This is Mazon Monday post #190. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Amarixys sulcata is a Mazon Creek spider. When it was first found in the late 1880's, it was mistaken for a beetle. A.L. (Axel Leonard) Melander (1878-1962) described it as Kustarachne sulcata in 1903 in the paper "Some additions to the Carboniferous terrestrial arthropod fauna of Illinois", which was published in the Journal of Geology. Melander was an American entomologist, who specialized in Diptera (flies) and Hymenoptera (ants, bees, and wasps). He spent the majority of his career at the City College of New York.
He describes the specimen as imperfect. The original document can be found on Google Books.
Kustarachne sulcata sp. nov. (Plate V, Fig. 5; Plate VII, Fig. 4).
Cephalothorax orbicular, nearly as broad as the abdomen, from which it is evidently, though not deeply, constricted. Coxae meeting along a narrow median space which extends along the whole length of the cephalothorax, stout, distinctly and deeply punctulate; remainder of legs punctulate also, more slen der than the coxa, especially on the tarsal portion; metatarsus as long as the basal portion of the leg together. Mouth parts not distinct. Abdomen somewhat broader than the thorax, elongate elliptical, its segmentation obscured, irregularly but deeply punctulate, the punctures becoming obsolete in the mid dle, provided with a prominent lateral sulcus concentric with and close to the margin, and with a broader and deeper longitu dinal one on the disc on each side of the middle. Abdomen terminated by a triangular sessile pygidium consisting of two and possibly three subsegments, its outline extending beyond the regular oval of the abdomen, not punctured. The basal appendages noticed in te?1uipes are not indicated, but there is a mark on the stone which might have been caused by a terminal seta. This is as fortuitous as in the other species, but its pres ence casts even darker gloom over the systematic position of the genus.
Length of body I5mm, width of cephalothorax 6.5mm, length of abdomen without the pygidium gmm, width of abdomen Jmm, width of first subsegment 2mm, length of second leg (imperfect) 24™, width of second leg beyond body o.75-0.3mra.
Carboniferous. Mazon creek, Illinois.
Type. Pal. Coll. No. 9235.
Although the imperfect type of this genus offers but few salient characters, the present form is placed congeneric with it in entire confidence. It concurs with the characters of no other Anthracomart, but agrees with Kustarachne tenuipes in its general form, slender, elongate, but somewhat stouter legs, and similar pygidium. However, it is quite distinct in the sculpture of the abdomen.
Kustarachne sulcatus was renamed to Curculioides sulcatus by Alexander Petrunkevitch (1875-1964) in 1913 in "A monograph of the terrestrial Palaeozoic Arachnida of North America", which was published in the journal Transactions of the Connecticut Acadamy of Arts and Sciences. The document is also available on Google Books.
It's interesting that he locates the type specimen at the Walker Museum of the University of Chicago. The collections of the Walker Museum now reside at the Field Museum in Chicago. Petrunkevitch also notes the condition of the specimen as "heavily covered with kaolin". After cleaning, the legs were much clearer, which made it possible for him to change the identification.
Curculioides sulcatus (Melander).
Plate VII , fig. 38 ; text figs . 49, 50.
= Kustarachne sulcata Melander, Jour. Geol. , Vol. XI , 1903 , p . 181 , pl. V, fig. 5 , pl. VII, fig. 4.
The type and only specimen of this species, No. 9235, is in the collection of the Walker Museum of the University of Chicago. The nodule containing it consists both of the obverse and reverse, but the whole specimen was heavily covered with kaolin, this being the reason why Melander's description is quite incorrect. Basing his opinion on the similarity in the relative measurements of Curculioides sulcatus and Kustarachne tenuipes, Pocock suggests in his Monograph that "one shows the dorsal, and the other the ventral view of specimens belonging to the same species. " This suggestion is excusable only in view of the fact that Pocock had no occasion to examine the specimens themselves and based his judgment on the incomplete and erroneous descriptions. The following description is drawn from the type specimen after it had been cleaned of the kaolin and the legs exposed as far as possible.
Total length 16.5 mm. Cucullus 1.15 mm. long, 3.0 mm. wide. Cephalothorax 4.25 mm. long, 6.0 mm. wide in posterior 1/3, 5.25 mm. wide at posterior edge, which is straight. abdomen with an entire shield, folded in median line but not with a median longitudinal ridge, folding being due to pressure. Behind the shield is visible a small segment representing probably the seventh to ninth segments. Legs very long and rather thin . The cucullus and legs minutely punctate, the cephalothorax and abdominal shield coarsely punctate. The tibia and metatarsus of the second leg and the terminal abdominal joint smooth.
The ventral surface is not sufficiently well preserved to show the arrangement of all coxae, but the third and fourth coxae are distinctly contiguous. In the anterior part of the abdomen there is a strongly procurved fold represented by the two lines in text figure 49.
Found in the Pennyslvanic (LowerAllegheny) of Mazon Creek, Illinois.
The species Amarixys sulcata was erected by Paul A. Seldon in 1992 in "Revision of the fossil ricinuleids" for Transactions of the Royal Society of Edinburgh: Earth Sciences. The paper can be found here. Selden is Distinguished Professor Emeritus at the University of Kansas. His research focuses on fossil arthropods, particularly spiders and their relatives.
Genus Amarixys gen. nov.
Type species. Kustarachne sulcata Melander, 1903
Derivation of name. Greek amara, a trench, and ixys, the loins, lower part of the back; referring to the longitudinal sulcus running down the dorsal abdomen.
Diagnosis. Curculioidids with dorsal median sulcus, which Sacks tubercles, on abdomen.
Included species. In addition to the type species, the following are included in the genus: Curculioides gracilis (Petrunkevitch, 19451, and Amartxys ste//anS so. nov.
Remarks. Study of the fossil ricinuleids shows that one group of specimens, previously included within Curculioides, is distinctly different in having a broad, median sulcus, which lacks tubercles, in place of the median line which characterizes the type and remaining species. The specimens with a sulcus are therefore removed from Curculioides, and placed in the new genus Amarixys. Additionally, this genus appears to have a subrectangular carapace, rather than the broadly pyriform shape which is typical of Curculioides. There are great differences in tubercle size and density between the two species placed in Amarixys. These characters do not correlate with any others, such as size, so that there is little doubt that, pending the availability of much more material of Amarixys, they must be considered as separate species.
Holotype and only known specimen. UC 9235, part and counterpart, in the Field Museum of Natural History, Chicago; from the Westphalian D of Mazon Creek, Grundy Co., Illinois. The specimen was originally housed in the Gurley Collection of the Walker Museum of the University of Chicago (Melander 1903)
Drawing from Selden.
Specimens
Holotype (Melander)
Holotype (Selden)
Specimen from Rich Rock
Thanks go out to Andrew Young on some of the detective work behind this post.
