Gbroidea dingaalana, Lowry & Azman, 2008

Lowry, J. K. & Azman, B. A. R., 2008, A new genus and species of cyproideid amphipod associated with unstalked crinoids on the Great Barrier Reef, Australia, Zootaxa 1760 (1), pp. 59-68 : 61-65

Gbroidea dingaalana sp. nov.

( Figs 2–4 )

Type material. Holotype female, 2.5 mm, AM P76155, off Watsons Beach, Lizard Island, Queensland, Australia (14º40’S 145º28’E), living in association with the zygometrid crinoid, Zygometra microdiscus (Bell, 1882) , 21 m, stn QLD 2010, R. T. Springthorpe, 10 February 1987. Paratypes: 2 females, AM P38471, stn QLD 2011; 4 females, AM P38472, off Watsons Beach, Lizard Island, Queensland, Australia (14º40’S 145º28’E), living in association with Comathus briareus (Bell, 1882), Comatula rotalaria Lamarck, 1816 and Zygometra microdiscus (Bell, 1882) , 21 m, stn QLD 2011, R. T. Springthorpe, 10 February 1987; 4 females, AM P38473, stn QLD 2010.

Type locality. Off Watsons Beach , Lizard Island, Queensland, Australia (14º40’S 145º28’E), living in association with the unstalked zygometrid crinoid, Zygometra microdiscus (Bell, 1882) , 21 m.

Etymology. The species name, dingaalana , is based on the aboriginal tribe that visited Lizard Island before it was occupied by Europeans.

Description. Based on holotype female, 2.5 mm, AM P76155.

Head. Lateral cephalic lobes apically acute. Eyes large, irregularly round with deep brown core. Antenna 1 flagellum with about 4 articles each with long aesthetascs distally; accessory flagellum 1 articulate. Antenna 2 slightly shorter than antenna 1, slender; flagellum with 4 articles, apex of terminal segment with few long setae. Mandible molar absent. Maxilla 2 reduced. Lower lip outer lobes apically produced with dense short apical setae. Maxilliped inner and outer plates reduced; inner plate not broad, apically truncate; outer plate extending beyond inner plate, apex with one small robust seta and several simple setae; palp 4-articulate, article 2 wider than long, dactylus apically falcate.

Pereon. Gnathopod 1 coxa vestigial; basis robust, anterior margin with 4 medium length setae, posterior margin with 1 seta posterodistally; merus not elongated, posterior margin with two setae; carpus distally expanded, anterodistally rounded with a pair of setae, posterior margin slightly produced with 3 posterodistal setae; propodus subrectangular, anterior margin with 3 setae, tooth-like process anterodistally, posterior margin straight; dactylus falcate. Gnathopod 2 basis robust, anterior margin lined with medium length setae, posterior margin without setae; merus posterodistal margin with long setae; carpus subtriangular, subequal in length with propodus, anterior margin without setae, anterodistal margin with two setae. Pereopod 3 coxa anterior margin expanded, rounded, posterior margin slightly concave; basis anterior margin densely setose; merus gradually expanding anterodistally. Pereopod 4 coxa enlarged, shield-like, anterior margin almost straight, posterior margin with well developed rounded posterodistal margin; basis anterior margin straight, posterior margin slightly concave. Pereopod 5 coxa anterior and posterior margin rounded; basis slender, rectolinear; merus posterodistal margin slightly produced. Pereopod 7 shorter than pereopod 6; coxa anteroventral margin produced, expanded; basis anterior margin straight, with 2 setae along margin, posterior margin expanded, with distal lobe extending beyond ischium.

Pleon. Epimeron 3 posterodistal margin rounded. Uropod 1 rami subequal, peduncle slightly shorter than rami, both margins of both rami pectinate. Uropod 2 biramous, inner ramus shorter than outer ramus, both margins of both rami pectinate. Uropod 3 biramous; peduncle subequal in length of inner ramus; inner ramus shorter than outer, outer margins pectinate. Telson entire.

Male. Unknown.

Colour. Antennae, head, eye, pereon and coxae deep brown with a diffused white stripe between pereon and coxae and between coxae 3–4; gnathopods, pereopods, pleopods, uropods and urosome translucent.

Habitat. Living in association with the crinoids, Comathus briareus (Bell, 1882), Comatula rotalaria Lamarck, 1816 and Zygometra microdiscus (Bell, 1882) .

Remarks. Gbroidea dingaalana is the only cyproideid amphipod currently known from the Great Barrier Reef. During a 1987 expedition to Lizard Island, M. Grygier, J. Lowry and R. Springthorpe examined 10 specimens of three crinoids: Comathus briareus, Comatula rotalaria and Zygometra microdiscus . There were 11 specimens of G. dingaalana living on these crinoids or about 1 amphipod per host. We suspect that G.dingaalana has evolved an obligate commensal relationship with unstalked crinoids or is possibly an epiparasite. Comathus briareus and Comatula rotalaria are both deep brown in colour and Zygometra microdiscus is deep purple. The deep brown camouflage colouration of G. dingaalana makes it undetectable on the crinoid hosts and by inference, less susceptible to predators. The weakly developed mouthparts of G. dingaalana indicate that it is probably feeding on sloughed mucous or soft tissue, possibly epidermal tissue from the crinoid, similar to the uristid amphipod, Euonyx chelatus , which is an epiparasite of the regular sea urchin, Echinus esculentus (see Vader 1978; Comely & Ansell 1988). We only have information from three species of unstalked crinoids, but Messing et al. (2006) found 12 species of unstalked crinoids at Lizard Island.

Interestingly Potts (1915) reported a purple amphilochid amphipod, Cyclotelson purpureum , associated with an unnamed crinoid, from Torres Strait. We did not find this species at Lizard Island.

Distribution. Australia: Queensland: Lizard Island.

Figures

FIGURE 2. Gbroidea dingaalana sp. nov., female paratype, AM P38471, off Watsons Beach, Lizard Island.

FIGURE 3. Gbroidea dingaalana sp. nov., holotype female, 2.5 mm, AM P76155, off Watsons Beach, Lizard Island.

FIGURE 4. Gbroidea dingaalana sp. nov., holotype female, 2.5 mm, AM P76155, off Watsons Beach, Lizard Island.