Protomyzostomum roseus Summers, Al-Hakim & Rouse, 2014, n. sp.

Protomyzostomum roseus n. sp. Summers & Rouse

Fig. 7 G–J

Holotype: SIO-BIC A4019 paragenophore (1 spm in 70% ethanol after formalin fixation). Off Monterey Canyon, California (36° 48' 7.9194" N, 121° 59' 42" W), 632 m. Collected via the R/V Western Flyer using the ROV Tiburon (Dive 1160) on 18 October 2007 by GWR, Nerida Wilson and R. C. Vrijenhoek.

Host. Asteronyx longifissus Döderlein (Asteronychidae, Euryalida, Ophiuroidea). SIO-BIC E6108. Genbank (16S—KM014337; 28S—KM014340).

Paratypes: SIO-BIC A3799 paragenophore (1 spm: 95% ethanol). Genbank (COI—KM014172); SIO-BIC 3797 paragenophores (2 spms: 1—in 70% ethanol after formalin fixation; 1—95% ethanol); SIO-BIC A3799 paragenophores (2 spms: in 70% ethanol after paraformaldehyde/glutaraldehyde fixation); SIO-BIC A4023 paragenophore (1 spm: embedded in Spurr’s resin after fixation in glutaraldehyde and osmium tetroxide, some in 1µm sections). Same host and locality as holotype.

Etymology. Latin for red, in reference its color in life.

Diagnosis and description. Holotype recovered from a host’s bursa (Fig. 7 H). Body elongate, tapering posteriorly and anteriorly (Fig. 7 I). Length ~ 4 mm, width ~ 2.5 mm following fixation. Mouth and cloaca terminal. Five pairs of parapodia, more pronounced in small specimen. Color red in life, white in preservative.

Remarks. This is the first species of myzostomid described that infests ophiuroids in the eastern Pacific, and the first record in Asteronyx longifissus.

Preliminary histological study showed the body to be ellipsoidal in transverse section (Fig. 7 J). The region sectioned (near anterior) showed the gut to lie dorsally above and adjacent to ovarian tissue, containing oocytes in various stages of development. No testis tissue was in this region. Bases of the chaetae were placed ventrolaterally in chaetal sacs with surrounding musculature for protrusion. Ventral nerve cord not discernable.