Paracalanus Boeck, 1864

Species of the genus Paracalanus Boeck, 1864 have been reported as abundant and often dominant in coastal to oceanic waters from temperate and tropical regions. They inhabit mainly the epipelagic zone (0–200m) and as small filter feeders (Benedetti et al., 2018) they represent an important link in marine food webs. Total length of the species ranges from 0.5 to 1.5 mm. In the ICES region, seven of the twelve Paracalanus accepted species are recorded: P. aculeatus, P. denudatus, P. indicus, P. nanus, P. parvus, P. pygmaeus and P. quasimodo. A taxonomic key of the Paracalanidae family is presented, allowing Paracalanus genus distinction. 
ICES Identification Leaflet for Plankton No. 35 (Farran, revised by Vervoort, 1951) provided information on and description of three Paracalanus species. This new leaflet is an update and revision of the original, based on the following: 
a) recent molecular studies (Cornils and Held, 2014; Hidaka et al., 2016; Kasapidis et al., 2018);
b) books by Bradford-Grieve (1994), Bradford-Grieve et al. (1999), Vives and Shmeleva (2007), and Soh et al. (2013); and
c) information provided by the website on marine planktonic copepods by Razouls et al.(2005–2022).

The leaflet presents the geographical distribution and a key to differentiate the twelve Paracalanus species. Possible confusions during identification are also discussed.