Aricidea (Acmira) filamentosa, Barroso & Paiva & Ranauro, 2020

Barroso, R., Paiva, P. C. & Ranauro, N., 2020, Three new species of Aricidea (Acmira) (Annelida: Paraonidae) from the Continental Shelf of Eastern Brazil, Southwestern Atlantic, Zootaxa 4838 (3), pp. 415-426 : 417-420

Aricidea (Acmira) filamentosa sp. nov.

Figures 2–4

Type material. Holotype ( MZUSP4066 ), 18º32’3.6” S, 39º23’16.91” W, 20 m deep, 17 Jan 2012, Espírito Santo Basin , Brazil . Paratypes: 18º32’3.6” S, 39º 23’ 16.91” W, 20 m deep: 22 specs (UFBA-1583), 17 Jan 2012, Espírito Santo Basin , Brazil .

Description. Holotype incomplete with 71 chaetigers (paratypes: 55–88), 7 mm long (paratypes: 4.6–10.7), 0.2 mm wide in branchial region (paratypes: 0.19–0.20). Body anteriorly enlarged and dorsoventrally flattened, gradually becoming slender and cylindrical in posterior region ( Fig. 2A ). Prostomium triangular, acuminate, slightly longer than wide, with a short median antenna, with a thin base and inflated and rounded tip, inserted in the mid-prostomium and not reaching its posterior margin ( Figs 2A, B ; 4A ). A pair of nuchal organs as oblique slits located in posterior region of prostomium ( Fig. 2B ), a band of cilia located on ventral side of prostomium. First two notopodial postchaetal lobes short and tuberculate, cirriform and longer from chaetiger 3, with rounded tips and bowl-shaped in anterior branchiate region, slightly longer and thinner in posterior branchiate chaetigers, and filiform from branchiate region to end of body ( Figs 2 A–F; 3A; 4A). Neuropodial postchaetal lobes absent ( Figs 2 C–F; 3 A–B; 4A). Branchiae starting from chaetiger 4, numbering 10 pairs in holotype; up to 16 pairs in paratypes; branchiae of first two pairs short and cirriform, followed by longer and foliaceous ones with rounded tips; last two pairs short and cirriform ( Figs 2A , C–E; 4A); bearing ciliary bands both on outer and inner margins. Anterior region with capillaries in noto- and neuropodia, ca. 12 in each, organized in two parallel rows in each fascicle ( Fig. 2B ). In post branchial region, noto- and neuropodia with ca. six capillaries organized in single rows; number of capillaries reducing to four in posterior chaetigers. Modified neurochaetae of two types from chaetiger 23 onwards: 1) recurved and smooth ( Figs 3B , 4B ), and 2) recurved bearing numerous pubescence at sub-distal and distal ends, with bent tips and a thin, ornate and delicate filament, with a few minute pubescence in its basal region ( Figs 3 A–D, 4B–C); under light microscope, the former appear as a hooded hook with distal filament barely visible; two types of modified chaetae occur in same row ( Fig. 3B ), with up to seven chaetae in midbody, progressively decreasing to 2–4 modified neurochaetae with distal filaments and 1–2 smooth ones towards posterior region ( Fig. 3 A–B). Pygidium not observed in holotype; complete paratypes bearing three anal cirri ( Figs 2G ; 4D ).

Remarks. Aricidea (Acmira) filamentosa sp. nov. was scarcely sampled and collected from only one specific area within the sampled region ( Fig 1 ). Although belonging to a group that have modified neurochaetae with a long distal filament, it differs from the others by the presence of a second type of modified neurochaetae, morphology of the antenna and/or the number of pairs of branchiae. For instance, Aricidea (Acmira) lopezi Berkeley & Berkeley, 1956 bears a long antenna (narrow at the base, broader in its middle section, and tapering long and thread-like at the tip), and possesses 18 pairs of branchiae. Aricidea assimilis Tebble, 1959 has a very long antenna (reaching chaetiger 8), and 21 pairs of branchiae; Aricidea (Acmira) rubra Blake, 1996 has antenna with an acuminate tip, and up to 30 pairs of branchiae; Aricidea (Acmira) taylori Pettibone, 1965 has a bifurcate antenna, and up to 29 pairs of branchiae; Aricidea (Acmira) catherinae Laubier, 1967 possesses a proximally enlarged antenna, and up to 25 pairs of branchiae; Aricidea (Acmira) philbinae Brown, 1976 bears similar number of pairs of branchiae, but differs in having an asymmetrically bifid antenna. Aricidea (Acmira) finitima Strelzov, 1973 differs by the presence of a longer antenna with an acuminate tip and by having up to 32 pairs of branchiae. The species Aricidea (Acmira) laubieri Hartley, 1981 has a similarly shaped but longer antenna, and similar modified neurochaeta, but differs in having up to 27 pairs of branchiae and up to 14 modified neurochaetae per parapodia, which starts after 30–37 segments in this species. Finally, the species Aricidea (Acmira) bispinata Cantone, 1994 bears a similar number of pairs of branchiae, but differs in the morphology of the antenna, which is broader proximally, tapers distally and reaches chaetiger 2.

Geographic distribution and bathymetric range. Aricidea (Acmira) filamentosa sp. nov. occurs in the southwestern Atlantic Ocean, off the Brazilian coast, in the Espírito Santo Basin, at depths between 20 and 34 meters.

Substrate. This species was collected from substrates with a high percentage of sand (86%), complemented by mud (9%) and pebbles (5%). Bottom temperatures varied between 24.4 and 24.6°C.

Etymology. The epithet filamentosa refers to the long and ornate filament attached to the distal region of the modified neurochaeta of this species.

Figures

FIGURE 1. Map with all sampled stations and the occurrence of the species described in this study.

FIGURE 2. SEM of Aricidea (Acmira) filamentosa sp. nov. A, Anterior region, lateral view; B, prostomium, lateral view; C–E, branchiate region, lateral view; F, posterior parapodia, lateral view; G, posterior region with pygidium, anal cirri missing.

FIGURE 3. SEM of Aricidea (Acmira) filamentosa sp. nov. A, postbranchiate parapodia, lateral view; B, mid-body neuropodium, lateral view; C–D, details of modified pubescent neurochaeta.

FIGURE 4. Holotype of Aricidea (Acmira) filamentosa sp. nov. A, anterior region, lateral view; B, parapodium, posterior body; C, modified neurochaetae, posterior neuropodium; D, pygidium.