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Fig. 2 | Swiss Journal of Palaeontology

Fig. 2

From: Origin and phylogeny of velatid asteroids (Echinodermata, Neoasteroidea)—new evidence from the Jurassic

Fig. 2

Respiration in Pteraster tesselatus Ives, 1888, following Nance and Braithwaite (1981) and personal observations. a Inflation phase. The opercular spines on the adambulacrals move to open the opercula, and water flows into the cavity beneath the canopy (red). At the same time, the interabactinal muscles contract, reducing the coelomic volume and causing the papulae to swell. The osculum remains tightly closed by use of powerful muscles which contract to pull down the array of spines. The muscles in the canopy relax. b Deflation phase. The opercula are closed by the opercular spines; the interabactinal muscles relax, and the muscles in the canopy contract. The osculum opens by relaxation of the muscles on the inside of the spines, and water is expelled. It can be seen that opercular spines, interabactinal muscles and muscles closing the osculum by depressing the spines are all essential for this complex manoeuvre. All of these were present in Oxfordian fossils described here. c Asthenactis fisheri Alton,1966. Large individual in abactinal aspect. Note numerous arms (10), abactinal skeleton comprised of reticulum of ossicles which bear a central cluster of spines (pedicels). British Columbia, Canada. Royal British Columbia Museum, Invertebrate Zoology, no. 004-00,055-006. dg Tropidaster pectinatus Forbes, 1850. d Adambulacral ossicle in oblique distal aspect. NHMUK EE 14,021 (original of Thuy et al. 2011 fig. 5h), e, group of well preserved individuals, actinal surfaces, to show overall form, broad adambulacrals and prominent oral ossicles. NHMUK E 3335. f, g Arm of well preserved individual, in actinal f and abactinal g aspects. NHMUK EE 13,981 (original of Thuy et al. 2011 fig. 5d). Note paxilliform abactinal ossicles with crown of spinelets. d Pliensbachian, davoei Zone, Mickleton Tunnel, near Chipping Camden, Gloucestershire, UK. d, f, g Pliensbachian, davoei Zone, Sedan, Ardennes, France (see Thuy et al. 2011 for details). Adambulacral articulations ada2–3 indicated. Scale bars c, 10 mm; eg, 5 mm; d, 0.5 mm

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