Metacyclops species, 1927

Athibai, Sujeephon, Wongkamhaeng, Koraon & Boonyanusith, Chaichat, 2022, Two new species of Metacyclops Kiefer, 1927 (Copepoda, Cyclopoida) from Thailand and an up-to-date key to the species recorded in Asia, European Journal of Taxonomy 787 (1), pp. 146-181 : 174-175

Identification key to the female of Metacyclops species recorded in Asia

Thirteen species of Metacyclops have been recorded in Asia, excluding M. sakaeratensis sp. nov. and M. brancelji sp. nov. ( Dussart & Defaye 2006; Kołaczyński 2015; Lee & Chang 2015; Boonyanusith et al. 2018b). Most of them have spines on the exp-2 of P1 – P 4 in the formula of 3.4.4.3, with one single apical spine on P4 enp-2, and only M. gracilis (Lilljeborg, 1853) bear two apical spines on P4 enp-2. At the regional-scale, four species have been recorded in Western Asia ( M. gracilis , M. planus (Gurney, 1909) , M. amoenus (Mann, 1940) , and M. minutus ), five in Southern Asia ( M. margaretae , M. gracilis , M. grandispinifer , M. minutus , and M. communis ), four in Eastern Asia ( M. ryukyuensis , M. pectiniatus , M. minutus , M. gracilis ), and six in Southeast Asia ( M. minutus , M. pectiniatus , M. malayicus , M. woni , M. amicitiae , M. thailandicus ). Based on zoogeographical perspective, five species have been recorded in the Palaearctic region ( Turkey, Mongolia, China: Guangdong, Israel, Syria, Iran, Pakistan, Afghanistan, Iraq, Lebanon) and eleven species in the Oriental region ( Japan: Ryukyu, Vietnam, Thailand, Cambodia, Indonesia: Sumatra, Malaysia, India, Sri Lanka). Furthermore, most of them were known before 1940, while all the most recently described species were from Southeast Asia ( M. amicitiae , M. thailandicus , M. woni ) increased interest in the diversity of Copepoda in this region ( Kołaczyński 2015; Lee & Chang 2015; Boonyanusith et al. 2018b). For this reason, an up-to-date key to the female of these species is provided hereafter.

1. Spine formula of exp-2 of P1 – P4 3.3.3.3 ........................... M. margaretae (Lindberg, 1938) [ India]

– Spine formula of exp-2 of P1 – P4 3.4.3.3 ........................................................................................... ....................................... M. thailandicus Boonyanusith, Sanoamuang & Brancelj, 2018 [ Thailand]

– Spine formula of exp-2 of P1 – P4 3.4.4.3 ......................................................................................... 2

2. P4 enp-2 with 1 apical spine ............................................................................................................. 3

– P4 enp-2 with 2 apical spines .................... M. gracilis (Lilljeborg, 1853) [ Turkey, Mongolia, India]

3. Antennule 9-segmented ............................................. M. planus (Gurney, 1909) [ Israel, Syria, Iran]

– Antennule 10-segmented .......................................................... M. amoenus (Mann, 1940) [ Turkey]

– Antennule 11-segmented .................................................................................................................. 4

– Antennule 12-segmented .................................................................................................................11

4. Seta III shorter than seta VI ................................ M. malayicus ( Kiefer, 1930) [ Indonesia: Sumatra]

– Seta III longer than seta VI ............................................................................................................... 5

5. Apical spine on P4 enp-2 as long as or longer than segment bearing it ........................................... 6

– Apical spine on P4 enp-2 shorter than segment bearing it ............................................................... 8

6. Caudal ramus 4× as long as wide or more than 4× as long as wide .................................................. ............................................................................................. M. minutus (Claus, 1863) [ Afghanistan, China, Iraq, Israel, Lebanon, Malaysia, Southern Iran, Sri Lanka, Mongolia, Pakistan, Syria]

– Caudal ramus less than 4× as long as wide ...................................................................................... 7

7. Seta V of caudal ramus ca 1.3× as long as seta IV ............... M. communis (Lindberg, 1938) [ India]

– Seta V of caudal ramus at least ca 1.5 × as long as seta IV ................................................................. ........................................................................... M. pectiniatus Shen & Tai, 1964 [ China, Malaysia]

8. Caudal ramus 3× as long as wide or more than 3× as long as wide .................................................. ................................................................... M. grandispinifer ( Lindberg, 1940) [ India, Turkey, Iran]

– Caudal ramus always less than 3× as long as wide .......................................................................... 9

9. Genital double-somite with transverse suture, representing remnant of ancestral articulation ...... 10

– Genital double-somite without transverse suture ............. M. woni Lee & Chang, 2015 [ Cambodia]

10. Apical spine of P5 ca 1.5× as long as segment bearing it; caudal ramus ca 2.7× as long as wide in female .............................................................................................. M. brancelji sp. nov. [ Thailand]

– Apical spine of P5 as long as segment bearing it; caudal ramus ca 2.2× as long as wide in female. ................................................................................................... M. sakaeratensis sp. nov. [ Thailand]

11. Intercoxal sclerite of P1–P4 with hairs on prominences and that of P4 with transversal row of spinule on caudal surface; enp-2 of antenna with nine setae ...... M. amicitiae Kołaczyński, 2015 [ Vietnam]

– IntercoXal sclerite of P1–P4 without ornamentation; enp-2 of antenna with eight setae ................... ......................................................................... M. ryukyuensis Ishida, 1995 [ Japan: Ryukyu Island]