Aricidea (Acmira) pearti, 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 : 420-422

Aricidea (Acmira) pearti sp. nov.

Figures 5–6

Type material. Holotype ( MZUSP 4067 ): 19º47’32.83” S, 39º 43’15.08” W, 37 m deep, 15 Dec 2011, Espírito Santo Basin , Brazil . Paratypes: 19º47’32.83” S, 39º43’15.08” W, 37 m deep, 15 Dec 2011, 4 specs (UFBA-1584); 19º54’56.16” S, 39º56’40.83” W, 32 m deep, 16 Dec 2011, 2 specs ( MZUSP 4068 ) .

Description. Holotype complete with 118 chaetigers (complete paratypes: 42–81), 7.6 mm long (complete paratypes: 2.5–6.0 mm), 0.2 mm wide in branchial region (paratypes: 0.2 mm). Body anteriorly enlarged and dorsoventrally flattened, gradually tapering and becoming cylindrical posteriorly. Prostomium triangular, slightly longer than wide, antenna inserted in mid-prostomium, short and digitiform with a rounded tip, reaching posterior margin of prostomium; a pair of nuchal organs as oblique slits located posteriorly ( Figs 5A ; 6A ), with a ring of cilia encircling mid-prostomium only interrupted by antenna ( Fig. 5 A–B); posterior lip of mouth not reaching chaetiger 2 ( Fig. 5B ). First chaetigers with short and tuberculate notopodial postchaetal lobes, cirriform from chaetiger 6 to end of branchiate chaetigers, longer and filiform and with spherical tips in postbranchial region. Neuropodial lobes absent. Branchiae starting from chaetiger 4; numbering 15 pairs (14–17 in paratypes); first pair short and cirriform then becoming longer and foliaceous ( Fig. 6A ); last two pairs short and cirriform with round tips. Anterior region with fascicles of capillaries with ca. 10 chaetae each and organized in rows in both noto- and neuropodia. Modified neurochaetae from chaetiger 22 onwards, recurved as ‘hooded’ hooks, organized in a single row; numbering one per chaetiger just behind branchiate region, reaching 4–5 in midbody chaetigers, and droping to 1-3 posteriorly ( Fig. 6 B–D); some chaetigers bearing additional neuropodial hook “without hood”. A row of ca. four capillaries located adjacent to row of modified chaetae in neuropodia ( Fig. 5 D–E). Pygidium bearing three anal cirri, one short ventrally and two longer dorsolaterally ( Fig. 6E ).

Remarks. ‘ Hooded hook’ forms are one of the most uncommon types of modified neurochaeta in the Paraonidae , since they have been reported from a few species within the subgenus Acmira , for instance: A. (Acmira) cerrutii Laubier, 1966 ; Aricidea (Acmira) philbinae Brown, 1976 ; and Aricidea (Acmira) rubra Blake, 1996 . However, these forms were never well figured and completely understood so, descriptions were generally controversial ( Brown 1976; Gaston 1984). SEM images showed that the hooded hooks herein described to actually consist of pubescence on and around the subdistal region of the recurved hook, thereby giving the impression of a hood when observed through an optical microscope.

Aricidea (A.) pearti sp. nov. is similar to A. (A.) Acmira cerruti Laubier, 1966 in the distribution of the branchiae along the body and morphology of modified neurochaeta. However, these species differ in the shape of the prostomium (truncate in A. (A.) cerruti and rounded in A. (A.) pearti sp. nov.) and branchiae (with an acute tip in A. (A.) cerruti and with a rounded tip in A. (A.) pearti sp. nov.).

Compared to the other species with similar modified neurochaeta, A. (A.) pearti sp. nov. can be distinguished from A. (A.) phibinae by the shape of the antenna, which in the second species is clavate and asymmetrically bifid and also differs from A. (A.) rubra in regards to antenna morphology, longer and with an acuminate tip in the latter, and the number of pairs of branchiae, 14–17 in the new species instead of 28–30 in A. (A.) rubra .

The resemblance of the array of sub-distal and distal pubescence of modified chaetae to a hood, when observed through optical microscopy, is possibly involved in complex delimitation of species, and even of the sub-genera, within the genus Aricidea . As the two species above described are likely to have this same pseudo-hood, really consisting on a dense group of minute terminal pubescence, the use of this peculiar trait needs to be investigated in these other species by means of SEM images.

Geographic distribution and bathymetric range. Aricidea (Acmira) pearti sp. nov. occurs in the southwestern Atlantic Ocean off the Brazilian coast, in the Espírito Santo Basin, at depths between 32 and 44 meters, close to the Doce river mouth.

Substrate. Specimens of Aricidea (Acmira) pearti sp. nov. were collected from substrates with a major percentage of sand (97%) and including mud (2.5%) and pebbles (0,5%). The bottom temperature was 22.5°C.

Etymology. The species name is in honor of the recently deceased Neil Peart, the drummer from the rock band Rush, whose wonderful and engaging lyrics accompanied the second author for many years while observing polychaetes through optical microscopy.

Figures

FIGURE 5. SEM of Aricidea (Acmira) pearti sp. nov. A, anterior region, dorso-lateral view; B, anterior region, ventro-lateral view; C, branchiate region, dorso-lateral view; D, parapodium, dorsal view; E–F, modified neurochaetae. Abbreviations: ant, antenna; bra, branchia; mo, mouth; nl, notopodial lobe; no, nuchal organ.

FIGURE 6. Aricidea (Acmira) pearti sp. nov. A, anterior region, dorsal view; B, parapodium from mid-body, lateral view; C, neuropodium from mid-body, lateral view; D, parapodium from posterior body, lateral view; E, pygidium, ventral view.