Spirodiscus grimaldii Fauvel 1909

Spirodiscus grimaldii Fauvel, 1909

Figures 1 A, 4, 5

Spirodiscus grimaldii Fauvel, 1909: 56 –57, fig. 4.

Spirodiscus grimaldii.— Fauvel 1914: 335 –338, pl. 29, fig.7–21.— Belloc 1953: 8.— Hartman & Fauchald 1971: 183 [in part, R/V ATLANTIS-II, St. 119 only, see Kupriyanova & Nishi 2011 for discussion of Hartman & Fauchald 1971 material].— in Zibrowius 1977: 299 [comments on Hartman & Fauchald 1971 material].—in Garcia-Diez et al. 2005: 44: [name only].—in Fabri et al. 2006 [database name only].

Serpulidae A.— Maurer & Williams 1988: 692.

Spirodiscus.—ten Hove, 1984: 189 [mentioned specimen off the Cape Verde Islands].

Nogrobs grimaldii.—ten Hove & Kupriyanova 2009: 68 –69, fig. 31; Kupriyanova & Nishi 2011: 2, fig. 1.

Material examined. Prince of Monaco, cruises 1896, 1902, off Azores: St. 1334, 13.8.1902, 39°30'N, 29°02'15"W, 1900 m (1 syntype in tube MNHN POLY TYPE 237, 4 syntypes, including 3 tubes and 1 spec. without tube MOM 18 0883); St. 698, 18.7.1896, 39°11'N, 30°44'40"E, 1846 m (2 syntypes in tubes and 4 tube fragments MOM 18 0475); St. 683, 7.7.1896, 38°20'N, 28°04'45"W, 1550 m (3 spec. MOM); St. 703, 19.7.1896, 39°21'20"N, 31°05'45"W, 360 m (3 spec. MOM); St. 719, 27.7.1896, 39°11'N, 30°24'15"W, 1600 m (3 spec. MOM); St. 738, 7.8.1896, 37°40'N, 26°26'15"W, 1919 m (1 spec. MOM).

R/V ATLANTIS-II, off Bermuda, cruise 24: St. A119, 19.8.1966, 32°15.8' to 32°16.1'N, 64°31.6' to 64°32.6'W, 2095–2223 m (2 tubes LACM-AHF).

Bathyscaph ARCHIMEDE, cruise 1969, Azores: Dive 12, 19.8.1969, 38°03.0'N, 25°28.3'W, 1990–2110 m (1 spec. MNHN PNT 37); Dive 15, 29.8.1969, 37°20.2'N, 25°27.5'W, 2000 m (1 spec. in broken tube MNHN PNT 38).

R/V JEAN CHARCOT, cruise BIACORES, Azores: St. 54A, 13.10.1971, 38°12'N, 28°15'W, 1810 m (1 empty tube MNHN PNT 34); St. 86, 17.10.1971, 39°25.5'N, 28°01.5'W, 1670 m (1 spec. MNHN PNT 35); St. 92, 17.10.1971, 39°03.5'N, 28°27.5'W, 2450 m (10 spec. MNHN PNT 36, 7 spec. AM W.46395, 1 spec. used for SEM AM W.46396); St. 95, 18.10.1971, 39°03.5'N, 28°25.5'W, 2440 m (5 spec. AM W.46397, 5 spec. NBCL ZMA V.P o l 5548, 5 spec. SMF 23974, 5 spec. NHMUK ANEA 2015.922–926, 5 spec. LACM-AHF Poly 7020, 5 spec. USNM 1283057); St. 120, 20.10.1971, 39°03.5'N, 32°43.5'W, 2100 m (1 empty tube SMF 23975); St. 126, 23.10.1971, 39°19.5'N, 32°47'W, 3360 m (6 spec. SMF 23976); St. 171, 1.11.1971, 37°58.5'N, 26°07'W, 3215 m (1 spec. SMF 23977); St. 173, 2.11.1971, 37°57'N, 26°08'W, 3225 m (4 spec. NBCL ZMA V. P o l 5547, 3 spec.

LACM-AHF Poly 7019); St. 174, 2.11.1971, 38°06'N, 26°15'W, 3050–3100 m (3 empty tubes SMF 23978); St. 206, 7.11.1971, 37°21'N, 26°28.5'W, 2085–2096 m (1 spec. SMF 23979); St. 227, 10.11.1971, 37°10'N, 26°19.5'W, 2160–2180 m (2 spec. NBCL ZMA V.P o l 5546).

R/V MARION DUFRESNE, cruise MD50, Amsterdam Island: St. 5-DC34, 13.7.1986, 37°40.33'S, 77°30.50'E, 2200 m (2 spec. MNHN PNT 33); same, cruise MD32, Reunion Island: St. DR104, 30.8.1982, 20°48.6'S, 55°01.4'E, 1875–1920 m (1 spec. SMF 23980); St. DR139, 3.9.1982, 20°46.5'S, 55°38.3'E, 1575–1600 m (1 empty old tube SMF 23981).

R/V LE SUROIT, cruise SEAMOUNT 2, Atlantis Seamount: St. TS 267: 4.2.1993, 34°22.48'N, 30°22.48'W, 2235 m (1 spec. MNHN PNT 32).

R/V VITYAZ-2, south-west of Azores, St. 78, 34º41′1” N, 40º38′6” W, 3160 m (1 tube prepared for SEM and for X-ray diffraction analysis PIN 5485/10).

Description. Tube: white opaque, free-lying, its most obvious part clockwise coiled into a flat spiral of 2.5 whorls (Fig. 1 A). However, initial tube straight, with circular cross-section (these posterior parts always broken off and lost, at best parts about 1 mm long may be preserved), growing straight upwards, abruptly turning to flat spiral perpendicular to initial tube, and with cross-section becoming quadrangular. Anterior tube part straight, pointing away from spiral in plane of coiling, smooth and circular in cross-section. Sides of quadrangular section flat to slightly convex. Outer convex side of spiral part with a median rib. Peristomes absent.

Tube ultrastructure: wall unilayered, structure is mostly irregularly oriented prismatic (IOP). Inner wall part (Fig. 4 D, H) made of more or less isometric crystals up to 0.5 µm in diameter. Middle part consisting of crystals of rice grain-like shape (length 2–2.5 µm, diameter 0.5 µm) loosely oriented parallel to tube surface (Fig. 4 C, I) and thus ultrastructure is transforming to semi-ordered irregularly oriented prismatic (SOIOP). Outer part of wall made of larger crystals (length 3–3.5 µm, diameter 1 µm), oriented subparallel to tube surface (Fig. 4 B, J). Neighbouring crystals with the same orientation may form “packets” (Fig. 4 J), such pattern sometimes can present in the middle part of wall (Fig. 4 I), but with smaller crystals and less definite orientation. Parabolic growth lamellae indistinct.

Tube mineralogy: 8% calcite (I calc=12), 92% aragonite (I arag=134).

Radiolar crown: radiole arrangement semi-circular, up to 8 per lobe.

Peduncle: pinnulated, without distal wings, with outer groove distally, with or without constriction beneath ampulla; inserted as second right radiole, up to 3 times as wide as other radioles (Fig. 5 A, B).

Operculum: inverse cone (ampulla) with chitinous endplate and central depression (Fig. 5 A). Pseudoperculum absent.

Thorax: with 6 thoracic chaetigerous segments, 5 of which uncinigerous (Fig. 5 A, B). Collar non-lobed with entire edge, no clear separation towards thoracic membranes that end at second chaetiger. No apron. Collar chaetae and remaining thoracic chaetae limbate, of two sizes; Apomatus chaetae absent (Fig. 5 C, D). Thoracic uncini sawto-rasp-shaped with numerous teeth (> 12) in profile, 4–5 teeth per row above flattened gouged anterior peg, one tooth per row posteriorly (dental formula P:4:4:4:3:3:2:1:1:1:1:1:1:1)(Fig. 5 E).

Abdomen: with up to 40 chaetigers. Chaetae short, with flat triangular denticulate blade (Fig. 5 F). Long posterior capillary chaetae absent. Uncini similar to thoracic ones, but rasp-shaped, dental (formula P:6:5:5: 4:4:4:3:3:3:2:2:2:2) (Fig. 5 G). Achaetous anterior abdominal zone absent. Posterior glandular pad absent.

Size: total body length up to 10 mm, including up to 3.5 mm long radioles, width of thorax up to 0.35 mm. Diameter of tube spiral 3–4 mm, tube outer diameter within coiled part 0.5–0.55 mm, corresponding lumen diameter 0.35–0.4 mm. Thickness of tube wall in between angular margins about 1/10th of outer diameter.

Distribution. North Atlantic Ocean, Indian Ocean (Amsterdam Island, Reunion Island), 360–3550 m.

Remarks. Spirodiscus grimaldii was described and illustrated by Fauvel (1909) based on multiple specimens (syntypes) from two stations of the Prince of Monaco expeditions to the Azores (St. 698 and St. 1334). In the catalogue of the polychaete type collection at MOM, Belloc (1953) mentioned material from four additional stations in the Azores (St. 683, 703, 719, 738), but did not provide any further information. These samples have been verified by Helmut Zibrowius (pers. comm.) who did not record the number of specimens in each sample (numbers of specimens were kindly provided by Michele Bruni, MOM), but confirmed them to be typical S. grimaldii already identified and labelled by Fauvel (labels are in his handwriting). However, specimens from these four stations did not appear to be the syntypes of S. grimaldii (Bruni, MOM, pers. comm.) as claimed by Belloc (1953). Kupriyanova & Nishi (2011) followed Zibrowius (pers. comm.) who stated that the label of the type at MNHN did not indicate the station of origin, but suggested the specimens were likely to be from St. 1334, as no material from this station had been deposited at MOM (Zibrowius, pers. comm.). However, the material from St. 1334 is present at MOM (Bruni, pers. comm.) and also the origin of the syntype MNHN POLY TYPE 237 is clearly indicated as St. 1334 (Mezaine, MNHN, pers. comm.).

The material (R/V JEAN CHARCOT, ZMA V.Pol. 3906) reported in ten Hove & Kupriyanova (2009) was collected in 1971 from the Azores and thereby is almost topotypical. Recently, Kupriyanova & Nishi (2011) summarised and refuted all previous records of S. grimaldii and provided several new ones, including topotypical material from the Azores collected by R/V VITYAZ-2. Hartman & Fauchald (1971: 183) reported Spirodiscus grimaldii from 3 stations in the western Atlantic. The specimen from R/V CHAIN, St. 100 from LACM-AHF available to Zibrowius (1977), proved to be a straight tube of Bathyditrupa hovei (see Kupriyanova & Nishi 2011). Material from R/V ATLANTIS-II stations not available to Zibrowius (1977) was re-examined by EKK (Kupriyanova & Nishi 2011), who confirmed that it was also partly misidentified since R/V ATLANTIS-II, St. A118 did not contain Spirodiscus grimaldii at all, whereas St. A119 contained two apparently empty coiled S. grimaldii tubes mixed with tubes of two unidentified species. The material reported here as new records was obtained in the Indian Ocean, near Reunion and Amsterdam Islands.

Kupriyanova & Nishi (2011) provided a new record of two Spirodiscus specimens in spiral tubes from the Pacific Ocean (LACM-AHF collection), but stated that specific attribution of these animals was uncertain. According to ten Hove & Kupriyanova (2009), the specimens from off the Galapagos (ZMA V.Pol. 3859) belong to an undescribed species of Spirodiscus. A specimen from the Pacific St. H361 of ECHO-1 survey (LACM-AHF) had a typical Spirodiscus - type tube, with six thoracic chaetigers and a thick pinnulated peduncle bearing typical for this species operculum covered with a concave endplate. It might also belong to the same species as ZMA V.P o l. 3859, and thus, further detailed comparative study is needed.

The form of coiling typical for S. grimaldii is similar to that found in some species of fossil Nogrobs, including N. vermicularis de Montfort, 1808 (the type species), N. tumidus (J. de C. Sowerby, 1829), and Tubulostium discoideum Stoliczka, 1868, that also have straight anterior tube parts. However, straight anterior parts are common for all free-lying spirally coiled medium-sized fossil genera, even those lacking tetragonal sections (e.g., Regenhardt 1961, pl. 8, fig. 9, 12). In the also spirally coiled tubes of spirorbins, the initial tube parts (if preserved at all) are not perpendicular to the whorls, but more or less in line with them (compare Malaquin 1904: 66 fig.1).