Kimcheres, Bandera, Eugenia & Conradi, Mercedes, 2016

Bandera, Eugenia & Conradi, Mercedes, 2016, Redescription of two species of Asterocheres Boeck, 1860 (Copepoda: Siphonostomatoida), A. corneliae Schirl, 1973 and A. boeckii (Brady, 1880), and proposal of a new genus for Asterocheres fastigatus Kim, 2010, Zootaxa 4174 (1), pp. 259-273 : 269-270

Kimcheres gen. nov.

Diagnosis. Asterocheridae . Body cyclopiform, with large prosome and small urosome. Siphon of medium size, extending beyond bases of maxillipeds. Sexual dimorphism in urosomal segmentation, antennules, maxillipeds, size of leg 5 and leg 6.

Urosome 4-segmented in female and 5-segmented in male. Antennule 17-segmented in female, with large aesthetasc on segment 14; 14-segmented in male, with large aesthetasc on segment 13. Antenna with very long 1- segmented exopod and 3-segmented endopod with terminal claw. Mandibular palp 2-segmented, second segment with two plumose distal setae. Maxillule bilobed. Maxilla 2-segmented, proximal segment with aesthetasc-like element and a claw-like basis, strongly curved distally. Maxilliped 6-segmented, comprising short syncoxa, long basis and 3-segmented endopod; male basis with weak proximal process. Legs 1–4 biramous, with 3-segmented rami. Inner seta on coxa of leg 4 lacking. Armature formula of second endopodal segment of leg 4 (0-1). Leg 5 with protopod incorporated into somite and 1-segmented exopod bearing three setae.

Etymology. The genus is named in honour of Prof. Il-Hoi Kim (Gangneung National University, Korea), who described its type species, in recognition of his contribution to the systematics on symbiotic copepods. The generic name is derived from “Kim” and the suffix – cheres, frequently used in the names of asterocherid genera.

Type species. Asterocheres fastigatus Kim, 2010 = Kimcheres fastigatus ( Kim, 2010) comb. nov. by original designation ( Kim 2010: 64–68; figs. 45A–I, 46A–G, 47A–E).

Discussion. Kim (2010) placed his new species Asterocheres fastigatus in Asterocheres but expressed some reservations about this generic assignment. He pointed out three characters as the most striking features of this species: (1) armature formula of second endopodal segment of leg 4 (0-1); (2) coxa of leg 1 lacking inner seta, and (3) the elongate antennary exopod. Three other species share the absence of the inner coxal seta of leg 1 with A. fastigatus : A. trisetatus Kim, 2010 , A. eugenioi and A. sarsi . However, the absence of this coxal seta is the only characteristic shared among these four species.

Although Kim (2010) mentioned that the elongate antennary exopod (longer than half the length of the first endopodal segment) is not present in other species of Asterocheres , there is one other species sharing this character. In A. ellisi the antennary exopod is six times longer than wide. The most striking differences between A. fastigatus and A. ellisi are the segmentation of the female antennule (17-segmented vs 21-segmented, respectively) and the body shape which is dorso-ventrally flattened in A. ellisi ( Hamond 1968; Bandera & Conradi 2009a). The morphology of the antenna is very similar to that displayed by the two species of the genus Stockmyzon Bandera & Huys, 2008 . Both Stockmyzon species had previously been included in Asterocheres ( Bandera & Huys 2008) but do not share any other characteristics of special relevance. Members of the genus Orecturus Humes, 1992 also exhibit a very elongate antennary exopod, but the segmentation of the antennary endopod, the remaining appendages and the general body appearance are completely different ( Humes 1992: Fig. 9C).

The striking segmentation pattern of the female antennule was not highlighted in the original description of A. fastigatus . The basic number of segments in the female antennule of Asterocheres is 21, and the reduction in the number of segments predominantly occurs in the distal part of the antennule ( Kim 2010). Typically, species belonging to Asterocheres have a compound segment 9(IX–XII) which usually bears seven or eight setae. Segmental fusions proximal to segment 9 are uncommon within the Asterocheridae and are often diagnostic at genus level (e.g., Acontiophorus Brady 1880 ). Asterocheres fastigatus displays three segmental fusions proximal to segment 9, i.e., the second segment with three setae, the third with eight setae and the fifth with six setae. However, this is not the only example in the genus showing antennulary fusions proximal to segment 9. In A. bahamensis Kim, 2010 the second segment is also a compound one, bearing four setae, but shows a vestigial articulation on the anterior side ( Kim 2010: Fig. 9E). Therefore, A. fastigatus is the only species in the genus with three clear and complete fusions proximal to segment 9, showing a total of seven segmental fusions in the female antennule: 1(I)- 2, 2(II–III)-3, 3(IV–VII)-8, 4(VIII)-2, 5(IX–XI)-6, 6(XII)-2, 7(XIII)-2, 8(XIV)-2, 9(XV)-2, 10(XVI)-2, 11(XVII)- 2, 12(XVIII)-2, 13(XIX)-2, 14(XX–XXI)-2 + aesthetasc, 15(XXII–XXIII)-2, 16(XXIV–XXV)-4 and 17(XXVI– XXVIII)-7.

Another characteristic considered being very relevant and of potential generic significance is the possession of only a single inner seta on the second endopodal segment of leg 4. According to Kim (2010) this characteristic is shared only by A. boeckii , as illustrated by Sars (1915), and A. fastigatus . Kim considered this similarity as potential evidence for assigning these species to a separate genus but the lack of other similarities between them prevented him from doing so. Our redescription of A. boeckii revealed that Sars’s (1915) illustration of leg 4 was incorrect and confirmed that the species has two instead of one inner setae on the second endopodal segment as is typical for the genus Asterocheres . Therefore, A. fastigatus is the only species in the genus which exhibits the 1- seta condition. Although some other characteristics (mandible, maxillule, maxilla, maxilliped, leg 5) resemble those of Asterocheres species, the four striking features listed above warrant the proposal of a new genus, Kimcheres gen. nov. Two other asterocherid genera display the armature formula (0,1) on the second endopodal segment of leg 4, i.e. Hermacheres Stock, 1987 and Gomumucheres Humes, 1996 . However, Hermacheres , characterized by several apomorphic reductions in the armature of legs 1 to 4, differs from Kimcheres in many others characters, such as (1) the exopodal segment of leg 4, (2) the minute antennary exopod being reduced to a bud, (3) the form of the mandibular stylet, being shortish, rather wide, sinuous and distally widened into a toothed blade, and (4) the barrel-shaped siphon without tubiform distal part (features shown by the type species Hermacheres diploriae Stock, 1987 ). Gomumucheres shows the armature formula (0,1) on the second endopodal segment of both leg 3 and leg 4. The formula 2,2,1,1, indicating the number of inner setae on the second endopodal segment of legs 1–4 differentiates the genus from all others in the Asterocheridae ( Humes 1996) .