Perotripus, Dougherty and Steinberg, 1953

Takeuchi, Ichiro & Lowry, James K., 2015, A taxonomic study on the Phtisicidae (Crustacea: Amphipoda) of New South Wales, Australia, Journal of Natural History 50, pp. 603-648 : 642-645

Perotripus sp.

( Figures 22 and 23 )

Material examined

1? male, AM P49034, 33°45'S, 151°19'E, Long Reef, New South Wales, 18 February 1996, attached to sipunculid;? 1 premature female, AM P49035, 33°45'S, 151°19'E, Long Reef , New South Wales, 18 February 1996, attached to a sipunculid .

Locality

New South Wales: Long Reef (this study).

? Male, body length 3.04 mm, AM P49034. Head/pereonite 1 combined length 0.34 mm; pereonite 2, 0.40 mm; pereonite 3, 0.31 mm; pereonite 4, 0.55 mm; pereonite 5, 0.69 mm; pereonite 6, 0.64 mm; pereonite 7, 0.10 mm.

Eyes large, distinctive.

Antenna 1 0.15 × body length; peduncle article 2 longest; flagellum 0.33 × peduncular length, with two articles. Antenna 2 0.8 × antenna 1 length; flagellum 0.12 × peduncular length, with two articles.

Pereon. Pereonite 2 with anterolateral rounded projection, with dorsodistal hump. Pereonite 3 with rounded anterolateral projection, with dorsodistal hump. Pereonite 4 with anterolateral projection, with broad dorsal hump. Pereonite 5 longest. Gnathopod 2 gill small, subovate; coxa vestigial; basis without anterodistal projection; carpus 0.1 × propodus length; propodus large; length 1.3 × width; propodus anterodistal margin convex; palm proximal projection with two robust (grasping) setae; propodus palm smooth, slightly convex. Pereopod 3 slender, 3- articulate; gill missing in this specimen. Pereopod 4 shorter than pereopod 3; gill small, subovate; length about 1.2 × width. Pereopod 5 slender. Pereopod 6 basis slightly shorter than propodus; carpus subequal to basis; propodus with one robust seta on posterior margin; dactylus falcate. Pereopod 7 similar to pereopod 6; merus subequal in length to basis.

Remarks

The genus Perotripus was established based on the single species, P. brevis ( La Follette, 1915) , which is distributed along the Californian to Alaskan coasts of the northeastern Pacific ( Dougherty and Steinberg 1953; Laubitz 1970). Two additional species, P. keablei Guerra-García, 2006 and P. koreanus Lee and Hong, 2010 have so far been reported ( Guerra-García 2006; Guerra-García and Lowry 2009; Lee and Hong 2010).

Of them, the present species, Perotripus sp., differs from P. brevis in the following distinctive characters: pereonite 2 is longer than pereonite 3 in Perotripus sp. from New South Wales, while pereonite 3 is longer than pereonite 2 in P. brevis . However, we have not described the present specimens as a new species because the specimens collected from New South Wales are only two small individuals. This indicates the possibility that these are juveniles, which have not developed specific diagnostic characters.

Perotripus keablei was recorded from Lizard Island, on the northern part of the Great Barrier Reef, Queensland. Unlike P. brevis , P. koreanus and Perotripus sp. in the present study, pereopod 3 of P. keablei has one tiny article with two apical setae, which is very similar to that of pereopod 4. Recently, Lim et al. (2012) established the genus Microtripus which differs from Perotripus by 3-articulate flagellum of antenna 1 with three articles and pereopod 3 with one article. While P. brevis and P. koreanus have preopod 3 with three articles, corresponding pereopod of P. keablei with one article. Hence, this indicates that P. keablei possibly belongs to a different new genus from Perotripus .

In addition to these three species of Perotripus and Perotripus sp. reported in the current study, an undescribed species of Perotripus was recorded in the ecological and phylogenic studies and checklist from the Pacific coasts of central Japan ( Takeuchi et al. 1987; Takeuchi and Hirano 1995; Takeuchi 1999; Aoki and Takeda 2006).

Key for the species of the Phtisicidae from New South Wales

The species key provided here is based on the characteristics that could be observed without dissection of the mouthparts using binocular microscope.

1. Pereopod 3 well developed, with seven articles ........................................................... 2 – Pereopod 3 vestigial, fewer than three articles ............................................................. 5

2. Pereopod 4 well developed, with seven articles ........................................................... 3 – Pereopod 4 degenerated ......................................................................................................... 6

3. Gills on pereonites 2 to 4 ........................................................................................................ 4 – Gills on pereonites 3 and 4 ............................................................................ Paraproto sp.

4. Basis of gnathopod 2 about 2 × length of pereonite 2 ................................................... .................................................................................................. Notoprotomima smithi sp. nov. – Basis of gnathopod 2 shorter than length of pereonite .................................................. ....................................................................... Metaproto novaehollandiae ( Haswell, 1879a)

5. Flagellum of antenna 1 with more than two articles ........................................................ ........................................................................................... Hircella cornigera ( Haswell, 1879b) – Flagellum of antenna 1 with two articles ................................................ Perotripus sp.

6. Pereonites 3 and 4 with pair of mid-dorsal projections ................................................... .................................................................................. Dodecas decacentrum Stebbing, 1910b – Pereonites 3 and 4 lacking mid-dorsal projections ............................................................ .......................................................................................... Dodecas hexacentrum Mayer, 1903

Figures

Figure 22. Perotripus sp. from east of Long Reef, New South Wales, Australia.? Male, 3.04 mm, AM P49034. Bar indicates 0.50 mm.

Figure 23. Perotripus sp. from east of Long Reef, New South Wales, Australia.? Male, 2.74 mm, AM P49034. Bars in A1, A2, G2, P6 and P7 indicate 0.10 mm and those in P3, P4 and P5 indicate 0.02 mm.