Leiocapitella sensibilis Silva & Amaral 2020, sp. nov.

Leiocapitella sensibilis sp. nov.

(Figs 3 A–B; 4A–F; 5A–G)

Material examined. Rio de Janeiro, Campos Basin (22°1’9’’S, 40°31’55’’W): Holotype (ZUEC POL 20150) 23 Jul 2009, subtidal, 47m, Stn. HAB17/FOZ32, 1 spec. Paratype 1 (ZUEC POL 20153) 12 Mar 2009, subtidal, 4m, Stn. HAB13/FOZ9, 1 spec. Paratype 2 (ZUEC POL 20162) 15 Mar 2009, subtidal, 59m, Stn. HAB13/FOZ34, 1 spec. Paratype 3 (ZUEC POL 20163) 23 Jul 2009, subtidal, 47m, Stn. HAB17/FOZ32, 1 spec. Paratype 4 (ZUEC POL 20173) 25 Feb 2009, subtidal, 52m, Stn. HAB11/G2, 1 spec. Paratype 5 (ZUEC POL 20174) 06 Jul 2009, subtidal, 55m, Stn. HAB16/F2, 1 spec. Paratype 6 (ZUEC POL 20175) 21 Jul 2009, subtidal, 103m, Stn. HAB17/I4, 1 spec. Paratypes 7−13 (ZUEC POL 20177) 06 Jul 2009, subtidal, 53m, Stn. HAB16/G2, 7 specs. Paratype 14 (ZUEC POL 20178) 26 Feb 2009, subtidal, 29m, Stn. HAB11/D1, 1 spec. Paratype 15 (ZUEC POL 20179) 06 Jul 2008, subtidal, 402m, Stn. HAB7/H6, 1 spec. Espírito Santo, Espírito Santo Basin (18°40’55,3’’S, 38°55’41,48”W): Paratype 16 (ZUEC POL 20151) 02 Dec 2011, subtidal, 45m, Stn. AMB7/B3, 1 spec. Paratypes 17−19 (ZUEC POL 20158) 12 Jul 2011, subtidal, 28m, Stn. AMB2/FOZ9, 3 specs. Paratypes 20 and 21 (ZUEC POL 20165) 17 Jul 2013, subtidal, 41m, Stn. AMB14/D2; 2 specs.

Additional material examined. São Paulo state: (ZUEC POL 5487) 24°37’S, 46°45’W, 14 Nov 1985, subtidal, 38m, Stn. 6669, 1 spec. (ZUEC POL 5488) 24°46’S, 46°59’W, 14 Nov 1985, subtidal, 36m, Stn. 6668, 2 specs. (ZUEC POL 6740) 25°11’S, 47°08’W, 16 Feb 1997, subtidal, 157m, Stn. 6658, 1 spec.

Comparative material examined. Holotype Leiocapitella atlantica (LACM-AHF POLY 423) and 1 Paratype (LACM-AHF POLY 424), 40°01.8’ N, 70°42’W, 200m, 28 Aug 1962. Holotype Leiocapitella glabra (LACM-AHF POLY 425), 24°26’39’’N, 110°22’53’’W, Baja California, Mexico, North Pacific, 13 Feb 1940. 1 Paratype (LACM- AHF POLY 205) 28°20’35’’N, 115°10’10’’W, Baja California Norte, Mexico, North Pacific, 28 Feb 1941.

Description. Holotype incomplete 1.1 mm wide for 162 chaetigers. Body robust; rounded on thorax and slightly flattened dorso-ventrally on abdomen; thorax almost same width than abdomen; abdomen becoming thinner toward posterior end. Whitish color in alcohol.

Prostomium triangular, short, with a palpode (Figs 3A; 5A); nuchal organs not everted; eyespots as small black dots (more than 15 each side), distributed obliquely on each side of prostomium. Proboscis globular-shaped, weakly papillated with short papillae (Fig. 4D); papillae with filamentous sensory cilia (Fig. 5C). Peristomium half-length of thoracic chaetigers (Figs 3A; 5A).

Thorax with 13 chaetigers. First chaetiger uniramous. Unilimbate capillaries in notopodia of chaetigers 1–13 and in neuropodia of chaetigers 2–12; neuropodium of chaetiger 13 with hooded hooks. Peristomium and first five chaetigers with strongly tessellated epithelium, subsequent chaetigers smooth (Figs 3A; 5A). Chaetigers 6–13 biannulate, divided in anterior and posterior portions to chaetal bundle, and with extremities strongly angled (Figs 3A; 5A); chaetae emerging from middle of segment; and with a mid-lateral lobe (MLL) between noto- and neuropodial chaetae and below lateral organ (Figs 3A; 5A). Notochaetae inserted dorso- laterally, bundles becoming closer and completely inserted dorsally on last 2–3 thoracic chaetigers; neurochaetae inserted ventro-laterally in the middle of the segment throughout. Chaetigers 1–5 with thick, white line ventrally (WVL) in the middle of segment, forming a continuous line (Fig. 4D). Lateral organs (LO) present from chaetiger 1 bearing short sensory cilia (Fig. 5A; D). Epithelia around lateral organ with small, rounded sensory furrows (SF) (Fig. 5D). Transition between thorax and abdomen evident, distinguished by the appearance of parapodial lobes and hooks, and by increasing width (Figs 3A; 5A).

Abdominal chaetigers with hooded hooks throughout. Large and globulous lateral organs throughout abdomen (Fig. 3B); lateral organ with long and numerous sensory cilia (C) (Fig. 5E). Notopodia with a unique globulous lobe; hooded hooks inserted dorsally, both bundles almost together, separated by a rounded part of the lobe (Figs 3B; 4A). Neuropodia with thin and poorly developed lobes, with an expansion projecting dorsally as a tip (Figs 3A; 4A; 5B); hooded hooks inserted ventral and laterally, in a long line. Abdominal chaetigers larger ventrally and narrower dorsally, chaetae emerging from last third of segment. First abdominal notopodia with 17 hooks per fascicle, decreasing on last chaetigers of abdomen; first abdominal neuropodia with 36 hooks per fascicle, decreasing on last chaetigers of abdomen. Notopodial hooks with long and large main fang, surmounted by approximately 12 teeth arranged in three rows (3–2–7) (Fig. 5F). Neuropodial hooks with long, thin and pointed main fang, surmounted by approximately 10 teeth arranged in three rows (2–1–7) (Fig. 5G). Small notopodial expansions (“branchiae”) inserted dorsally, but laterally on the notopodial lobe, beginning after segment 47; first expansions small and triangular (Fig. 4B), becoming more filamentous (branched) toward posterior end (up to seven filaments) (Fig. 4C, F). Pygidium unknown.

Variation. All specimens examined incomplete ranging from 0.4–1.5 mm wide for 22–162 chaetigers. Notopodial hooks ranging from 3 to 25 and neuropodial ones ranging from 3 to 42 hooks per fascicle.

Methyl green staining pattern (MGSP). Thorax staining darker than abdomen; chaetigers 1–4 staining lighter than remaining thoracic chaetigers (Fig. 4E). Dorsal region of abdomen with a large continuous dark band throughout (Fig. 4E). Posteriormost segments with a dorsal dark band near the division between each segment (Fig. 4F).

Remarks. Leiocapitella sensibilis sp. nov. is characterized by having peristomium and first five thoracic chaetigers with strongly tessellated epithelium, presence of a small neuropodial expansion lobe, branched notopodial expansions on posterior abdomen, and mid-lateral lobe on thorax (Figs 3A; 4A; 5A). Among the known species of Leiocapitella, only L. atlantica presents mid-lateral lobe on thorax, although this species lacks noto- and neuropodial expansions, palpode and eyespots. Additionally, the number of thoracic chaetigers in L. atlantica ranges between 13 and 14 and in L. sensibilis sp. nov. is 13. Leiocapitella dollfusi also has branched notopodial expansions, described previously as branchiae; however, it lacks palpode, neuropodial expansion, and mid-lateral lobe on thorax. Its thoracic formula is also 13–14 chaetigers as in L. atlantica. Finely, L. sensibilis sp. nov. differs from L. glabra, L. fujianensis and L. hartmanae because these species lack noto- and neuropodial expansions and mid-lateral lobe on thorax; L. glabra also lacks eyespots and palpode, and L. fujianensis has a smooth thoracic epithelium.

Etymology. Latin word that means “sensitive”. This species was named after its great amount of sensitive structures, i.e., thoracic and abdominal lateral organs and papillae with cilia and sensory furrows on thorax.

Habitat. Subtidal regions 29–402m, in soft-bottoms.

Type locality. Rio de Janeiro, Campos Basin, Brazil, South Atlantic Ocean (22°1’9’’S, 40°31’55’’W).

Distribution. Espírito Santo, Rio de Janeiro and São Paulo states, Brazil, South Atlantic Ocean.