Caligus undulatus, Shen & Li, 1959

Özak, Argun Akif, Kurt, Tuba Terbiyik, Kamanli, Seyit Ali, Akbulut, Gürkan, Yanar, Alper & Boxshall, Geoffrey A., 2024, Two new species of planktonic Caligus O. F. Müller 1785 (Copepoda: Caligidae) from Türkiye with an updated review and checklist of planktonic caligids, Zootaxa 5437 (3), pp. 301-335 : 327

Updated key to species of Caligus undulatus -group (females only)

1. Distal segment of antennule short (less than 2.5 times length of proximal segment)................................. 2

- Distal segment of antennule elongate (about 2.5 times length of proximal segment)....................... C. longiramus

2. Sternal furca present................................................................................... 3

- Sternal furca absent.............................................................. C. yucatanensis comb. nov.

3. Genital complex at least 3 times longer than abdomen................................................ C. evelynae

- Genital complex less than 3 times longer than abdomen....................................................... 4

4. Postantennal process with accessory tine on base part......................................... C. sarosensis sp. nov.

- Postantennal process simple, lacking accessory tine.......................................................... 5

5. Sternal furca with tines closely adpressed along midline...................................... C. izmiriensis sp. nov.

- Tines of sternal furca clearly separated.................................................................... 6

6. Abdomen distinctly 2-segmented and about as long as genital complex.................................... C. chelifer

- Abdomen 1-segmented and shorter than genital complex...................................................... 7

7. Abdomen more than 2 times longer than wide...................................................... C. undulatus

- Abdomen less than 2 times longer than wide................................................................ 8

8. Dorsal cephalothoracic shield subtriangular, with straight lateral margins................................ C. tripedalis

- Dorsal cephalothoracic shield rounded, with evenly convex lateral margins................................ C. ogawai