Prosphaerosyllis modinouae Neal & Paterson, 2020

Neal, Lenka, Paterson, Gordon L. J., Blockley, David, Scott, Ben, Sherlock, Emma, Huque, Cate & Glover, Adrian G., 2020, Biodiversity data and new species descriptions of polychaetes from offshore waters of the Falkland Islands, an area undergoing hydrocarbon exploration, ZooKeys 938, pp. 1-86 : 1

Prosphaerosyllis modinouae Neal & Paterson sp. nov. Figures 5 , 6 , 7 , 8 , 9 , 10 , 11

Materials.

Sample 63MFA, 448 m, -49.2457310, -59.1254934, coll. 17/03/2012, ind. 1, holotype (NHM.2018.25100). Sample 21MFC, 445 m -49.2866453, -59.1130539, coll. 16/04/2012, ind. 1, paratype (NHM.2018.24236). Sample 28MFB, 451 m, -49.3044189, -59.0852225, coll. 23/04/2012, ind. 1, paratype (NHM.2018.24386). Other materials: Sample 15MFB, 454 m, -49.2686572, -59.1133764, coll. 16/04/2012, ind. 1, NHM.2018.24080. Sample 25MFA, 447 m, -49.3050428, -59.1677492, coll. 16/04/2012, ind. 1, NHM.2018.24302. Sample 25MFC, 438 m, -49.3050428, Longitude: -59.1677492, coll. 16/04/2012, ind. 1, NHM.2018.24324. Sample 35MFC, 450 m, -49.3221858, -59.0573711, coll. 15/04/2012, ind. 1, NHM.2018.24498. Sample 40MFA, 450 m, -49.3403947, -59.0845558, coll. 23/04/2012, ind. 1, NHM.2018.24605.Sample 41MFA, 439 m, -49.3401736, -59.0570275, coll. 14/04/2012, ind. 1, NHM.2018.24637. Sample 44MFB, 429 m, -49.3585975, -59.1117606, coll. 14/04/2012, ind. 1, NHM.2018.24719. Sample 60MFC, 450 m, -49.2545270, -59.0494527, coll. 19/03/2012, ind. 1, NHM.2018.25062. Sample 64MFC, 447 m, -49.2455380, -59.1060962, coll. 18/03/2012, ind. 1, NHM.2018.25127. Sample 69MFC, 442 m, -49.2887900, -59.1005700, coll. 19/03/2012, ind. 1, NHM.2018.2521. Comparative materials: Prosphaerosyllis kerguelensis : Kerguelen Islands (off Cumberland Bay), 232 m, -48.750000, -69.233333, holotype, BMNH.85.12.1.155. Sphaerosyllis palpopapillata : Antarctic Peninsula, 300 m, -63.27777778, -63.72166667, holotype, ZMH P-20751.

Description.

Holotype (NHM.2018.25100) a complete, very small, slender specimen, 4.5 mm long and 0.5 mm wide (at mid-body) for 31 chaetigers. Paratype (NHM.2018.24236), complete specimen 2.8 mm long and 0.4 mm wide (at mid-body) for 31 chaetigers. Paratype (SEM specimen, NHM.2018.24386) complete specimen 3.5 mm long and 0.4 mm wide (at mid-body) for 30 chaetigers. Paratype (SEM specimen, NHM.2018.24236) incomplete specimen 1.2 mm long and 0.25 mm wide for 12 chaetigers. Integument of body appearing smooth under light microscopy (Fig. 5a ), upon staining (Fig. 6a-d ) and under SEM (Fig. 7a, c, f ) sparse papillation detected dorsally with two alternating longitudinal rows of digitiform papillae on each side of the body (= 4 rows in total); palps with some diffused small papillae (Fig. 8b ); papillation on body venter diffused (Fig. 6d );parapodial with few tiny papillae (Fig. 9d ); slender and elongated lateral body papillae observed in-between parapodia (Fig. 9b, c ). Colour in alcohol pale yellow, no pigmentation observed (Fig. 5a ).

Prostomium short, wider than long (Figs 5b, c ; 8a ). Three antennae present (Figs 7d ; 8a ), all pyriform and very small (difficult to observe under stereo microscope); median antenna positioned near posterior margin of prostomium, ca. 30 µm long; lateral antennae positioned lateromedially on prostomium, smaller than median antenna, ca. 25 µm long (Figs 7d ; 8a ).

Palps very short, almost entirely obscured by prostomium in dorsal view (Figs 5b, c ; 7a-d ; 8a ) with only their lateral margins visible in dorsal view; fully fused along their length; provided with some small papillae (Fig. 8b ). Two pairsof large red eyes present (Figs 5b-d ; 8a ), in trapezoid arrangement, with anterior and posterior pair close together (almost appearing as a single eye), anterior pair cup-shaped, posterior pair circular; presence of additional eyespots not confirmed.

Proventricle starts between chaetigers 3-4 and ends between chaetigers 6-7, with ca. 20 muscle rows (Figs 5b ; 6b ). First segment achaetous; with small pair of tentacular cirri, ca. 20 µm long, pyriform (similar to antennae) (Figs 7d ; 8a ). Pharynx everted in paratype (NHM.2018.24236) (Fig. 7c, d ), without terminal papillae, pharyngeal tooth far from anterior margin.

Parapodia uniramous, short but distinct, conical (Fig. 9a-c ). Dorsal cirri in all chaetigers, including chaetiger 2 (Figs 7e ; 8a ) (missing in some parapodia due to damage); dorsal cirri in anterior chaetigers small (but easy to observe, ca. 40 µm in length, Fig. 5e ), similar in form to tentacular cirri and antennae, becoming more elongated in posterior chaetigers (ca. 55 µm long, Fig. 5f ). Ventral cirri as extremely slender cirriform structures, inserted near the base of neuropodia (Fig. 9a-c ), becoming progressively longer posteriorly.

Chaetae often missing (broken off). One simple dorsal chaeta commonly observed (Fig. 10a ), present from chaetiger 1; straight and smooth; increasing in size throughout body measuring 30 µm in anterior parapodia, 85 µm in mid-body parapodia and 110 µm in some posterior parapodia (Fig. 10b ). Simple ventral chaeta observed only in posteriormost parapodia, slightly sigmoid and smooth (Fig. 10c ). Other chaetae compound falcigers (Fig. 10d-g ); ca. six per fascicle; all blades unidentate and serrated to greater (Fig. 10d, g ) or lesser degree (Fig. 10e, f ). Blades of falcigers of varying lengths with greatest length difference between dorsalmost (Fig. 10d ) and ventral most (Fig. 10e ) chaetae in anterior parapodia, this difference becomes particularly pronounced in mid-body parapodia, where long dorsalmost chaeta (Fig. 10f ) bears particularly short blade (as ratio to length of its shaft); length of blades 5-13 µm (total chaetal length 35-60 µm) in anterior chaetigers; 5-13.5 µm (total chaetal length 75-100 µm) in mid-body chaetigers and 12-20 µm (total chaetal length ca.100 µm) in posterior chaetigers (Fig. 10g ). Acicula in anterior and posterior chaetigers mostly solitary, acuminate (Figs 5g, h ; 9e ).

Pygidium broad, rounded, pygidial cirri not observed in any specimens examined (Fig. 5a ).

Remarks.

Falkland Island specimens were assigned to genus Prosphaerosyllis San Martín, 1984 based on morphological characters only as no reproductive specimens were observed. San Martín (2005) emended the generic diagnosis and further distinguished Prosphaerosyllis from the similar genus Sphaerosyllis , however here we provide a comparison for species in both genera with the type locality inthe southern waters because not all species have been revised. Sphaerosyllis antarctica , S. hirsuta , S. sublaevis , S. capensis , S. dubiosa , S. lateropapillata uteae and Prosphaerosyllis kerguelensis (holotype BMNH.85.12.1.155 examined as part of this study) can be easily distinguished from the Falkland Island species due to absence of dorsal cirrus on chaetiger 2. Of species with a dorsal cirrus on chaetiger 2 present ( S. semiveruccosa , P. joinvillensis , P. capensis chilensis , S. brandhorsti and P. brachycephala ) the new species can be easily distinguished by having small antennae and short palps (often with only their lateral margins observable in dorsal view, otherwise mostly obscured by prostomium).

Falkland Islands species is most similar to P. isabellae De Nogueira, San Martín & Amaral, 2001 described from intertidal depths in Brazil in having short antennae and a sparse distribution of body papillae. However, other than length of the palps, P. modinouae sp. nov. can be further differentiated by having all falcigerousblades serrated (these are smooth from mid-body chaetigers in P. isabellae ), in lacking iridescent inclusions in the dorsal cirri and in the dorsal cirri becoming elongated throughout the body in P. modinouae sp. nov. There also appear to be greater differences in length of falcigerous blades in P. modinouae sp. nov. (Fig. 10d-g ) compared to P. isabellae (see DeNogueira et al. 2001; Fukuda et al. 2009). We also suggest that Brazilian specimens from bathyal depths assigned to P. isabellae by Fukuda et al. (2009) may in fact represent a different species, even more closely aligned to P. modinouae sp. nov. This suggestion is based mainly on much deeper distribution (down to 650 m) reported by Fukuda et al. (2009) compared to 4-7 m depth at the type locality of P. isabellae , which was also reported to be associated with coral colonies ( De Nogueira et al. 2001). However, specimens of P. isabellae were not available for examination as part of this study.

Another similar species is Sphaerosyllis palpopapillata Hartmann-Schröder & Rosenfeldt, 1992 described from the Antarctic Peninsula, 300 m depth. Unfortunately, the description and drawings provided by Hartmann-Schröder and Rosenfeldt (1992) are of limited value. Therefore, the holotype (ZMH P-20751) was loaned from Zoologisches Museum Hamburg and photographed here for the first time (Figs 11a ; 12a-f ). The holotype, which is the only known specimen of this species, was found to be a small anterior fragment, with structures such as the antennae now missing andsome chaetae broken off. As a result, S. palpopapillata remains a poorly known species, until new material from the type locality becomes available. The holotype (ZMH P-20751) (Fig. 11a ) is similar to P. modinouae sp. nov. (Fig. 11b, c ) in the form of the palps and also possesses the elongated lateral body papillae (Fig. 12d ), which were not reported by Hartmann-Schröder and Rosenfeldt (1992), although the rows of dorsal papillae were not confirmed by us. The main differences observed were the form and length of ventral cirri, which are distinctly longer and slender in S. modinouae sp. nov. (Figs 9b, c ; 12b, c ). While both species have unidentate falcigers, their blades in S. palpopapillata are shorter (6-7 µm) and similar in size where observed (Fig. 12e, f ), but in the new species their lengths are more variable (Fig. 10d-g ) as already discussed in comparison with P. isabellae . Furthermore, the image provided in the original description ( Hartmann-Schröder and Rosenfeldt 1992: fig. 34) suggests that antennae in S. palpopapillata are large, not small as in the new species or in P. isabellae . Unfortunately, as already mentioned, the antennae have since been lost in the holotype of S. palpopapillata and this character cannot be verified.

The lack of detailed descriptions and reliable drawings/images of the known species from the southern waters, complicate the efforts in describing new species. While we believe that observations provided in this study justify the establishment of a new species from the Falkland Islands material, the known species are clearly in need of revision. However, such an undertaking is beyond the scope of this study.

Etymology.

This species is dedicated to Yvett Modinou, a passionate science communicator, who inspired the fourth author (BS) to join the NHM London.

Distribution.

This species is only known from its type locality, North Falklands Basin, ca. 450 m depth.

Figures

Figure 5. Prosphaerosyllis modinouae sp. nov. (paratype, NHM. 2018.24386) a complete specimen in dorsal view b detail of anterior end in dorsal view c detail of prostomium and palps in dorsal view d detail of eyes e anterior dorsal cirrus f posterior dorsal cirrus g posterior parapodium (arrow marking acicula) h detail of acicula. Scale bars: 1000 µm (a); 100 µm (b, c); 25 µm (e, f); 50 µm (g).

Figure 6. Prosphaerosyllis modinouae sp. nov. (holotype, NHM. 2018.25100; specimen Shirla-stained) a complete specimen in dorsal view b pattern of dorsal body papillae (= darkly stained dots) in anterior end c pattern of dorsal body papillae (= darkly stained dots) in mid-body segments d pattern of ventral papillae (= darkly stained dots). Scale bars: 500 µm (a); 200 µm (b, d).

Figure 7. Prosphaerosyllis modinouae sp. nov. (SEM micrograph) a specimen (paratype, NHM. 2018.24386) in dorsal view b anterior end in dorsal view c paratype (NHM. 2018.24236) in dorso-lateral view d detail of prostomium of paratype (NHM. 2018.24236) with palps (P), median antenna (Ma), lateral antennae (La), tentacular cirrus (Tc) and dorsal cirrus (Dc) e detail of dorsal cirri with those on chaetigers 2 - 4 (paratype, NHM. 2018.24386) f pattern of dorsal body papillae (marked by white circles) (paratype, NHM. 2018.24386). Scale bars: 500 µm (a); 100 µm (b, e); 200 µm (c); 50 µm (d).

Figure 8. Drawing of anterior end of Prosphaerosyllis modinouae sp. nov. in dorsal view (a) and detail of palps (b).

Figure 9. Prosphaerosyllis modinouae sp. nov. (holotype, NHM. 2018.25100) a specimen in partial ventral view b, c examples of ventral cirri (Vc) and elongated lateral body papillae (Lp) d example of parapodium e detail of aciculae. Scale bars: 250 µm (a); 50 µm (c, d); 20 µm (e).

Figure 10. Prosphaerosyllis modinouae sp. nov. (paratype NHM. 2018.24386) a simple dorsal chaeta from anterior chaetiger b simple dorsal chaeta from posterior chaetiger c simple ventral chaeta from posterior chaetgier d dorsalmost falciger from anterior chaetiger e ventralmost falciger from anterior chaetiger f dorsalmost chaeta from mid body chaetiger g falcigers from posterior chaetiger. Scale bar: 50 µm.

Figure 11. Comparative figure of Sphaerosyllis palpopapillata (holotype, ZMH P- 20751) (a) and Prosphaerosyllis modinouae sp. nov. (b, c). Scale bars: 1 mm.

Figure 12. Sphaerosyllis palpopapillata (holotype ZMH P- 20751) a anterior end in dorsal view b, c examples of ventral cirri (marked by arrows) d example of lateral body papillae (marked by arrow) e acicula and simple ventral chaeta f falcigers. Scale bars: 1000 µm (a); 20 µm (c, f), 25 µm (d).