Leiocapitella Hartman 1947

Genus Leiocapitella Hartman, 1947, amended

Leiocapitella Hartman, 1947: 437, Pl.54, fig. 1–3; Fauchald, 1977: 34; Ewing, 1984a: 42; Green, 2002: 290–291; García-Garza & de León-González, 2011: 28; El Haddad, Capaccioni-Azzati & García-Carrascosa, 2013: 101; Capaccioni-Azzati & El Haddad, 2015: 344; Magalhães & Blake, 2017; Lin, García-Garza & Wang, 2019: 192.

Type species: Leiocapitella glabra Hartman, 1947

Generic diagnosis. (amended after Magalhães & Blake 2020 and Lin, García-Garza & Wang 2019). Prostomium conical or rounded, palpode present or absent; eyespots present or absent, when present in multiple spots. Peristomium clearly distinct from prostomium; sub-equal (trapezium format). Achaetous segment absent. First chaetiger uniramous. Thirteen to fourteen thoracic chaetigers. Chaetigers 1–12 with only capillaries; chaetigers 13–14 may have only capillaries or notopodium with capillaries and neuropodium with hooded hooks. Anterior thorax slightly or strongly tessellated. Thorax not clearly demarked from abdomen. Genital pores in four to eight pairs from chaetigers 7/8. Abdominal segments with hooded hooks in both rami. Poorly-developed parapodial lobes. Noto- and neuropodial expansion present or absent, when present, posterior notopodial expansion branched (branchiae). Conspicuous lateral organs present on thorax and abdomen. Hooded hooks with 2–3 teeth in first row above main fang. Pygidium may bear four short cirri.

Remarks. The definition of Leiocapitella has changed a few times to include species with different configuration of thoracic segments in relation to the number of chaetigers bearing only capillaries and number of transitional chaetigers with notopodial capillaries and neuropodial hooks, species with the first chaetiger uni- or biramous, and species with branched branchiae. Hartman (1947) described L. glabra with only capillaries to chaetiger 13 and chaetiger 14 being transitional; however, after an examination of the type material it was possible to observe that this species presents 13 thoracic chaetigers, only capillaries to chaetiger 12 and chaetiger 13 being transitional. Nevertheless, all described species, including the new one described here, have 13–14 thoracic chaetigers, so we suggest shortening the previous variation (13–17) until a re-examination of the species mentioned by Ewing (1984a), Leiocapitella sp. B, and a formal description could be made. The informal description made by Ewing included eight specimens of Gulf of Mexico with the largest one measuring 0,9 mm wide for 56 chaetigers. The specimens presented thorax with 15 chaetigers with capillaries and only two specimens presented thorax with two additional chaetigers bearing hooded hooks on neuropodia.

Ewing (1984a) expanded the definition of the genus to include a species having chaetiger 1 biramous, Leiocapitella sp. A; however, all described species have chaetiger 1 uniramous, so we also suggest not to include this character until a formal description could be made, as with the number of thoracic chaetigers. Additionally, the four specimens examined presented a broadly oval peristomium, thoracic epithelium faintly tessellated, absence of lateral organs, and abdominal hooded hooks with first row above main fang having six teeth; characters that do not fit into the generic diagnosis of Leiocapitella.

Leiocapitella dollfusi (Fauvel 1936), first described as Mastobranchus dollfusi, was the first species of the genus mentioned having branchiae, but it is known that these structures do not have respiratory functions because capitellids lack a typical circulatory system, and these projections from the body wall contain coelomic extensions rather than loops from the circulatory system (Fauchald & Rouse 1997). As the new species also presents these structures we suggest calling them “notopodial expansions” instead of branchiae, until new studies explore their nature and function. Finaly, the pygidium of L. dollfusi was described as having four short cirri, but it is unknown for the remaining species; for this reason we described it as “may bear four short cirri”.

Leiocapitella atlantica Hartman, 1965, amended

(Figs 1 A–F; 2A–H)

Leiocapitella atlantica Hartman, 1965: 193–194. Type material. Holotype Leiocapitella atlantica (LACM-AHF POLY 423) and Paratypes (5 specs) (LACM-AHF POLY 424) 40°01.8’N, 70°42’W, 200m, 28 Aug 1962, New England continental slope, North Atlantic, USA.

Redescription. Incomplete holotype 0.9 mm wide for 32 chaetigers. Body triangular, wider ventrally and narrower dorsally (Fig. 1E); slightly flattened dorso-ventrally on abdomen; thoracic chaetigers same width than abdomen and rounded. Whitish color in alcohol.

Prostomium rectangular, 1.5x longer than wide, slightly rounded on posterior end (Figs 1A; 2C); nuchal organs not everted; without eyespots. Proboscis globular-shaped, strongly papillated, with large globular papillae queued (Figs 1B; 2C). Peristomium achaetous; 2x longer than thoracic segments; slightly tessellated; 2x wider on posterior margin than on anterior (Fig. 1A; E–F).

Thorax with 13 chaetigers. First chaetiger uniramous. Unilimbate capillaries in notopodia of chaetigers 1–13 and in neuropodia of chaetigers 2–11; neuropodia of chaetigers 12 and 13 with hooded hooks. Thoracic chaetigers moderately biannulate; chaetae emerging from middle of segment. Notochaetae inserted dorsally; neurochaetae inserted ventro-laterally (Fig. 2 A–B). Chaetigers 1–2 slightly flattened dorso-ventrally; chaetigers 3–9 triangular, larger ventrally and narrower dorsally, with deep lateral groove; chaetigers 10–13 discreetly triangular, slightly larger ventrally than dorsally (Fig. 1D). Chaetigers 6–13 with a mid-lateral lobe (MLL) between noto- and neuropodial chaetae and below lateral organ (Fig. 1F). Lateral organs present from chaetiger 1, bearing a bundle of sensorial cilia (Fig. 2E). Transition between thorax and abdomen subtle, distinguished by increasing number of hooks on neuropodia and by size difference between thoracic and abdominal lateral organs, being thoracic more conspicuous (Fig. 2A; D). Thoracic hooks with long and rounded main fang, curved, almost parallel to shaft, surmounted by approximately 11 teeth arranged in three rows (3–2–6); thin hood with smooth edge, regular aperture (Fig. 2F).

Abdominal chaetigers with hooded hooks throughout. Lateral organs throughout abdomen. Notopodial lobes absent, hooded hooks emerging directly from body wall, inserted dorsally, both bundles almost together along abdomen; neuropodia with poorly developed lobes, hooded hooks inserted ventro-laterally (Figs 1C; 2B). Abdominal chaetigers slightly larger ventrally and narrower dorsally, chaetae emerging from last third of segment (Fig. 2 A–B). Notopodia with eight hooks per fascicle, neuropodia with 15 hooks per fascicle. Noto- and neuropodial hooks similar with long and pointed main fang, curved, surmounted by approximately 10 teeth arranged in three rows (2–1–7); thin hood with smooth edge, regular aperture (Fig. 2 G–H). Pygidium unknown.

Variation. Paratypes ranging from 0.4–1.6 mm wide. Specimens with 13 or 14 thoracic chaetigers (Figs 1D; 2A); and with only capillaries or the last one or two neuropodia with hooded hooks.Abdominal notopodia with 4–11 hooks and neuropodia with 11–22 hooks per fascicle.

Methyl green staining pattern (MGSP). Chaetigers 1–5 staining lighter; chaetigers 6–13 staining darker than the others and chaetigers 10 and 11 even darker (Fig. 1 D–E).

Remarks. The original description is very short and does not present any drawings or photos. As the examination of the type material was possible, we decided to include the redescription of this species with optical photos and the scanning electron microscopy in order to assist further taxonomic studies. Hartman (1965) did not mention the variation on the number of thoracic chaetigers (13–14) nor on the number of thoracic chaetigers with hooded hooks (0– 2). Here we also describe several characters of the species, as detail of the papillae, shape of thoracic chaetigers, type of parapodial lobe, and the hooded hooks teeth formula.