Fellodistomidae Nicoll 1909

Family Fellodistomidae Nicoll, 1909

Steringophorus liparidis Zdzitowiecki, 1997 (Figure 2 (a,b); see also Figure 5 from Sokolov and Gordeev 2015)

Host. Muraenolepis marmorata.

Site of infection. Intestine.

Locality. The Ross Sea (75°47ʹ2 N & 171°53ʹ7 W) at a depth of 1316 m.

Prevalence. 1 of 20 host specimens (5%).

Intensity of infection. 2 worms in a single infected host.

Deposited material. Paragenophore (IPEE RAS 14292) and two syngenophores (IPEE RAS 14293, 14294).

Representative DNA sequences. Two partial sequences of 28S rRNA and nd1 genes were deposited in Genbank (NCBI) as MT872201 and MT876568.

Description (based on a paragenophore and two syngenophores). Body pyriform, length 2,142 –2,373, maximum width 938–980 in testicular area, 41.3–45.6% of length. Tegument unarmed. Oral sucker subglobular or subelipsoidal, 256–269 × 220–281, length 11.3–11.8% of body length; oral opening subterminal. Ventral sucker rounded, 305–330 × 305–336, length 12.9–14.6% of body length. Oral sucker to ventral sucker width ratio 1:1.1–1.5. Forebody 36.6–41.6% of body length. Prepharynx very short. Pharynx 122 × 110, length 5.1–5.4% of body length. Oral sucker to pharynx width ratio 1:0.39–0.52. Oesophagus 122–220, 6.5–9.7% of body length. Intestinal bifurcation in middle third of forebody. Caeca blind, terminating in post-testicular region; post-caecal distance 42.3–- 73.6% of post-testicular region length and 14.7–18.9% of body length.

Testes deeply lobed, opposite, in anterior half of hindbody, separated from ventral sucker; left 366–427 × 366, length 15.4–18.9% of body length; right 317–488 × 305–342, length 17.7–20.6% of body length. Post-testicular region length 23.5–34.8% of body length. Cirrus-sac broad, oblong, contiguous with anterior edge ventral sucker, 354–366 × 183–208, length 15.4–16.3% of body length. Internal seminal vesicle bipartite. Pars prostatica tubular, with filamentous lining, length 43.7% of cirrus-sac length (accurately measured in only one specimen). Ejaculatory duct short and broad. Genital pore slightly sinistral, postbifurcal, intercaecal.

Ovary acinous, dextro-submedian, partly overlapping by ventral sucker and sinistral testis, 244–305 × 208–256, length 11.1–13.5% of body length. Seminal receptacle uterine. Laurer’s canal opening dorso-medially at level of posterior third of ovary. Mehlis’ gland median. Uterus forming numerous convoluted loops, filling almost entire post-testicular region. Metraterm not clearly delineated. Eggs operculate, with abopercular knob, 44–47 × 20–25. Vitellarium follicular, in two lateral fields extending from anterior part of testes to or slightly beyond anterior edge of ventral sucker; fields length 19.3–26.5% of body length. Pre-vitelline distance 34.6–39.8% of body length; post-vitelline distance 40.3–50.7% of body length. Excretory pore terminal. Vesicle Y-shaped; main stem reaching to ovary.

Remarks. Steringophorus liparidis was originally described from Paraliparis antarcticus Regan, 1914 (Liparidae) caught in the Weddell Sea (Zdzitowiecki 1997). The specimens from M. marmorata examined in this study correspond to the original description by Zdzitowiecki (1997). In particular, the body is 2.2–2.5 times more long than wide, the testes are symmetrically opposed and deeply lobed, the ovary is partly overlapped by the ventral sucker, the anterior border of the vitelline fields is positioned at the level of anterior edge of the ventral sucker or slightly anterior of it, the ventral sucker is slightly larger than the oral one, the caeca are relatively long and end, at least in some specimens, posteriorly to the midlevel of post-testicular area, and there is a knob on an abopercular end of the eggs. The body size and the size of the eggs in our specimens correspond to those of S. liparidis from the type host, but the minimum size of the gonads, both suckers and the pharynx is slightly smaller given than in Zdzitowiecki (1997).