Hu et al.—A possible early Cambrian pterobranch hemichordate
Stage 5 of the Cambrian Period (Maletz, 2014; LoDuca et al., 2015a; Maletz and Steiner, 2015). In this study, we reinterpret Malongitubus kuangshanensis Hu, 2005 from the early Cambrian Chengjiang Konservat-Lagerstätte (Series 2, Stage 3) as a possible pterobranch, judging mostly from the identification of a resistant internal stolon system.
Geological setting, materials, and methods
All material is from a single bedding plane in a small quarry on the northwest slope of a hillside near Kuangshan village, ~10km southwest of the county town Malong, 100 km east of Kunming in Yunnan Province, China (25°20'15''N, 103°30'20''E). Stratigraphically, this interval belongs to the upper part of the Eoredlichia–Wutingaspis Zone within the Yu’anshan Formation and is equivalent to the strata containing the renowned Chengjiang Biota in Chengjiang County and the Haikou district of Kunming (Luo et al., 1994; Zhang et al., 2001). Associated fossils from the same interval include arthropods (trilobites, bradoriids, and other arthropods), sponges, cnidarians, anomalocaridids, lobopodians, priapulids, hyolithids, brachiopods, chancelloriids, vetulicolians, and algae (a detailed list of fossils is available in the appendices of Hu, 2005 and Zhao et al., 2012), representing a local assemblage of the Chengjiang biota. The lithology of the section and the occurrence of the pterobranch-bearing layer were illustrated previously (Hu, 2005, text-fig. 9; Wang et al., 2012, fig. 1B). The preservation of the probable pterobranchs and other associated fossils was interpreted to be the result of rapid burial by a distal storm event (Hu, 2005; Zhao et al., 2012). The specimens of Malongitubus kuangshanensis are com-
pressed, often fragmentary, and commonly partly superimposed on one another on the bedding surface. In most cases, the tubes are whitish or pale in color due to intense weathering, with occasional dark remains of original organic material. The materials were prepared using a sharp blade under a binocularmicroscope.Overall images of the specimens were obtained with a Canon Mark II Camera with an EF 100mm f/2.8L IS USM close-up lens under direct light. Enlargements of details at the millimeter scale were
photographedwith a Zeiss Smartzoom 5microscope system under fiber-optic lights. BSE pictures were obtained using a HITACHI SU3500 in the Nanjing Institute of Geology and Palaeontology, ChineseAcademy of Sciences,China,with an accelerating voltage of 20–30kV. SEM microphotographs were obtained and energy- dispersive spectroscopic analysis was conducted at the State Key Laboratory of Continental Dynamics, Northwest University, Xi’an, China, with a ZEISS-SUPRA 40VP.
Repositories and institutional abbreviations.—Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, China (NIGP); Early Life InstituteofNorthwestern University (ELI).Aspecimen ofDalyia racemata from theBurgess Shalewas also examined in this study (specimen number USNM 194121, Smithsonian Institution, Washington DC, USA). The nomen- clature applied in this study follows that of recent works on pterobranchs (Maletz et al., 2005; LoDuca and Kramer, 2014; Maletz, 2014; LoDuca et al., 2015a; Maletz and Steiner, 2015).
Systematic paleontology
? Phylum Hemichordata Bateson, 1885 ? Class Pterobranchia Lankester, 1877
? Subclass Graptolithina Bronn, 1849, emend. Mitchell et al., 2013 Genus Malongitubus Hu, 2005
Type species.—Malongitubus kuangshanensis Hu, 2005.
Diagnosis (emended).—Colonial organism with long, slender, and branching thecal tubes. Thecal tubes parallel-sided, each with an internal continuous thread. There are usually four, or less commonly five, terminal thecal tubes,which are free and in similar widths and lengths. Fine annulations present on the surface of thecal tubes. Terminal thecal tubes narrow distally, commonly with thickened apertures.
Remarks.—Malongitubus closely resembles Dalyia Walcott, 1919 from the Burgess Shale (Cambrian Series 3, Stage 5) in overall colony shape and in having nearly parallel-sided thecal tubes and inner threads of relatively constant dimensions, herein interpreted as a stolon system. The close similarity between the two taxa led to the suggestion of possible synonymy (Maletz and Steiner, 2015). However, Malongitubus differs in having a greatly variable branching distance, from millimeters to centimeters. In addition, the presence of round structures at the branching points of Dalyia (Maletz and Steiner, 2015) allows differentiation of the two taxa. On the basis of this difference, Malongitubus is retained as a separate taxon. Holdfast structures and initial (larval) development of both taxa are unknown. The development of fuselli cannot be proven, but is likely. No zooid remains have been preserved. Comparing to Yuknessia from the Cambrian of British Columbia and Utah, the thecal tubes of Malongitubus are completely free and parallel-sided or slightly expanding, whereas those of Yuknessia conspicuously widen distally. In addition, the presence of repent and erect thecae in Yuknessia also distinguish it from Malongitubus. The absence of more differentiated thecal types, such as autothecae, bithecae, and stolothecae, in M. kuangshanensis indicates that it differs from dendroid graptolites, which have been reported from the traditional “middle Cambrian” and younger strata (Rickards et al., 1990; Johnston et al., 2009; LoDuca and Kramer, 2014).
Malongitubus kuangshanensis Hu, 2005 Figures 1, 2
2005 Malongitubus kuangshanensis Hu, p. 187, pl. 18, figs. 1–7.
2012 Malongitubus kuangshanensis; Wang et al., p. 62, fig. 2A–G.
Holotype.—NIGP-165028 (labeled as Kuangshan-01 in Hu, 2005), a large, nearly complete (base missing) multibranched tubarium with four terminal thecal tubes (Fig. 2.1).
Occurrence.—Kuangshan village, Malong County, Yunnan Province, China. Upper part of the Eoredlichia–Wutingaspis Zone, Yu’anshan Formation, Cambrian Stage 3, Series 2, early Cambrian.
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