Merlionia, Uyeno & Hashimoto & Watanabe, 2023

Uyeno, Daisuke, Hashimoto, Rina & Watanabe, Hiromi K., 2023, What causes transformation of the parasitic copepod? A new example of host switching in the family Anthessiidae (Cyclopoida) from Singaporean waters, with the proposal of a new genus, Zoological Journal of the Linnean Society 199 (1), pp. 216-227 : 218

Merlionia gen. nov.

ZooBank registration: urn:lsid:zoobank.org:act:244B6127-3862-43BC-8EF0-B3C7B6CB293D

Type species: Merlionia zeeae , gen, et sp. nov., by present designation.

Etymology: The generic name is derived from the Merlion, which is the official mascot of Singapore, which has the head of a lion and the body of a fish. The fact that the new genus has characteristics of two different families (i.e. Anthessiidae and Chondracanthidae ) is reminiscent of the mythical animal. The gender is feminine.

Diagnosis: Female holotype. Body elongate cyclopiform, composed of cephalosome, first to fifth pedigerous somites, genital double somite and three-segmented abdomen. Cephalosome bearing dorsal chitinous frame, separated by constriction from the first pedigerous somite. Genital double somite with genital openings situated dorsolaterally. Caudal rami bearing six setae.

Antennule five-segmented; all segment bearing naked setae. Antenna two-segmented, composed of short coxobasis and endopod represented by uncinate claw. Labrum bilobed, with median incision, and lamellar on posterior margin; posterolateral lobes bearing small spinules. Mandible two-segmented, composed of unarmed coxa and gnathobase bearing two long setiform flagellum covered with numerous spinules and row of fine spinules on the posterior margin. Maxillule knob-like and bifid; inner tip with one small seta; outer tip with three unequal setae. Maxilla composed of unarmed syncoxa and basis tapering into blunt tip covered with numerous spinules bearing two elements. Labium lobate. Maxilliped absent.

Legs 1–4 biramous, composed of distinctly segmented coxa and basis; both rami three-segmented. Leg 5 two-segmented; proximal segment unornamented, fused to pedigerous somite; distal segment rod shaped, bearing one outer spine and with two spines and one simple seta on the distal tip. Leg 6 not observed.

Adult male: body cyclopiform, flattened dorsoventrally, composed of cephalosome, first to fifth pedigerous somites, genital somite and four-segmented abdomen. Cephalosome bearing dorsal chitinous frame. Genital somite bearing paired opercula. Caudal rami as in female.

Antennule five-segmented; all segments bearing naked setae. Antenna,mandible, maxillule and maxilla as in female.Maxilliped subchelate, five-segmented; first segment (syncoxa) small; second segment (basis) robust; third (proximal endopodal segment) and fourth (middle endopodal segment) segments small; fifth segment (distal endopodal segment) forming terminal claw bearing two tips and one subdistal conical process.

Legs 1–5 as in female. Leg 6 represented by genital flap.

Remarks: Merlionia has the mandible with two long flagella, which is one of the characteristics of the families Anthessiidae and Shiinoidae (see Cressey 1975, Humes 1986). The new genus is, however, not accommodated in the family Shiinoidae by not having the unique antenna composed of two recurved segments and the reductions of legs 4 and 5. Although there are several differences between the new genus and the known anthessiid genera, the mandible with two sclerotized teeth at the base of outer flagellum is considerable as a proof that the new genus is accommodated in the family Anthessiidae . Furthermore, except for having a chondracanthid-form antenna in both sexes and absence of the maxilliped in the female of the new genus, the combination of other characters matches the general concept of the family Anthessiidae , except for the maxilla ornamented with numerous fine spinules (see Izawa 1976, Humes 1986, 1997, Boxshall and Halsey 2004, Kim 2009, Uyeno and Nagasawa 2012a, Uyeno 2016). This attribution of the new genus in the family is supported by the phylogenetic analysis using the partial sequence of the 18S rRNA gene ( Fig. 1 ).

Figures

Figure 1. Phylogenetic reconstruction of the order Cyclopoida using both maximum likelihood and Bayesian inference based on 1110 bp of the 18S ribosomal RNA gene sequence of selected taxa. The values beside each node indicate the maximum likelihood bootstrap value (left) and the Bayesian posterior probability (right). Numbers in parentheses are GenBank accession numbers.