Gyrocotyle discoveryi, Bray & Waeschenbach & Littlewood & Halvorsen & Olson, 2020

Bray, Rodney A., Waeschenbach, Andrea, Littlewood, D. Timothy J., Halvorsen, Odd & Olson, Peter D., 2020, Molecular circumscription of new species of Gyrocotyle Diesing, 1850 (Cestoda) from deep-sea chimaeriform holocephalans in the North Atlantic, Systematic Parasitology 97, pp. 285-296 : 292-293

Gyrocotyle discoveryi n. sp.

Type-host: Hydrolagus mirabilis (Collett) ( Chimaeriformes : Chimaeridae ), large-eyed rabbitfish.

Type-locality: Goban Spur, North-East Atlantic.

Other localities: Porcupine Seabight (51°09 0 N, 11°55 0 W, depth 1,200 m, 30.xi.2002, RRS Discovery Cruise, No. 15048-14, 15) ; Goban Spur (49°49 0 N, 11°44 0 W, depth 1,175–1,250 m, 27.iv.2001, RRS Discovery Cruise 252, No. 13963/17, 20, 24, 72; 49°41 0 N, 11°53 0 W, depth 1,053–1,077 m, 23.iv.2001, RRS Discovery Cruise 252, No. 13962/4; 49°47 0 N, 11°58 0 W, depth 1,240–1,360 m, 19.x.2002, RRS Discovery Cruise D 266, No. 15066-124, 125; 51°09 0 N, 11°55 0 W, depth 1200 m, 30.ix.2002, RRS Discovery Cruise D 266, No. 15063-103), North-East Atlantic .

Type-material: Holotype ( NHMUK 2019.11.21.3 ), paratypes ( NHMUK.2019.11.21.4-13 from Goban Spur; NHMUK.2019.11.21.14-19 from Porcupine Sea Bight).) .

Site in host: Spiral intestine.

Representative DNA sequences: MN655879 and MN655881 (ssrDNA); MN657003 - MN657005 , MN657007 - MN657009 , MN657011 (lsrDNA, domains D1-D3).

ZooBank registration: The Life Science Identifier (LSID) for Gyrocotyle discoveryi n. sp. is urn:lsid:- zoobank.org:act:7B028A0B-B8EB-495E-A9F1- F29DDB60B89A.

Etymology: The species is named after the RRS Discovery, the NERC research vessel on which the specimens were collected.

Description

[Based on 17 specimens; Figs. 4–6.] With characters of the order. Body relatively squat, with deeply crenulated margins, 8,634 –17,586 X 4,996 –8,439 (12,071 X 6,676), width 36–98 (60)% of length. Anterior sucker distinct, 1,149 –1,621 (1,347) long, 596–1,022 (771) wide. Uterus large, in central part of body, 1,546 –2,996 (2,232) from anterior extremity, 2,453 –6,226 (4,533) long, 35–43 (38)% of body length. Rosette distinct, fairly complex, 1,797 –3,092 (2,575) long, junction with soma not clear. Eggs tanned, operculate, 85– 97 X 39–56 (89 X 49).

Diagnosis

Gyrocotyle discoveryi n. sp. can be diagnosed from other congeners on the basis of unique nucleotide characters in our rDNA alignments (listed as alignment position-nucleotide): ssrDNA: 176-G, 782-G, 862-G, 973-C; lsrDNA: 573-A, 800-T, 1,245-C, 1,246- C, 1,247-G, 1,360-T, 1,369-T, 1,375-C, 1,379-G, 1,382-G, 1,391-A, 1,449-T, 1,468-T, 1,477-T.

Remarks

Mauchline & Gordon (1984) reported a ‘‘cestode’’ in Hy. mirabilis from the Rockall Trough off NW Scotland, which is, as far as we are aware, the only possible record of a Gyrocotyle from this host. Two species of Gyrocotyle , G. major van der Land & Templeman, 1968 and G. abyssicola van der Land & Templeman, 1968 , have been reported from its congener, the small-eyed rabbit fish Hydrolagus affinis (de Brito Capello) on the edges of the continental shelf off the eastern coast of Newfoundland ( van der Land & Templeman, 1968). These two species are illustrated as much more elongate than our specimens, with less complex lateral wrinkling and small rosettes. The worms were recovered from frozen hosts, so the gross morphology may well not be of significance in differentiating these species. Subsequently, these two taxa have been reported from the same host species off south-western Greenland by Karlsbakk et al. (2002) and, puzzlingly, from a rhinochimaerine species, the straight-nosed rabbit fish Rhinochimaera atlantica Holt & Byrne , off the Scotian Shelf by Hogans & Hurlbut (1984). In the North-East Atlantic, R. atlantica has not been found harbouring Gyrocotyle , but it does harbour the strobilate tapeworm Chimaerocestos prudhoei Williams & Bray, 1984 and a congeneric host, the Pacific spookfish R. pacifica (Mitsukuri, 1895) also harbours a species of Chimaerocestos Williams & Bray, 1984 (see Caira et al., 1999, 2014). Other records of Gyrocotyle spp. from Hydrolagus spp. are from the Pacific Ocean (see Bandoni & Brooks, 1987).

There are no reliable morphological characters to differentiate this species or indeed any of the gyrocotylidean species circumscribed by molecular means. Therefore, the species is diagnosed by its relatively marked sequence divergence from those of recognised species.