Restudyof the enigmatic arthropod Necrogammarus salweyi Woodward, hitherto considered to be a crustacean or myriapod, reveals that it is the infracapitulum (fused labrum and palpal coxae) and palp of a large but unspecified pterygoid curypterid

Selden, Paul A.

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A N E W I D E N T I T Y F O R T H E S I L U R I A N A R T H R O P O D NECROGAMMARUS by P A U L A . S E L D E N ABSTRACT. Rcsludy of the enigmatic arthropod Necrogammarus salweyi Woodward, hitherto considered to be a crustacean or myriapod. reveals thai it is the infracapitulum (fused labrum and palpal coxae) and palp of a large but unspecified pterygoid curypterid. 1 N the quest for the oldest representative of a laxon the fossil record commonly presents a number of poorly preserved specimens of doubtful assignation. Such is the case with the myriapods (Almond 1985). but one contender. Necrogammarus salweyi Woodward, can now be rejected with certainty. N. salweyi was collected by Mr Humphrey Salwcy in Church Hill quarry at Leintwardine. Herefordshire. The fauna there occurs in a channel-fill of Lower Leintwardine Beds (middle Ludlow) cut down into Middle Elton Hi-ds (sec Whilaker 1962), hence the age of lower Ludlow assigned to the specimen by its first describcrs, Huxley and Salter (1859. pp. 25, 97, pi. 13, fig. 17). They considered the specimen to be a crustacean and not a Plerygotus, but since it had been "accidentally introduced into this plate' (Ibid., p. 97. referring to pi. 13. fig. 17) they probably thought it was euryplerid in the first instance. Woodward (1870) rcdcscribcd the specimen as an am phi pod crustacean and named and sketched it. Peach (1899) did not sec the specimen but rcfigured it and referred it to the Diplopoda because it appeared to show diploscgmcnts and a uniramous limb. In the Treatise it was mentioned under Crustacea Pcracarida incerlae sedis (Hessler 1969), but was discussed in connection with myriapods again, and rcfigured. by Rolfe (1980). Both Rolfc (1980) and Almond (1985) preferred to regard Necrogammarus as a possible aquatic relative of the myriapods. No photograph of Necrogammarus has hitherto been published, but when Almond showed a colour slide of it at the Palaeontological Association's annual meeting in Cambridge. 1984, I immediately recognized it as part of a ptcrygotid eurypterid. Investigation of the feeding mechanism of ErettOplenis biiobus (Salter) (unpublished except for the biomechanics of the chela system: Selden 1984) had revealed that this species, and probably other pterygotids. possesses only three pairs of slender walking legs (limbs III. IV and V) and that limb II is a small palp. The palpal coxae and labrum arc fused into a discrete plate; such a structure occurs in other chelicerates (e.g. Ricinulci: van dcr Hammen 1979) and is termed the infracapitulum. As in other Chelicerata the infracapitulum is intimately associated with the chcliccrae in Ereliopterus, but the arrangement is complex, not yet fully understood, and is not described herein. It is obvious, however, from a comparison of text-figs. 1 and 2 that Necrogammarus is the infracapitulum and attached palp (of one side only) of a large pterygotid curypterid. Two pterygotids are known from Church Hill: P. arcualus Salter and E. marsloni Kjellcsvig-Wacring. as well as numerous pterygotid fragments (Kjellesvig-Waering 1961). It is not possible to assign Necrogammarus to either of these species since they are diagnosed solely on features of cheliccrae. coxal gnathobase, and mclastoma. It may belong to one of these species, or be a new form: in any case, it was evidently a large animal. Acknowledgements. I thank R. A. Fortcy, British Museum (Natural History) and A. W. A . Rushton. British Geological Survey, for the loan of specimens in their care. |P> l> ran lo loE> . V o l . 2 9 . P « n 3. 198* , pp. 6 2 9 6.11. | P A L A E O N T O L O G Y . V O L U M E 29 TEXT-FIG. I. Infracapilulum and palp of pterygotid euryptends. A. Necrogammarus salweyi Woodward, British Museum (Natural History) In 43786. holotype; Church Hill quarry, Leintwardine. Hereford; Lower Leintwardine Beds, middle Ludlow, x I. B. Erelloplerushilobus(Salter), British Geological Survey GSM 59651; Logan Water, Lesmahagow. Scotland; Pricsthill Group. Llandovcry/Wenlock, x 2. TEXT-FIG. 2. Explanatory drawings for text-fig. 1. A. Necrogammarus salweyi Woodward. B. Erelloplerus bilohus (Salter). For explanation of homologous terms see Sclden (1981). SELDEN: S I LUR IAN ARTHROPOD 63 R E F E R E N C E S A L M O N D , J. E. 1985. The Siluro-Devonian fossil record of the Myriapoda. Phil. Trans. R. Soc. B309, 227-237. I I A M M E N , L. V A N M R . 1979. Comparative studies on Chclicerala [. The Cryptognomae (Ricinulei, Architarbi and Anactinotrichida). Zool. Verh. Leiden, 174, 1-62. HESSLfcR, R. R. 1969. Peracarida. In M O O R E , R. C . (ed.). Treatise on invertebrate paleontology. Part R. Arthropoda 4(1), R360-R393. Geological Society of America and University of Kansas Press, Boulder. Colorado, and Lawrence. Kansas. H U X L E Y , T . H . and S A L T E R , J. w. 1859. On the anatomy and affinities of the genus Pterygotus and description of new species of Pterygotus. Mem. geol. Surv. U.K., Monogr. I, 1-105, 16 pis. K J E L L E S V I G - W A E R I N G , E. N . 1961. The Silurian Euryptcrida of the Welsh Borderland. J. Paieont. 35, 789-835. P E A C H , it N . 1899. On some new myriapods from the Palaeozoic rocks of Scotland. Proc. R.pltys. Soc. Edinh. 14, R O L F E , w. D . I. 1980. Early invertebrate terrestrial faunas. In P A N C H E N , A . L . (ed.). The terrestrial environment and the origin of kind vertebrates, 117-157. Systematics Association Special Volume No. 15. Academic Press, London and New York. S E L D E N . P. A . 1981. Functional morphology of the prosoma of Baltoeuryplerus tetragonophthalmus (Fischer) (Chelicerata: Eurypterida). Trans. R. Soc. Edinb. 72,9-48. 1984. Autecology o f Silurian eurypterids. In BASSETT, M . G. and L A W S O N . J. D . (eds.). Autecology of Silurian organisms. Spec. Pap. Palaeont. 32, 39-54. W H I TAKER , J. II. M C D . 1962. The geology of the area around Leintwardine, Herefordshire. Q. Jl geol. Soc. Land. 118,319 351. wooi J W A R D , H . 1870. On Necrogammarus SQbvtyiQA. Woodward), an amphipodous crustacean from the Lower Ludlow of Leintwardine. Trans. Woolhope Nat. Fid Club, 1870, 271 -272, I pi. 113-126. P A U L A . S E L D E N Typescript received 13 September 1985 Revised typescript received 6 November 1985 Department of Extra-Mural Studies University of Manchester Manchester M I 3 9PL 

A new identity for the Silurian arthropod Necrogammarus

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A new identity for the Silurian arthropod Necrogammarus

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