Ctenophoricola rousei, Martín & Álvarez-Campos & Kondo & Núñez & Fernández-Álamo & Pleijel & Goetz & Nygren & Osborn, 2021

Martín, Guillermo San, Álvarez-Campos, Patricia, Kondo, Yusuke, Núñez, Jorge, Fernández-Álamo, María Ana, Pleijel, Fredrik, Goetz, Freya E., Nygren, Arne & Osborn, Karen, 2021, New symbiotic association in marine annelids: ectoparasites of comb jellies, Zoological Journal of the Linnean Society 191 : -

CTENOPHORICOLA ROUSEI SP. NOV.

Figs 8–11

lsid: zoobank.org:act: 55C8FC03-98BA-4590-987A- 2C92217B4A88

Holotype: MNCN 16.01 /17900. Las Lapillas (Mar de las Calmas), south-west of El Hierro Island, on Leucothea multicornis (Quoy & Gaimard, 1824) , fixed in 4% formaldehyde buffered in seawater, preserved in 70% ethanol, March 1994.

Paratypes: MNCN 16.01 /17898 (six adults, two juveniles) Radazul , south-east of Tenerife Island, on Eurhamphaea vexilligera Gegenbaur, 1856 and Cestum veneris Lesueur, 1813 , December 1996 ; MNCN 16.01 /17899 (one adult used for SEM) from same locality ; MNCN 16.01 /17901 (three specimens) January 1997 ; MNCN 16.01 /17902 (two specimens), same data .

Additional material: One specimen, Cape Spartel, Tangier, Morocco, 35°47.534’N, 5°55.630’W, 18 October 2010, on E. vexilligera .

Diagnosis: Species of Ctenophoricola with minute size, having scattered red spots on dorsum. Posterior gut wall with one pair of lateral caeca per segment protruding up to twice width of gut, sometimes extending into parapodia.

Description: Holotype ( Fig. 8) 3 mm long, longest complete specimen, anterior region 0.5 mm wide excluding parapodia, posterior region 0.65 mm wide excluding parapodia. Body cylindrical, somewhat flattened in posterior region, divided in two distinctly different regions ( Figs 8, 9A–D, 10 A-B), sparsely ciliate. Translucent yellowish, with reddish spots, more numerous on posterior segments ( Figs 8, 9A–D) two white spots distally on parapodial lobes of posterior region ( Fig. 9A–D). Prostomium small, semicircular, without external eyes, with two minute, retractile palps, not ciliate ( Fig. 10C), partially retracted inside peristomium ( Fig. 8A). Peristomium similar in length to subsequent segments; peristomial (tentacular) cirri not found. Two conspicuous, anterior, lensed eyes, internally reaching to segment 4–5 in preserved (2–3 in vivo) specimens ( Figs 8A, 9A–C, E-F), strongly pigmented dark reddish-brown in adults, paler orange to yellow in juveniles. Anterior region with 12–16 segments, with parapodia conical, triangular, acute, with a thin, internal acicula, without chaetae ( Fig. 8A), with minute dorsal and ventral lobes; anteriormost parapodia of anterior region anterolaterally directed ( Fig. 8A). Posterior region with 17 segments, distinctly wider than those of anterior region ( Figs 8A, 9A–D, 10A–B), with larger and longer, acute parapodia ( Fig. 10B), with internal slender acicula and a fascicle of several, thin capillary chaetae ( Fig. 9B, D), thin dorsal and ventral lobes ( Fig. 10B, D) and groups of cells (likely gonads, gametes or maybe developing embryos) on posterior parapodia ( Fig. 11). Pharynx cylindrical, everted in some specimens ( Fig. 9F), unarmed, without papillae. Gut straight in anterior region, visible through body wall, distinctly wider in posterior region, with one pair of lateral caeca per segment, individual caeca length to at least twice width of gut, sometimes protruding into parapodia ( Figs 8, 9A–D). Living specimens with bright yellow material inside gut and caeca of posterior region. Pygidium small with two rounded, short anal cirri. Juveniles similar, with less-developed posterior region.

Remarks: Ctenophoricola rousei resembles C. masanorii , except in having scattered spots instead transversal bands, more acute parapodia carrying more numerous chaetae, a less ciliated body and distinct laterally projecting caecae in the gut wall.

Type locality: Las Lapillas, Mar de las Calmas, El Hierro, Canary Islands, Spain.

Habitat and distribution: Canary Islands and Cape Spartel ( Tangier), Atlantic coast of Spain and Morocco, on the surface of the ctenophores, E. vexilligera , L. multicornis and C. veneris .

Etymology: The species is named after Dr Greg Rouse, renowned polychaetologist, colleague and friend, for his invaluable contributions to the knowledge of annelid morphology and evolution.