Syndesmis selknami, Brusa & Montes & Marcotegui & Martorelli, 2017

Brusa, Francisco, Montes, Martin M., Marcotegui, Paula & Martorelli, Sergio R., 2017, Two new species of Syndesmis (Platyhelminthes, Rhabdocoela, Umagillidae) from the sea urchin Pseudechinus magellanicus (Echinodermata, Echinoidea) in the Southwestern Atlantic Ocean, International Journal for Parasitology: Parasites and Wildlife 6 (2), pp. 54-58 : 55-56

3.1. Syndesmis selknami n. sp.

( Figs. 1 — 2 ).

3.1.1. Morphology

Worms 0.54 — 0.81 mm (0.69 ± 0.07, n = 8) long, 0.35 — 0.47 mm (0.43 ± 0.02, n = 8) maximum width at level of middle part of body ( Figs. 1 and 2 ). Epidermis ciliated and epithelial cells taller in anterior region of body. In the anteriordorsal region, there are invaginations of the body wall forming sensory pits ( Fig. 2F ), internally associated with projections on the brain. Mouth anteroventral, opening into a doliiform pharynx. Pharynx 62.5 — 75 M m (67.5 ± 6.94, n = 8) in diameter. Vacuolated cells in the transition region between pharynx and intestine ( Fig. 2E ).

Paired testes on both sides of anterior body midline ( Fig. 1 ), slightly lobulated, extending from posterior half of pharynx to posterior first 1/3 of body length, slightly overlapping vitellaria posteriorly ( Fig. 1 ). The ejaculatory duct ( Fig. 2C ) connects the testes with a small seminal vesicle connected with the stylet by a narrow duct. Long penis stylet, beginning at funnel-like structure and projecting into male antrum, 190 — 250 M m (221.6 ± 30.13, n = 3) long ( Fig. 2D ). Male antrum muscle walls with circularly oriented, opening into a common genital atrium. Genital pore at posterior tip of body.

Massive vitellaria overlapping to posterior region of testes, slightly lobulated, fan-like. Paired ovaries between vitellaria and filament glands, overlapping both. They are lobulated. Filament glands grouped in the last part of the body ( Fig. 2 ).

Vitellaria join ovaries and enter the seminal receptacle at its anterior-most portion. Seminal receptacle ( Fig. 2B and C ) formed by spherical anterior portion, becoming elongated posteriorly, lumen with sperm. Vagina gradually wider distally, reaching a common genital atrium. Uterus ventrally, about 2/3 of the body length. Entry of uterus into common genital atrium ventral to entrances of male antrum and vagina. Filament glands occupying almost whole posterior third of body. Mature egg capsules ovoid, with the opening area forming by small plates ( Fig. 2B and C ). Eggs 100 — 132.5 M m (117.5 ± 13.38, n = 4) long, 62.5 — 85 M m (68.125 ± 11.25, n = 4) wide, brown, with a long filament on one pole; filament long and in distal part rolled on itself ( Figs. 1 and 2A ); in some specimens, filament straight and thick and with distal region threaded with thickening at tip.

3.1.2. Etymology This species is named in honor of the Selk'nam or Onas tribe who lived in the region where this species was found.

3.1.3. Study material

Eight whole mount specimens stained with Gill's Hematoxylin, three specimens cleared in polyvinyl-lactophenol and two specimens serially sectioned at 4- M m thick stained with Masson's trichrome method.

3.1.4. Specimens deposited

The studied specimens have been deposited at the Invertebrate Collection of Museo de La Plata. Holotype MLP-He 7266, whole mount specimen stained with Gill's Hematoxylin. Paratype MLP-He 7268, whole mount specimen stained with Gill's Hematoxylin. MLP-He 7273, sagittal section specimens stained with Masson's trichrome method .

3.1.5. Localities

Bahía Camarones (44 Ǫ 51, 2.09́S, 65 Ǫ 40, 52́W) and Beagle Channel (54 Ǫ 10, 2.4́S, 65 Ǫ 30, 0.8́W) .

3.1.6. Prevalence of infection 47% (17/36 urchins).

Figures

Fig. 1. Schematic reconstruction of Syndesmis selknami n. sp. in dorso-ventral view. Abbreviations:eg, egg; f, filament; fg, filament glands; ov, ovary; st, stylet; t, testes; vit, vitellaria.

Fig. 2. Syndesmis selknami n. sp.A, D, whole mount preparations.B, C,E, F, sagittal sections of the body. Abbreviations:b, brain; ed, ejaculatory duct; eg, egg; f, filament; fg, filament glands; i, intestine; ov, ovary; sp, sensory pit; sr, seminal receptacle; t, testes; u, uterus; vc, vacuolar cells; vit, vitellaria.The white arrow heads marks the proximal part of the stylet and black arrow heads mark the distal part.