Neoleanira solitaria, Cruz-Gómez & Blake, 2024

Cruz-Gómez, Christopher & Blake, James A., 2024, Description of new species of deep water Sthenolepis Willey, 1905 and Neoleanira Pettibone, 1970 (Annelida, Sigalionidae) from off Northern California, with the redescription of Sthenolepis spargens Fauchald, 1972, Zootaxa 5507 (2), pp. 224-244 : 235-240

Neoleanira solitaria new species

Figs. 6–9 , Table 2

urn:lsid:zoobank.org:act:382DCFC6-29FD-4CD9-9CC5-F8A5DECD9A59

Holotype. Eastern Pacific Ocean, Continental slope off northern California. W of Farallon Island, SF-DODS Benthic Monitoring Program , Sta. 02, 28 Jun 2015, 37.68334°N, 123.50025°W, 2560 m (LACM-AHF-Poly 14415). Left middle segment (34th segment) and elytron coated in gold and palladium on SEM stub.

Description. Holotype incomplete with 34 anterior segments, 12.7 mm long, 11.2 mm to segment 30, 3.7 mm wide ( Fig. 6A ). Body slender, cylindrical; pale orange. Mid-dorsal line smooth, some elytra remain, venter smooth. Elytrophores on segments 2, 4, 5, 7, then alternate to segment 25, then present in all segments. Elytrophores bulbous, slightly larger in posterior segments.

Prostomium pale orange, slightly whitish on cerebral lobes; oval, wider than long. Eyes lacking. Lateral antennae 2× as long as prostomium length, inserted on anterior dorsal margin of the tentacular segment. Median antenna with ceratophore, 1/3 as long as prostomium, style 8× as long as ceratophore length; inserted centrally on prostomium. Auricles oblong, half as long as ceratophore; inserted basally and laterally on ceratophore. Tentacular segment uniramous, chaetae verticillate. Dorsal tentacular cirri 3× longer than neuropodia, ventral tentacular cirri short, as long as neuropodia ( Fig. 6E ). Inner tentacular lobes 2× larger than inner palpal sheaths. Palps reaching segment 20, with palpal sheaths. Inner and outer palpal sheaths subequal ( Fig. 6F ). Buccal cirri, long, 2× longer than remaining ventral cirri. Buccal ctenidial pads, enlarged, inserted on the antero-upper margin of the buccal aperture. Ctenidial pads from segment 1; segment 1 with only 1 dorsal ctenidial pad, succeeding segments with 3 ctenidial pads: 2 pads on the parapodial dorsal surface, and 1 smaller, boot-shaped pad, inserted ventrally ( Figs. 8A–B, E , 9A , arrow). Branchiae from segment 2, small, becoming larger from segment 7, filiform, cilia not observed. Nephridial papillae not observed.

Elytra from anterior region lost. Median elytra large, oblong ( Fig. 6B–C ). Posterior elytra larger, oblong ( Fig. 6D ). All elytra with smooth surface, and small fimbriae along lateral margins ( Fig. 8C ).

Segment 3 ( Fig. 7A ). Dorsal cirri longer than parapodia ( Fig. 7A , arrow). Notopodia ovate, small, half as long as neuropodia; acicular lobe with a few stylodes, inserted distally. Notacicula thick, protruding into a stylode. Notochaetae with up to 20 simple verticillate chaetae, smallest slightly smaller than notopodia, longest 4× as long as notopodia ( Fig. 7A , inset). Neuropodia conical. Prechaetal lobe entire, with a few long dendritic stylodes, one bifurcated inserted distally in acicular lobe. Postchaetal lobes differentiated, without stylodes. Neuracicula thick, inserted in prechaetal lobe. Neurochaetae, differentiated in spines and composed chaetae ( Fig. 7B ). One small smooth spine inserted in upper position. Upper group (unit A) with 6 chaetae, handles thick with 6–7 subdistal rows of spines, blades long, 29–30× as long as wide. Upper middle group (unit B) with 10 chaetae, blades long, 39–40× as long as wide. Middle group (unit C) with 14 chaetae, blades medium-sized, 22–24× as long as wide. Lower middle group (subunit 1) with 1 chaeta, blade long, 42× as long as wide. Lowest group (unit D) with 12 chaetae, blades medium-sized, 20× as long as wide. Ventral cirri as long as neuropodia ( Fig. 7A ).

Segment 21 (middle segment) ( Figs. 8B–C, E ). Notopodia distally pointed, slightly oblanceolate, large, longer than neuropodia; acicular lobe with a few stylodes, inserted distally. Notacicula thick, not protruding from body wall. Notochaetae with up to 40 simple verticillate notochaetae ( Fig. 8E , inset), smallest, half as long as notopodia, longest 5× as long. Neuropodia subconical. Prechaetal lobe entire, with small filiform stylodes. Postchaetal lobes differentiated, divided by a deep notch, with a long upper and lower stylodes. Neuracicula thick, inserted in prechaetal lobe. Neurochaetae spinigers ( Fig. 8F ), and 1 small smooth spine in upper position ( Fig. 8D , arrow). Upper group (unit A) with 5 chaetae, handles thick with 5–12 subdistal rows of spines; blades long, 30–62× as long as wide. Upper middle group (unit B) with 13 chaetae, handles thick with 1–2 subdistal rows of denticles; blades long, 36× as long as wide. Middle group (unit C) with 13 chaetae, blades short, 15× as long as wide. Lower middle group (subunit 1) with 1 chaeta, blade long, 32× as long as wide. Lowest group (unit D) with 10 chaetae, blades short to medium-sized, 20× as long as wide. Ventral cirri as long as neuropodia ( Fig. 8E ).

Segment 33 (posterior segment) ( Fig. 9A ). Similar features as in middle segments. Notochaetae simple verticillate chaetae ( Fig. 9D ). Neurochaetae spinigers ( Fig. 9E ) and simple chaeta. One simple, fusiform, spinous neurochaeta, inserted in upper position ( Fig. 8G , 9B–C ).

Posterior region lost. Pygidium unknown.

Remarks. In the Eastern Pacific, only two species of Neoleanira are known, N. racemosa Fauchald, 1972 from the Guaymas Basin, and N. areolata McIntosh, 1885 described from the south of Yedo, Japan, but recorded in Washington, California, and the Gulf of California ( Hartman 1960 as Leanira calcis Hartman, 1960 ; Pettibone 1970b; Fauchald 1972 as L. calcis ). These two species are similar to N. solitaria n. sp., in having small auricles, a long median antenna, and bulbous boot-shaped ventral ctenidia. However, they differ in the length of the appendages from the first anterior segments, the shape of the branchiae, and the type of neurochaetae.

Neoleanira solitaria n. sp. differs from N. areolata in having the dorsal cirri from segment 3 longer, ¼ longer than the ones on N. areolata ( McIntosh 1885; pl. 21, fig. 3; Imajima 2003: 57, fig. 32a). The main feature that distinguishes N. areolata from N. solitaria n. sp., and from the rest of the species of Neoleanira is the presence of spur-like processes in the basis of the branchiae from the median and posterior region ( Hartman 1960: 185, Pl. 4; Pettibone 1970b: 373, fig. 5b–c, fig. 6a–b; Imajima 2003: 59, fig. 34a–b). While all the known species of Neoleanira possess entire branchiae, including N. solitaria n. sp., records of N. areolata in the Eastern North Pacific should be reevaluated. Ideally this would include examination of the type material of its regional junior synonym, L. calcis Hartman, 1942 , since it is unlikely that a species described from Japan occurs along the Eastern Pacific coast.

On the other hand, N. solitaria n. sp. differs from N. racemosa in having longer median and lateral antennae, as well as longer dorsal cirri from segment 3. Neoleanira solitaria n. sp. has longer anterior appendages, the median and lateral antennae are ¼ longer than the ones on N. racemosa , and regarding the dorsal cirri from segment 3, N. solitaria n. sp. it is twice as long as the ones in N. racemosa ( Fauchald 1972: 425, pl. 2, fig. b; Pettibone 1989: 165, fig. 5A).

Regarding the chaetae, N. solitaria n. sp. possesses neurochaetae of two types, simple and compound. The simple chaetae are either small spines, slightly thicker than the notochaetae, or thick fusiform chaetae. Neurochaetae are spinigers with thick handles, either smooth or with several subdistal rows of denticles, and canaliculated blades. In contrast, N. racemosa has only compound spinigers as neurochaetae, with slender handles with a terminal row of denticles, and non-canaliculated blades ( Fauchald 1972: 425, pl. 2, fig. a; Pettibone 1989: 166, fig. 6c).

Another species that N. solitaria n. sp. resembles is N. tetragona ( Örsted, 1845) from Norway with a wide distribution in the North Atlantic. These two species have small auricles, long palps, branchiae without large processes, neurochaetae with thick handles, and elytra with lateral fimbria. However, N. solitaria n. sp. differs from N. tetragona in having slightly longer appendages such as median and lateral antennae, and the dorsal cirri from segment 3; whereas N. tetragona has shorter antennae and dorsal cirri ( Table 2 ). Also, some other differences are found in the neuropodia and neurochaetae. Neoleanira solitaria n. sp. has a deep notch between the upper and lower postchaetal lobes, and neurochaetae of two types, simple and compound chaetae, the latter being spinigers with rather long blades; whereas the notch between the upper and lower postchaetal lobes in N. tetragona is shallow, with only compound spinigers with short blades. The shape of ventral ctenidia also differs between these species, N. solitaria n. sp. possesses bulbous boot-shaped ventral ctenidia, while N. tetragona has clavate ventral ctenidia ( Pettibone 1970b: 368, fig. 1a, b; 370, fig. 3c; 371, fig. 4b).

Finally, Neoleanira solitaria n. sp. differs from all Neoleanira species in having a simple fusiform spinous neurochaeta in the upper position in the neuropodia. This is the first record of this kind of chaeta in the genus.

Biology. The holotype of Neoleanira solitaria n. sp. from Station 2 of the 2015 survey is the only specimen of this species to have been identified after the collection and analysis of approximately 235 benthic samples collected from SF-DODS since monitoring began in 1996. Station 2 is located northeast of the disposal site boundary (see Blake et al. 2009: fig. 2). During the site selection process for SF-DODS by the US EPA and a companion site planned by the U.S. Navy, oceanographic dispersion models were developed that predicted dredged material would drift to the north-northwest of the disposal site ( Courtney et al. 1994). Station 2 is directly in the path of such a drift pattern and during years of heavy dredged material disposal, the sand content of the sediments increased. The 2015 sediment data for Station 2, was sand 8.6% and silt + clay 41.4% (averaged over three replicates); TOC was 1.9%. Dredged material depth at the site averaged 7.64 cm (EPA, unpublished data). Therefore, the site where N. solitaria n. sp. occurred outside of SF-DODS had increased sand content over ambient sediments, low TOC, and deep deposits of dredged material. The more typical habitat of N. solitaria n. sp. has yet to be discovered.

Etymology. The specific epithet solitaria (- us, - um) is a Latin singular feminine adjective in the nominative case, which means ‘solitary’ or ‘lone’ ( ICZN 1999, Art. 31.2). The sole specimen of Neoleanira solitaria n. sp. was found after many samplings in the area where other species of sigalionids were found. The name also refers to the presence of a solitary fusiform chaeta in the neuropodia of posterior segment, a characteristic that makes this species unique.

Distribution. Northeastern Temperate Pacific, lower continental slope off northern California, 2,560 m.

Figures

FIGURE 6. Neoleanira solitaria n. sp. Holotype (LACM-AHF-Poly 14415). A. Incomplete specimen. B. Median right elytron. C. SEM image from same, marginal fimbriae. D. Posterior left elytron. E. Drawing of anterior end, dorsal view. F. Drawing of anterior end, ventral view. Abbreviations: au= auricle, ct= ctenidia, dc= dorsal cirrus, dtc= dorsal tentacular cirrus, ipas= inner palpal sheath, itl= inner tentacular lobe, lan= lateral antenna, man= median antenna, opas= outer palpal sheath, pa= palp, vtc= ventral tentacular cirrus. Scale bars: A: 5 mm, B, D: 200 µm, C: 50 µm, E, F: 1 mm.

FIGURE 7. Neoleanira solitaria n. sp. Holotype (LACM-AHF-Poly 14415). A. Parapodium from segment 3, anterior view, inset: close-up of notochaetae, arrowhead indicates dorsal cirrus. B. Neurochaetae from segment 3. Abbreviations: S1= lower middle group, UA= upper group, UB= upper middle group, UC= middle group, UD= lowest group. Scale bars: A: 200 µm, B: 50 µm.

FIGURE 8. Neoleanira solitaria n. sp. Holotype (LACM-AHF-Poly 14415). A. Drawing of parapodium from segment 21, anterior view. B. Drawing of same, posterior view. C. Diagrammatic of same, lateral view, color lines indicate the insertion of neurochaetal groups, color scheme following that shown in F. D. Interramal section of segment 21, anterior view, arrowhead indicates the spine inserted in neuropodium. E. Parapodium from segment 21, anterior view, inset: close-up of notochaetae. F. Neurochaetae from segment 21. G. Simple fusiform spinous neurochaetae from segment 33. Abbreviations: S1= lower middle group, UA= upper group, UB= upper middle group, UC= middle group, UD= lowest group. Scale bars: A–C: no scale, D, F, G= 50 µm, E: 200 µm.

FIGURE 9. Neoleanira solitaria n. sp. Holotype (LACM-AHF-Poly 14415). A. SEM image from segment 34, anterior view, arrowhead indicates ventral ctenidium. B. Upper fusiform spinous neurochaetae. C. Close-up to the surface of same. D. Notochaetae. E. Upper group neurochaeta. Scale bars: A: 200 µm, B, E: 50 µm, C: 20 µm, D: 10 µm.