Spirodiscus Fauvel, 1909

Kupriyanova, Elena K. & Flaxman, Beth, 2023, A New Species of the Mysterious Genus Spirodiscus (Annelida: Serpulidae) of the Eastern Australian Abyss, Records of the Australian Museum (Rec. Aust. Mus.) 75 (3), pp. 155-166 : 161

Genus Spirodiscus Fauvel, 1909

Spirodiscus Fauvel, 1909: 56–57 .—Fauchald, 1977: 147; Kupriyanova & Ippolitov, 2015: 162–163.

Nogrobs (not Montfort, 1808).—ten Hove & Kupriyanova, 2009: 68–69; Kupriyanova & Nishi, 2011: 1–2.

Type species. Spirodiscus grimaldii Fauvel, 1909

Diagnosis (after Kupriyanova & Ippolitov, 2015). Tube white, free-lying, polygonal in cross-section, quadrangular or octagonal (= modified quadrangular), straight to slightly curved (tusk-shaped), or initially cylindrical, then quadrangular in cross-section and coiled clockwise into a flat spiral, finally with short cylindrical straight distal part. Peristomes absent. Operculum inverse cone (ampulla) with chitinous endplate and central depression. Peduncle thick, pinnulated, without distal wings, with dorsal groove distally, with or without constriction beneath ampulla; inserted as second right radiole, up to three times as wide as other radioles. Pseudoperculum absent. Arrangement of radioles semi-circular, up to eight per lobe. Inter-radiolar membrane, branchial eyes, and stylodes absent. Mouth palps absent. Five to six thoracic chaetigerous segments. Collar non-lobed with straight edge, no clear separation towards thoracic membranes that end at second chaetiger; tonguelets between ventral and lateral collar parts absent. No apron. Collar chaetae limbate. Apomatus chaetae absent. Thoracic uncini saw-to-rasp-shaped with numerous teeth (> 12) in profile, 2–3 teeth per row; anterior peg gouged. Thoracic triangular depression absent. Abdominal chaetae short, with flat triangular denticulate blade; uncini similar to thoracic ones. Achaetous anterior abdominal zone absent. Long posterior capillary chaetae absent. Posterior glandular pad absent.

Remarks. Jäger (2005) synonymized the Recent monotypic at the time genus Spirodiscus with the fossil Nogrobs de Montfort, 1808 . In their review, ten Hove & Kupriyanova (2009) followed Jäger (2005) and used the name Nogrobs for Spirodiscus grimaldii . Zibrowius (pers. comm.) expressed doubts that the name Nogrobs should be used for the extant material suggesting that the fossil tubes of “ Nogrobs ” may be so convergent that synonymizing the Recent Spirodiscus would result in a loss of a well-defined genus. This point of view was supported by Kupriyanova & Ippolitov (2015), who demonstrated significant ultrastructural and mineralogical differences between in tubes of Recent and Mesozoic species. The authors concluded that similar tetragonal tube morphology of the Recent forms is a result of convergence due to adaptation to similar soft-sediment habitats of the deep sea and reinstated the genus Spirodiscus , previously synonymized with fossil Nogrobs .