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 Arthropoda :: xiphosura :. Order Synziphosurida
Cyamocephalus - Silurian period
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 Weinberginidae
WeinberginaFamily 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 Bunodidae
family 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

Limuloidesnew 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

Bunodesnew 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 Pseudoniscidae
Pseudoniscusfamily 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 Kasibelinuridae
KasibelinurusFamily 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
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