Ctenophoricola undetermined

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 SP.

Figs 12, 13, Supporting Information, Movies S4 and S5

Material: Gulf of California , near the mouth, between 26 º and 23 º 50´N, Mexico. Single complete specimen, 29 anterior fragments and numerous posterior fragments; zooplankton samples from GOLCA 8404 (20 March–7 April 1984) and El Golfo I expeditions .

Description: Single complete specimen a mature female with developing gonads/oocytes in anterior and posterior parapodia, 5 mm long, 1.7 mm wide, 26 chaetigers ( Figs 12-13). Other specimens only with anterior region and few posterior region segments or with only posterior region and pygidium. Body yellowish, with small pigment spots in rows on dorsum and ventrum of anterior segments and on posteriormost anterior region parapodia and all parapodia of posterior region. Prostomium usually contracted. Single pair of short, indistinct palps. Mouth with one ventral and two lateral lips. One pair conspicuous, internal lensed eyes with pigments visible posteriorly ( Fig. 13). Everted proboscis smooth, cylindrical, unarmed. Anterior parapodia reduced compared to posterior, lacking ventral cirri and having short chaetal lobes; acicula not exceeding lobe length. Parapodia of posterior region stout, trilobed, with laminar ventral and dorsal cirri fused with parapodia ( Fig. 12C), with acicula and simple capillary chaetae arranged in fan, surrounded basally by prechaetal and postchaetal lamella. Pygidium with a pair of elongated cylindrical cirri. Hosts are unknown.

Histology of eyes: The eyes are large, from just posterior to the central brain through the second chaetiger ( Fig. 13 and Supporting Information, Movie S4). The eyes are approximately cylindrical, with a diameter slightly smaller in the anterior half (possibly a handling artefact); the width/length ratio is 0.4. The lenses are approximately spherical, slightly elongate (again, possibly a handling artefact) and apparently denser in the centre and outer margin ( Fig. 13B–C, Supporting Information, Movie S4). This type of pigmented receptor with nuclear and plexiform layers were also found in the eyes of the Alciopini Vanadis tagensis Dales, 1955 by Hermans and Eakin (1974), but only in the posterior half of the eye. Additionally, there are extensive microvilli extending from the photoreceptor cells that fill the back half of the eye ( Fig. 13F). The pigment granules are not numerous. There may be a small secondary retina ventrolateral to the lens and anterior to the optic nerve (Supporting Information, Movie S5; Fig. 13B). The optic nerve is large and exits the eye ventrally, just anterior to its midpoint (Supporting Information, Movies S4 and S5, Fig. 13D). A distinct, continuous basal lamina encapsulates the eyes, optic nerves and brain ( Fig. 13B).

Remarks: Entire specimen minute, likely damaged by crushing together with other organisms during net collection,piercedbyseveralspinesfromotherplanktonic organisms (Supporting Information, Movie S5). All this damage and the extreme delicate nature of the specimen prevent us to describe many relevant morphological structures.