Rhachotropis

Lörz, Anne-Nina, 2010, Deep-sea Rhachotropis (Crustacea: Amphipoda: Eusiridae) from New Zealand and the Ross Sea with key to the Pacific, Indian Ocean and Antarctic species, Zootaxa 2482, pp. 22-48 : 45-46

Rhachotropis sp.

Material examined. NIWA 60487, 4 specimens, female? 9.8mm; male/juvenile? 3.2 mm; male/juvenile? 3.6 mm; male/juvenile? 3.6 mm, Kermadec Trench, 36° 31.02’S 179° 12.03’W, 5173 m, KAH0910/2, 5 November 2009.

Remarks. Four damaged specimens were collected in a baited trap in the Kermadec Trench. Unfortunately the larger specimen (9.8 mm), in which the telson is intact, lacks most of its appendages. All three smaller specimens were missing the telson and most pereopods. Even though the specimens were in too bad condition to be identified further or potentially be described, some characteristics are worth noting.

In agreement to Dahl’s (1959) note of a damaged Rhachotropis specimen from the Kermadec Trench, 7140–7180 m, which is also missing the urosome, the present species also has a small, downward pointing rostrum and a first coxal plate which is “not at all produced anteriorly”. Dahl (1959) noted “In the maxilliped the outer plate reaches well past the first segment of the palp, and the second segment of the palp is rather broad in the middle and tapers both distally and proximally”. The recently collected specimens also show an outer maxillipedal plate that reaches past the first segment of the palp, but the second palp segment does not appear broad in the middle.

While Dahl’s Rhachotropis specimen from the Kermadec Trench is a female with large oostegites, the three recently collected smaller specimens are males. They might be juveniles, since they are all less than 4 mm in length. One of the three specimens has at least one first antenna intact, and calceoli occur on all articles of the flagellum, indicating maturity. The recently collected specimen NIWA 60487 could be a female with no oostegites developed.