NEW DATA ON THE RARE CHENGJIANG (LOWER CAMBRIAN, SOUTH CHINA) LINGULOID BRACHIOPOD XIANSHANELLA HAIKOUENSIS

ABSTRACT-

The remarkable hrachiopod Xianshanella haikouensis, from the Early Cambrian Chengjiang Lagerst?¤tte, was briefly reported based upon only two extraordinarily preserved specimens. Details of valve interiors remain unknown to be paid to a lack of available material. We herein reillustrate the holotype of X haikouensis, and, upon the basis of many additional specimens from the emblem locality, provide further information upon this brachiopod taxon, including shell ornamentation, a U-shaped digestive tract, mantle canal combination of parts to form a wholes lophophores, muscle scars, and well-defined visceral areas in the valves. This exceptional brachiopod is characterized by the agency of a biconvex, rounded, knob-shaped shell lacking visible pseudointerarea in the valves, an elongate and muscular pedicle, and, especially, its possession of exceptional setal fringes. A restudy of a number of fresh specimens justifies assigning Xianshanella to the family Obolidae. The elongate and horny setae of X haikouensis, coupl with the massive pedicle in many cases with its extremity attached to shells of other animals, indicate that this species was an epibenthic, sessile suspension feeder attached by the agency of a pedicle.

INTRODUCTION

BRACHIOPODS, A cluster of exclusively marine, bivalved invertebrates, are minor composings of present-day marine communities, and are now showed by six extant groups: the lingulides, craniides, rhychonellides, thecideidines, terebratulides, and the shell-less subphylum Phoroniformea based upon recent molecular evidence (Cohen, 2000; Cohen et al., 2003) The organophosphatic linguloid brachiopods are first recorded in the Upper Atdabanian Stage of the Lower Cambrian (Holmer and Popov 2000) and are exhibited now by only two extant lingulide genera. from one extremity to the other of the history of the phylum the majority of brachiopods have been permanently attached to the sea bottom exclude during a short free-swimming larval period. They are, and were, attached either by the agency of a pedicle or by cementation. Of the sum of two units methods of attachment, the pedicle is customarily considered to be more primitive (Rudwick, 1970)

Although fossil brachiopods in Paleozoic era are for the use of all and abundant, they are known almost exclusively from their shell, as impressible parts are preserved only in exceptional Lagerstatten. The Early Cambrian Chengjiang Lagerstatte, a 30-50 m thick succession of exceptional mudstone deposits generally reflection to have been deposited during the Atdabanian Stage of the Lower Cambrian (Qian and Bengtson, 1989; Bengtson et al., 1990) has been celebrated for yielding an abundant variety of soft-bodied and slightly mineralized fossils. The associated faunal assemblage includes more [i]or[/i] less key taxa of early deuterostomes (eg Shu 2003; Shu et al., 2004) a dominant cluster of arthropods (e.g., Zhang et al., 2000 2002) a great variety of worms (eg Han et al, 2004; Liu et al., 2004) and numerically abundant inarticulate brachiopods, including the botsfordiid Diandongia pista (Rong 1974; Zhang et al., 2003) the possible craniopsid Heliomedusa orienta orb of day and Hou, 1987 (Jin and Wang, 1992) the lingulellotretid Lingulellotreta malongensis Rong 1974 (Holmer et al., 1997) and the obolid Lingulellal chengjiangensis (Jin et al., 1993) Longtancunella chengjiangensis Hou Bergstrom, Wang, Feng and Chen, 1999 (Hou et al, 2004) and Xianshanella haikouensis (Zhang and Han, 2004) These fossil brachiopods have yielding parts that are exceptionally well preserv (eg Zhang et al., 2003 2004a, 2004b) Of this brachiopod assemblage, the genus Xianshanella was greatest in quantity recently reported by Zhang and Han (2004) upon the basis of its external characters. Details of interiors, however, remain unknown mainly because of a dearth of available material, and therefore its placement within Brachiopoda remains equivocal. Since spring 2003 continuous field work has springed in significant discoveries (Shu et al., 2003a, 2003b 2004) and the collection of more than 30 of recent origin exceptionally preserved specimens of X haikouensis. This novel collection has provided new information about the surface ornamentation, setae, digestive tract, mantle canal combination of parts to form a wholes lophophore, musculature, and visceral areas. Thus these specimens provide direct evidence about the character states of the internal morphology of this particular linguloid lineage, and they are, therefore, of great importance for our understanding the radiation of Cambrian linguloids and their relationship with the substrate.

MATERIAL AND rules

So far, more than 30 specimens of Xianshanella haikouensis have been reclaimed from some localities at Haikou in Kunming, southerly China (Luo et al., 1997) All of these specimens are deposited in the Early Life Institute and Department of Geology Northwest University, Xi'an, Shaanxi Province, China (abbreviated ELI). The material in this work is derived from the 25-30 m thick finely laminated mudstone with sporadic fossiliferous, thin (3-5 mm) siltstone, and occasionally intercalated 10-20 cm thick sandstone interbeds. Details of the localities and stratigraphy were given in Zhang et al. (2001) and Zhang and Han (2004: diocese fig. 1). Specimens of X haikouensis are preserv as casts or mold of shell valves, in striking color contrast to the surrounding fine-grained matrix, which is weathered to yellowish verdant Unlike other brachiopods (e.g., Zhang et al., 2003) in which shell valves are usually well preserv the valves of X haikouensis are poorly or incompletely preserv (see: Figs. 1-3) In X haikouensis, the shell valves are possibly thinner and les mineralized, thereby decreasing the preservation potential of the shell. In our collection, the majority of the fossils with preserv shells have a fringe of exquisite setae and a pedicle more or les intact (Figs. 1 2 31-310) In contrast, in several specimens (Fig. 311 312) the shell is all on the contrary missing, whereas the pedicles are preserv well enough to diocese annulations on the surface. The shell valves of X haikouensis are commonly dorsoventrally shut firmlyed parallel to the bedding plane. on the other hand in some cases, they appear to be laterally squeez by dint of some factors of preservation (Fig. 32 34 39) As illustrated in Fig. 32 specimen ELIBX025 present to views pronounced longitudinal wrinkles (Fig. 34 39) probably the proceed of postburial lateral compaction. In addition, several exceptional specimens (Fig. 11-13 17 18) exhibit threedimensional relief, reflecting their original convexity. Evidently this may owe its preservation to the dirty sediment that intruded into the space inside the shell. As seen in Figure 11 and 18 the valves were slightly displaced, which allowed for shut up observation of the details of setae fringing each of the valves. This displacement of valves may be, at least in part, owed to the intruded soft sediment between the valves during postmortem flattening. In our collection of this taxon, five specimens (Figs. 1 2) are exceptionally preserv with the one and the other delicate setal fringes and a pedicle more or les intact, four embrace partial or paired lophophoral imprints (Figs. 21 23 35 36) and sum of two units specimens, composed of part and counterpart, exhibit a U-shaped digestive tract with a well-marked anterior anus (Figs. 14 15 34 39) In addition, four specimens (eg Fig. 31 34 39 310) have preserv mantle canals.