Eusyllis assimilis Marenzeller, 1875

Fukuda, Marcelo V., Nogueira, João M. M. & Martín, Guillermo San, 2015, Eusyllinae and “ Incertae sedis ” syllids (Annelida: Syllidae) from South America, with a new species from Brazil and a new combination for a Peruvian species, Zootaxa 3936 (4), pp. 507-537 : 516-517

Eusyllis assimilis Marenzeller, 1875

Figures 6–7

Eusyllis assimilis Marenzeller, 1875: 158 –160, pl. 3, fig. 2; San Martín 1984: 82 –83, figs 10, 12A–C; 2003: 114–117, figs 52–53; San Martín & Hutchings 2006: 273 –276, figs 10–12A–C.

Material examined. Project ' REVIZEE '. State of São Paulo— 24º07´S 44º42´W, 101 m: 6 specs (ZUEC-POL 10459), 11 Jan 1998; 24º07’S 45º51’W, 147 m: 34 specs ( MZUSP 1384), 9 Jan 1998; 24º20´S 44º09´W, 258 m: 2 specs ( MZUSP 1383), 10 Jan 1998; 25º36’S 45º13’W, 380 m: 1 spec., 13 Jan 1998.

Project ' Habitats '. 21°22'58"S 40°19'41"W, 52 m: 3 specs ( MZUSP 1392; ZUEC-POL 12927), 5 Mar 2009, and 2 specs ( MZUSP 1393), 21 Jul 2009; 21°42'53"S 40°10'15"W, 98 m: 4 specs ( MZUSP 1391; ZUEC-POL 12725), 9 Mar 2009; 21°43'9"S 40°11'30"W, 73 m: 5 specs ( MZUSP 1390; ZUEC-POL 11040), 9 Mar 2009; 22°3'38"S 40°6'59"W, 89 m: 1 spec. ( MZUSP 1389), 6 Jul 2009; 22°3'45"S 40°9'59"W, 75 m: 1 spec. (ZUEC-POL 10555), 25 Feb 2009; 22°4'14"S 40°6'59"W, 91 m: 1 spec. ( MZUSP 1388), 25 Feb 2009; 22°31'7"S 40°31'32"W, 139 m: 1 spec. ( MZUSP 1387), 23 Feb 2009; 22°46'54"S 41°3'32"W, 77 m: 1 spec. (ZUEC-POL 10552), 22 Feb 2009, and 2 specs ( MZUSP 1386), 2 Jul 2009; 22°52'1"S 40°57'28"W, 92 m: 1 spec. (ZUEC-POL 10464), 22 Feb 2009; 22°57'28"S 40°50'30"W, 142 m: 1 spec., 21 Feb 2009; 23°10'4"S 41°3'6"W, 105 m: 2 specs ( MZUSP 1385), 21 Feb 2009.

Additional material examined. Eusyllis assimilis — Spain, Castellón, Columbretes Islands, N of Columbrete Grande, 45 m: 8 specs ( MNCN 16.01/8640), coll. Campanha Fauna III, 12 Jul 1994, det. G. San Martín; W of Columbrete Grande, 65–67.8 m: 1 spec. ( MNCN 16.01/8645), coll. Campanha Fauna IV, 18 Jul 1996, det. G. San Martín. Australia, Western Australia, Kalbarri, Red Bluff, rocky shore (27°42'S 114°09'E), 3 m: 5 specs (AM W28941), coll. J.K. Lowry, 10 Jan 1984, det. G. San Martín. Tasmanian Sea, Taupo Seamont (33°16'51"S 156°09'09"E), 244 m: 17 specs (AM W28925), coll. J.K. Lowry and party, R/V 'Franklin', 0 2 May 1989, det. G. San Martín.

Description. Relatively small-sized body, largest specimens examined 3.15 mm long, 0.56 mm wide, with 35 segments. Palps ovate, divergent, basally fused. Prostomium ovate with 2 pairs of eyes in trapezoidal arrangement and 1 pair of anterior eyespots ( Fig. 6 A); lateral antennae inserted on anterior margin of prostomium; median antenna inserted more posteriorly, on middle of prostomium, about twice as long as lateral antennae; nuchal organs as one pair of broad semi-circular rows of cilia close to posterior border of prostomium ( Fig. 7 A, C). Peristomium shorter than subsequent segments; dorsal peristomial cirri about same length as median antenna, ventral peristomial cirri approximately same size as lateral antennae. Dorsal cirri of chaetiger 1 longer than remaining dorsal cirri, up to twice as long as dorsal peristomial cirri; remaining dorsal cirri alternating long cirri, as long as dorsal peristomial cirri, and short cirri, as long as ventral peristomial cirri, dorsal cirri progressivelly shorter towards posterior body. Antennae, peristomial, some anterior body dorsal cirri and anal cirri irregularly articulated distally ( Figs 6 A; 7A). Ventral cirri shorter than parapodial lobes, ovate on anterior body ( Fig. 7 B), progressively pyriform towards posterior body. Parapodial lobes conical. Anterior parapodia with up to 30 falcigers each, midbody with 9–15, posterior parapodia with ~5 falcigers each; shafts of falcigers subdistally spinulated, with straight tips ( Figs 6 B–C; 7E–J); parapodia with 1–4 dorsalmost falcigers with thinner shafts, blades longer and thinner than remaining falcigers; blades of these longer falcigers bidentate, teeth of even size throughout, and up to ~42 Μm long on anterior body, ~25 Μm long on mid- and posterior body ( Figs 6 B; 7E, H); remaining falcigers with blades with short spinulation; blades bidentate, teeth of even size on anterior body ( Figs 6 B; 7F), subdistal tooth progressively larger and slightly hooked towards posterior body ( Figs 6 C; 7G, I–J); blades 25–15 Μm long on anterior body and midbody, 17–12 Μm long on posterior body. Dorsal simple chaetae only present on posterior body, thinner than shafts of falcigers, subdistally spinulated, unidentate ( Fig. 6 D); ventral simple chaetae only present on posterior body, slightly spinulated subdistally, bidentate, subdistal tooth larger than distal one ( Fig. 6 E). Anterior parapodia with 2 aciculae each, one of them subdistally bent, with rounded tip, another straight, distally pointed ( Fig. 6 F); midbody and posterior parapodia with only 1 acicula each, thicker than those of anterior body chaetigers and more pronouncedly curved, with rounded tip ( Fig. 6 G). Pygidium with pair of elongate anal cirri, up to same length as dorsal peristomial cirri. Pharynx through ~6 segments, opening surrounded by 10 large papillae; large, conical central tooth close to opening and complete or incomplete trepan formed by 25–45 denticles, more evident on ventral half ( Figs 6 A; 7A–B, D); proventricle through ~8–9 segments, with 45–50 muscle cell rows ( Fig. 6 A).

Remarks. The number of denticles in the trepan may vary and, usually, is difficult to assess, as these structures are tiny and only visible in dissected specimens, or in those with fully everted pharynx. Brusa et al. (2013) report that some specimens from the Mediterranean Sea and the Pacific Ocean may present a complete trepan, as observed in some of our specimens ( Fig. 7 D).

Type locality. Italy—around Triest (Adriatic Sea).

Distribution. Pacific Ocean: New Zealand; Australia; Japan. Indian Ocean: Australia. Mediterranean Sea. Atlantic Ocean: East Atlantic Ocean, from English Channel to South Africa; Northwest Atlantic Ocean, from Canada to México ( San Martín 2003; San Martín & Hutchings 2006; Brusa et al. 2013). First occurrence in South American coasts.

Figures

FIGURE 6. Eusyllis assimilis. (A) anterior body, dorsal view; (B) falcigers, anterior and midbody; (C) falcigers, posterior body; (D) dorsal simple chaeta; (E) ventral simple chaeta; (F) aciculae, anterior body; (G) acicula, posterior body. Scale bars: A = 200 µm; B – G = 10 µm.

FIGURE 7. Eusyllis assimilis, SEM. (A) anterior body, dorsal view; (B) anterior body, ventral view; (C) detail of prostomium and peristomium, dorsal view; (D) pharynx opening, showing tooth and trepan; (E) dorsalmost falciger, anterior to midbody; (F) intermediate falciger, anterior to midbody; (G) ventralmost falciger, anterior to midbody; (H) dorsalmost falciger, mid- to posterior body; (I) intermediate falcigers, midbody; (J) ventralmost falciger, mid- to posterior body. Scale bars: A – B = 100 µm; C – D = 50 µm; E – I = 5 µm; J = 10 µm.