Chaetasterina gracilis Hess, 1970

Gale, Andrew S., 2020, The fossil record of the asteroid (Echinodermata) family Chaetasteridae Sladen 1889 and subfamily Hyalothricinae Fisher, 1911, Zootaxa 4858 (1), pp. 144-150 : 148

Chaetasterina gracilis Hess, 1970

Figure 2 C–I

1970 Chaetasterina Hess : p. 1082, figs 9–14, pl. 3: fig. 5.

Diagnosis. As for genus.

Type. The unique holotype is from the Upper Hauterivian of Neuchâtel, Switzerland ( NMB Hess A 94) .

Remarks. The sole specimen is small (R approximately 12 mm) and probably juvenile, but well-preserved, and parts of the specimen are covered in tiny, dense spines, similar to those on Hyalinothrix . The abactinal ossicles ( Fig. 2C ) of the arm are arranged in transverse rows diverging from mid-radius, very different from situation in Chaetaster in which the abactinals form well-defined columns extending from the disc to the arm tip ( Fig. 1F ). The abactinals of C. gracilis ( Fig. 2 E-I) are small and paxillose, with flanged, imbricating bases, like those in Hyalinothrix ( Fig. 2M ) and unlike the robust, block-like ossicles of Chaetaster ( Fig. 1D, F ). The inferomarginals of C. gracilis ( Fig. 2H, I ) are small and similar to those of Hyalinothrix ( Fig. 2I ). The body shape of C. gracilis , with short, straplike arms ( Fig. 2C, D ) and broad disc, is unlike those of Hyalothrix specimens, which have long, cylindrical arms and a small disc. However, the unique specimen of C. gracilis is probably a juvenile, and many asteroid juveniles have proportionately short arms.

Figures

FIGURE 1. A, B, Arthraster dixoni Forbes, 1848. Holotype specimen NHMUK 47000, “Lower Chalk”, probably Middle Turonian, Balcombe, Sussex, UK.A, actinal surface, B, enlargement of abactinal surface and base of arms. C–F, Chaetaster longipes (Bruzelius, 1805). C, enlargement of actinal arm. D, enlargement of abactinal disc. E, actinal view of specimen. F, abactinal view of specimen. Recent, Mediterranean.

FIGURE 2. A, B, Arthraster dixoni Forbes, 1848, small individual, in abactinal (A) and actinal (B) views; Middle Turonian, Dieppe, France; Collection of Nicolas Cottard, Offranville, Normany, France. C–I, Chaetasterina gracilis Hess, 1970. Holotype (NMB Hess A 94), Upper Hauterivian, Neuchâtel, Switzerland, original of Hess (1970: figs 9–14, pl. 3: fig. 5); C, abactinal view; D, actinal view; E–G enlargement of abactinal ossicles; H, I, enlargement of adambulacrals (ad) and inferomarginal (im). J–M, Hyalinothrix sp., Recent, Philippines, AS Gale coll. J, actinal view; K, abactinal view; L, enlargement of ossicles of denuded ambulacral groove; M, enlargement of denuded abactinal surface.