Sternaspis aff. nana Zhadan et al., 2017

Craveiro, Nykon & Filho, José Souto Rosa, 2021, Record of the non-indigenous species Sternaspis aff. nana Zhadan, Tzetlin & Salazar-Vallejo, 2017 (Annelida: Sternaspidae) in the Southwest Atlantic Ocean, Papéis Avulsos de Zoologia 61, pp. 1-8 : 2-5

Sternaspis aff. nana Zhadan et al., 2017 ( Figs. 1-3 )

Sternaspis nana Zhadan et al., 2017: 79-82 , fig. 3-5; Salazar-Vallejo, 2017: 4.

Examined material

Two specimens collected at the external area of the Suape Harbor, Pernambuco, Brazil (08°23′37.6″S, 34°57′19.3″W), mud substrate, 15 m depth, 16-II-2018, MOUPFE 003.

Description

The morphology of the two specimens agree with the descriptions of Sternaspis nana by Zhadan et al. (2017), but due to the impossibility of observing the gametes due to the small size of the specimens, the morphological differences of the shield and the amount of papillae in the species found here in Brazil, we classify the specimens as Sternaspis aff. nana . Our specimens seem to be more rugose than the type specimens and the posterior shield margin has a round projection, as opposed to having a sharp one, or none as in the type species (Zhadan et al., 2017).

Complete specimens with 26 segments without clear borders (Body: 2.20 mm long, 0.82 mm wide). Body hourglass-shaped, introvert narrower than abdomen, constriction between segments 5 and 6. Body wall semi-transparent; introvert colorless, abdomen creamish-white with abundant minute papillae evenly distributed, both dorsally and ventrally, and papillae cirriform ( Fig. 1C ). Intestine and ventral nerve are visible through body wall ( Figs. 1 A-B, 2B).

First three chaetigers with 13 falcate hooks per bundle, not subdistally expanded, hooks transparent ( Fig. 3 ). Genital papilla small, digitate, protruding ventrally from sixth chaetiger ( Fig. 1A, C ). Pre-shield region with 7 segments, with 1-2 fine capillary chaetae laterally in some segments ( Fig. 2A ).

Ventrocaudal shield soft, smooth, papillae not observed and no sediment particles attached. Left shield plate 0.21 mm long, 0.25 mm wide. Shield plates nearly square. Ribs and concentric lines not visible. ( Fig. 2B ). No visible borders between lateral plates and fan ( Fig. 2B ). Anterior keels visible, suture well-defined, visible throughout shield ( Fig. 2B ).

Bundles of shield chaetae with eight lateral shield chaetae, ovally arranged and five posterior fascicles each containing only one thick chaeta, slightly curved ( Fig. 2B ). Peg-chaetae not observed. Branchial filaments arranged in discrete branchial plates.

Distribution

Type locality: Pacific Ocean – Nha Trang Bay, South China Sea (15-40 m depth). New occurrence: Atlantic Ocean – Suape Harbor Area, Pernambuco, Brazil (15 m depth).

Remarks

On the Brazilian coast, only one species of Sternaspidae has been recorded to date, Petersenaspis capillata (Nonato, 1966) [= Sternaspis capillata Nonato, 1966 ], which is native and found in Brazilian waters (Nonato, 1966). The morphology of our specimens is similar to the original description of Sternaspis nana by Zhadan et al. (2017) and resembles S. papillosa Zhadan et al., 2017 and S. africana Augener, 1918 . Sternaspis aff. nana markedly differs from these species by combined features related to hooks of introvert, papillae pattern and ventral shield characteristics.

In S. aff. nana there are 13 falcate hooks per bundle in the introvert chaetigers, while the number of falcate hooks per bundle is 16 in S. papillosa and 15-20 in S. africana . Sternaspis aff. nana has abundant micropapillae and regular rows of long cirriform papillae along the body. In S. papillosa digitiform papillae are organized in more or less regular transverse rows, and in S. africana minute papillae are densely present on segments 7 and 8, but evenly spaced in other segments. Ventral shield in S. aff. nana is without ribs and papillae, usually without concentric lines, with eight lateral shield chaetae in oval pattern, and six posteri- or shield chaetae consisting of a single thick chaeta in slightly curved pattern. In S. papillosa , ventral shield is with underdeveloped ribs and concentric lines, covered by fine papillae, with nine lateral shield chaetae in oval pattern, and five posterior shield chaetae in oval pattern; in S. Africana , ventral shield is with ribs and concentric lines barely visible, without papillae, with nine lateral shield chaetae in oval pattern, and five posterior shield chaetae in slightly curved pattern. The morphological features remarks are resumed in Table 1.

Figures

Figure 1. Sternaspisaff.nana collected in Suape Harbor (Pernambuco,Brazil).(A)Ventralview.White arrows showing genital papillae;(B) Dorsal view;(C) Detailed ventral view of abdomen (pre-shield).Black arrows showing long filiform papillae and white arrows showing genital papillae.

Figure 2. Sternaspis aff. nana collected in Suape Harbor (Pernambuco,Brazil).(A) Detailed view of the margin of abdomen wall.White arrows showing pre-shield capillary chaetae;(B)Ventrocaudalshields.Black dottedshowing shield plates nearly square.White arrows showing fascicles containing only one thickchaeta each, black arrow showing fan corners extended.

Figure 3. Sternaspis aff.nana collected in Suape Harbor (Pernambuco,Brazil).Detail of Introverthooks of the first chaetiger.