Calliostoma bullatum ( Philippi, 1844 )

Hoffman, Leon, Beuck, Lydia, Heugten, Bart Van, Lavaleye, Marc & Freiwald, André, 2019, Last snails standing since the Early Pleistocene, a tale of Calliostomatidae (Gastropoda) living in deep-water coral habitats in the north-eastern Atlantic, Zootaxa 4613 (1), pp. 93-110 : 96-98

Calliostoma bullatum ( Philippi, 1844)

( Figs 2–20 )

Trochus bullatus Philippi, 1844: 226 , tab. 28, fig. 8

Calliostoma bullatum: Barrier et al. (1996) : 43

Calliostoma bullatum: La Perna & D’Abramo, 2010: 31 –34, fig. 2A–D

Type material. The whereabouts of the type material is unknown; it is not in the Museum für Naturkunde–Leib-niz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, where part of the Philippi collection is retained. Philippi (1844) reported Calliostoma bullatum from Calabrian (0.8-1.8 Ma, Early Pleistocene) outcrops near Messina, Sicily. A neotype needs to be designated, preferentially a topotype.

Material. Mauritania, Tanoûdêrt Canyon, MSM16-3 /GeoB 14796 ( ROV3 ), 20.247°N, 17.670°W, 642 m, live individuals observed, 03-XI-2010 ; MSM16-3 /GeoB 14799, 20.243°N, 17.668°W, 490 m, three shells, grab, 03-XI- 2010 ; MSM16-3 /GeoB 14801, 20.246°N, 17.670°W, 568 m, one shell, grab, 04-XI-2010 ;

Nouamghar Canyon, MSM16-3/GeoB 14779 (ROV2) 19.180°N, 16.806°W, 618 m, live individuals observed, 30-X-2010.

Inchiri Canyon , MSM16-3 /GeoB 14871 ( ROV4 ) 19.139°N, 16.764°W, 566 m, live individuals observed, 09- XI-2010 ; MSM16-3 /GeoB 14871 ( ROV5 ) 19.139°N, 16.765°W, 588 m, live individuals observed, 2 specimens collected and retained in ethanol, 09-XI-2010 .

Timiris Mound Complex, MSM16-3/GeoB 14873 (ROV7), 18.951°N, 16.875°W, 485–574 m, live individuals on live sponges observed, 10-XI-2010; MSM16-3 /GeoB 14876, 18.962°N, 16.870°W, 548 m, two shells, box corer, 12-XI-2010 ; MSM16-3 /GeoB 14877, 18.963°N, 16.869°W, 498 m, 13 shells, box corer, 12-XI-2010 ; POS346/GeoB 11587, 18.983°N, 16.866°W, 482 m, one shell, box corer, 09-I-2007; POS346/GeoB 11588, 18.983°N, 16.864°W, 474 m, nine shells, box corer, 09-I-2007.

Tioulit Canyon, MSM16-3/GeoB 14886 (ROV8), 18.650°N, 16.726°W, 640 m, live individuals observed, 12- XI-2010; MSM16-3 /GeoB 14891 ( ROV9 ), 18.664°N, 16.724°W, 592 m, live individuals observed, 13-XI-2010 .

Banda Mound Complex, POS346/GeoB 11564, 17.646°N, 16.666°W, 442 m, 10 shells, box corer, 07-I-2007; POS346/GeoB 11567, 17.659°N, 16.668°W, 428 m, eight shells, box corer, 07-I-2007; POS346/GeoB 11568, 17.664°N, 16.673°W, 514 m, six shells, box corer, 08-I-2007; POS346/GeoB 11569, 17.667°N, 16.672°W, 440 m, 17 shells, box corer, 08-I-2007; POS346/GeoB 11578, 17.675°N, 16.670°W, 458 m, eight shells, box corer, 08-I- 2007; POS346/GeoB 11579, 17.679°N, 16.668°W, 450 m, two shells, box corer, 08-I-2007, ( Figs 2–5 ); POS346/ GeoB 11580, 17.684°N, 16.668°W, 481 m, three shells, box corer, 08-I-2007; MSM16-3 /GeoB 14908 ( ROV11 ), 17.670°N, 16.681°W, 574 m, live individuals observed, 16-XI-2010 .

Tamxat Mound Complex, MSM16-3 /GeoB 14902 ( ROV10 ), 17.540°N, 16.668°W, 580 m, live individuals observed, 15-XI-2010 ; MSM16-3 /GeoB 14903, 17.548°N, 16.662°W, 414 m, three shells, box corer, 15-XI-2010 ; MSM16-3 /GeoB 14904, 17.543°N, 16.663°W, 510 m, eight shells, box corer, 15-XI-2010 ; MSM16-3 /GeoB 14905, 17.541°N, 16.667°W, 486 m, two shells, box corer, 15-XI-2010 ; MSM16-3 /GeoB 14910, 17.483°N, 16.694, 535°W m, one shell, box corer, 16-XI-2010 ; MSM16-3 /GeoB 14911, 17.482°N, 16.692°W, 450 m, 2 live juveniles dried, box corer, 16-XI-2010 .

Tiguent Mound Complex, MSM16-3/GeoB 14914 (ROV12), 17.137°N, 16.825°W, 514 m, live individuals observed, 17-XI-2010.

Description by Philippi (1844). Trochus Testa tenui, late et convexo-conica; anfractibus convexis, sutura satis profunda distinctis, sulcis circa sex, latissimis, superficialibus sculptis, ultimo obtuse angulato; basi ad columellam striata, caeterum laevi. [Shell thin, wide, convex-conical; whorls convex, with rather deep suture, and about six very wide shallow grooves, the last whorl with a blunt keel; the base with striae near columella, the rest smooth]

Testa 15´´´ alta, 15´´´ lata et major, primo adspectu Tr. Granulato simillima sed distinctissima. Forma multo latior, convexo conica, non concavo-conica; anfractus convexiusculi, non marginati, laevissimi, minime granulate, ultimus longe magis rotundatus; basis laevissima praeter sulcus seu strias 4 columellam cingentes. [Shell with a height of 15 lines (34 mm) and maximal width of 15 lines (34 mm), similar but distinct from Tr. Granulato (now Calliostoma granulatum ). Form much broader, convex-conical, not concave-conical; whorls convex, rounded, smooth, with minimal granulation, the last whorl more rounded; basis smooth with 4 spiral grooves]

Additional description. Adult specimen with about seven slightly convex whorls (excluding protoconch). Teleoconch whorls with fine spiral striation, spire conical with slightly convex outline ( Figs 6–8 ). Top angle of spire about 65°. Base flattened. Height of the largest specimen 36 mm, width 36 mm ( Fig. 6 ).

Protoconch swollen, 0.8 whorls, with hexagonal-reticulated sculpture on smooth background, reticulated cells about 0.02 mm diameter ( Fig. 5 ). Varix at transition to teleoconch rounded, prosocyrt. Size 0.47 x 0.35 mm.

First teleoconch whorl convex with five rounded spiral ribs above periphery; shoulder area flattened with weaker spiral ribs ( Figs 2–4 ). Base of first teleoconch whorl with nine, broad-flattened ribs and narrow, open umbilicus. Aperture angular, columella convex, inner shell nacreous. Outer lip of a juvenile blunt, prosocline at about 25° with shell axis. After 2 teleoconch whorls, outline more flattened; whorls with 6–14 spiral ribs which are finer, more numerous and evenly distributed; additional spiral ribs emerge as thin threads between two stronger ones. Spiral ribs stronger near the periphery on whorls six and seven; fine beads frequently present on the first and second spiral rib below the suture in the first whorls. Body whorl slightly more convex with blunt keel at periphery. Some specimens show slightly more convex whorls and a more regular pattern of fine spiral ribs on the whorl face. Base flattened with spiral ribs that are strongly developed near periphery and near columella. Umbilicus closed in adult specimens. Aperture angular and inside of the shell smooth and nacreous, columella convexly curved and its callus clearly demarcates the transition to the external shell. Lip blunt, strongly prosocline under 45° with shell axis. Colour cream white with a nacreous shine; periostracum absent ( Figs 6–8 ).

Head white, centrally swollen, snout wide oblong with thin necklobes; necklobe rectangular at the front; lobes pinkish posteriorly ( Fig. 9 ). Two long pointed cephalic tentacles, greyish at tips. Eyes black, situated on short ommatophores behind base of cephalic tentacles. Foot muscular with remarkable ability to adapt to rugose and variable substrates ( Fig. 11 ). Back of the foot with wide dorsal groove ( Fig. 10 ). At least four epipodial sensory tentacles on either side in dorsal position, emerging between shell and foot ( Figs 9–12 ). Base of foot with wide edge corrugated up front ( Fig. 9 ). Operculum circular, spirally developed, brown translucent, thin, chitinous.

Distribution. Calliostoma bullatum is commonly found as fossil in Early to Mid-Pleistocene formations that were deposited in bathyal depths in association with remains of the colonial Lophelia pertusa ( Linnaeus, 1758) and Madrepora oculata Linneaus, 1758 ( Barrier et al. 1996; La Perna & D’Abramo 2010). The fossil record suggests that this species has been living for about 2.5 million years.

Recent including living specimens have only been from off Mauritania in DWC habitats, dead at 414–588 m, alive at 450–642 m ( Fig. 1 ). The species is unknown from Morocco’s Atlantic Margin or from the Lusitanian islands or seamounts. It is possible that the species is living further south along the African shelf as DWC habitats along this coast are poorly sampled.

Remarks. Our findings are the first living records of this species that up to now was only known as fossil. They resemble Philippi’s (1844) figure very well ( Fig. 8 ) especially on size, outline, the incremental convexity of the body whorl, shape of the aperture, development of the columellar callus and the sculpture on the base of the body whorl, particularly that near the columella. Philippi (1844) mentioned about six spiral grooves. Fossil specimens from Sicily have 6–10 grooves or ribs on the body whorl. Specimens from Mauritania show typically 10–14 ribs. We consider this difference variability within the species. Variability of spiral rib sculpture is common in calliostomatids, for example in the European species Calliostoma zizyphinum ( Cossignani & Ardovini 2011) and in several species in Maurea from New Zealand (Marshall 1995a).

Calliostoma bullatum is the largest representative of the genus in the NE Atlantic and the Mediterranean Sea. Calliostoma bullatum Coen 1933 (non Philippi, 1844) is a synonym of Calliostoma conulus . The deep-water species Calliostoma maurolici (G. Seguenza, 1876) will be discussed in the following; it is smaller, with a stronger spiral ornament, more convex whorls, a wider top angle and an open umbilicus when adult. Calliostoma cleopatra ( Locard, 1898) is another deep-water species described from off Western Sahara at 1035–1056 m; it is smaller, with more convex whorls, stronger spiral sculpture and stronger beads on the top spiral ribs. Calliostoma caroli Dautzenberg 1927 was described from the Azores at 1250 m; it has a more angular outline with a stronger spiral structure, and it is smaller than our species. Calliostoma leptophyma Dautzenberg & H. Fischer, 1896 will be discussed below; it is similar to Calliostoma cleopatra but it lacks the strong carinae on the ribs and it has a more compressed outline. Calliostoma normani (Dautzenberg & H. Fischer, 1897) is described from the Azores at 1600 m; it is similar to C. caroli but has finer spiral ribs, inflated whorls and lacks a blunt keel. We also considered other Western and Eastern Atlantic calliostomatids but we did not find a match with our specimens; all have either a stronger spiral (beaded) structure, are smaller or show a stronger keel. Interestingly, live and dead scleractinian corals were found in all above cited dredge hauls together with the calliostomatids.

We observed this species with ROV surveys on various live fauna: Porifera ( Figs 15–16 ), Hydrozoa ( Fig. 9 ), Scleractinia ( Figs 10–14 ), Octocorallia ( Fig. 20 ), and Mollusca ( Figs 17–20 ). It appears to be preferentially feeding on soft tissue of Lophelia pertusa , Madrepora oculata , epibionts and rarely on other tissue e.g., of Cladorhiza corallophila Göcke et al., 2016 . We have retained the two specimens in ethanol for future study at Senckenberg am Meer, Wilhelmshaven (SaMID1435, SaMID1516).

Figures

FIGURE 1. Distribution maps of Calliostoma bullatum and Calliostoma leptophyma (left) and of Calliostoma maurolici (right). In the left map, empty shells of Calliostoma bullatum as red diagonal crosses, live observations as yellow triangles, empty shells of Calliostoma leptophyma as red normal crosses, live observations in this study as green triangles, live observations from literature as green diamonds. In the right map, empty shells of Calliostoma maurolici as red normal crosses, live observations as yellow triangles, live observations from literature as green diamonds. Bathymetry data source: GEBCO, depth contour intervals 500 m.

FIGURES 2–8. Calliostoma bullatum, 2–5. POS346/ GeoB 11579, 2–3. H 1.4 mm, W 1.7 mm. 4–5. W 2.0 mm, T 1.6 mm, protoconch W 0.47 mm, T 0.35 mm, scale bar 0.1 mm. 6–7. MSM16-3/ GeoB 14871, live-collected, scale bars 10 mm, 6. H 36 mm, W 36 mm. 7. H 31 mm, W 32 mm. 8. Trochus bullatus, original illustration by Philippi (1844), H 34 mm, W 34 mm.

FIGURES 9–14. Calliostoma bullatum on various substrates. 9. MSM16-3/GeoB 14871 (ROV4). Grazing on hydroids. 10. MSM16-3/GeoB 14871 (ROV4). Elongated, muscular foot supports feeding on polyp tissue (Madrepora oculata). Operculum and dorsal groove on foot indicated by arrow. 11. MSM16-3/GeoB 14873 (ROV7). Muscular foot enables elevation of body above substrate (live Lophelia pertusa). Epipodial sense organs spread directly below the shell (arrow). 12. MSM16-3/GeoB 14871 (ROV4). Feeding on apical portions of a live Madrepora oculata. 13. MSM16-3/GeoB 14779 (ROV2). Two individuals feeding on Lophelia pertusa tissue; note the grazing tracks showing the bare, white coral skeleton devoid of polyp tissue in contrast to the orange to pale-pinkish live portions. 14. MSM16-3/GeoB 14891 (ROV9). Three individuals of different sizes all feeding on epibionts of Lophelia pertusa framework; note the grazing traces on adjacent live Lophelia pertusa portions (see arrow). [Figs 9-20 were taken by ROV “Sperre”, Tomas Lundälv, Sven Lovén Centre for Marine Infrastructure, Tjärnö, University of Gothenburg, Strömstad, Sweden].

FIGURES 15–20. Calliostoma bullatum on substrates. 15. MSM16-3/GeoB 14871 (ROV5). Grazing on carnivorous sponge Cladorhiza corallophila; arrow indicating grazing effect. 16. MSM16-3/GeoB 14902 (ROV10). On framework encrusting sponge. 17. MSM16-3/GeoB 14902 (ROV10). Grazing on a valve of live Acesta excavata, which is colonised by epibionts; the two laser points are at a distance of 6 cm. 18. MSM16-3/GeoB 14902 (ROV10). Grazing on a valve of dead Acesta excavata (note in direct surrounding the free portions of epibionts on the valve and the white framework portions of Lophelia pertusa lacking any tissue). 19. MSM16-3/GeoB 14902 (ROV10). Grazing on a gastropod shell (Ranella olearium). 20. MSM16-3/ GeoB 14891 (ROV9). Grazing on dead hydroid axis in close vicinity to a Solenogastres.