Myzostoma josefinae Summers, Al-Hakim & Rouse, 2014, n. sp.

Myzostoma josefinae n. sp. Summers & Rouse

Fig. 5 A–D

Holotype: SIO-BIC A4016 paragenophore (1 spm: in 70% ethanol after paraformaldehyde/glutaraldehyde fixation). Near ‘Francisco’ whalefall, Monterey Canyon, California (36° 46' 19.1994"N, 122° 4' 58.7994"W), 1020 m. Collected via the R/V Western Flyer using the ROV Doc Ricketts (Dive 9) on 10 March 2009 by GWR.

Host. Psathyrometra fragilis (AH Clark). SIO-BIC E4567. Genbank (COI—KM491780).

Paratypes: SIO-BIC A3798 paragenophores (7 spms: 6—in 70% ethanol after paraformaldehyde/ glutaraldehyde fixation; 1—95% ethanol). Same host and locality as holotype. Genbank (COI—KM014189). SIO- BIC A3829 syngenophores (12 spms: 6 spms—in 70% ethanol after paraformaldehyde/glutaraldehyde fixation; 6 spms—95% ethanol). Guaymas Basin (26° 45' 12.8514"N, 111° 10' 19.632"W), 1314 m. Collected via the R/V Western Flyer using the ROV Doc Ricketts (Dive 390) on 16 April 2012 by GWR. Genbank (COI—KM491749). Host: Psathyrometra fragilis (AH Clark, 1907), SIO-BIC E6149 (DNA subsample only).

Etymology. Named for Josefin Stiller, an enthusiast of polychaetes.

Diagnosis and description. Holotype body circular disc with two elongated, cylindrical caudal appendages, approximately as long as body (Fig. 5 A–D). Length ~ 2.1 mm; width ~ 1 mm, following fixation. Body margin with 18 cirri, alternating in length, most anterior pair up to twice as long as the rest (Fig. 5 C–D). Caudal appendages with long terminal cirri. Mouth terminal. Proboscis smooth [seen in paratypes]. Cloaca terminal, between caudal appendages. Paired penes. Five pairs of parapodia, positioned two-thirds of way from center of disc to margin.

Remarks. Myzostoma josefinae n. sp. is the first myzostomid with paired elongate caudal appendages described from the eastern Pacific and Psathyrometra fragilis. Four other species are known to possess paired elongate caudal appendages, two recovered on Antedonidae, one from Comatulidae, one possibly with a Mariametroidea, and one associated with an uncertain host (Table 1).

Myzostoma josefinae n. sp. is most similar in form to M. divisor Grygier, 1989, M. filicauda Graff, 1883, and M. tentaculatum Jägersten, 1940a. Myzostoma filicauda was recorded on Coccometra hagenii (Pourtalès) (Antedonidae) from Sand Key, Florida. Myzostoma divisor was described from Promachocrinus kerguelensis Carpenter (Antedonidae) from Antarctica, and the description includes notes on the juvenile stages. Myzostoma tentaculatum was described from Japan, on an unknown host. As all identified hosts for this set of taxa are Antedonidae, it is likely that M. tentaculatum was collected on a Japanese antedonid. In addition to differences in host and locality, Myzostoma josefinae n. sp. is distinguished from M. divisor by molecular data published by Summers & Rouse (2014) and in having marginal cirri of unequal length (equal in M. divisor), M. filicauda by lacking papillae on the proboscis, and from M. tentaculatum by the length of the most anterior pair of cirri (six times longer than rest, resembling ‘tentacles’, in M. tentaculatum).

Two other taxa have two elongate caudal appendages. Myzostoma bicaudatum Graff, 1883 was described from Comactinia meridionalis (Agassiz) west of Tortugas in the Caribbean. Myzostoma filiferum Graff, 1884a was recorded on Antedon bidentata (nomen nudum) (possibly Heterometra variipinna (Carpenter) from the Torres Strait. [Nomenclatural issue of M. filiferum and M. filicauda discussed in Grygier (1989)]. Myzostoma bicaudatum and M. filiferum differ from M. filicauda, M. divisor, and M. josefinae n. sp. by possessing 20 (rather than 18) marginal cirri on the main body. In addition, M. bicaudatum is unique among all of the forms by having a subterminal mouth and lacking terminal cirri on the caudal appendages.

Myzostoma divisor and M. josefinae n. sp. were recovered as well-supported sister-taxa in the molecular phylogeny of Summers & Rouse (2014). We suspect that M. filicauda and M. tentaculatum will form a clade with these two taxa, while the evolutionary affinity of M. bicaudatum and M. filiferum may instead be with myzostomids with caudal processes and 20 marginal cirri, associated with Comatulidae and Mariametroidea respectively. The type specimens for M. bicaudatum, M. filiferum, and M. filicauda have been lost, and the location of types of M. tentaculatum is unknown.