Setacheres, Johnsson, Rodrigo, Bahia, Cristiano & Neves, Elizabeth, 2016

Johnsson, Rodrigo, Bahia, Cristiano & Neves, Elizabeth, 2016, A new genus of Asterocheridae (Copepoda: Siphonostomatoida) ectoassociate of the ascidian Eudistoma vannamei Millar, 1977 (Polycitoridae) from Brazil, Zootaxa 4114 (2), pp. 162-170 : 164

Setacheres gen. nov.

Diagnosis. Asterocheridae . Body with ovoid or discoid prosome. Urosome 4-segmented in female, 5-segmented in male. Antennule of female with ancestral segments IX-XII fused, 19-21-segmented, with large aesthetasc on 18th segment and 1 to 3 distal segments, respectively. A fusion on the ancestral segments IX to XIII may be observed and the antennule will show 18 to 20 segments, with aesthetasc on 17th segment and 1 to 3 distal segments, respectively. Antenna with 1-segmented exopod and 3-segmented endopod bearing distal claw or spine. Oral cone short or elongate, siphon-like. Mandible consisting of apically pointed stylet and 1- or 2-segmented palp bearing 2 distal setae. Maxillule bilobed. Maxilla 2-segmented; distal segment forming claw. Legs 1-4 with 3-segmented exopod and endopod. Basis of leg 1 with 2 elements, one on each outer and inner margins. Female armature formula of third exopodal segment III,2,2 for leg 1, III,I,4 or III,1,4 for legs 2-4. Female armature formula of third endopodal segment 1,2,3 for legs 1 to 3 or 1,1+I,2 for leg 4. Second endopodal segment of legs 1-4 with 2 inner setae. Free segment of leg 5 with 2 or 3 setae.

Remarks. The females of Setacheres gen. nov. have a 4-segmented urosome, a 2-segmented mandibular palp armed with 2 distal setae, legs 1-4 with both rami 3-segmented. The third exopodal segment of leg 1 has 7 elements and that of legs 2-4 8 elements. The third endopodal segment of legs 1-3 has 6 elements and leg 4 5 elements. These characters are shared with other asterocherid genera like Phyllocheres Humes 1996 , Chelacheres Stock & Humes 1995 , Asterocheres Boeck 1860 , Stockmyzon Bandera & Huys 2008 and Hetairosynella Kim, 2010 ( Kim 2010, Bandera & Huys 2008, Stock & Humes 1995, Humes 1996). In Chelacheres the autapomorphy is the setation of the third endopodal segment of the antenna, with two robust opposed setae forming a chela-like structure ( Stock & Humes 1995). Phyllocheres shows a broad prosome, leaf-like, with the tergite of the third pedigerous somite expanded posteriorly over the rest of the prosome ( Humes 1996, Boxshall & Halsey 2004). Stockmyzon has a distinctly annulated stylet on the antennule.

Despite the strong resemblance between Setacheres gen. nov. and Asterocheres , the latter genus shows the third endopodal segment of leg 3 armed with 3,1+I,1 and the former shows 3,2,1, as in legs 1 and 2. Such pattern on the leg 3 endopodal was relevant for Kim (2010) to use it as criteria to transfer some species originally placed in Asterocheres , to species inquirendae. Cheramomyzon Humes, 1989 is the only genus within the Asterocheridae that shows the third endopodal segment of leg 3 armed with 3,2,1. However Johnsson & Neves (2004), when redescribing C. abyssale Humes, 1989 , concluded that Cheramomyzon has many characters which are observed either in Asterocheridae or in Artotrogidae , but never on both genera, and therefore the genus should be placed within its own family. Another relevant characteristic of Setacheres gen. nov. is the presence of a distal seta instead of a spine on the third exopodal segment of legs 2 to 4 of almost all species of the new genus has not been reported in any other genus of Asterocheridae .

In the revision of Asterocheres by Kim (2010), the generic diagnosis focused mainly on the female antennule and leg setation pattern. The antennule bears an aesthetasc on the 18th segment and the distal section has 1–3 segments resulting from fusions for a total of 19–21 segments. The leg setation pattern is strict, with no variations. Consequently, 12 Asterocheres species are considered by Kim (2010) species inquirendae. Among these species, 8 of them show the third endopodal segment of leg 3 armed with two setae: Asterocheres abrolhensis Johnsson, 1998 , A. aplysinus Johnsson, 2002 , A. lunatus Johnsson, 1998 , A. paraboecki Johnsson, 1998 , A. picinguabensis Johnsson, 2001 , A. spinopaulus Johnsson, 1998 , A. unicus Johnsson, 2001 , A. ventricosus ( Brian, 1927) ( Johnsson 1998, 2002, Johnsson et al. 2001, Brian 1927) and therefore should be transferred to the new genus.

Etymology. The generic name Setacheres is a combination of the Latin seta (bristle) and cheres, apparently derived from the Greek achtheros meaning distressing or troublesome to.

Type species. Setacheres eudistomus sp. nov.