Ambicholestes (Ambicholestes) cygnatratus, Just, 1998

Just, Jean, 1998, Siphonoecetinae (Crustacea: Amphipoda: Ischyroceridae) 7: Australian Concholestids, Ambicholestes n. gen., with a Description of Six New Species, and a New, Restricted Diagnosis for Caribboecetes Just, 1983, Records of the Australian Museum 50 (1), pp. 27-54 : 32

Ambicholestes (Ambicholestes) cygnatratus n.sp.

Figs 3-5

Material examined. HOLOTYPE: male. 2.5 mm, Bush Bay , 5 km off shore, 30 km S of Carnarvon, 29°1Q'S 114°39'E, 2 m, extensive shallow sea-grass beds and detritus, airlift, 6 January 1984, RT. Springthorpe & J.K. Lowry, Stn WA-431, AM P44599 . PARATYPES: (77 specimens, all from Western Australia). Same data as holotype, AM P34966 (28 specimens) . One kilometre W of Red Bluff, Kalbarri , 27°42'S 114°09'E, 18 m, Ecklonia bed, rocky bottom, "curly" bryozoans, 9 January 1984, J.K. Lowry, Stn WA-452, AM P34967 (4) . Green Island, Rottnest Island , 32°01'S 115°S 30'E, off jetty, 0.5 m, coralline algae at base of jetty pilings, 21 December 1983, R. T . Springthorpe , AM P34968 (1) . Kalbarri, 500 m off Chinaman's Rock , 27°42'S 114°09'E, 6 m, rocky bottom, "curly pink" bryozoans, 10 January 1984, RT. Springthorpe, Stn WA-460, AM P34979 (18) . Kalbarri, 500 m off Chinaman's Rock , 27°42'S 114°09'E, 6 m, brown algae on rock shelf, 10 January 1984, J.K. Lowry, Stn WA-465, AM P34980 . Kalbarri, Red Bluff , 27°42'S 114°09'E, 3-4 m, rocky shore, mixed coralline algae, 10 January 1984, R. T . Springthorpe, Stn WA-480, AM P34981 . Cathedral Rock, Rottnest Island , 32°01'S 115°27'E, 1 m, edge of reef flat, mixed algae and sponges, 21 December 1983, RT. Springthorpe and J.K. Lowry, Stn WA-250, AM P34982 (1) . Green Island, Rottnest Island , 32°01'S 115°30'E, off jetty, 1 m, mixed algal turf on rock, 21 December 1983, R. T . Springthorpe, Stn WA-268, AM P35070 (2) . Cape Range National Park, off Ned's Camp, channel in Ningaloo Reef , 21°59'S 113°54.5'E, 6 m, tubular brown algae, 31 December 1983, R. T . Springthorpe, Stn WA-320, AM P35074 (2) . Cape Range National Park, off South Ned's Beach , 22°00'S 113°55'E, inshore limestone reef, 2 m, mixed algae, 31 December 1983, J.K. Lowry, AM P35076 (2) . North side of Point John, Rockingham , 30 km S of Perth, 0.75 m ( LW), sand with some detritus, inside sea-grass and algal belt, hand dredge, 8 March 1984, J. Just, Stn AU-7, ZMUC (1) . Denham, Shark Bay , near head of jetty (east side), along edge of dense Posidonia bed, 2 m ( MW), sand, foraminiferans, detritus, hand dredge, 21 March 1984, J. Just, Stn AU-19, ZMUC (3).

Diagnosis. Rostrum present in normal position. Antennal peduncles with smooth cuticle (not counting ordinary setae).

Further description. Rostrum short, triangular. Subrostral part offrons with microsetules. Antennal peduncles without robust setae. Antenna 2 ventroapical projection of article 2 as long as broad, rounded, with 3-5 apical setae.

Coxal plates 5 and 6 posterior lobe rounded with upward turned part rounded. Posterior lobe of coxal plate 7 microsetulose. Pleonal sideplates 1 and 2 evenly rounded.

Mouthparts normal. Mandibular palp laterally and distally with very dense cover of microsetules hiding tiny second article.

Pereopod 1 article 6 without posterodistal tooth, with up to 4 posterior robust setae. Pereopod 2 article 6 with up to 4 posterior robust setae, article 2 with straight anterior margin carrying a few long and a few short setae.

Uropod 1 outer ramus 3 times longer than broad, with up to 5 lateral robust setae; inner ramus half the length of outer ramus, with apical and lateral robust setae.

Urosomites 1 and 2 separate or partly fused dorsally (fusion appears to be more common in larger specimens). Telson free.

Size. Largest male: 3.1 mm; largest female: 2.8 mm.

Colour (specimens from Denham, Stn AU-19). Cephalon semitransparent with light brown shining through, with light beige bar between eyes and onto rostrum. Dorsum light brown in mottled, reticulate pattern. Eyes white with black ommatidia. Antennae colourless transparent with white blotches and dots. Coxal plates, pereopods and urosome colourless transparent.

Biology. Specimens were found on detritus-enriched sand in and around sea-grass and algal beds, in low algal mats, and under large algae on hard substrate. The only type of abode observed (most specimens listed above) is small prosobranch shells with a short coarse-grained entrance tube.

Distribution. Western Australia; 0.5-18 m depth.

Etymology. The specific epithet refers to the black swan, Cygnus atratus , the state symbol of Western Australia.