Described first in 1983 by Klaus Müller, this species has been investigated by Dieter in his habilitation thesis, later published in the monograph series Fossils and Strata (1993). R. kinnekullensis was found, as the Skaracarida, only in the lowermost Zone 1, the Agnostus-pisiformis zone of the Upper Cambrian Alum-shale sequence. By contrast, a large series of 30 instars could be assembled, most of them documented, the largest still being a larva with undeveloped posterior limbs (buds) and an undifferentiated abdomen.

Rehbachiella kinnekullensis, named after Mrs. Helga Rehbach who had sorted much of the material for Klaus Müller, and the beautifull hill area at the southern edge between lakes Vännern and Vättern in Västergötland, Sweden, is considered by me as a branchiopod crustacean, possibly related to Anostraca (Lepidocaris rhyniensis Scourfield,1926, from the Devonian + Euanostraca). Jørgen Olesen, Copenhagen, provides another approach in positioning Rehbachiella kinnekullensis at the base of Branchiopoda. In either way representing the earliest record of Branchiopoda so far. Other fossils mentioned as branchiopods from the Cambrian may not even be euarthropods.

Examples of larvae (SEM). a) Ventrolateral view of early, metanaupliar stage. b) Advanced stage with developed head shield and first few functional trunk limbs. c) Penultimate stage, limbs broken off distally, large head shield covering much of the trunk too. d) Last instar with distorted head region (from Walossek 1996). SEMs of details. a) Early larva in anterior view showing the large eyes. b) Head shield (cs) with neck organ (no). c) Stage TS10 (with 10 trunk segments) lacking the right limb series which permits to view on the filter apparatus. d) seta with double row of setulae used for filtration. e) Comb seta (arrow). f) Whip-like seta of the proximal endite at the inner proximal edge of the limb stem (from Walossek 1996).

Ontogeny: Known now from a series of 30 larval stages, ranging from a 160 µm long ortho-nauplius to an instar approx. 1,7 mm in length having 13 trunk segments, 12 of which bear limbs. Series most likely not terminated since there are larger fragments in the material, and several features of the largest stage are still of larval shape (posterior trunk limbs, trunk of latest stages still lacking abdominal segmentation).

Morphology: Compound eyes present from the beginning, feeding and locomotion from the beginning recognizable in the presence of well-developed naupliar limbs; naupliar neck organ = (osmoregulatory organ of larval extant branchiopods) becomes reduced after a few stages, also loss of dorsocaudal spine (structure well-known from e.g. barnacle nauplii). Further development includes the formation of a large shield, of a complex filter-feeding apparatus with limbs carrying more than 200 setae of different types, and reduction/modification of the original naupliar limbs. Head with a large shield (ples.) in contrast to Euanostraca (known since the Jurassic) having an extremely reduced shield.

Remarks: Filter apparatus incompatible to that of e.g. the Phyllocarida Malacostraca (example: Nebalia): this feature, including a deep sternal food groove produced by an infolding of the two sternitic plates of each sternite, and various other details, is regarded as a complex autapomorphy of the stem species of the Branchiopoda founding the monophyly of this taxon and also serving to identifying R. kinnekullensis as a member of this taxon.

Life habits of R. kinnekullensis: Nauplius clearly feeding and swimming (limbs, labrum, mouth and anus developed), subsequent development of filter-feeding structures, larger stages possibly very mobile and swimming above flocculent bottom zone – which may be the reason that larger stages are missing.

Additions: the monograph of Walossek (1993) includes, among other items, a comparison of ontogeny patterns within the major groups of Crustacea using R. kinnekullensis as a reference system, and a discussion of various morphological characters of phylogenetic value for Crustacea and Arthropoda in general, such as for example the maxillulae and maxillae, the trunk limbs, the segmentation of limbs in general (with a colour illustration of the evolution of the crustacean limbs from an basal arthropod limb), the dorsal or neck organ of Branchiopoda and Arthropoda, the tagmosis of head and trunk, and the formation of head shields ('carapace' discussion).

Remarkably, the second maxilla (mx2) has the shape of a trunk limb in the fossil, a character known for Recent Eucrustacea only from the Cephalocarida and some Ostracoda. The 'Orsten' Bredocaris admirabilis (below) and possibly the Devonian Lepidocaris rhyniensis, however, also share this feature with Rehbachiella kinnekullensis. This is very important since it shows that a specialized second maxilla was not developed in the stem species of the Eucrustacea, thus not a character of the groundplan of Eurustacea – and, of course not of Labrophora and Crustacea s. l. Special maxillae as differentiated cephalic feeding aids developed, accordingly, separately in each of the major eucrustacean lineages.

1.6. Skaracarida Müller & Walossek, 1985

The Upper Cambrian Skaracarida (= Skara Müller, 1983) are, in my view, maxillopod crustaceans that are closely related to the extant Copepoda and Mystacocarida (Walossek & Müller 1998), sharing the cephalo-maxillipedal locomotory and feeding apparatus, the special subdivision of the 'protopod' of maxillula, maxilla and maxilliped, the lack of compound eyes, and the reduction of extending rims on either side of the head shield with these two taxa. This possibly monophyletic group, the copepod lineage or Copepodoida, is considered as the sister-group of the "thecostracan lineage" (not formally named yet), embracing Bredocaris admirabilis (see below), Tantulocarida, Ascothoracida, Facetotecta and Cirripedia (see also Walossek & Müller 1998).

Skaracarida were found only in the lowermost Zone 1, the Agnostus-pisiformis zone of the Upper Cambrian Alum-shale sequence, and no larval stages were recognized of the two species differentiated in 1985. Of each species about 150 specimens have been sorted from the rock residues. A few more specimens have been found by Hubert Szaniawski in Northern Poland (core samples of a drill), where the Alum shale occurs about 2000m below the surface (see Walossek & Szaniawski 1991).

Systematic position: close to mystacocarid and copepod maxillopods, together seen to form a monophyletic group, which might best be named Copepodoida. This name was proposed by Beklemishev in 1954 for Maxillipoda – in parallel to Dahl (1954) proposing Maxillopoda –, but Beklemishev highighted only copepod characters, which are missing in the thecostracan line. Funnily also the name Maxillopoda is misleading because Thecostraca don't have a maxilliped. This is the "irony of the fate" as we Germans say. We propose the Name Maxillopoda for all, comprising the sister taxa Thecostraca and Copepodoida.

Skara anulata Müller, 1983

SEM of Skara anulata Müller, 1983 (from Müller & Walossek 1985). Limbs broken off. Only large labrum and ventral surface of head preserved. Shield and trunk with proximal segments of furcal rami complete. Reconstruction of Skara anulata Müller, 1983 (from Müller & Walossek 1985).

Skara anulata was the first record of true Maxillopoda from the Cambrian (ostracodes have for long been considered for that, but phosphatocopines as well as bradoriids turned out to be not even Eucrustacea; see, e.g., Siveter et al. 1996, for pictures of Kunmingella and Walossek 1999).

Morphology: Generally elongate, with short head, 11 trunk segments and a conical telson, seemingly fairly flexible in dorso-ventral aspect (see set of specimens). Length approx. 1,2 mm. Short-sided head shield (exposing muscle scars of the head legs in some specimens) protruded by forehead carrying a rostrum-like structure. No facet eyes recognizable, but a2-glands and excretory pores at the basis of A2 and the side of the very prominent labrum. Only six pairs of developed limbs. A1 elongate, with outer side covered by several sclerotized plates (with rows of denticles) proximally, a soft inner side and 2-3 rod-shaped distal podomeres carrying setae. More seta also on inner side (pointing posteriorly due to a slight rotation of the limbs - as in eucrustaceans in general). Second antenna with long swimming setae on exopod. Mandible with a poorly developed coxa bearing just two median setae. Maxillules and Maxillae (mx1 and 2) almost alike, both carrying a paddle-shaped exopod. Only one pair of thoracopods of the same design as the 2 maxilles and functioning as maxillipeds in a cephalo-maxillipedal feeding apparatus. All three limbs with a fancy subdivision of their protopod, differing anteriorly and posteriorly.

Trunk composed of 11 annular segments, which reveal little differentiation of the trunk into a thorax and an abdomen. Pivot joints connect the trunk segments, they are located laterally, permitting only up-and-down movements of the tail. First trunk segment with a tergite with weakly defined lateral margins, next segment annular but with a concavity in its anterior ventral side covered by soft cuticle to permit posterior flexure of the maxillipeds. All trunk segments with well developed joint membrane dorsally and slightly posteriorly extended at their ventrocaudal margins, limiting ventral flexure of the tail. Trunk segments 7–9 with 3 teeth each at their ventrocaudal margins (grooming structures?), these and other segments with rows of fine denticles to protect the wide arthrodial membranes between the segments. The telson is long and conical, carrying the anus dorsoterminally and articulated furcal rami. Furcal rami two- respectively three-segmented, with few very long setae inserting only along the inner margin.

Life habits: Possibly benthic meiofaunal, either having lived at the sediment-surface boundary layer or slightly below.

Skara huanensis Liu & Dong, 1985

More soon.

1.7. Yicaris dianensis Zhang, Siveter, Maas & Waloszek, 2007

Here already a few images of the new form from China.

More text will be added soon, which means as soon as I find the time.

The anterior body ––––The tail ––––––––––––––––––––Reconstruction –––––––––––– The epipodites ----- SEM of epipodites