This is Mazon Monday post #187. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Figure 32.1, left: Palaeocampa anthrax, dorsal view; right top: segment in anterior view; bottom left to right: detail of spines and ventral view of median segments; modified after Shabica and Hay (1997). Scale bar = 10 mm.
Palaeocampa anthrax was an polychaete worm, believed to be similar to a group of modern day annulid worms referred to as fireworms. It was described by Fielding Bradford Meek (1817-1876) and Amos Henry Worthen (1813-1888) in "Notice of some new types of organic remains from the Coal Measures of Illinois", which was published in 1865. Meek worked for the USGS and the Smithsonian, while Worthen served as the second State Geologist of Illinois. Worthen later became the first curator of the Illinois State Museum in Springfield, IL. He directed the Geologic Survey of Illinois, which was published in 1866.
P. anthrax was one of the first animals described from the Mazon Creek fossil beds. The original type specimen was collected in the Mazon River fossil deposits by Joseph Even in the 1850's. That specimen was unfortunately lost in a fire that destroyed Even's collection in the middle 1860's. Yale University's Peabody Museum has 10 specimens of P. anthrax, all of which were collected by Samuel S. Strong in the 1800's. Strong's collection was purchased by O.C. Marsh in the 1880's.
Originally labeled as a land-based caterpillar, a specimen, with exceptionally well preserved jaws, collected by Dick Fisher in the early 1980's led Eugene Richardson to conclude that it was a marine worm.
P. anthrax appears on page 32 of Jack Wittry's "The Mazon Creek Fossil Fauna".
Palaeocampa anthrax Meek and Worthen, 1865
In its initial description, Palaeocampa anthrax was labeled a caterpillar by Meek and Worthen. Although this classification is incorrect, it is a most apt description of the animal's appearance. Its body dimensions, excluding the bristles, are approximately 7 mm in diameter and 40 mm in length. The triangular head reveals two eyespots and small, ringed antennae. There are 10 segments to the body, the first of which is the shortest, bearing short bristles. The remaining nine segments are almost equal in size, each equipped with a pair of fleshy, stout, conical, ringed legs that are approximately one body diameter in length. The bristles or needle-like spines are set in tufts on each segment and are one and one half times the body diameter in length. Under a lens, each spine appears hollow and tapers slightly. The spines are decorated with ridges or serrations that run the entire length. This animal is now considered to be a polychaete annelid of unknown affinities.
The hollow spines of P. anthrax are similar to that of an extant group of polychaete worms commonly called Fireworms. In the present-day forms, the hollow spines are filled with venom for protection. When touched, Fireworms can cause a painful burning sensation.
The "Richardson's Guide to the Fossil Fauna of Mazon Creek" discusses in Chapter 7A "Polychaete Worms" on pages 80-81.
Palaeocampa anthrax Meek and Worthen, 1865 Figures 7A.29, 7A.30
Description. All specimens incomplete; total body length 27-43 mm, rectangular in cross section, with 10 to 11 segments (Figures 7A.29A, 7A.29C, 7A.30A). Prostomium rarely preserved, appears to be partially retracted into anterior end; anterior prostomial margin of some specimens with what appear to be two short antennae or palps. Caruncle-like structure (median antenna?) present at posterior prostomium margin (Figure 7A.29A). Eversible proboscis not observed, jaws absent. Parapodia biramous (Figure 7A.29C), aciculae absent. Notopodia situated along dorsolateral surface (Figure 7A.29A), spirally twisted cirri (presumed ventral) sometimes preserved in association with neuropodia (Figure 7A.29B, 7A.29C). Noto- and neurosetae very stout, about 1.5 times longer than body width, hollow and appear calcareous (Figures 7A.29D, 7A.30B); setal surfaces ornamented with fine, longitudinal ridges.
Remarks. Palaeocampa anthrax, originally described as a caterpillar by Meek and Worthen (1865), then considered a myriapod by Scudder (1882, 1884), is now believed to be a polychaete. While the reconstructions in Figure 7A.29 are still preliminary, the species appears to be a member of the family Amphinomidae, to which Rhaphidiophorus hystrix Thompson belongs (see above). In fact, Rolfe et al. (1982) regarded Palaeocampa as a senior synonym of Rhaphidiophorus Thompson. A formal redescription of P. anthrax is being prepared by Henderson.
Specimens
From Wittry.
