Sternaspis chilensis Díaz-Díaz & Rozbaczylo, 2017, n. sp.

Sternaspis chilensis n. sp.

(Figures 2 A–I, 3A–B; 4)

Sternaspis scutata: Montiel et al., 2004: 62; Rozbaczylo et al., 2006a: 85 –86, figs. 5 l–o; Rozbaczylo et al., 2006b: 98 (non Ranzani, 1817).

Type material. Chile, Magellan Province, Moraleda Channel: Holotype (MNNCH-ANN 15024) 28.5 mm long, 12.0 mm wide, with 23 segments (Fig. 2 A); ten paratypes (MNNCH-ANN 15025–15034), 15.5–35.0 mm long, 10– 15.0 mm wide (45°06’S, 73°38’W, 250 m).

Additonal material. One hundred fifty-three specimens: CIMAR 7 Fiordos cruise: Moraleda Channel, St-6 (43°59,19´S, 73°21,87´W, 179 m), 2 specimens (SSUC 7223); fjord Aysén St-21 (45°24,69´S, 72°51,64´W, 156 m), 2 specimens (SSUC 7224); Costa Channel, St-22 (45°29,56´S, 73°31,03´W, 304 m), 2 specimens (SSUC 7225); Estero Elefantes, St-24 (45°51,50’S, 73°35,41’W, 110 m), 1 specimen (SSUC 7226); Estero Elefantes, St-25 (46°05,01´S, 73°37,82´W, 56 m), 1 specimen (SSUC 7227); Jacaf Channel, St-32 (44°17,76´S, 73°10,78´W, 444 m), 1 specimen (SSUC 7228); seno Ventisquero St-37 (44°31,85´S, 72°40,09´W, 258 m), 19 specimens (SSUC 7229); Puyuhuapi Channel, St-41 (44°53,69´S, 73°02,60´W, 238 m), 1 specimen (SSUC 7230); CIMAR 8 Fiordos cruise: Boca del Guafo, St-1 (43°45,29´S, 74°36,78´W, 240 m), 1 specimen (SSUC 7231); Moraleda Channel, St-8 (44°26,11´S, 73°27,54´W, 380 m), 2 specimens; Moraleda Channel, St-9 (44°41,37´S, 73°30,10´W, 322 m), 3 specimens (SSUC 7232). CIMAR 13 Fiordos cruise: Estero Quitralco, St-31 (45°41’S 73°16’W, 263 m), 5 specimen (SSUC 7549); Moraleda Channel, St-40 (44°49´S, 73°30’W, 192 m), 1 specimen; Moraleda Channel, St- 41 (45°06’S, 73°38’W, 250 m), 6 specimens (SSUC 7550); SW Churrecue Island, St-45 (45°21’S, 73°39’W, 120 m), 7 specimens (SSUC 7551); Costa Channel St-46 (45°31’S, 73°32’W, 300 m), 2 specimens (SSUC 7552); Estero Elefantes St-50 (46°12’S, 73°40’W, 66 m), 1 specimen; Costa Channel, St-76 (45°23’S, 73°30’W, 297 m), 11 specimens (SSUC 7553); fjord Aysén St-79 (45°21’S, 73°05’W, 324 m), 51 specimens (SSUC 7554); fjord Aysén St-80 (45°25’S, 73°01’W, 200 m), 2 specimens (SSUC 7555); fjord Aysén St-81 (45°26’S, 72°53’W, 150 m), 1 specimen (SSUC 7556); Puyuhuapi ChannelSt-87 (44°39’S, 72°44’W, 260 m), 2 specimens (SSUC 7557). CIMAR 17: Estero Reloncaví, St-7C (41°32’54”W, 72°19’48”W, 199 m), 2 specimens (SSUC 7791); Gulf of Ancud, St-20 (42°20’06”S, 72°56’00”W, 249 m), 1 specimen (SSUC 7792); Gulf of Ancud, St-14 (41°59’24”W, 73°00’00”W, 257 m), 1 specimen (SSUC 7793). CIMAR 18 Fiordos cruise: Peligroso Island, St-34 (43°47,8’S, 73°37,7’W, 192 m), 1 specimen (SSUC 7794); Paso del Medio St-76 (45°22,9’S, 73°31,9’W, 315 m), 1 specimen (SSUC 7795). CIMAR 20: St-20 (1 specimen), St-93 (1 specimen).

Description. Holotype (MNNCH-ANN 15024) 28.5 mm long, 12.0 mm wide, with 23 segments (Fig. 2 A); ten paratypes (MNNCH-ANN 15025–15034), mm long, 15 mm wide (10 specimens). Prostomium hemispherical, opalescent, translucent, eyespots absent (Fig. 2 B). Peristomium oval, extended as a wide band over the prostomium, with filiform papillae. Mouth oval, surface densely covered with thick filiform papillae (Fig. 2 C), extending from the base of prostomium to anterior edge of second segment. Integument of segments 1–6 densely covered by cuticular filiform papillae (Fig. 2 A´), papillae less numerous on ventral surface. Genital papillae protrude ventrolaterally from intersegmental groove between segments 7 and 8. Surface of segments seven and eight with many stout cuticular papillae especially near genital papillae; some cuticular papillae with small grains of sediment adhered to bases, genital papillae with long papillae on proximal end and few rounded papillae in middle region (Fig. 2 D, right genital papilla).

First three chaetigers with 15–19 light bronze, widely separated, slightly falcate introvert hooks per bundle (Fig. 2 E). The base and subdistal falcate chaetae end with dark areas. The integument closer to falcate chaetae with dark spots.

Pre-shield region with 7 segments, without fine capillary chaetae but with abundant minute papillae, both dorsally and ventrally, and rows of clusters of short filaments closer to ventro-caudal shield, especially on dorsal surface. Many thin filiform papillae in the inferior margin of the ventro-caudal shield, with capillary chaetae protruding laterally from body wall, with long papillae surrounding the base of the bundle.

Ventro-caudal shield violaceous-gray, with radial ribs and concentric lines distinct (Fig. 2 F), outer margin blue. Fan continuous, with crenulated margin; median notch indistinct. Anterior margins rounded; anterior depression shallow; anterior keels not exposed. Lateral margins medially expanded, reduced posteriorly.

Marginal shield chaetal fascicles include: 11 lateral ones, with 10–14 hirsute capillary chaetae arranged with an inverted C- shaped pattern (Fig. 2 G), pubescence less obvious basally; pubescence fragile, brittle sheath covering chaetal axis (Fig. 2 H). Posterior most fascicle, in the corner of the shield, with long, delicate capillaries between peg chaetae and first bundle of posterior chaetae; posterior shield margin with six fascicles, with 8–10 chaetae arranged in lineal pattern. Peg chaetae short, with a broad base in cross section, emerge from cuticle on a slightly raised mound. Two subtriangular branchial plates diverging (Fig. 2 I). Branchiae abundant; interbranchial papillae long, filamentous (Fig. 3 A).

Variation. Specimens smaller than 15 mm in length with 12–15 bronze chaetae on first three chaetigers and the colour of the shield red (Fig. 3 B, F); specimens with 28–35 mm long, have blue shields (Figs. 3 C–E). Three specimens with anterior keels partially exposed. The number of bronze chaetae of the introvert increases with the size of the specimens. In some specimens the posterior chaetal bundles are covered by a hyaline structure, which seems to encapsulate each bundle.

Remarks. Sternaspis chilensis n. sp. is included in the group of sternaspids having shields with ribs and concentric lines, fan continuous, without a distinct median notch and with margin crenulated. The group includes: Sternaspis rietschi Caullery, 1944 (from Indonesia), Sternaspis thalassemoides Otto, 1821 (from Northeastern Atlantic Ocean and Mediterranean Sea), Sternaspis thorsoni Sendall & Salazar-Vallejo, 2013 (from Indian), Sternaspis piotrowskiae Salazar-Vallejo, 2014 (from the Philippines) and Sternaspis maior Chamberlin, 1919 (from Gulf of California). Sternaspis thalassemoides, S. thorsoni and S. piotrowskiae have shields with posterior corners distinct, such that S. chilensis n. sp. Furthermore, S. chilensis n. sp. differs to S. thorsoni mainly that the posterior margin in the new species is smooth to crenulate whereas it is denticulate in S. thorsoni.

Sternaspis chilensis n. sp. is very similar to S. maior Chamberlin, 1919, both have similar shields, but their main difference would be the development of the shield anterior depression, being deeper in S. maior and shallower in S. chilensis, another differences are peristomium round, without papillae in S. maior and with filiform papillae in S. chilensis, and marginal shield chaetal fascicles in oval pattern in S. maior and an inverted C- shaped pattern in S. chilensis.

Two Spernaspis species have been recorded in South America with S. maureri from Peru, and S. magellanica from the Magellanic biogeographical Province. Two other species have been recorded for relatively nearby areas, in Southern Ocean, S, sendalli and S. monroi (Fig. 4). With the description of S. chilensis n. sp., the knowledge and richness of polychaetes in the South Eastern Pacific Ocean off Chile, in the Magellanic biogeographical Province and for the family is increased. Compared with the other species recorded in the region, S. chilensis n. sp. is different from S. maureri and S, sendalli because both species have the ventro-caudal shield fan with a distinct median notch; and S. monroi have the s hield with ribs; concentric lines indistinct. Sternaspis scutata recorded by Gambi & Mariani (1999) and Bremec et al. (2000) cannot be confirmed, but they might belong to the same species we are describing in this contribution.

Type locality.,Moraleda Channel, Southern Chile (45°06'S, 73°38'W), 250 m depth Southern Chile (45°21’S, 73°05’W), 324 m depth.

Etymology. The species name is derived from the name of the country Chile and the suffix indicates it lives in this region.

Distribution. Austral Chilean channel and fjord region from Estero Reloncaví (41°32’54”W, 72°19’48”W) to Strait of Magellan (53°34’S, 70°04’W), between 50 and 515 m depth.