Scalidophora Lemburg, 1995

Eokinorhynchus gen. nov.

Etymology

Eo-, dawn; kinorhynchus, kinorhynchs.

Type species

Eokinorhynchus rarus gen. et sp. nov.

Diagnosis

Same as type species by monotypy.

Eokinorhynchus rarus gen. et sp. nov.(

Figures 1, 2, 3; Supplementary S2–S3; Supplementary Table S1; Supplementary Movies S1–S4)

Figure 1 SEM images of Eokinorhynchus rarus gen. et sp. nov., holotype, NIGP160400. (a–c) Dorsal, ventral and left lateral views, respectively. (d–f) Close-up views of zones 2 and 3 to show the arrangement pattern of pharyngeal teeth (numbered in the two basal circlets), with white arrows denoting the 3rd and black arrows denoting the 4th circlet of pharyngeal teeth. Abbreviations in this and other figures: A1–A20, 1st to 20th trunk annulus; an, anus; cs, caudal spine; hsc, head scalid; ls, large sclerite; 1ls–5ls, 1st to 5th pair of large sclerites; mg, midgut; nsc, neck scalid; spl, small plate; ss, small spine; vls, ventral large sclerite. Scale bar beneath (c) applies to (a–c) and scale bar beneath (d) applies to (d–e). SEM images acquired by authors. Full size image

Figure 2 SEM and microCT images of Eokinorhynchus rarus gen. et sp. nov., paratype, NIGP160401. (a–c) SEM images of dorsal, ventral and right lateral views respectively. (d) microCT saggital section, with dorsal side to the left. (e) Dorsal view of microCT reconstruction, with large sclerites rendered yellow and everything else semi-transparent to show their bilateral arrangement. Scale bar applies to all images. SEM and microCT images acquired by authors. Full size image

Figure 3 SEM images of Eokinorhynchus rarus gen. et sp. nov., paratype (NIGP160402) and a fragmented trunk (NIGP160414). NIGP160402 was originally a complete specimen, but was accidentally broken during preparation and only the head (NIGP160402a) and tail (NIGP160402b) were recovered and illustrated. (a,b) Dorsal and ventral views of NIGP160402a, with white rectangle marking area magnified in (f). (c–e) Dorsal, ventral and left lateral views of NIGP160402b, with white rectangle marking area magnified in (g). (h,i) Two opposite views of NIGP160414. Scale bar beneath (c) applies to (a–e,h,i). SEM images acquired by authors. Full size image

Etymology

From Latin, rarus, rare.

Type specimens

Holotype NIGP160400 (Fig. 1). Paratypes NIGP160401 (Fig. 2) and NIGP160402 (Fig. 3a–g). Deposited at Nanjing Institute of Geology and Palaeontology (NIGP).

Additional material

NIGP160414 (Fig. 3h,i).

Locality and horizon

Xinli section25, Nanjiang County, Sichuan Province (Supplementary Fig. S1); Xinli Member, Dengying Formation, small shelly fossils Anabarites trisulcatus–Protohertzina anabarica Assemblage Zone23, about 535 Ma, Fortunian Stage22.

Diagnosis

Worm-like animal composed of a head, a neck region and a trunk. Head consists of an introvert with pentaradially arranged hollow scalids and a pharynx with octaradially arranged teeth. Neck region covered with 5 circlets of neck scalids. Trunk has at least 20 annuli and each annulus is covered with a circlet of tightly sutured small plates and armored with spinose sclerites. Five pairs of large spinose sclerites are bilaterally arranged and a single large spinose sclerite is midventrally located. Two pairs of caudal spines are located slightly ventral to the terminal anus.

Description

The head is demarcated from the neck by a constriction (Figs 1a and 2a,c,d). It includes a pharynx armed with teeth (zone 3), an unarmed transitional zone (zone 2) and an introvert with head scalids (zone 1). These zones are easily recognizable in the holotype (Fig. 1a), but only zone 1 is partially visible in the paratypes because their pharynx and part of the introvert are retracted (Figs 2a and 3a).

The everted pharynx (zone 3) has at least 4 circlets of radially arranged and anteriorly directed pharyngeal teeth, surrounding a terminal mouth. The outermost circlet has 16 conical teeth (Fig. 1f) and the second circlet has 8 much larger teeth, interdigitally positioned between every pair of teeth in the outermost circlet (Fig. 1d). Two additional circlets are inferred on the basis of partly preserved and much smaller teeth close to the center (Fig. 1d–f).

Zone 2 is unarmed, but has densely-spaced longitudinal wrinkles (Fig. 1d–f). The everted introvert (zone 1) bears 7 circlets of posteriorly directed head scalids (Fig. 1a–c; Supplementary Fig. S2). The first (anteriormost) and second circlets each have 25 radially arranged scalids that are aligned to form 25 longitudinal rows. The following 5 circlets each have 13, 12, 12, 11 and 9 scalids respectively, but they are more irregularly distributed and do not follow the longitudinal rows defined by the first two circlets. The introvert of the paratypes is only partly everted, thus the arrangement pattern of the scalids is difficult to discern (Figs 2a and 3a). The scalids are conical in shape, internally hollow (Fig. 3f; Supplementary Fig. S3a) and their length decreases posteriorly (Fig. 1a).

The neck region consists of five circlets of neck scalids, which do not form longitudinal rows (Supplementary Fig. S2). Neck scalids are numbered 10, 11, 11, 13 and 12 from the first (anteriormost) to the fifth circlets. They are short and have a slightly expanded base, different from the relatively long and conical introvert scalids.

The trunk begins at the first annulus bearing a pair of large spinose sclerites. The trunk annuli are undifferentiated or poorly differentiated in NIGP160400 and NIGP160402 (Figs 1 and 3a,b), but in NIGP160401 20 trunk annuli are clearly recognizable (“A1–A20” in Fig. 2c). They vary in length, with A4 being the longest (110 μm). They are each covered with a single circlet of ~20–40 tightly sutured rectangular small plates. The trunk is armored with internally hollow small spines (“ss” in Fig. 2b; Supplementary Fig. S3e), which are of various sizes and somewhat irregularly distributed but are more concentrated postero-ventrally (Figs 1b, 2b, 3d; Supplementary Fig. S3e). Some small spines—for example, the two dorsal spines (Fig. 1a) and one ventral spine (Fig. 1b) in A1 of NIGP160400—resemble the neck scalids in size and shape. The five pairs of large spinose sclerites (“1ls–5ls” in Figs 1a–c and 2a–c) distinguish the trunk from the neck and their arrangement gives the animal a strong bilaterality and dorsoventrality (Fig. 2e; Supplementary Movie S1). They are located ventrolaterally on A1–2, laterodorsally on A5–6, midlaterally on A10–11, midlaterally on A15–17 and laterodorsally on A19–20. In addition, a single large sclerite is placed midventrally on A6–7. These sclerites have an enlarged base straddling two or more annuli and supporting a robust conical spine. A possible anus is present at the posterior end of the trunk (“an” in Fig. 2a; Supplementary Fig. S3b). There are two pairs of caudal spines (“cs” in Figs 1a–c, 2b, 3c,d; Supplementary Fig. S3e) located slightly ventrally to the presumed anus.

The trunk of NIGP160401 is internally filled with diagenetic phosphatic minerals (Supplementary Fig. S3f–i; Supplementary Movies S2–4). The only preserved internal organ is a tubular lumen in the posterior neck and anterior trunk (“mg” in Fig. 2d). It is nearly constant in diameter (~60 μm), widens both anteriorly and posteriorly, has a triangular or oval cross section (Supplementary Fig. S3i; Supplementary Movie S4) and extends to A5. This tubular lumen is interpreted as part of the midgut which is anteriorly connected with the esophagus. The midgut may also be partially preserved in NIGP160402 (Fig. 3e,g).

NIGP160402 (Fig. 3a), NIGP160400 (Fig. 1) and NIGP160401 (Fig. 2) probably represent progressively advanced developmental stages: as the body lengthens, large sclerites enlarge and trunk annuli become better differentiated. A trunk fragment (Fig. 3h), whose large sclerites reach ~290 μm in diameter, may represent a still later developmental stage. If true, the three type specimens may be juveniles or young adults and mature specimens may have ≥20 trunk annuli.

Nomenclature note

This article is published in an electronic journal with an ISSN (2045–2322) and has been archived in PubMed Central. Taxonomic nomenclature published in this article conforms to the requirements of the amended International Code of Zoological Nomenclature (ICZN) and hence is available under ICZN. This publication and the nomenclatural acts it contains have been registered in ZooBank (www.zoobank.org). The ZooBank LSID (Life Science Identifier) for this publication is urn:lsid:zoobank.org:pub:30F1E3C2-9D68-45A0-9CA0-E9CBA762C888.

Unnamed Forms (Fig. 4)

Figure 4 SEM images of fragmented specimens of unnamed forms. (a,b) Form I. (a) XXDW001, with 7 visible annuli and 3 large spinose sclerites. (b) XXDW002, with 3 visible annuli and 1 large spinose sclerite. (c) Form II, XXGZQ001, with 6 annuli. Scale bar applies to all images. SEM images acquired by authors. Full size image

Additional material includes several fragmented fossils (Fig. 4) from the coeval Kuanchuanpu Formation at Xixiang section, South China (Supplementary Fig. S1)18,24,26,27, representing two unnamed forms. Form I (Fig. 4a,b) is represented by two specimens, with seven and three preserved trunk annuli, respectively. Each annulus is covered with a circlet of ~20‒40 tightly sutured small plates, which have an expanded base supporting a centrally located circular or elliptical hole likely representing a broken hollow spine. The trunk is also armored with large spinose sclerites that straddle two adjacent segments and bear a centrally located hole representing a broken hollow spine. Form II (Fig. 4c) is represented by a single specimen with six annuli, each of which is covered with a circlet of ~10–15 tightly sutured small plates with an expanded base and a centrally located hollow spine. The expanded base is defined by two lateral slopes separated by two indentations, which match the imbrication with neighboring plates. No large sclerites are present in this incompletely preserved specimen.

Eokinorhynchus rarus and the two unnamed forms are similar in their trunk annuli that are covered with circlets of small plates. However, they are distinguishable from each other by the presence/absence of large sclerites and the shape of small plates (e.g., spinose plates in the two unnamed forms). Thus, we interpret them as different species of a closely related group of animals.