as broad, with 6 lateral robust setae; inner ramus with 6 lateral robust setae. Uropod 2 peduncle with 4 robust setae; outer ramus with 10 lateral robust setae; inner ramus with 9 lateral robust setae. Uropod 3 peduncle longer than broad, less than 2 x length of rami, without marginal slender setae, with 5 distal robust setae, with 4 distal slender setae; outer ramus with 2 large striated recurved distal robust setae, with 1 lateral robust seta and 8 lateral slender setae; inner ramus with 5 distal robust setae, 9 distal slender setae and 1 lateral seta. Telson subtrapezoidal, apically truncated, with small apical cusp on each distolateral corner, with oblique medial rows of slender setae, with 1 pair of lateral slender setae, and with 2 pair of lateral and one pair of apical plumose setae.

Female (sexually dimorphic characters). Based on paratype, female, 8.7 mm, AM P76246. Gnathopod 1 subequal is size to gnathopod 2; basis subequal in length to coxa, anterodistal lobe rounded, with 1 slender seta; carpus anterior margin with slender setae; propodus subtriangular; palm straight. Gnathopod 2 propodus with 1 robust palm defining seta .

Colour. Body clear to white with mottle brown patches and white spots.

Habitat. Green alga, Codium sp.

Remarks. Cymadusa alyxis sp. nov. is similar to C. panwa Peart, 2002 , from Thailand and C. vadosa Imbach, 1967 , from Vietnam. In C. alyxis the male gnathopod 2 palm is straight, and in C. panwa and C. vadosa it is sinusoidal. These species can also be differentiated by the anterior margin of the gnathopod 1 coxa, which is convex in C. alyxis , straight in C. panwa and C. vadosa . The anterodistal corner of the gnathopod 1 coxa is also more broadly rounded in C. alyxis than in the other two species.

Cymadusa alyxis can be distinguished from other GBR Cymadusa species by the male gnathopod 2 which is not densely setose and has a straight, entire propodus palm.

Adults of C. alyxis are particularly large amphipods, 12+ mm. Subadult males (~ 10 mm) have a gnathopod 2 palm which is slightly sigmoidal.

Distribution. Australia. Queensland: Lizard Island (current study).

Figures

FIGURE 11. Cymadusa alyxis Hughes & Lowry sp. nov., holotype, male, 7.7 mm, AM P76245, Palfrey Island, Great Barrier Reef.

FIGURE 12. Cymadusa alyxis Hughes & Lowry sp. nov., holotype, male, 7.7 mm, AM P76245, paratype, female, 8.7 mm, AM P76246, Palfrey Island, Great Barrier Reef.