Oestokerkus megacholix, Edgecombe & García-Bellido & Paterson, 2011

Edgecombe, Gregory D., García-Bellido, Diego C. & Paterson, John R., 2011, A new leanchoiliid megacheiran arthropod from the lower Cambrian Emu Bay Shale, South Australia, Acta Palaeontologica Polonica 56 (2), pp. 385-400 : 387-393

publication ID	https://doi.org/10.4202/app.2010.0080
persistent identifier	https://treatment.plazi.org/id/038BE425-1B48-551F-7F67-FAC1FBD32D3B
treatment provided by	Felipe
scientific name	Oestokerkus megacholix
status	sp. nov.

Treatment

Oestokerkus megacholix sp. nov.

Figs. 2–7 View Fig .

Etymology: From Greek mega, large, and cholix, gut, in reference to the voluminous midgut glands.

Type material: Holotype: SAM P43631 View Materials a, b, part and counterpart preserved in lateral aspect ( Figs. 2 View Fig , 3), from the Emu Bay Shale , Buck Quarry, preserving cephalon, including spinose projections and flagella of great appendages, all 11 trunk segments, and most of telson, including a few marginal spines; midgut glands exposed in head and anterior two−thirds of trunk; some exopod setae of cephalic appendages as well as lobes and setae of those associated with entire trunk . Paratypes: All preserved in lateral aspect. SAM P45167 View Materials ( Fig. 4 View Fig ): cephalon exposing eye and peduncle of great appendage, most of trunk with exopod setae and a few endopods. SAM P43630 View Materials a,b ( Fig. 5B): part and counterpart preserving cephalic shield, spinose projections of great appendage, and anterior eight trunk segments; two midgut glands and exopod setae of cephalic and trunk appendages exposed. SAM P15531 View Materials ( Fig. 5A): part only, preserving cephalon, including spinose projections of great appendage, and most of trunk with midgut glands. SAM P15438 View Materials (unfigured), incomplete cephalic shield with parts of great appendage, complete trunk and apparently proximal part of telson. SAM P45168 View Materials ( Fig. 6 View Fig ): part only, cephalon with partial great appendages, most of trunk, with midgut glands and exopod setae. SAM P45169 View Materials a, b (unfigured): cephalon with partial great appendages, trunk with midgut glands. SAM P45177 View Materials a, b; SAM P45178 View Materials a, b (unfigured): two weathered specimens .

doi:10.4202/app.2010.0080

SAM P45904a, b (unfigured): poorly−preserved cephalic shield, trunk with well−preserved midgut glands, proximal part of telson. SAM P45905a,b (unfigured): cephalic shield lacking great appendages but exposing an eye, trunk with incomplete telson. SAM P45906a, b (unfigured): great appendages with spinose projections, oriented anteriorly, trunk preserved to end of midgut glands. SAM P45908a, b (unfigured): cephalic shield, great appendages with flagella, most of trunk (telson missing), showing midgut glands and exopod setae. SAM P45909 (unfigured): small specimen with great appendages and series of mineralised midgut glands. SAM P45910a, b (unfigured): incomplete great appendages oriented anteriorly, trunk with complete series of midgut glands but indistinct appendages.

Type locality: Buck Quarry, Big Gully ( Fig. 1 View Fig ).

Type horizon: Emu Bay Shale (Cambrian Series 2, Stage 4) .

Diagnosis.—As for genus. Description.—Cephalic shield 36% length of the trunk sagittally; dorsal margin of cephalic shield gently convex in lateral view, anteromedian margin inferred to be evenly rounded (based on comparison with lateral versus dorsal preservation of Burgess Shale Leanchoilia and Alalcomenaeus ), lacking an upturned median process. Eye visible in SAM P54167 ( Fig. 4A View Fig ) and P45905, relatively large (20% sagittal length of cephalon), exposed under anterolateral part of cephalic shield ( Fig. 4A View Fig 2 View Fig ).

doi:10.4202/app.2010.0080

Great appendage robust, proportions of peduncle and distal spine−bearing articles as in other members of Leanchoiliidae ; more commonly preserved with posterior orientation but anteriorly oriented in SAM P45906 and SAM P45910. Each of the three long spinose projections terminating at the same length, the projections evenly tapering distally, with margins straight for much of their length or slightly curved terminally; distal spinose projection distinctly stouter at its base than the two more proximal projections and more markedly tapering along its length. Dark, irregular−shaped low relief lump on basal spine−bearing article of great appendages of SAM P45168 (eo in Fig. 6 View Fig ) and SAM P45908, corresponding to excretory organ of Bruton and Whittington (1983). Long flagella extending from each of the three spinose projections, seen only in SAM P43631 ( Figs. 2 View Fig , 3A 3), of similar, narrow width along its preserved extent; annulations indistinguishable.

Trunk of 11 segments of even length. Maximum height of trunk relative to length (excluding telson) ca 39%, body deepest at tergite 4. Trunk tergite boundaries marked as narrow ridges in several specimens, corresponding to narrow band of overlap between adjacent tergites (ol in, Figs. 2 View Fig , 3A 1 View Fig , 4A View Fig 1 View Fig , B). Some specimens show tergites to be bisected by a narrow but sharp furrow of uncertain identity (e.g., possibly impression of dorsal transverse tendon, cf. Stein 2010: fig. 12B, C, E) (arrows in Figs. 3A 1 View Fig , 4B View Fig ).

Exopods with fringe of long setae on cephalic and trunk appendages ( Fig. 2 View Fig ), setal fringe gradually shortening from about the fourth trunk segment. Setae project ventrally by more than 30% height of tergites in deepest part of trunk ( Fig. 2B View Fig ); setae flattened, narrow and parallel−sided along most of their length, tapering near their distal ends to terminate as a pointed tip ( Figs. 2B View Fig , 3A 3, arrows). Endopods exposed only in SAM P45167 ( Fig. 4 View Fig ); two pairs associated with cephalon ( Fig. 4B View Fig ), those of anterior segments of trunk of similar morphology to those in cephalon, all slender, lacking obvious endites, podomere boundaries unrecognisable.

Midgut glands occupy a large extent of the dorsoventral height of the trunk, two midgut glands in cephalon of similar size to those in each of the first seven segments of the trunk ( Figs. 3A 1 View Fig , 5A, 6A View Fig ); all developed as radiating grooves emanating from a globular structure at their ventral edge as in Leanchoilia superlata ( García−Bellido and Collins 2007: pl. 2: 6). Foregut trace in SAM P43631 ( Fig. 2 View Fig ) indicates that gut curves ventrally in anterior part of cephalon, mouth region not preserved. Terminal part of hindgut (in trunk segment 11) with closely spaced longitudinal lineations ( Fig. 2 View Fig ) that apparently correspond to folds in the gut wall; hindgut terminating at base of telson.

Telson most completely preserved in holotype ( SAM P43631 View Materials , Figs. 2B View Fig , 3A 2 View Fig , B). In this specimen the telson, like rest of body, compressed in lateral aspect. Telson shows median and marginal reinforcing ridges connecting a flat triangular surface; this surface appears to be partially broken in SAM P43631 View Materials , showing underlying surface of other (left) half of telson. Lateral preservation of specimen implies that top corresponds to an axial structure and bottom to a marginal one; 30–35 ° angle in posterior edge of vane connecting these two structures requires that in dorsal aspect, telson would appear forked and widening distally. Five stout, pointed, dorsally curved marginal spines attached to outer posterior edge on each side of telson .