Spiralia I: Animals with Lophophores
As discussed previously, the monophyly of Spiralia is well supported by molecular and morphological evidence. We now consider "Lophophorata" animals with ciliated feeding appendages called lophophores. Note: there are other animals with lophophore-like appendages that we aren't considering, including:
- Pterobranchia: Tiny colonial deuterostomes.
Bryozoan lophophore from Iowa State University -
Department of Ecology, Evolution, and Organismal Biology
- Lophophores (right):
- Hollow extensions of the second (of three) parts of the coelom. (Note: Many bilaterians have a three-part coelom.)
- Surrounds the mouth (anus may be inside or outside.)
- Function sin collection of food and in gas exchange
they do display clear similarities:
- Essentially headless
- U-shaped guts with distinct mouth and anus.
Two major groups (and two minor):
- Bryozoa: (AKA Ectoprocta. Ord - Rec.) Tiny colonial "moss animals." Secrete colonial skeletons (either organic or calcareous). Distinguished by their anuses being outside the base of their hollow lophophores.
Terebratulid brachiopods from BBC
- Brachiopoda: (C - Rec.) Macroscopic solitary bilaterians that attach to the substrate with a pedicle (stalk) and are protected by two calcareous or chitinophosphatic valves (shells).
Phoronid from Verschiedene Marine Würmer
- Phoronida: No unambiguous fossil record. Soft, burrowing, worm-like creatures that project their unprotected lophophores into the water column to feed.
Barentsiid entoprocts from Cifonauta
- Entoprocta: (C - Rec.) Solitary or colonial zooids superficially resemble bryozoans, but with solid lophophores that encircle both mouth and anus. There is no coelom, and colony skeleton is chitinous. Unambiguous fossil entoprocts date from the Jurassic, but Zhang et al. 2013 have identified the solitary Chengjiang taxon Cotyledion tylodes as an entoproct. Opinion is divided about the Burgess Shale taxon Dinomischus.
Plumatella from Goldfish Garage
The relationships of these groups are discussed below. Mostly, we are concerned with Bryozoa and Brachiopoda, which have substantial fossil. records.
Phoronid anatomy from Kennesaw University
Phoronida:(No record) Represent what we might imagine to be the ideal ancestral lophophorate. Characteristics:
- Always solitary
- Infaunal benthic marine
- Nephridia for waste excretion
- Closed circulatory system with blood cells and hemoglobin (no distinct heart)
- you ignored phoronids
- you weren't aware of synapomorphies linking halkeriids to mollusks.
Brachiozoa?: Cohen et al., 1998 and Cohen and Weydmann, 2005 indicated that phoronids are a valveless form of brachiopod. More recently, however, Hausdorf et al. 2010 find Phoronida to be the sister taxon of a monophyletic Brachiopoda. They name the Brachiopoda + Phoronida clade "Brachiozoa."
Recently, Sutton et al., 2010 described Drakozoon kalumon, a soft-bodied lophophore-bearing creature of Silurian age that might represent an intermediate grade between phoronids and brachiopods. Unlike phoronids, it attaches to the substrate by a broad attachment, but unlike brachiopods, has no mineralized valves - only a broad soft-tissue "hood."
Brachiopod in anatomical position from Invertebrate Paleontology Knowledgebase
Brachiopoda:(Cambrian - Rec.) General characteristics:
- Always solitary
- Always encased inside brachial and pedicle valves (except for pedicle)
- Always benthic marine
- Nephridia for waste excretion
- Closed circulatory system with a distinct heart but which doesn't seem to be involved in gas transport. (In contrast to Phoronida.)
- Coelomic fluid with the oxygen-binding protein hemerethryn.
- "Mantle tissue" that secretes the valves. (Not homologous to mollusk mantle.)
- Simple nervous system coordinated by one or two ganglia near the base of the lophophore. Sensory neurons concentrated near anterior portion of the valves.
- Living brachiopods are sensitive to sudden changes in illumination, and avoid light generally, preferring cryptic environments.
- Brachiopod flesh is bad-tasting and avoided by potential predators.
- Refer to lab for details of valve morphology.
Antarctic terebratulid brachiopods from BBC Nature
Brachiopod ecology: Although brachiopods encompass much diversity, certain generalizations are valid throughout.
- All are shallow marine benthic
- They typically require hard substrate. Those without pedicles (E.G. concavo-convex Chonetes) lay on soft substrate. Some were cemented to the substrate.
- The utility of such strategies depended on the energy of the environment.
- Moderate energy: E.G. a reef environment below low tide line. A direct pedicle or spiny attachment to a rigid substrate or host.
- Low energy only: E.G. a sandy bottom below wave base. Rafting on soft sediment. (Even moderate energy here would bury the rafter.)
- High energy: E.G. Intertidal zone. Here, sessile creatures must be firmly attached to a hard substrate, as in craniiform brachiopod cemented to strophomenid brachiopod.
- Positioning and attachment: Position has two crucial aspects:
Orientation: Using the pedicle, it can adjust its orientation to optimize suspension feeding. Its feeding, however, is limited to within 2 - 3 cm of the substrate, and the substrate must be rigid.
- Location: Some brachiopods overcame this limitation by attaching to larger suspension-feeding organisms like stalked echinoderms, either with their pedicle (in which case they could still control their orientation somewhat) or using spines on their valves (in which case they depended on the substrate-host to orient them properly).
- Others pioneered soft substrates, rafting on them by means of deep globular morphologies or the support of elongate spines.
- Brachiopods retain strong bilateral symmetry, even internally. Food particles are filtered from water brought inside the valves and mantle cavity by mucus secreted by the the lophophore tentacles. Intercepted particles are moved to the mouth by ciliary action. Upper and lower valves control the flow of the ciliary current across the lophophore, eliminating the need to be able to capture food coming from any direction.
- Plicae: In many bivalved organisms, most notably brachiopods, the commisure at which the valves meet forms a series of zig-zag plicae. Functions include:
- Feeding: The area of the gape is increased but not the width. A greater volume of water cna be processed while large particles are excluded. Additionally, many brachiopods have a median fold and sulcus separating incurrent from excurrent water.
- Strength: It is much more difficult for the valves of a plicate shell to be twisted apart.
Carlson, 2007. For a more detailed phylogeny see 3D Brachiopod Images at UC Davis.
In traditional taxonomy brachiopods were divided between "articulates" - those possessing tooth-in-socket hinged articulations between valves, and "inarticulates" - those lacking such articulations that rely on soft tissue to control valves. The application of phylogenetic methods, in contrast, reveals three major clades:
Lingula dissection from Udo Savilli,
Arizona State University - BIO385
Linguliformea: (AKA "Lingulata") (C - Rec.)
- Chitinophosphatic valves with chaetae, lacking hinge articulation
- Large muscular pedicle invaded by coelom. Coelomic hydrostatic skeleton and adductor muscles coordinated in the opening and closing of valves.
- Valves typically elongate and somewhat rectangular.
- Burrowing infaunal habit.
- Living members do not attach to the substrate. Instead they burrow in muddy substrate with anterior edge of valves near sediment-water interface. From the Cambrian onward, linguliforms have specialized in muddy inter and subtidal habitats, making them a classic facies fossil.
- Linguliforms are the only brachiopods known to tolerate brackish water.
- Craniiformea (Sometimes erroneously referred to as "Craniata" (not to be confused with the TRUE Craniata) (Cambrian - Rec)
- Valves calcareous and punctate (perforated by small openings)
- Valves typically sub-circular.
- Pedicle reduced or absent. Instead, the pedicle valve is typically cemented to a hard substrate (often another brachiopod valve.).
Coptothyris adamsi from Behance
Ptychopeltis incola from Virtual Museum
- Greatest diversity of brachiopods, living or extinct
- Calcareous valves with complex hinge articulation
- Valve histology: In cross-section, rhynchonelliform valves display obliquely layered inner layers of calcite overlain by low-angle lamellae. These can be:
- Diductor muscles open valves, adductors close them.
- Valve identities are distinct:
- Pedicle valve houses pedical foramen through which the pedicle exits.
- The lophophore is associated with the brachial valve and may be supported by a brachidium projecting from it.
- Valves can be:
- Interarea: The region between the valve's beak and hinge.
- The pedicle foramen may take the form of a triangular delthyrium. This may be partly sealed by a distinct midline plate - the deltidium or by paired deltidial plates.
- Valves are typically biconvex but can also be plano-convex or concavo-convex.
- All valves, to some degree, display fold in brachial valve and sulcus in pedicle valve.
- Pedicle variously developed, but always dead horny tissue, not invaded by the coelom.
- Anus lacking. Gut tube is blind ended, with waste periodically being expelled through mouth. (In stark contrast to lingulids, which have a proper gut tube.) Note: The lophophorate filtration system normally rejects indigestible particles prior to ingestion, so the elimination of feces is not a big problem for these animals.
- Epifaunal, with a wide variety of habits and substrate preferences, some of which change during ontogeny.
Rhynchonelliform systematics: A complex topic. Your text provides a detailed list of currently acknowledged monophyletic rhynchonelliform taxa. Here, we present six groups that are heavily cited in traditional century literature. In some cases, their monophyly is not certain:
- "Orthida": (C - P. Abundant in C, O) Morphologically the most ancestral of articulates. Possibly paraphyletic.
- Distinct interarea with open delthyrium
- Lacking elaborate brachidium
- Strophomenida: (O - Carb. Most abundant in Ordovician)
- Strophic with D-shaped profile.
- Often lacking pedicle and colonizing soft substrates.
- Frequently concavo-convex - an adaptation to "floating" on soft substrates.
- Productida: (D - Tr. Most abundant in Carb.)
- Develop long spines on pedicle valve for stabilization in soft substrate.
- Pentamerida: (C - D. Peak abundance in Sil.)
- Astrophic with biconvex valves.
- In transvcerse cross-section Large cruralium and spondylium divided mantle cavity into five chambers.
- Rhynchonellida: (O - Rec.)
- Astrophic with pointed beak and biconvex valves.
- Strongly plicate with deep fold and sulcus.
- Spiriferida: (O - J. Peak abundance in Devonian.) Possibly paraphyletic.
- Strongly strophic
- Large interareas with open delthyria
- Brachidium developed into complex spiralium.
- Terbratulida: (D - Rec.) Never terribly abundant, but the most common post-Paleozoic brachiopods.
- Smooth biconvex valves
- Looping brachidium
- Their characteristic shape gives brachiopods the common name "lamp-shell."
Evolutionary trends: The relative abundance of different groups of these common fossils imparts a distinct character to shallow marine deposits of different systems. Thus even a geologist wit no interest in brachiopods, per se, should learn to identify them:
- Cambrian: The earliest brachiopod communities dominated by linguliids and craniiforms in near-shore environments.
- Ordovician-Devonian: Proliferation of rhynchonelliform brachiopods into deeper water, carbonate, and soft substrate environments. Strophic, deltidiodont, D-shaped types such as strophomenids and orthids predominate. Severe reductions during Ordovician mass extinction and Silurian recovery.
Leptodus nobilisfrom www.ne.jp
- Carboniferous-Permian: Following the decline of stromatoporoids during the Late Devonian extinctions, brachiopods emerged in the Late Paleozoic as the major encrusting suspension-feeders of reef environments, but became less dominant on soft substrates:
- Proliferation of encrusters, including odd-ball productids with specializations for cementation to hard substrate (E.g. Prorichthofenia, Leptodus - right).
- Other productids developed morphology for support in soft sediment.
- This interval also saw the emergence of rhynchonellids and spiriferids as major components of the fauna.
- Massive extinctions at the end of the Permian.
- Post-Paleozoic: The Permian extinction all but eliminated the more basal rhynchonelliformes, and the Triassic extinction finished off the survivors, leaving linguliids, craniiforms, rhynchonellids, and terebratulids with essentially modern ecologies as marginal inhabitants of cryptic reef environments.
Burgess Shale linguliform Acanthotretella spinosa from The Royal Ontario Museum
- Xianshanella haikouensis: Zhang et al. 2006. From Chengjiang, this early lingulid had a long pedicle but lived attached to hard substrates. (right)
- Tommotian stem brachiopods?: Members of the earliest Cambrian small-shelly fauna, including Micrina were proposed by Holmer et al., 2008 as near the ancestry of brachiopods.
- Oldest crown brachiopod: This honor goes to Aldanotreta sunnaginensis from the Tommotian of Siberia. Aldanotreta is a paterinate linguliform with a phosphatic shell, however it displays rhynchonelliform characters such as interareas, delthyria and notothyria, and proper diductor muscles. Could the absence of these features in other linguliforms be a reversal?
But what does any of this tell us about everyone's favorite group?
Phylactolaemate bryozoan zooid from Biodidac
- Ectoprocta, (the original "Bryozoa") whose anuses were outside the circle of their lophophores,
- Entoprocta, whose anuses were inside this circle.
You've probably seen them without knowing it. General characteristics:
- Exclusively colonial
- Non-living skeleton (zooecium)
- Each "individual" is a zooid
- Colony (zoarium) begins with an initial zooid, the ancestrula, which buds off clones to form the remainder of the colony. (But a soft tissue connection persists.)
- Individual zooids connected by funiculus and stolon through which nutrients are shared.
- Lophophore is protracted when it "inflated" by coelomic fluid when circumferential muscles of body wall contract. It is retracted by retractor muscles. (In contrast, the lophophore tentacles of entoprocts are solid.)
- The anus lies outside the circle of the lophophore (hence the obsolete name "Ectoprocta," in contradistinction to Entoprocta)
- Small enough to handle gas-exchange by simple diffusion.
- Lack nephridia (organs for excretion of insoluble wastes) These, thus, accumulate in tissues.
- Great powers of regeneration. Occasionally, all cells of the zooid except for the body wall degenerate into a brown body that is ultimately ejected from the zooecium. The zooid then regenerates from the body wall. Possible functions:
- Resting stage during stressful intervals
- A radical means of ridding the body of insoluble wastes.
- Reproduction of both zooids and colonies is often by budding. Individuals reproduce sexually, as well. Most zooids are hermaphroditic, although ovaries and testes are usually not active simultaneously.
- Ova are retained in the zooecium
- free-swimming sperm are snared by the lophophore and conveyed to the ovum.
- The zygote escapes as it transforms into a planktonic larva.
- The zooids are proper bilaterians with distinct mouths and anuses.
- Zooecia are tiny, and completely lack septa, tabulae, or dissepiments.
- Chitinous (i.e.soft) zooarium
- All zooids similar
- Zooecial walls incomplete, allowing zooids freely to share coelomic fluid.
- Can propagate through statoblasts - little capsules of cells enclosed in calcareous capsules that form along the funiculus. In times of stress, when the zooid dies, these disperse. When proper conditions return, they open and a new ancestrula regenerates.
- Orifice protected by operculum
- Zooecia box-like with nearly complete walls perforated only by pore plates thus...
- Lophophore protraction requires deformation of zooecium. Achieved differently in different taxa.
- Colonies include specialized non-feeding zooids, including
- Two major groups:
- Ctenostomata: (Ord. - Rec.)
- Persistent fossil record, based in part on borings and traces in other fossils
- Membranous chininous zooecia.
- Because zooecium is flexible, lophophore protraction is similar to that in phylactolaemates.
Cheilostomate zoarium from Neogene Bryozoa of Britain
- Cheilostomata: (Jurassic - Rec.)
- excellent fossil record
- encrusters with largely calcareous zoaria. Because the zooecium is rigid, hydrostatic protraction of the lophophore is facilitated by adaptations like:
- Protractor muscles attach to a flexible frontal wall inside of zooecium.
- Zooecium contains a water-filled compensation sack that communicates with the exterior. This empties or fills to compensate for protraction or retraction of the lophophore.
- Aperture is closed by a mobile operculum.
- Ctenostomata: (Ord. - Rec.)
- Zooids and zooecia tall and cylindrical
- Calcareous zooecia
- Dominant bryozoans of Paleozoic.
- Major groups:
- Trepostomata: (Ord. - Tri.)
- Three morphs of zooecia:
- Autopores: Largest - presumed inhabited by typical zooids
- Mesopores: Smaller - presumed inhabited by specialized zooids
- Acanthopores: Very small, at the tops of small cones - surmounted by spine
- Autopores and mesopores display diaphragms - sequential floors of zooecium, analogous to cniderian tabulae.
- Zoarium surface has regular mounds - monticules.
Hornera frondiculata from Zipcodezoo
- Three morphs of zooecia:
- Cyclostomata: (AKA Tubuliporata)(Ord. - Rec.)
- Nomenclature: Your text uses the traditional "Cyclostomata," but as this is synonymous with the Chordate taxon containing lampreys and hagfish (monophyletic?), Tubuliporata is preferred.
- Mural pores perforate zooecia.
from Scripta Geologica
- Cryptostomata: (Ord. - Per.)
- True aperture of zooecium is hidden behind a vestibule :
- Hemiseptum: separates vestibule and proper zooecium
- Fenestrata: (Ord. - Per.)
- Upright, lacy zoaria perforated by fenestrules allowing flow of water.
- Zooecia occupy obverse side only.
Constellaria emaciata from The Digital Atlas of Ordovician Life
- Cystoporata: (Ord. - Tri.)
- Zooecia separated by curved partitions known as cystiphagms.
- Lunaria - crescentic projections surrounding aperture.
Heterotrypa sp. from Wikipedia
- Trepostomata: (Ord. - Tri.)
Small phylactolaemate zoarium from Idaho Department of Fish and Game
Reteporella beaniana zoarium from Seawater.no
Vesicularia spinosa from britishbryozoans
Stenolaemata: (Ord - Rec).
- Phylactolaemata have no record.
- Early Paleozoic: Trepostomata and Cryptostomata dominant in Ordovician, but sharply curtailed by Ordovician extinction, never regaining dominance and suffering again in Devonian and Permian events, with only some trepostomatids straggling into the Triassic.
- Silurian - Devonian: Peak diversity for Cystoporata and Trepostomata.
- Late Paleozoic: The age of Fenestrata, some of which are Carboniferous index fossils. These are extinguished by Permian event.
- Late Mesozoic: Great proliferation of Cyclostomata (= Tubulipora) and Cheilostomata. All suffered in K-P extinction,
- Cenozoic: The age of Cheilostomata. Cyclostomata (= Tubulipora) recovers from K - P extinction but never regains preeminence.
The Linnean "subkingdom" Lophophorata has been recognized as problematic since the early days of phylogenetic systematics, and remains controversial.
- Early applications of phylogenetic methods to the problem suggested that phoronids and brachiopods might be:
- Deuterostomes, based on morphology (Nielsen, 2003)
- Spiralians, based on molecular data. (Halanych et al., 1995)
Interpretation of morphology was frustrated but ambiguities of homology, however. (E.G. the endodermal coelom of larval bryozoans is resorbed during metamorphosis and replaced by a new "coelom" resembling the three-part coelom of deuterostomes, except that it is derived from ectoderm.) Most recent clarity on this topic, therefore, comes from molecular phylogenies.
- Numerous molecular studies support the monophyly of Spiralia, including (but not limited to) Trochozoa, Phoronida, Brachiopoda, and Bryozoa.
This says little about bryozoans. They seem to be closer to Trochozoa than to Ecdysozoa or Deuterostomia in most molecular analyses. Alas, the bryozoan genome is as derived as its morphology, making it a difficult subject for molecular methods:
- Bryozoa and its three major clades (Phylactolaemata, Gymnolaemata, and Stenolaemata) seem to be monophyletic. (Jang and Hwang, 2009, Waeschenbach et al., 2011).
- Helmkampf et al. 2008 present a phylogenetic analysis suggesting that:
- bryozoans and entoprocts are sister taxa.
- Brachiopods and phoronids are sister taxa.
- (Brachiopods + phoronids) are sister taxon to Trochozoa.
- (Bryozoans and entoprocts) are sister taxon to ((Brachiopods + phoronids) + Trochozoa.)
- Paps et al. 2009 present a phylogenetic analysis suggesting that:
- (Brachiopods + phoronids) are inside Trochozoa, sister taxon to Mollusca.
- Entoprocts are sister taxon to Cycliophora, ectoparasites living on the mouthparts of lobsters, first described by Funch and Kristensen, 1995.)
- (Entoprocta + Cycliophora) is sister taxon to Bryozoa.
- The last word, reminding us never to get too comfortable, belongs to Nesnidal et al., 2013 (including Helmholtz): who find that:
- Bryozoa, not brachiopods, are the sister taxon to phoronids.
- Brachiopods, are the sister taxon to (Bryozoa + Phoronida).
The whole question of lophophorate phylogeny is unsettled. We seem to know only that:
- They belong to a monophyletic Spiralia
- Better fossils
- Improved taxonomic sampling for molecular phylogenies
- Better understanding of the complexities of the interpretation of molecular data.
- Carlson, S. J. 2007. Recent research on brachiopod evolution. Pp. H2878–H2900 in A. Williams et al. Brachiopoda 6 (revised), Supplement. Part H of P. A. Seldon, ed. Treatise on invertebrate paleontology. Geological Society of America, Boulder and University of Kansas, Lawrence.
- Cohen, B.L., Gawthrop, A., and Cavalier-Smith, T. 1998. Molecular phylogeny of brachiopods and phoronids based on nuclear-encoded small subunit ribosomal RNA gene sequences. Philosophical Transactions of the royal Society B 353(1378): 2039-2061.
- Bernard L. Cohen, Agata Weydmann. 2005. Molecular evidence that phoronids are a subtaxon of brachiopods (Brachiopoda: Phoronata) and that genetic divergence of metazoan phyla began long before the early Cambrian. Organisms Diversity & Evolution 5(4): 253-273.
- S. Conway Morris, J. S. Peel. 1995. Articulated Halkieriids from the Lower Cambrian of North Greenland and their Role in Early Protostome Evolution. Philosophical Transactions of the royal Society B 347(1321).
- Peter Funch and Reinhardt Kristensen. 1995. Cycliophora is a new phylum with affinities to Entoprocta and Ectoprocta. Nature 378, 711 - 714.
- Halanych KM, Bacheller JD, Aguinaldo AM, Liva SM, Hillis DM, Lake JA. 2010. Evidence from 18S ribosomal DNA that the lophophorates are protostome animals. Science 268(5210): 485.
- Bernhard Hausdorf, Martin Helmkampf, Maximilian P. Nesnidal, Iris Bruchhaus. 2010. Phylogenetic relationships within the lophophorate lineages (Ectoprocta, Brachiopoda and Phoronida). Molecular Phylogenetics and Evolution 55(3): 1121-1127.
- Martin Helmkampf, Iris Bruchhaus, Bernhard Hausdorf. 2008. Phylogenomic analyses of lophophorates (brachiopods, phoronids and bryozoans) confirm the Lophotrochozoa concept. Proceedings of the Royal Society B 275(1645).
- Holmer L. E., Skovsted C. B., Brock G. A., Valentine J. L., Paterson J. R. 2008. The Early Cambrian tommotiid Micrina, a sessile bivalved stem group brachiopod. Biology Letters 4(6):724-8.
- Kuem Hee Jang and Ui Wook Hwang. 2009. Complete mitochondrial genome of Bugula neritina (Bryozoa, Gymnolaemata, Cheilostomata): phylogenetic position of Bryozoaand phylogeny of lophophorates within the Lophotrochozoa. BioMed Central Genomics 10(167).
- M. P. Nesnidal, M. Helmkampf, A. Meyer, A. Witek, I. Bruchhaus, I. Ebersberger, T. Hankeln, B. Lieb, T. H. Struck, B. Hausdorf. 2013. New phylogenomic data support the monophyly of Lophophorata and an Ectoproct-Phoronid clade and indicate that Polyzoa and Kryptrochozoa are caused by systematic bias. BioMed Central Evolutionary Biology 13(253).
- Claus Nielsen. 2003. The Phylogenetic Position of Entoprocta, Ectoprocta, Phoronida, and Brachiopoda. Integrative and Comparative Biology 42: 685-691.
- Jordi Paps, Jaume Baguñá and Marta Riutort. 2009. Lophotrochozoa internal phylogeny: new insights from an up-to-date analysis of nuclear ribosomal genes. Proceedings of the Royal Society B 276: 1245-1254.
- M. D. Sutton, D. E. G. Briggs, David J. Siveter, Derek J. Siveter. 2010. A soft-bodied lophophorate from the Silurian of England. Biology Letters 7(1).
- Andrea Waeschenbach P.D. Taylor, D.T.J. Littlewood. 2011. A molecular phylogeny of bryozoans. Molecular Phylogenetics and Evolution 62(2): 718-735.
- Zhifei Zhang, Lars E. Holmer, Christian B. Skovsted, Glenn A. Brock, Graham E. Budd, Dongjing Fu, Xingliang Zhang, Degan Shu, Jian Han, Jianni Liu, Haizhou Wang, Aodhan Butler, and Guoxiang Li. 2013. A sclerite-bearing stem group entoproct from the early Cambrian and its implications. Scientific Reports 3(1066)
- Zhifei Zhang, Degan Shu, Jian Han, Jianni Liu. 2006. New Data on the rare Chengjiang (Lower Cambrian, South China) linguloid brachiopod Xianshanella haikouensis. Journal of Paleontology 80(2):203-211.
To Previous Lecture.