Chthamalus fissus, Darwin, 1854

Pitombo, Fábio Bettini & Burton, Ron, 2007, Systematics and biogeography of Tropical Eastern Pacific Chthamalus with descriptions of two new species (Cirripedia, Thoracica), Zootaxa 1574 (1), pp. 1-30 : 17-18

Key to the species of the Chthamalus fissus group of species

1.- Articular ridge of scutum short, limited to tergal border; lateral depressor muscle pit smooth. Cirrus I without bidenticulate setae. Cirrus II with bidenticulate setae with basal guards on last 2 articles of anterior ramus..................................................................................................................................................... 2

1’- Articular ridge of scutum wide, developed, sometimes projected beyond tergal border; lateral depressor muscle pit smooth or divided by septa/ridges. Cirrus I with bidenticulate setae with or without basal guards. Cirrus II with bidenticulate setae with basal guards from last 2 to last 5 articles of anterior ramus ..................................................................................................................................................................... 4

2- Scutum inner face with growth lines on less than 15% its width. Tergum triangular without noticeable spur; outer face without longitudinal ridge close to scutal border .................................................... C. fissus

2’- Scutum inner face with growth lines on more than 15% its width. Tergum triangular with noticeable spur; outer face with longitudinal furrow close to scutal border in one or both plates (better seen with cleaned plate) ............................................................................................................................................................ 3

3- Shell brown to white, narrow, deeply folded up to apex. Tergum with well marked longitudinal furrow on both plates; parietes usually white .......................................................................................... C. panamensis

3’- Shell brown, smooth, folding limited to lower half. Tergum with weak longitudinal furrow frequently only on one plate; parietes usually brown in uneroded specimens. ................................................. C. hedgecocki

4- Scutum inner face with growth lines on more than 15% its width.............................................................. 5

4’- Scutum inner face with growth lines on less than 15% its width ................................................................ 6

5- Opercular plates strongly asymmetric. Cirrus II with bidenticulate setae with basal guards on last 4 or 5 articles of anterior ramus ......................................................................................................... C. anisopoma

5’ - Opercular plates weak asymmetric. Cirrus II with bidenticulate setae with basal guards on last 2 articles, sometimes down to last 3 articles of anterior ramus ........................................................ C. southwardorum

6- Scutum lateral depressor muscle pit smooth. Cirrus II with bidenticulate setae with basal guards on last 4 or 5 articles of anterior ramus ........................................................................................................ C. fragilis

6’- Scutum lateral depressor muscle pit divided by septa/ridges, sometimes not. Cirrus II with bidenticulate setae with basal guards on last 3 or 4 articles of anterior ramus ................................................... C. proteus