Cirolana Leach, 1818

Rodcharoen, Eknarin & Bruce, Niel L., 2021, Two new species of the marine isopod genus Cirolana Leach, 1818 (Crustacea Isopoda: Cirolanidae) from the coast of the western Gulf of Thailand, Zootaxa 4950 (3), pp. 469-486 : 471

Genus Cirolana Leach, 1818

Remarks. Cirolana can be identified by having the following combination of relatively easy to observe characters: frontal lamina with a relatively wide and ventral flat surface, clypeus always flat (i.e., without ventral or anterior projecting blade), pleonite 5 always laterally entirely overlapped by pleonite 4; mandible incisor visibly broad, more than 0.5 mandible width (see Bruce & Hughes 2020), pereopods all ambulatory (i.e., without marked flatting of articles or presence of long natatory setae), pereopods 1–3 without anterolateral margins of ischium and or merus strongly produced and pleopod 2 appendix masculina attached basally.

The concept of what constituted Cirolana Leach, 1818 , then with 114 species, was wholly revised by Bruce (1981), resulting in the genus including just 44 species. Since that time the genus has again grown, now the largest in the family with 144 species (see Sidabalok & Bruce 2018a), and in the course of that time it has been increasingly recognized that there are distinct groups within the genus ( Bruce 1986, 2004; Sidabalok & Bruce 2017, 2018a). Sidabalok (2019) demonstrated that there are five definable monophyletic clades within Cirolana , each clade supported by definable synapomorphies.

One such clade was termed the Cirolana ‘ pleonastica -group’ by Sidabalok & Bruce (2018a); both new species described here belong to that group. The critical apomorphic characters that define the Cirolana ‘ pleonastica -group’ include: rostral point absent, transverse sutures present on all or most pereonites, pleonites 3 and 4 with small nodules, uropod endopod with setae on distal third, and uropodal exopod lateral margin with three widely spaced relatively slender robust setae. There are several other characters consistently shown by species of this group, including all species in the group with the lateral margins of pleonite 3 not posteriorly produced, not overlapping pleonites 4 and 5 and the posterolateral margins (epimera) of pleonite 4 are posteriorly rounded. At present the Cirolana ‘ pleonastica -group’ has been recorded primarily from the tropical Indo-Pacific Ocean with one species from the Antarctic.

Both new species described here belong to the Cirolana ‘ pleonastica -group’.