Spirodiscus ottofinamusi, Kupriyanova & Flaxman, 2023

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 : 161-164

Spirodiscus ottofinamusi sp. nov.

urn:lsid:zoobank.org:act:D1A2535B-20DD-4B68-BEE0-CB12A63DE5F4

Figs 1–5

Holotype Op 98, Australia, New South Wales, off Byron Bay (28°22'17"S 154°38'50"E), 8 June 2017, 3811– 3754 m, Australian Museum ( AM) W.54171 . Paratypes AM W.49511, as above (5 spec.) .

Additional material. Op. 66, Australia, New South Wales, off Newcastle (33°26'54"S 152°43'58"E), 30 May 2017, 4378– 4195 m: W.49691 (2 spec.) . Op 79, Australia, New South Wales, Hunter Commonwealth Marine Reserve (32°7'51"S 152° 31'38"E), 4 June 2017, 4031 m: W.49683 (2 spec.) . Op 98, Australia, New South Wales, off Byron Bay (28°22'17"S 154°38'50"E), 8 June 2017, 3811– 3754 m: W.49704 (20 spec.) , W.49687 (6 spec.) . Op 103, Australia, Queensland, off Moreton Bay (27°1"S 154°13'23"E), 10 June 2017, 4260–4280 m: W.49671 (1 spec.), W.49684 (16 spec. ), W.49685 (3 spec.), W.49740 (53 spec.). Op 110, Australia, Queensland, off Fraser Island (25°13'11"S 154°9'37"E), 11 June 2017, 4005–4010 m: W.49512 (3 empty tubes.), W.49686 (15 spec.) , W.52131 (1 spec.).

Comparative material examined

Spirodiscus groenlandicus ( McIntosh, 1877) — W.46398, North Atlantic Ocean , Porcupine Seabight, off Brittany (50°4'N 13°55'36"W), 15 April 1978 ; W.46399, western Indian Ocean , Mozambique Channel , north of Madagascar, south-east of Glorioso Islands (11°44'S 47°30'E), 4 April 1977 .

Bathyditrupa hovei Kupriyanova, 1993 —W.46391, North Atlantic Ocean , Iberian Basin, west of southern Spain (37°18'N 15°33'W), 17 May 1981; W.46392, North Atlantic Ocean , Iberian Basin, north of Madeira (34°6'6"N 17°6'18"W), 30 May 1981 ; W.46394, North Atlantic Ocean , Iberian Basin, west of northern Spain (42°51'12"N 15°55'18"W), 11 Jun 1981 .

Description

Tube: Less than 1 cm long, white opaque, free-lying, tusk-shaped, slowly expanding, octagonal in cross-section, with 8 smooth keels (longitudinal ridges) arranged all around the tube and grouped by pairs ( Figs 1E , 4A,B ). In spaces between two neighbouring keels (forming one pair) walls slightly thicker than in spaces separating different pairs. Sides between keels concave. Short growth stops resembling tiny irregularly displaced transverse constrictions present.

Radiolar crown: 3–5 pairs of radioles not joined by inter-radiolar membrane ( Figs 4C , 5B ). Radiolar eyes absent.

Peduncle: inserted as 2nd dorsal radiole, 3–4 times as thick as radioles ( Fig. 5B ), with pinnules.

Operculum: funnel-shaped (bell-shaped), covered with concave brownish endplate ( Figs 4A,B,C , 5B ); opercular ampulla continuing smoothly into peduncle or with slight constriction.

Collar and thoracic membranes: collar five-lobed, two latero-dorsal lobes and ventral one clearly subdivided into a longer middle and two shorter lateral lobes ( Fig. 5B,C ), continuing into thoracic membranes reaching up to 2nd chaetiger ( Fig. 4C ). Collar chaetae simple limbate only ( Fig. 5D ), of two sizes.

Thorax: with five thoracic chaetigers, four of which uncinigerous ( Fig. 5A, B ). Thoracic tori decreasing in length towards abdomen, with the second chaetiger being twice as short as the fourth chaetiger ( Fig. 5B ). Chaetae thick with distal limba, of two sizes, Apomatus chaetae absent ( Fig. 5E ). Uncini saw-to-rasp-shaped, with 3–4 rows above wide gouged underneath anterior peg divided into two lobes; with 12–14 teeth in profile view ( Fig. 5F ). Dental formula P:3:3:3:2:2:2:2:1:1:1:1:1:1:1 or similar (e.g., P:4:3:3:2: …). Achaetigerous zone between thorax and abdomen absent ( Fig. 5A ).

Abdomen: with up to 50 segments. Chaetae short, with flat narrow denticulate blade ( Fig. 5H ), each torus with a single chaeta. Chaetae slightly longer on posterior-most segments ( Fig. 5A ), but long posterior capillary chaetae absent. All uncini rasp-shaped, with 9–12 teeth in profile view and 5–6 rows, dental formula P:6:5:5:5:5:4:4:3:3:3 ( Fig. 5G ); flat anterior peg subdivided in 5–6 shallow lobes ( Fig. 5G ). Posterior glandular pad absent.

Size: total body length up to 10 mm, including up to 1.5 mm long branchia, width of thorax up to 0.2 mm. Tube length up to 12 mm.

Etymology. The species is named in honour of Otto Nielson Simpson, whose parent’s generous donation to the Australian Museum Research Institute made this research possible.

Distribution. Southern Pacific Ocean, along east coast of Australia, 3754–4378 m.

Remarks. The new species is the third species described in the deep-sea genus Spirodiscus . The two previous species, Spirodiscus grimaldii and S. groenlandicus , have very similar morphology (except for five thoracic chaetigers in S. groenlandicus and six in S. grimaldii ) and have identical chaetation patterns but differ remarkably by their tube morphologies (coiled tetragonal in the former and tusk-shaped octagonal in the latter).

Spirodiscus ottofinamusi sp. nov. from the eastern Australian abyss is morphologically most similar to S. groenlandicus originally described from the bathyal of North Atlantic Ocean. Both S. ottofinamusi sp. nov. and S. groenlandicus species have five thoracic chaetigers, thick pinnulated peduncles bearing opercula in the shape of inverse cone with chitinous convex endplate, and short thoracic membranes. Both species have tusk-shaped unattached tubes with eight longitudinal ridges. However, they show relatively subtle, but clear morphological differences. Collar four-lobed with straight edge in S. groenlandicus , while it is five-lobed in S. ottofinamusi sp. nov. In S. groenlandicus thoracic tori are of the same size, but they decrease in length towards abdomen in S. ottofinamusi sp. nov. Finally, abdominal chaetae are elongated flat narrow geniculate in S. ottofinamusi sp. nov. but are short flat triangular geniculate in S. groenlandicus (and in S. grimaldii ).

Figures

Figure 1. External morphology of Bathyditrupa and Spirodiscus tubes.(A, B) Bathyditrupa hovei (from Kupriyanova & Ippolitov, 2015); (C) Spirodiscus grimaldii (from Kupriyanova & Ippolitov, 2015); (D) Spirodiscus groenlandicus (from Kupriyanova & Ippolitov, 2015); (E) Spirodiscus ottofinamusi sp. nov. W.49511.

Figure 2. Map of sampling sites from RV Investigator voyage IN2017_V03 along eastern Australia. Red arrows indicate stations where Spirodiscus ottofinamusi sp. nov. was found.

Figure 3. Bayesian majority rule consensus phylogram of the concatenated data set. Nodes with posterior probabilities <0.70 or bootstrap values <70 posterior probabilities 1.0 or bootstrap values 100 are indicated by * (asterisk). Numbers above branches are posterior probabilities, obtained from branches are bootstrap values obtained from Maximum Likelihood analysis.

Figure 4. Light microscopy photographs of the holotype of Spirodiscus ottofinamusi sp. nov. (A, B) Specimens in tube; (C) close-up of the dorsal view of the specimen removed from the tube, stained with methyl blue. Scale bars: A, B, 500 µm; B, 200 µm.

Figure 5. SEM micrographs of Spirodiscus ottofinamusi sp. nov. paratype W.49511. (A) Entire specimen, ventral view; (B) anterior view of the specimen, showing the operculum and thick pinnulated peduncle; (C) view of the ventral collar lobe subdivided into three lobes; (D) collar chaetae; (E) chaetae and uncini of the second thoracic chaetiger; (F) close-up view of saw-to-rasp thoracic uncini; (G) anterior abdominal uncini; (H) anteriorabdominal chaeta.Scale bars:A, 1 mm; B, 200 µm; C, 50µm; D, 10 µm; E, 20µm; F,G, H, 5 µm.