Cyamocephalus loganensis Currie 1927 Length about 5 cm - family Pseudoniscidae Late Llandovery or possibly early Wenlock, Silurian period, Scotland (Euramerica) image by, and courtesy of, Lyall Anderson.
The Synziohosurines are a small, fairly diverse, paraphyletic / ancestral group of primitive Xiphosura. Rather trilobite-like in appearance. Large prosoma (headshield), simple eyes only. 9 or 10 opisthosomal (abdominal) segments, most or all of which are free (unfused). The segments are not chelate. Mostly brackish or freshwater environments, although some forms were marine (marginal marine?). Usually found in association with eurypterids and ostracoderms.
family WeinberginidaeFamily Weinberginidae Richter and Richter, 1929 time range: (Pragian to Emsian habitat: Marine representative taxa: Weinbergina opitzi Richter and Richter, 1929, Willwerathia laticeps (Størmer, 1936); Legrandella lombardi Eldredge, 1974 status: monophyletic description: Medium-sized forms with large semicircular smooth prosoma, short 10-segmented Small trilobite-like abdomen, post-abdomen with 3 segments, 5 pairs of walking legs, spines. These late surviving forms seem to be among the most primitive of the Synziphosurida, or in any case they represent a side branch away from the main axis of Xiphosuran evolution. They are also the only Synziphosurines found in a proper marine environment.
family Bunodidaefamily Bunodidae Packard 1886
Small elongate forms, ornamented prosoma, abdomen with broad axis, 9 free segments, post-abdomen with 3 or 4 segments. In the Treatise considered a distinct family, but perhaps it should be included under the Bunodidae (I have it as a subfamily here).
subfamily Limuloidinae
new ranking; formerly family Limuloididae Størmer, 1952 time range: Wenlock to Ludlow habitat: Marginal Marine representative taxa: Limuloides limuloides Woodward, 1865 description: Small forms, ridged and spiny prosoma, post-abdomen with 3 segments. Only one genus.
subfamily Bunodinae
new ranking; family Bunodidae Packard 1886 time range: Llandovery to Ludlow habitat: Marginal Marine representative taxa: Bunodes lunula Eichwald, 1854 description: Small trilobite-like forms, vaulted, radially-lobed prosoma, post-abdomen with 3 to 4 round segments.
family Pseudoniscidaefamily Pseudoniscidae Packard 1886 time range: Llandovery to Pridoli habitat: Marginal Marine representative taxa: Pasternakevia podolica Selden and Drygant, 1987, Cyamocephalus loganensis Currie, 1927, Pseudoniscus aculeatus Nieszkowski, 1859 description: Small forms with large, somewhat flat, smooth prosoma, 9 or 10 free segments with pleural (marginal) spines, no post-abdomen. Pasternakevia is transitional between the Bunodidae and Pseudoniscidae proper.
family KasibelinuridaeFamily Kasibelinuridae Pickett, 1993 time range: Givetian to Famennian habitat: Marginal Marine representative taxa: Kasibelinurus amicorum Pickett, 1993 description: The last of the synziphosurnes, and also the most derived (advanced). Live in south-East Gondwanaland (Australia). Presumably ancestral to the Xiphosurida. status: monospecific |