Westheidesyllis splendida, Fukuda & Paiva, 2024

Rodolfo Leandro Nascimento, Marcelo Veronesi Fukuda & Paulo Cesar de Paiva, 2024, Two new incertae sedis syllids (Annelida: Syllidae) from Brazilian oceanic islands, European Journal of Taxonomy 925 (1), pp. 46-66 : 55-62

Westheidesyllis splendida sp. nov.

urn:lsid:zoobank.org:act:D172737A-CC06-4DAB-B6E7-F82FDBD4A8E2

Figs 2–7

Diagnosis

Westheidesyllis with parapodial glands.

Etymology

This species is named in honor of its type locality, the Rocas Atoll , a splendid place.

Type material

Holotype

BRAZIL • Rocas Atoll ; 3.8805091° S, 33.8780718° W; depth 1 m; 16 Oct. 2000; on coralline sand; MZUSP 6098 .

Paratypes

BRAZIL • 4 specs; same collection data as for holotype; MZUSP 6099 .

Additional material examined

BRAZIL • 135 specs; same collection data as for holotype; MNRJP • 57 specs (four mounted for SEM); Piscina das Âncoras; 3.8638266° S, 33.8263897° W; depth 1 m; 16 Oct. 2000; on coralline sand; MNRJP • 6 specs; “along of the Rais”; depth 1 m; 23 Oct 2000; on coralline sand; MNRJP.

Description

Small-sized, slender bodies, longest specimen 2.6 mm long, 0.25 mm wide, with 32 chaetigers; specimens preserved in ethanol without pigmentation. Palps subtriangular, basally juxtaposed for ~¼ their length, distally rounded, slightly shorter than prostomium ( Figs 2A , 3 , 4A , 5A, C–D ). Prostomium ovate to subpentagonal; eyes absent; lateral antennae inserted close to anterior margin of prostomium, about half length of median one; median antenna inserted on midline of prostomium, almost four times as long as palps and prostomium ( Figs 3 , 5A–D ). Two large ciliated nuchal organs between prostomium and peristomium ( Fig. 5B ). Peristomium distinct, shorter than subsequent segments; dorsal peristomial cirri about same length or slightly shorter than median antenna ( Fig. 3 ); ventral peristomial cirri almost half length of dorsal ones. Ciliated pits transversally arranged on midline of peristomium and first chaetiger, from the second to at least chaetiger 15 ( Fig. 5B, G ), ciliated pits distributed dorsally close to the base of dorsal cirri. Dorsal cirri alternating in length, on chaetiger 1 about four times as long as width of segment ( Fig. 3 ); on chaetiger 2 absent; on chaetigers 3, 5 and 7, shorter than width of corresponding segments; on chaetigers 4, 6, 8 and 9, three to four times as long as width of corresponding segment ( Fig. 3 ); from chaetiger 10 onwards, dorsal cirri with regular alternation in length, short cirri shorter than corresponding segment, long cirri three to five times as long as corresponding segment ( Fig. 4D ). Antennae, peristomial and dorsal cirri with cirrophores ( Figs 3 , 4B, D , 5A–D, G ). Ventral cirri digitiform, shorter than parapodial lobes, inserted distally, extending beyond parapodial lobes, shorter towards posterior body ( Figs 4A–B , 5H ). Parapodial lobes elongated, rectangular, slightly bilobed ( Figs 3 , 4B ); parapodial glands presents after proventricle, close to bases of parapodial lobes, with rounded to subpentagonal granules ( Figs 2A–C , 4B–D ). Parapodia with three falcigers each throughout; shafts of falcigers smooth, homogomph, with irregular, usually quadrilobate acute tips ( Figs 6A–C , 7F ); blades bidentate, with teeth about same size or distal tooth slightly larger throughout; blades spinulated, with short and thin spines ( Figs 6A–C , 7A–B, F, J ); blades varying in length on dorsalmost, intermediate and ventralmost chaetae, with 6 µm, 12 µm and 8 µm on anterior parapodia ( Figs 6A , 7A–B ); 7 µm, 13 µm and 10 µm long on midbody ( Figs 6B , 7E–F ); and 5 µm, 12 µm and 9 µm on posterior body ( Figs 6C , 7H–J ). Dorsal simple chaetae present from chaetigers 3–4, tapering distally, with rounded tip, subdistally spinulated on anterior body ( Figs 6D , 7C–D ), slightly sigmoid towards posterior body ( Figs 6E–F , 7G, K ). One acicula per parapodium throughout, distally inflated, hollow ( Fig. 6G ), with tip protruding from parapodial lobe ( Fig. 4B ). Pharynx through about 4 segments ( Figs 2A , 3 ), with conical to rhomboidal pharyngeal tooth located on anterior rim, surrounded by 10 soft papillae; proventricle through around 2.5 segments, with 14–15 muscle cell rows ( Figs 2A , 3 ). Pygidium rounded ( Figs 4C , 5H ), with pair of cirri about same length of long posterior body dorsal cirri.

Remarks

None of the specimens of Westheidesyllis splendida sp. nov. examined in this study showed cilia at the bases of the dorsal cirri or transverse ciliary bands on the segments, as observed in other species of the genus. However, using scanning electron microscopy (SEM), a set of pits was observed, which are usually the location where these cilia are projected. These pits were observed at the bases of the dorsal cirri, located almost above the parapodial glands and arranged transversely, more or less in line, on anterior segments and peristomium.

The new species is similar to W. corallicola , which was originally described from Hainan Island in South China and later found in Australia (New South Wales and Lizard Island), all in the Pacific Ocean. Both species lack eyes, share the overall body morphology and have similar compound chaetae. However, there are several differences between them. For instance, W. splendida sp. nov. lacks eyespots, has the median antenna inserted medially on the prostomium, aciculae that are distally hollow with tips protruding from the parapodial lobes, a proventricle extending for ~2.5 segments, and internal glands at the bases of the parapodia. Conversely, W. corallicola has eyespots, the median antenna inserted posteriorly on the prostomium, aciculae distally knobbed but not hollow nor protruding from the parapodial lobes ( Ding & Westheide 1997: fig. 6d–e, i), a proventricle extending for about 1.5 segments ( Ding & Westheide 1997: fig. 6a), and lacks internal glands ( Ding & Westheide 1997; San Martín & Hutchings 2006). Additionally, specimens of W. splendida examined herein showed signs of cilia and ciliary pits indicating differences in the ciliation pattern to that found in W. corallicola , that has tufts dorsally and ventrally located close to the bases of the parapodia and on the pygidium ( Ding & Westheide 1997).

As mentioned above, Westheidesyllis splendida sp. nov. is the only known species of the genus where glands have been observed. Although outside the scope of the present paper, some ideas could be shed about functions of these glands in Westheidesyllis . The presence of glands, especially those associated to the parapodia, is commonly reported in interstitial species on soft-bottom substrates ( Worsaae et al. 2021). Accordingly, the glands now observed could be related to some adhesive ability to deal with sediment grains, which could provide greater stability to the substrate, or enhance camouflage, and reduce palatability, both potentially decreasing predation risk. Indeed, various specimens of W. splendida were covered in small grains across the body. Also, glands could be associated to reproduction processes in the animals, as has been indicated in other syllids ( Haswell 1920), although, to our knowledge, no information on the reproduction of Westheidesyllis is currently known. The parapodial glands in W. splendida sp. nov. are best observed after methyl green staining ( Fig. 2A–B ), but they can be relatively easily visualized without the aid of this technique ( Fig. 2C ).

Type locality

Rocas Atoll.

Distribution

Atlantic Ocean: Rocas Atoll , Brazil.

Figures

Fig. 2. Westheidesyllis splendida sp. nov., paratype (MZUSP 6099). A. Whole body of methyl green stained specimen, dorsal view. B. Midbody of methyl green stained specimen, white arrows showing parapodial glands, black arrows showing digestive tube content.C. Midbody parapodial glands on a not stained specimen. Scale bars: A = 0.22 mm; B = 0.15 mm; C = 0.1 mm.

Fig. 3. Westheidesyllis splendida sp. nov., paratype (MZUSP 6099). Anterior body, dorsal view. Scale bar = 0.22 mm.

Fig. 4. Westheidesyllis splendida sp. nov., paratype (MZUSP 6099). A. Anterior body, ventral view. B. Midbody parapodium, with dorsal cirrus and parapodial glands, dorso-lateral view. C–D. Midbody and posterior end, dorsal view. Scale bars: A, C–D = 0.2 mm; B = 15 µm.

Fig. 5. Westheidesyllis splendida sp. nov., non-type specimen (MNRJP), SEM. A. Anterior body, dorsal view. B. Details of prostomium, peristomium, and nuchal organs, dorsal view. C. Anterior body of specimen with retracted nuchal organs, dorsal view. D. Anterior end, dorsal view. E–F. Details of retracted ciliated nuchal organs. G. Anterior segments showing details of ciliary pits, dorsal view. H. Posterior end, dorsal view. Red arrows pointing to ciliated nuchal organs, white arrows pointing to ciliary pits. Scale bars: A, C = 50 µm; B, G = 10 µm; D, H = 20 µm; E = 2 µm; F = 5 µm.

Fig. 6. Westheidesyllis splendida sp. nov., paratype (MZUSP 6099). A–C. Falciger chaetae, anterior, mid- and posterior body, respectively. D–F. Dorsal simple chaetae, anterior, mid- and posterior body, respectively. G. Acicula. Scale bar = 6 µm.

Fig. 7. Westheidesyllis splendida sp. nov., non-type specimen (MNRJP), SEM. A–B. Falciger chaetae, anterior body. C–D. Dorsal simple chaetae, anterior body. E–F. Falciger chaetae, midbody. G. Dorsal simple chaeta, midbody. H–J. Falciger chaetae, posterior body. K. Dorsal simple chaeta, posterior body. Scale bars: A, C, F = 5 µm; B, D, G, I–K = 2 µm; E, H = 10 µm.