African cichlid fish genera (Pseudocrenilabrinae): counts of vertebrae, supraneurals, dorsal and anal pterygiophores; pterygiophore insertion patterns

This is the first survey in cichlids of the considerable variation in numbers of vertebrae, supraneurals, and dorsal- and anal-fin supports (pterygiophores), as well as the patterns with which the pterygiophores insert between the neural or hemal spines. The study includes some 1700 specimens of nearly 400 cichlid species. Focusing on the largest subfamily, the African cichlids or Pseudocrenilabrinae, the survey furnishes data from species in all but one of its 166 genera. Limited data from species in the other cichlid subfamilies (Etroplinae, Ptychochrominae, and Cichlinae) and from the related leaffishes, Polycentridae, are also presented.

The character complex here surveyed is a promising source of taxonomically and phylogenetically informative characteristics distinguishing or uniting cichlid taxa at multiple hierarchical levels, from species through subfamily. This reference set of novel character data can also inform paleontological studies of African cichlids. These attributes are skeletal features potentially available for study in well preserved fossils and may help determine their correct taxonomic placement.

Methods
This study is based on data recorded from radiographs, microCT image stacks, and a few cleared-and-stained specimens. In all, data from 1705 specimens of 391 cichlid species are included, representing all tribes within the African cichlid subfamily Pseudocrenilabrinae and exemplars of the other three cichlid subfamilies. Limited data from a few leaffishes (Polycentridae) are included for purposes of outgroup comparison. The primary type specimens (holotype or lectotype) of 90 species are among the cichlid specimens included; their values are signaled in the supplementary spreadsheets/tables by an asterisk (*). At least one imaged specimen was available from 165 of the 166 currently recognized genera of Pseudocrenilabrinae. Only Enigmatochromis Lamboj, 2009 (Chromidotilapiini) is not represented.

Film radiographs were scanned at a resolution of 1200 pixels per inch (ppi) and enlarged on a monitor and the raw meristic data and pterygiophore insertion patterns were recorded on a spreadsheet. For radiographs and microCT images available online, I enlarged the image on the monitor to fullscreen size and captured one or more screenshots, saved in .jpg format at 96 ppi. I later recorded meristic and pattern data while displaying each image on the monitor at sufficient enlargement to enable seeing all required small details, notably the supraneurals and the posterior dorsal and anal pterygiophores. If the specimen was not imaged with head to the left, I reversed the image. If the fish’s image was not approximately horizontal or adequately clear to permit reasonable certainty of interpretation, I rotated it or applied one or more digital enhancements in Corel PaintShop Pro X8 18.3.0.13 x64. These techniques included sharpening with the unsharp mask, adjusting brightness and contrast, adding fill light, increasing image clarity, and applying local tone mapping (LTM). LTM proved particularly helpful in bringing out details on low-contrast images. A few images, especially those created from microCT volumes, could not be made usably clear because the small posterior pterygiophores were inadequately resolved in the original image stack. I did not use such images.

The data were recorded on the spreadsheet (Table_S10_Raw_data.xlsx) as follows. Two successive rows are allocated for each specimen. The number of cells in the upper row, starting from the left (craniad), equals the total count of precaudal plus caudal vertebrae, including the compound terminal centrum. For a specimen with a count of 13+16=29 vertebrae, a “c” is placed in column 29 of both rows. For the lower row, the first entry is placed below the cell of the first caudal vertebra. Thus, for a 13+16 count, a temporary “x” is placed in the second row column 14 (the precaudal count plus 1) to mark where the contents of the first insertion space immediately anterior to the first anal pterygiophore is to be entered. 

The entry for each cell records the contents of the corresponding insertion space anterior to that centrum’s neural or hemal spine. In column 1 of the upper row an entry is made representing the first dorsal insertion space in front of the first neural spine. A separate “0” is entered for each supraneural; a numeral is entered to indicate the number of pterygiophores. If more than one element is present in a space, the elements are separated by hyphens. Thus, if the insertion space has two supraneurals and two pterygiophores, 0-0-2 is recorded. The contents of each dorsal insertion space is similarly entered. An empty insertion space is indicated with a dash (–). The contents of the interhemal spaces are similarly entered in the lower of the two rows. The first (most anterior) anal pterygiophore(s) are situated either in the first anal insertion space (immediately in front of the first hemal spine), or the first space is empty and they occur in the second space (between first and second hemal spines), with a single exceptional genus: Uniquely in the Lake Tanganyikan genus Cyprichromis, five to seven anal pterygiophores are abdominal in position, located anterior to the first anal insertion space and inserting toward or between successive pairs of pleural ribs. These abdominal pterygiophores are indicated in Table_S10_Raw_data.xlsx by placement in gray-shaded cells.

The analytical spreadsheets (Table_S1.xlsx through Table_S9.xlsx) demonstrate some of the possible ways of comparing the counts and insertion patterns in the raw data. The primary type specimens (holotype or lectotype) of 90 species are among the cichlid specimens included; their values are signaled by an asterisk (*).