Pseudambasia Stephensen, 1927

Kilgallen, N. M. & Lowry, J. K., 2013, The lysianassid genus Pseudambasia in Australian waters (Crustacea, Amphipoda, Lysianassidae, Lysianassinae), Zootaxa 3710 (4), pp. 301-321 : 301-302

Pseudambasia Stephensen, 1927

Pseudambasia Stephensen, 1927: 305 . Barnard & Karaman, 1991: 522. Lowry & Stoddart, 1995: 113.

Type species. Pseudambasia bipartita Stephensen, 1927 , monotypy (= junior subjective synonym of Parambasia rossii Stephensen, 1927 ).

Diagnosis. Antenna 2 peduncular article 3 elongate (length 3 – 3.6 × breadth), geniculate between articles 3 and 4. Maxilla 1 inner plate without apical setae. Mandible left lacinia mobilis absent, palp attached slightly to extremely proximally. Labium without inner plates. Gnathopod 1 sexually dimorphic, simple or weakly to strongly subchelate. Urosomites 2–3 coalesced. Telson entire.

Included species. Pseudambasia includes 11 species: P. acuticaudata (Ledoyer, 1984) ; P. dartnalli sp. nov.; P. indentata (Ledoyer, 1986) ; P. kalaupapa Longenecker & Bolick, 2007 ; P. l o ch i sp. nov.; P. nui (Myers, 1985) ; P. ponderi sp. nov.; P. poorei sp. nov.; P. rossii (Stephensen, 1927) ; P. sheardi sp. nov.; P. springthorpei sp. nov.

Remarks. The type taxon of the genus Parambasia , P. forbesii Walker & Scott, 1903 , from Abd-el-Kuri, may be part of this species complex, but important diagnostic characters for the taxon are not known and the type material is lost (see Lowry & Stoddart 1995, Barnard & Karaman 1991). Until such time as new material of this species is discovered and a neotype can be designated, the name Parambasia must be treated as dubious. See Lowry and Stoddart (1995) for further remarks.

Pseudambasia differs from other lysianassids by a combination of geniculate antenna 2, no well-developed apical setae on the inner plate of maxilla 1, sexually dimorphic subchelate gnathopod 1 and coalesced urosomites 2–3. It may be related to the highly derived genus Azotostoma (which has peculiar mouthparts and non-coalesced urosomites). Pseudambasia is also similar to Kakanui Lowry and Stoddart (1983) , but Kakanui has well-developed apical robust setae on the maxilla 1 palp and free urosomites.

Some species of Pseudambasia have peculiar distolateral tubular stylets on the outer lobes of the labium. These stylets protrude from a duct which opens externally via an apical pore. The role of these structures is unknown but, given their position on the labium, they may play a role in digestion.

Pseudambasia species variously display a strong dark pigment on the head and body (Longenecker & Bolick 2007), which may be sexually dimorphic in some species (see Lowry & Stoddart 1983 for P. rossii ). In general, species described from Australia do not show any strong colouration pattern, with the exception of some specimens of P. s h e a rd i sp. nov. from Tasmania.

Key to species of Pseudambasia

Longenecker and Bolick (2007) published a key to the species of Pseudambasia , which was based mainly on body pigment. Here we present an updated morphology-based key to include the species described herein.

1. Uropod 2 inner ramus strongly to slightly constricted........................................................ 5

- Uropod 2 inner ramus not constricted..................................................................... 2

2. Pereopod 7 basis with posteroventral corner rounded........................................................ 3

- Pereopod 7 basis with posteroventral corner excavate................................................. P. ponderi

3. Gnathopod 1 simple (in female). Uropod 3 rami short and stout........................................... P. poorei

- Gnathopod 1 subchelate (in male and female). Uropod 3 rami slender............................................ 4

4. Eyes round. Uropod 3 inner ramus shorter than outer............................................... P. kalaupapa

- Eyes oval. Uropod 3 rami subequal in length................................................... P. springthorpei

5. Epimeron 3 posteroventral corner without notch............................................................ 6

- Epimeron 3 posteroventral corner minutely notched......................................................... 9

6. Gnathopod 2 carpus length greater than 6 × breadth. Telson strongly tapering distally, apically subacute............. P. nu i

- Gnathopod 2 carpus length less than 4 × breadth. Telson distolateral margins subparallel, apically rounded or truncated..... 7

7. Pereopod 7 basis with posteroventral margin excavate................................................... P. rossii

- Pereopod 7 basis with posteroventral margin oblique.......................................................... 8

8. Lateral cephalic lobes broadly rounded. Epimeron 3 posterior margin straight, posterodistal corner subquadrate...... P. lochi

- Lateral cephalic lobes distally truncated. Epimeron 3 posterior margin with small cusp above broadly rounded posterodistal corner......................................................................................... dartnalli

9. Antenna 1 peduncular article 1 without anterodorsal lobe.................................................... 10

- Antenna 1 peduncular article 1 with anterodorsal lobe................................................. P. sheardi

10. Lateral cephalic lobe broadly rounded. Uropod 3 peduncle with dorsolateral flange..................... P. acuticaudata

- Lateral cephalic lobe subquadrate. Uropod 3 peduncle without dorsolateral flange......................... P. indentata