Skeletons of Burgess Shale Animals

Abstract.- This file documents the characterization of elements of the skeletons of Burgess Shale animals in terms of the descriptors that constitute the Skeleton Space (Thomas and Reif, 1993, The skeleton space: a finite set of organic designs. Evolution 47: 341-360). The forms of animal skeletons or their subunits are defined in terms of seven essential properties, each with two to four possible states, yielding a total of 21 variables. The seven-character formulae, listed here for each skeletal element of a taxon, constitute the data set on which the analyses of Thomas, Shearman and Stewart (2000, Evolutionary exploitation of design options by the first animals with hard skeletons, manuscript in review) are based. Excel files listing these formulae and the character pairs they incorporate are also available at this web site. Modifications to this data base, made since the analyses of Thomas, Shearman and Stewart (2000) were conducted, are listed in a separate file.

Key to Character States.- (1) Situation: A, internal; B, external. (2) Material: C, rigid; D, flexible. (3) Number: T, one element; V, two elements; W, > two elements. (4) Shape: G, rods; H, plates; J, cones; K, solids. (5) Growth: L, accretionary; M, serial units + branching; Z, replacement/moulting; N, remodeling. (6) Assembly: X, growth in place; Y, prefabrication. (7) Interplay of elements: P, no contact; Q, jointed; R, sutured or fused; S, imbricate.

Uncertainty.- Where no data bearing on a character state are available, a blank "_" appears in the formula. Where knowledge of a character state is tenuous, based more on analogy with structures of related taxa than on direct observation, it is recorded in (parentheses). In one or two cases, formulae have been determined for structures that have not, in our judgment, been definitely shown to constitute parts of hard skeletons. These formulae are shown in [square brackets]. The character states recorded in parentheses and square brackets have not been included in the counts on which our numerical analysis is based.

PORIFERA

CLASS DEMOSPONGIA

Capsospongia - Demospongea (class), Lithistida (ord), Anthaspidellidae (fam.) = Corralia of Walcott
Spicules ACWG(L)XP - "tracts are composed, in part, of tiny, vertically elongate, monaxial (?) spicules...neither upper nor lower terminations are clearly preserved. Five or six spicules occur in cross sections of vertical tracts." (p. 52).
Dendroclones,spicules,trabs ACWG(L)XR - "Fused ray tips of horizontal dendroclones combine with the vertical spicules to produce vertical trabs...These dendroclones have a smooth shaft...that increases in diameter toward both ends and bifurcates to form clads. Clad tips are lost, however, in the generally massive trabs." (Rigby, p. 52).

Choia - Demospongea (class), Verongida (ord), Choiidae (fam.)
Spicules ACWG(L)XP and ADWG(L)XP - Long coronal spicules extend out well beyond a central disc, composed of a thatch of much smaller spicules. Oxeas of central disc taper in both directions, sharp tips. Coronal and thatch spicules "show no evidence of lateral fusion" (Rigby, p. 27).

Crumillospongia - Demospongea (class), Verongida (ord), Hazeliidae (fam.)
Spicules ACWG(L)XR - "Skeletal tracts between large openings generally 1.5 - 2.0 mm wide, made of a dense thatch of vertically aligned, brush-like monaxial spicules (oxeas?) in uniform unclustered texture." "The entire skeleton looks like a fine brushwork of delicate spicules." (Rigby, p. 45). Originally described as Morania (?) frondosa (alga) by Walcott.

Falospongia - Demospongea (class), Verongida (ord), Hazeliidae (fam.)
Spicules ACWG(L)XR - Skeleton an open framework or scaffold. "... strong, subcylindrical radiating tracts [made of oxeas] that are cross-braced by abundant horizontal tracts." "Spicules are...small, calcareous needles ..." "In only a few intersections do disctinctly curved spicules round out the openings. " (Rigby, p. 44).

Fieldospongia - Demospongea (class), Monactinellida (ord), Halichondrina (subord.)
Spicules ACWG(L)XR - "short spicules cross-connecting vertical trabs or strands . . . . regular skeletal net, although "trabs" may be arranged in radial almost
Trabs ADWG(L)XR - blade-like elements." (Rigby, p. 50). Trabs are vertical strands of organic material (flexible?). "In general the skeleton appears more rod-like than blade-like, where details of the few spicule (?)-like rods are preserved. (p. 51). Sponge wall has a very regular, ladder-like structure (see Plate 17, figs. 1-3, especially 5).

Halichondrites - Demospongea (cl.), Verongida (ord), Halichondritidae (fam.)
Spicules ADWG(L)XP and ACWG(L)XR - Long monaxial spicules. "Main body a thatch... in dense brush-like patterns, with a few cross-bracing isolated oxeas that produce a weakly articulate margin." (Rigby, p. 31). "cross-bracing horizontal spicules ..."

Hamptonia - Demospongea (class), Verongida (ord), Hamptoniidae (fam.)
Spicules ADWG(L)XP - Monaxons single or clustered in bundles, dense thatch of small monaxons between larger bundles. "[In] smaller specimens there is little evidence of cross-bracing" (Rigby, p. 26).
Spicules ACWG(L)XR - Large specimen, "both walls show cross-bracing or cross-connecting and interweaving of the large spicule bundles." (Rigby, p. 26).

Hazelia - Demospongea (class), Verongida (ord), Hazeliidae (fam.)
Spicules ACWG(L)XP - "closely spaced tracts of plumose small monaxons, principally oxeas." (Rigby, p. 37).
Stauract (??) - "One fragment of a large, pyritized stauract is preserved" "possible diagonal small stauracts"
(Hazelia grandis ). (Rigby, p. 41). Single specimen poorly preserved. Walcott was uncertain about attribution to this genus. Is it secure? Omit here?

Leptomitus - Demospongea (class), Verongida (ord), Leptomitidae (fam.)
Spicules ADWG(L)XP - "there appears to be no fusion....probably much spongin holding individual elements together" (Rigby, p.22). Spicules of Cambrian demosponges presumed to have been silica, replaced by calcite or limonite (Rigby, p. 8). L. flexilis refers to "apparently flexible nature" (Rigby, p. 24).

Moleculospina - Demospongea (class), Verongida (ord), Piraniidae (fam.)
Spicules ACWG(L)XR - "tufts or tracts of cross-connecting spicules"
Large spicules ACWG(L)XP - "Molds ... at right angles to the surface ...broken fragments were central spicules of the tufts." (Rigby, p. 35)
Spicules ACWG(L)XR - "There may be as many as 100 spicules in a section across a single tuft and in tips that form nodes in the skeleton. Individual nodes or tufts ... are cross-connected to adjacent tufts with spicule tracts through saddle areas, thus forming a relatively solidly cross-braced skeleton." (Rigby, p. 33).

Pirania - Demospongea (class), Verongida (ord), Piraniidae (fam.)
Spicules ACWG(L)XR - "There may be as many as 100 spicules in a section across a single tuft and in tips that form nodes in the skeleton. Individual nodes or tufts ... are cross-connected to adjacent tufts with spicule tracts through saddle areas, thus forming a relatively solidly cross-braced skeleton." (Rigby, p. 33).
Spicules ADWG(L)XP - Densely packed, long, subparallel monaxons, not fused but surely imparting rigidity to the wall of the sponge as a whole.
Tylostyes ACWG(L)XP - Massive protective (?) spines inserted in the sponge wall and extending far out from it.

Sentinelia - Demospongea (class), Monactinellida (ord), Halichondrina (subord.)
Spicules ACWG(L)XP - "reticulate mesh formed of slender, straight spicules." "minute, simple, straight spicules". (Walcott 1920, SMC 67, p. 290).

Takakkawia - Demospongea (class), Verongida (ord), Takakkawiidae (fam.)
Spicules ACWG(L)XP - "closely spaced tracts of plumose small monaxons, principally oxeas." (Rigby, p. 37).
Vertical fins ACWH(L)XR - "less obviously spicular and may have included much spongin. They must have been rigid or semi-rigid ... distinct molds or casts...where they have been pressed " into the matrix. (Rigby, p. 46).
Ribbon tracts ACWH(L)XR - Spiral tracts composed of monaxial spicules, within the chamber, opposite each of the exterior fins.
Oscular apparatus ACWH(L)XR - "Elements of the oscular apparatus look somewhat like petals or leaves, but must have been solid structures ..." (Rigby, p.48).

"no other sponges known to [Rigby] that have spiralling internal ribons, relatively resistantly radial fins, and associated coronal structures ..." "one might wonder whether Takakkawia should be properly classified with the Porifera ..." "because of the spicular makeup of the skeleton."

Tuponia - Tuponia of Walcott. No direct evidence on growth process.

Vauxia - Demospongea (class), Verongida (ord), Vauxiidae (fam.)
Spicules ADWGLXR - fused cored fibers united to produce a single-layered open net" (Rigby, p. 16) "non-mineralized elements" "No siliceous spicules have been identified" (Rigby, p. 17) "show weak annulations, like growth lines" "annulate growth habit" (Rigby, p. 18)

Wapkia - Demospongea (class), Verongida (ord), Wapkiidae (fam.)
Spicules ADWG(L)XP and ACWG(L)XP - "All of the known specimens ... have irregular discontinuous, vertical wrinkles, up to 1.5 mm high as though vertically elongate sponges had collapsed." (p. 30). "Individual spicules within the skeleton are not fused to one another, but must have been held in position by considerable spongin..." (Rigby, p. 29).


CLASS HEXACTINELLIDA

Diagoniella - Hexactinellida (class), Reticulosa (ord), Protospongiidae (fam.)
Stauractines ACWG(L)XP - "skeletal net consists of uniformly spaced, diagonally oriented ... stauract or stauract-based spicules. Intervening skeletal area covered with diagonally-arranged small stauractines and diactines (?)." (Rigby, p. 54).

Protospongia - Hexactinellida (class), Reticulosa (ord), Protospongiidae (fam.)
Stauractines ACWG(L)XP - "skeletal net composed of regularly arranged, uniformly rectangularly to rhomboidally spaced stauract and stauract-based spicules ..." "spicular mesh composed of stauract spicules arranged in rectangular fashion in ranks that produce at least six orders of quadrules ..." (Rigby, p. 53). Note that these are not simple rods, but rather three-dimensional elements composed of three or six intersecting rods. "The protosponges probably broke apart relatively easily because their skeletons were not fused ..." (Rigby, p. 53).
Monaxons ACWG(L)XP - "There are other fine-rayed spicules, but these may be monaxial spicules and part of the dermal layer." (Rigby, p. 54).

Stephanospongia - Hexactinellida (class), Reticulosa (ord), Hintzespongiidae (fam.)
Spicules ACWG(L)XP - "wall composed of numerous irregularly oriented, hexactine-based spicules that are unclumped or clustered" "All spicules are fine-textured, of irregular length, many with rays several millimeters long" (Rigby, p. 55).


CLASS CALCAREA

Canistrumella - Calcarea (class), Heteractinida (ord), Eiffeliidae (fam.)
Spicules ACWG(L)XP - "Skeleton made of moderately regularly arranged spicules that have dominantly 5 tangential rays and largely aborted proximal and distal rays (pentiradiates); spicules with 4 and 6 tangential rays . . . relatively rare."
Discs ACWH(L)XR, Rays ACWG(L)XR- (Rigby, p. 58). These spicules have distinct central "discs". Hence we can distinguish the distinct formulae for discs and rays.

Eiffelia - Calcarea (class), Heteractinida (ord), Eiffeliidae (fam.)
Spicules ACWG(L)XP - "skeletal nets made of relatively large, solid, sexiradiate or related spicules, generally of several ranks ..." (Rigby, p. 56). "Spicules lack proximal-distal rays and have solid rays." Six radiating rays of a spicule lie in a plane. "First-order spicules have central disks ..." Here again, the element as a whole is not in any meaningful sense a rod. In fact, Fig. 24 (Rigby, p. 58) rather strongly suggests that we should regard these spicules as solids. However, a skeletal net composed of solids seems self-contradictory. The interlocking rays, which are rods, are crucial here. So, we have isolated spicules composed of rod-like rays fused to solid disks.

CNIDARIA


POSSIBLE CLASS ANTHOZOA

Mackenzia - ?Class Anthozoa, ?Order Actinaria
No hard parts. "a large saclike organism", "similar to modern anemones" (Briggs et al. 1994, p. 93). "No evidence of calcareous plates or spicules" (Conway Morris 1993, p. 612) Comment relates to Walcott's presumption that this was a holothurian.

Thaumaptilon - ?Class Anthozoa, ?Order Pennatulacea or Vendobionta
Rachis [BDTGLXP] - No hard parts? If this is a vendobiont, skeleton presumably entirely hydrostatic. If it is a sea pen, a stiff, horny branching rachis is possible. No explicit reference to any hard parts by Conway Morris (1993,p. 604). If only the axis was skeletonized, T....P; if branches were also skeletonized, these would W....R.


POSSIBLE CLASS HYDROZOA

Gelenoptron - ?Class Hydrozoa, ?Suborder Chondrophorina
[BCTHLXP] and [BCTHLXR] - If this was a sailor-by-the-wind, it should have had a chitinous 'sail'. Inadequate evidence to be sure of hard parts. Close call on rigidity. Disc and sail could be regarded as two separate plates, the sail fused (R) to the disc. Concentric chambers of the disc suggest growth by accretion. (Conway Morris, 1993).


POSSIBLE CNIDERIANS

Cambrorhytium - ?Phylum Cnidaria
Tube BCTJLXP - "Many specimens show evidence of crumpling or other distortion, which suggests strongly an originally thin wall, probably composed of an organic substance and lacking mineralization." (Conway Morris 1988, p. 19) But, "Unless the tube lay on the sediment, it is likely that it was partially embedded. Growth was by marginal additions to the apertural region, resulting in the annulations on the tube wall." (p. 19)

CTENOPHORA

Fasciculus - Phylum Ctenophora
No hard parts. Geometric arrangment of the "combs" is not radial around a single center. If these were in fact bilaterally symmetrical, what does this signify? Might not these structures, which are preserved in extraordinary detail, have had some form of skeltal support?

POSSIBLE LOPHOPHORATA

Odontogriphus - Phylum uncertain (new?)
"Teeth" ACWKLXP - This formulation follows CM's (1976) interpretation of these "teeth" as internal or support structures comparable to conodonts. However, we cannot be certain that they BCWKLXP were internal or that they grew by accretion. Could these be real teeth of a parasite? Or, are they worm jaws, i.e. scolecodonts?

BRACHIOPODA


CLASS INARTICULATA

Acrothyra - Class Inarticulata, Order Acrotretida, Family Acrotretidae
Shell BCVJLXS - Should this be regarded as a pair of like elements, or as two dissimilar structures?
Median ridge BCTHLXR - Ridge or plate on interior of brachial valve.

Lingulella - Class Inarticulata, Order Lingulida, Family Obolidae
Shell BCVJLXS - Two valves are relatively little differentiated.
Pseudointerarea BCVHLXR - Dorsal pseudointerarea well developed as a striated triangular plate divided into two propareas by a... median depression. Treatise.

Micromitra - Class Inarticulata, Order Paterinida, Family Paterinidae
Shell BCVJLXS - Two valves not greatly dissimilar in external form.
Homeodeltidium and homeochilidium BCTHLXR - Homeochilidium unusually large in this genus. Treatise.

Paterina - Class Inarticulata, Order Paterinida, Family Paterinidae
Shell BCVJLXS - Two valves not greatly dissimilar in external form.
Homeodeltidium BCTHLXR - Homeodeltidium usually large. Treatise.
Delthyrium BCVHLXR - "lateral margins of delthyrium with two strong ridges on internal face..." Treatise.


CLASS ARTICULATA


Diraphora - Class Articulata, Order Orthida, Family Eoorthidae
Shell BCVJLXQ - Two valves not greatly dissimilar in external form.
Dental plates BCVHLXR - Dental plates variably developed. Treatise.

Nisusia - Class Articulata, Order Orthida, Family Nisusiidae
Shell BCVJLXQ - Shell subequally biconvex.
Pseudodeltidium BCTHLXR - Pseudodeltidium strong. Treatise.

POSSIBLE MOLLUSCA


CLASS HELICIONELLOIDA

Scenella - Mollusca according to most authors, including most recently Landing and Narbonne (1992, JP 66: 338), but see also Yochelson and Gil Cid (1984) and Babcock and Robison (1988) who regard type species of Scenella as a chondrophorine
Shell BCTJLXP - Shells do not appear completely flattened, relaining some three-dimensional relief, suggesting a rigid construction. Illustrations of Burgess Shale "Scenella" only hint at a poorly defined concentric structure or ornament. No evidence of radial ornament or interior muscle scars.
[Sail] - None of the species of "Scenella" regarded by some authors as a chondrophorine has a differentiated "sail".

HYOLITHA

Haplophrentis - Phylum uncertain, Mollusca of many authors, or discrete.
Shell BCTJLXP - Shell regarded as an isolated structure on the basis of its hierarchical relationship with the operculum, which is seen as a subsidiary element.
Operculum BCTHLXS - The growth process here is that of a cone, but the two upper and lower parts of this structure meet in such a way that it was concave facing outward. Was this structure attached at a joint, or did it have a sliding articulation? Marek and Yochelson (1976,Lethaia 9: 74) suggest the latter. They regard hingement of the cardinal processes with the dorsal rim of the shell as improbable. "these structures on the interior of the operculum are interpreted as attachment for muscles."
Helens BCVGLXQ - Helens were inserted in slots in the margin (appendages) of the operculum. Several authors see these as having a roll in "rowing" locomotion, but Marek and Yochelson doubt this.

PRIAPULIDA

Ancalagon - Priapula, classes not differentiated, Ancalagonidae
Cuticle BDWHZXP - Continuous, flexible 'sheath', presumed to have molted periodically by analogy with other priapulids.
Proboscis spines BCWGZXR - Two varieties of proboscis hooks. Spines Probosicis hooks also present.

Fieldia - Priapula, classes not differentiated, Fieldiidae
Cuticle BDWHZXP - Continuous, flexible 'sheath', presumed to have molted periodically by analogy with other priapulids.
Proboscis spines BCWGZXR - Two or three varieties of proboscis spines. Probosicis hooks

Louisella - Priapula, Miskoiidae (Miskoia is a synonym)
Cuticle BDWHZXP - Continuous, flexible 'sheath', presumed to have molted periodically by analogy with other priapulids. Note two tracts of trunk papillae, presumed respiratory, and Conway Morris' statement "this worm was soft-bodied." (p. 50).
Proboscis spines BCWGZXR - Three ranks of spines present.

Ottoia - Priapula, classes not differentiated, Ottoiidae
Cuticle BDTHZXP - Continuous, flexible 'sheath', molted periodically. "USNM 198592 may have been on the threshold of moulting ...." (Conway Morris, p. 11).
Proboscis hooks BCWGZXR - Hooks presumed to be fused to the flexible Posterior hooks cuticle. Proboscis spines also present.
Proboscis spinules BCWKZXR - Simple forms could be regarded as rods, but most are very conodont-like in form.

Selkirkia - Priapula, classes not differentiated, Selkirkiidae
Conical tube BCTJLXR - 80% specimens are empty tubes. "the rigid tube...." (Conway Morris, p. 36). "decay which left the empty and more resistant tube...." (p. 44). "harder parts, such as the tubes..." (p. 45). "The tube has fine annulations..... a 4 cm long tube has about 1600 annulations..... a specialized division of the cuticle. The rate of accretion is unknown." (p. 36).
Cuticle BDTHZXP - Flexible 'sheath' protruding from anterior end of the tube. If the tube is fused to the cuticle, this must be regarded as a single, free-standing skeletal element.
Proboscis spines BCWGZXR - Two categories of spines.
Proboscis spinules BCWKZXR - Conodont-like in form.


PROBABLE PRIAPULIDS

Lecythioscopa
Probable archaeopriapulid. Canadia simplex of Walcott (1931)
Cuticle BDWHZXP - Continuous, flexible 'sheath', presumed to have molted periodically by analogy with other priapulids.
"Head" spines BCWGZXR " - slender, straight spines..." ( Conway Morris,p. 64).

Scolecofurca - Probable archaeopriapulid. Inadequate skeletal information.

ANNELIDA


CLASS POLYCHAETA

Burgessochaeta - Class Polychaeata
Setae BDWGLXP - These setae inferred to be flexible from their length and occurrence in arched sets of 11-17, splaying back from each appendage. Briggs et al., (1994), p. 127.

Canadia - Class Polychaeata
Setae BCWGLXP - Flattened setae projected back, covering the trunk, but hardly plates. Isolated setae retain the same arcuate form as those that are preserved in place on the body. Briggs et al., (1994), p. 128-129, especially Fig. 79.

Insolicorypha - Class Polychaeata, Family Insolicoryphidae
Setae BDWGLXP - Setae inferred to be flexible on the same basis as those of Burgessochaeta. Briggs et al.,(1994), p. 130-131.

Peronochaeta - Class Polychaeata, Family Peronochaetidae
Setae BCWGLXP - Setae are inferred to have been rigid from their relatively small size (even those characterized as 'long'). Briggs et al. (1994, p. 132-133) refer also to 2-4 smaller 'flexed' setae, but this appears to be a reference to their curvature rather than to flexibility.

Stephenoscolex - Class Polychaeata, Family Stephenoscolecidae
Setae BCWGLXP - Setae are inferred to have been rigid from their relatively small size and the fact that each limb ended in a bunch of 10-15 straight setae. Briggs et al., (1994), p. 134-135.

ONYCHOPHORA

Aysheaia - Onychophora, Protonychophora (ord.), Aysheaiidae (fam.)
"does not fit readily into any extant higher taxon." Sole representative of an early group of metamerically segmented lobopods from which Onychophora and Tardigrada were derived? (Whittington, 1978, p. 195).
Spines BCWGLXP - No evidence of manner of growth, but no need to moult if inserted in pits in the leathery 'skin'.
Claws BCWGLXP - Curved rods. Growth by accretion? (see evidence from Peripatus cited below).

Hallucigenia - Onychophora, Hallucigeniidae (fam.)
Spines BCWGLXR - Seven pairs, invariant, even in smallest known specimen (CM, p. 630). No contact (P) if inserted in body wall, fused (R) if attached to basal plates. Growth by accretion?
Plates? BCWHLXP - If the spines are attached to basal plates (Ramsksld, 1992, Lethaia 25: 454-455) and not inserted in the body wall (CM, p. 632), how did the spines grow? However, CM notes that "the proximal end of the spine is sometimes raised with respect to the rest of the spine ....". This seems consistent with attachment to a plate. Growth by accretion?
Claws BCWGLXP - Ramsksld (1992): Six legs toward anterior end (new orientation) all have paired claws. Growth by accretion, as implied by lamellar microstructure of Peripatus claws? See K. W. Schwab, 1966, J. Paleont. 40: 416-423.

ARTHROPODA

ARTHROPODA: "PRIMITIVE"

Branchiocaris - Arthropoda, class uncertain, Protocarididae (fam.)
Carapace BCVHZXQ - Structure interpreted as muscle scar indicates
"some possible movement of the valves about the hinge or fold" (Briggs, p. 8). Dorsal margin straight, with anterior and posterior &pi0;projections' = best evidence for a true hinge.
Cephalic region BCTHZXR - Anterior appears to have been regularly convex (p. 6). Carapace attached axially, in front of the principal appendages. No reason to think this attachment would have been a point of articulation?
Trunk BCWHZXS - Numerous somites (40+) or annulations? Variation in number of somites extending beyond posterior margin of carapace "may indicate that the trunk was capable of telescoping." "Boundaries diverge near the dorsal margin of the trunk and the gap increases ventrally, possibly indicating the overlap of successive somites" (p. 9).
Telson BCTHZXQ
Telson processes BCVHZXR - "telson extended ventrally into a pair of broad, lanceolate processes ....... preservation does not indicate whether or not the process articulated proximally" (p.9). Attached beneath the telson, all preserved in same relative positions (see figures).
Appendages BCWGZXQ - Paired antennae and "principal" appendage.
Trunk BDWHZXQ - "the trunk bore a series of wide thin, appendages presumably flexible, lamellate appendages" (p. 10). Note that each somite bears a pair, so could be classified as 'V' unless the whole set is considered as one organ.
Spines BCVGZXQ - Spines terminating 'principal' appendages. Briggs discusses very limited evidence that these structures might in fact be chelae (p. 8).
Spines BCWGZXR - Minute spines on postero-dorsal margins of last four or five somites, in front of telson.

Marrella - Arthropoda, class uncertain, Marrellidae (fam.)
Cephalic shield BCTHZXQ - Whittington (1971) reconstructs this shield as being wedge-shaped (p. 8-9), triangular from the front, with the narrow end of the wedge running ventrally. This would seem to make the structure a solid, but the published descriptions do not refer to it standing up in strong relief, as this would imply. Furthermore, Whittington's reconstructions (figs. 5 and 6) appear to suggest that this structure enclosed the anterior soft parts.
Ventral projection of cephalic shield BCTHZXR or BCVHZXR - "a curved, elongated, backwardly directed projection of or projection from the posteroventral edge of the cephalic shield." (p. 9) One specimen shows "not a single projection but a pair, arising from the ventral, posterior corners of the shield .... appear to be parts of a labrum..."
Spines BCVGZXR - Pairs of striking anterior "lateral" spines and posteriorly directed dorsal "median spines" (p. 8 and fig. 5).
Trunk BCWHZXQ - Twenty-six or twenty-seven somites, extended straight back between the median spines, with slight curvature. No evidence of more than limited curvature (max. 30¡) in any direction. Hence, we infer that the somites were jointed, not imbricate.
Telson BCTHZXQ - "short and rounded posteriorly" (p.10)
Appendages BCWGZXQ - Segmented first, second anterior appendages, followed by biramous appendages, each with a walking leg and a gill branch (p. 11-13). No plate-like elements, note "shafts of the gill branches" (p. 14-15).
Spines BCWGZXQ - Two, or probably three spines at tip of walking leg. Setae inserted in joints of anterior antennae, walking legs. Whittington implies that this animal grew by moulting, which is consistent with its overall design, but there is no direct evidence. Assemblage is bimodal in size, interpreted as a death assemblage resulting from catastrophic burial.

ARTHROPODA: SUBPHYLUM CRUSTACEA AND ALLIES

Canadaspis - Arthropoda, Malacostraca (cl.), Phyllocarida (s.cl.), Canadaspididae
Cephalic spine BCTGZXR - Anterior extension of cephalon? "No indication that it was an extension of the carapace, and it is unlikely to represent a displaced rostral plate." (Briggs, p. 454)
First antenna BDVGZXR - Flexibility inferred from observed flexure. Does this mean it was a flexible unit, or was it segmented? "No unequivocal evidence", one specimen may be. The nature of this structure is "unknown". Designation as first antenna evidently based on expectation that a crustacean should have such an appendage. The same logic would lead us to expect that it would have been segmented, with stiff units. Otherwise, two elements, flexible, = DV, with a fixed base (hence R), as implied in Fig. 62 (Briggs). But, surely flexible cylinders are mechanically improbable!!
Second antenna BCWGZXQ - Conventional pair of segmented antennae.
Labrum BCTHZXQ - Rigid ("original convexity") or flexible ("may have extended posteriorly.....as an area of flexible, unsclerotized tissue") (Briggs, p. 456).
Eye stalks BDVGZXR - "apparently unsegmented" "probably flexible" (Briggs, p.454-455).
"Mandible" BCWGZXQ - Articulation of components required by function, suggested by analogy with other crustaceans.
Carapace BCVHZXQ - If 'bivalved', must be articulated. "The hinge line forms a groove on the dorsal surface" (Briggs, p. 457). Attached anteriorly to the cephalon.
Thorax BCWHZXS - "Limited flexing....appears to have been achieved by telescoping" (Briggs, p. 460).
Abdomen BCWHZXS - "the inter-somite boundaries overlap"
Telson BCTHZXQ
Ventral BCVHZXR - "a pair of deeply divided spinose projections" projections "inserted into the pre-telson somite....do not appear to have articulated proximally" (Briggs, p. 471-472).
Spines BCWGZXR - Multiple spine on ventral projections, spines on the appendages
Appendages BCWHZXQ - Elements include both plates and rods.
Claws BCWGZXQ - Note terminal claws of the inner ramus.

Carnarvonia - Arthropoda, class and family uncertain
Carapace BCVH(Z)XQ - Pseudobivalved carapace only is known. Rigid or flexible? Hinge a simple ridge or groove, very well defined. Distinct venation. Jointed, as we have assumed, or sutured, or one element? Walcott (1912, p. 189).

Isoxyx - Arthropoda, class and family uncertain.
Carapace BCVH(Z)XQ - "two valves attached along the straight hinge line" (Briggs et al., 1994). Excellent illustration in this book shows a sharply defined outline, with two irregular indentations that seem to represent crease/fractures resulting from compaction.
Spines BCVG(Z)XR - Anterior and posterior paired spines, the former corresponding in position to the rostrum of phyllocarids. In some specimens, "extremely elongated horns of the carapace" (Simonetta and DC, 1975, p. 6)
Appendages - Seen in one specimen by Simonetta and DC but not recognized by later authors.

Odaraia - Arthropoda, class uncertain, Odaraidae (fam.)
Cephalon BCTHZXQ - Briggs (p. 551) guesses that the carapace is derived from the posterior margin of the cephalon, as in Crustacea. This connection must be jointed to allow articulation of the bivalved carapace?
Carapace BCVHZXQ - "a clear V-shaped indentation"= hinge
Trunk somites BCWHZXS - "could overlap by up to half their length"
Mandible BCVGZXQ - Inferred from presence of a row of teeth. Each one presumed to be a single element.
Teeth BCWKZXQ - "preserved in relief suggesting ... cuticle was thickened or strengthened (p. 550).
Appendages BCWGZXQ and BCWHZXQ - Biramous, inner ramus segmented, outer ramus "a lamellate branch" (p. 558)
Spines BCWGZXR - "most prominent feature of the inner rami is a large spine" (p. 559); "posterior margin of each somite was fringed with spines" (p. 557).
Telson  - Is it skeletonized?
The description of Odaraia includes no direct reference to growth. Moulting
inferred from the 'arthropodan' nature of the exoskeleton. Eyes: lenses not hard?

Perspicaris - Arthropoda, Malacostraca (cl.), Phyllocarida (s.cl.), fam. uncertain
Carapace BCVHZXQ - How was the carapace attached to the body? Anteriorly, trunk moved independently. Inferred muscle scars indicate attachment was cephalic. "In the absence of evidence to the contrary the valves are assumed to have been joined by a band of flexible cuticle". No rostral plate. (Briggs, p. 602).
Cephalon BDTHZXQ - Poorly defined even when carapace is off, infer that it was little sclerotized, flexible. Eyes (?) attached to flexible projections.
Antennae BCVGZXQ - A pair of segmented antennae.
Trunk BCWHZXS - Very flexible, achieved by varying degrees of overlap of the somites.
Telson BCTHZXQ - Presumed to have artriculated with trunk.
Furcal rami BCVGZXQ - Similar dimensions in lateral and parallel preservation (Briggs, p. 603). But, many specimens suggest that these were relatively flat plates. Diverged to varying degrees, but no evidence articulated with the telson.
Spines BCWGZXR - Spines on antennae and furcal rami.
Spines BCWHZXR - Spines fringing posterior of trunk segments.
Appendages BCWHZXQ - "large, flattened, lamellate, suboval" (p. 603)

Plenocaris - Arthropoda, Malacostraca (cl.), Phyllocarida (s.cl.), fam. uncertain
Carapace BCVHZXQ - How was the carapace attached to the body? It may or may not be preserved and is quite often missing (Whittington, 1974, p. 16). Should we regard it as having been sutured, here and in other phyllocarids?
Rostral Plate BCTGZXR - "an elongated spine-like object ..... presumed to represent the rostral plate ..... its shape and relation to the rest of the carapace isconjectural" (Whittington, p. 18)
Trunk BCWHZXS - "of 13 somites including the telson".
Appendages BCWGZXQ - "poorly preserved ..... narrow, elongate carbonaceous strips, but showing no joints." Joints at point of attachment to the trunk at least, we supposed.
Telson BCTGZXQ - "presumably subcircular in cross-section"
Furca BCVHZXQ - "Each ramus of the furca appears sub-oval in outline" and "blade-like distally". But presumably sub-circular in cross-section at point of insertion into telson (?).

Tuzoia - Arthropoda, class and family uncertain.
Carapace BCVH(Z)XQ - Bivalved carapace only is known for certain. Rigid or flexible? In Walcott's original single specimen, "the test was thin, as it has been crowded and wrinkled near the longitudinal center." (Walcott, 1912, p. 187). But, excellent illustration of Briggs, Erwin and Collier (1994, p. 154) show this ridge as a regular feature, with apparent structural integrity. Spinose outline of this carpace is also sharplydemarcated. Hinge a distinct groove, very well defined. Distinct reticulate venation.

Waptia - Arthropoda, Crustacea, class uncertain.
Carapace BCVHZXQ - "The valves of the carapace did not separate easily but folded along a median line that functioned as a hinge." (Briggs et al., 1994).
Rostral plate BCTHZXR - "A small triangular rostral plate ..... between the antennae". (Walcott, 1931, p. 22).
Antennae BCWGZXQ - "A pair of long, jointed antennae ...".
Eye stalks BCVGZXQ - "a stalk or peduncle that projects from beneath and on each side of the rostral plate", each with "at least one joint", and apparently attached to a prostomium. (Walcott, p. 22). Is this joint certain? Might these have been flexible, as the term peduncle implies?
Trunk appendages BCWGZXQ - "The first four limbs consisted only of a appendages walking limb." (Briggs et al., 1994). Walcott (1931) reports/figures five of these.
Trunk appendages BCWHZXQ - "..... the following six of a gill branch with blade-shaped filaments." (Briggs et al., 1994). Walcott (1931) reports/figures eight of these.
Spines BCWGZXQ - Marginal and terminal spines on the walking limbs, figured by Walcott (1931). Presumed to be jointed at their points of attachment. Similar spines attached along antennae.
Spines BCWGZXR - "The posterior margin of the abdominal segments bears four or more strong spines ..." (Walcott, 1931, p. 20).
Abdomen BCWHZXS - Abdomen of five somites, cylindrical or tubular plates that appear to have been imbricate from the photographs and reconstructions of Walcott and Briggs et al. The latter authors distinguish a telson, but Walcott (1931, p. 20) treats this simply as "the last or anal segment." It does not appear very distinct in any of the available figures.
Caudal furca BCVHZXQ - "two large segmented flaps at the extremity" (Briggs et al. 1994, p. 158). Each caudal furca has "three transverse lines indicating four fused segments." (Walcott, 1931, p. 20).


CLASS OSTRACODA

Aluta? - Arthropoda, Ostracoda
Valves BCVH(Z)XQ - "One kind of ostracode shell is quite common in the Burgess Shale, either as separate or linked valves, but no traces of soft parts have been recognized. In Walcott's collection it is labelled as belonging to the genus Aluta, . . . but it has never been described." (Whittington, 1985, p. 62).


POSSIBLE CLASS CIRRIPEDIA

Priscansermarinus - Arthropoda, Maxilliopoda (cl.), Cirripedia (s.cl.)
Plates BCVHZXP - "Body appears to be almost wholly encased between two triangular chitinous plates"(Collins and Rudkin, 1981).