Gap-coding permits the use of continuous metric characters in cladistic analyses. Character means are converted to integer equivalents by placing character state divisions in the locations of phenetic breaks between specimen clusters, under the assumption that these breaks represent the locations of bottlenecks in character distributions. Similarities and differences between specimens from closely related species of cystoporate bryozoans were evaluated for the first time by converting continuous morphometric measurements into gap-coded binary and multistate characters and analyzing them cladistically, rather than just phenetically, across multiple species of Strotopora, Cliotrypa ramosa and Fistulipora compressa. Our results demonstrate that cladistic analysis of gap-coded morphological characters can be effective in resolving phylogenetic relationships at low taxonomic levels (within and among genera) while objectively highlighting both the morphological features that specimens (taxa) share and those characteristics that differentiate them. Differences in cystiphragm abundances and sizes, especially in the proximal portions of colonies, discriminate between species of Strotopora. Colony size and growth form, abundances and lengths of hemiphragms, and sizes of cystopores discriminate between Strotopora and the closely related genus Cliotrypa. Cladistic patterns indicate that Strotopora foveolata Ulrich is a valid species with Strotopora dermata as its junior subjective synonym. Fistulipora compressa is reassigned to the genus Strotopora whereas a decision on the taxonomic status of Cliotrypa ramosa requires a broader cladistic analysis of fistuliporine genera.
Appendix 1
Means of morphometric measurements for each specimen. Missing measurement indicators (?) were retained for cladistic analysis whereas species’ means were substituted for missing measurements (bold) for phenetic analyses. BSLC and BSLZ were removed from analyses because missing values substantially outnumbered measurements.
Appendix 2
Summary statistics for morphological characters measured in Strotopora compressa. Characters are defined in Table 1. N = number of measurements. Means for each measured specimen are listed in Appendix 3.
Appendix 3
Character means for specimens of Strotopora compressa. Characters are defined in Table 1. Ten replicate measurements were collected for each quantity unless indicated by a superscript value. Missing values indicated by dashes. All specimens are from the UMMP; UMMP 6547G has been selected as the lectotype, with UMMP 6547A-F, and H designated as paratypes.
Appendix 4
Summary statistics for morphological characters of Strotopora foveolata. Characters are defined in Table 1. N = number of measurements. Character means for each specimen are listed in Appendix 5.
Appendix 5
Character means for specimens of Strotopora foveolata. Characters are defined in Table 1. Ten replicate measurements were collected for each quantity unless indicated by a superscript value. Missing values indicated by dashes. All specimens are from the USNM with accession numbers indicated for individual specimens.
Appendix 6
Summary statistics for morphological characters of Strotopora dermata. Characters are defined in Table 1. N = number of measurements Character means for each specimen are listed in Appendix 7.
Appendix 7
Character means for specimens of Strotopora dermata. Characters are defined in Table 1. Ten replicate measurements were collected for each quantity unless indicated by a superscript value. Missing values indicated by dashes; all specimens are from the USNM.
Appendix 8
Summary statistics for morphological characters of Cliotrypa ramosa. Characters are defined in Table 1. N = number of measurements. Character means for each specimen are listed in Appendix 9.
Appendix 9
Character means for specimens of Cliotrypa ramosa. Characters are defined in Table 1. Ten replicate measurements were collected for each quantity unless indicated by a superscript value. Missing values indicated by dashes. All specimens are from the USNM with accession numbers indicated for individual specimens. The holotype is USNM 92133.
Appendix 10
Integer codes for 21 characters used in cladistic analysis. Characters are defined in Table 1, original measurement means are in Appendix 1, and gap-coding intervals, character weighting factors, and final character weights are listed in Table 2. Missing codes (not measureable) indicated by question marks.
Appendix 11
Apomorphies separating specimens assigned to Strotopora and Cliotrypa. Labeled nodes in the cladogram are referred to in the apomorphies listed below. Character abbreviations are described in Table 1 and codes are listed in Appendix 10.