Mauretanaspis longichaeta Fiege & Barnich 2020, gen. et spec. nov.

Mauretanaspis longichaeta gen. et spec. nov.

urn:lsid:zoobank.org:act: AA378791-074B-4349-B2E2-235FD632E35C

Figs 1–4, Table 1

Etymology

The species epithet is a combination of the Latin ‘ longus ’ (= ‘long’) and the Greek ‘ chaeta ’ (= ‘bristle’) characterizing the striking length of the posteriormost lateral chaetae of the ventro-caudal shield.

Material examined

Holotype

NORTHEAST ATLANTIC – Off Mauritania • 1 complete specimen (body slightly contracted, introvert fully everted, length 5.0 mm, width 1.6 mm, abdomen length 3.0 mm, left shield plate length 1.2 mm, width 0.9 mm); Block C9, stn C9-15 (B3); 18°21.27′ N, 17°57.44′ W; depth 2712 m; 24 Oct. 2018; deepsea mud, box core; MNHN-IA-TYPE 2005.

Paratype

NORTHEAST ATLANTIC – Off Mauritania • 1 complete specimen (introvert partly retracted, length 3.5 mm, width 1.8 mm, abdomen length 1.0 mm, left shield plate length 1.2 mm, width 1.2 mm); Block C9, stn C9-15 (B1); 18°21.27′ N, 17°57.44′ W; depth 2712 m; 24 Oct. 2018; deep-sea mud, box core; SMF 27777.

Other material

NORTHEAST ATLANTIC – Off Mauritania • 1 spec. (bad condition, anterior end retracted, length n.d., width 2.6 mm, abdomen length 3.7 mm, left shield plate length 1.6 mm, width 1.0 mm); Block C9, stn C9-20 (B1); 18°26.91′ N, 17°59.25′ W; depth 2714 m; 27 Oct. 2018; deep-sea mud, box core; SMF 27776.

SOUTHEAST ATLANTIC – Off Angola • 1 spec. (juvenile with capillary chaetae in pre-shield segments, without gonopodial lobes, anterior end missing, length n.d., width 0.35 mm); stn S48-03A; 6°53.107′ S, 10°30.762′ E; depth 2935 m; 7 Sep. 2018; box core; MNHN-IA-PNT 120 • 1 spec. (juvenile, anterior end damaged, length n.d., width 0.65 mm, left shield plate length 0.5 mm); stn S48-08A; 6°59.047′ S, 10°36.748′ E; depth 2736 m; 9 Sep. 2018; box core; SMF 28061 • 1 spec. (gonopodial lobes present, length 3.2 mm, width 1.1 mm, left shield plate length 1.1 mm); stn S48-09C; 7°4.931′ S, 10°13.003′ E; depth 4373 m; 14 Sep. 2018; box core; SMF 28062 • 1 spec. (juvenile, body wall translucent, with chaetae in some abdominal segments, without gonopodial lobes, length 2.5 mm, width 0.9 mm); stn S48-14C; 7°10.998′ S, 10°13.064′ E; depth 4363 m; 14 Sep. 2018; box core; MNCN 16.01/18762 • 1 spec. (strongly bent and wrinkled, gonopodial lobes not seen, posteriormost lateral chaetae ca 4× length of body, length n.d., width n.d., left shield plate length 1.0 mm); stn S48-23A; 7°23.159′ S, 10°24.921′ E; depth 4375 m; 15 Sep. 2018; box core; MNCN 16.01/18763 • 1 spec. (juvenile, body wall translucent, anterior end missing); stn S48-23B; 7°23.159′ S, 10°24.921′ E; depth 4375 m; 15 Sep. 2018; box core; DBUA0002349.01 • 1 spec. (anterior end retracted, gonopodial lobes retracted but visible, length n.d., width n.d., left shield plate length 1.0 mm); stn S48-26C; 6°58.715′ S, 10°17.741′ E; depth 4191 m; 10 Sep. 2018; box core; DBUA0002349.02.

Description

Based on holotype (Figs 1, 2 A–C, 3A–C), complete specimen (body slightly contracted but introvert fully everted), complemented by paratype (Fig. 4 A–C) where indicated.

BODY COLOUR. Pale yellow.

PROSTOMIUM. Small hemispherical cupule, pale, semi translucent. Eyes absent.

PERISTOMIUM. Surrounding mouth projecting to level of prostomial cupule, about 1.5 × diameter of prostomium. Mouth small, round.

INTROVERT. First three chaetigers each with 15–17 hooks on either side (segment 1: left 9 +6 small, right 8 +8; 2: left 9+ 7, right 9 +8; 3: left 9+6, right 8+7); hooks golden, tapering to blunt transparent tip; decreasing gradually in length and diameter from dorsal to ventral in each fascicle. Ventralmost 6–8 hooks small to minute. Hooks equally spaced in fully everted introvert (Figs 1, 2 A–C, 3A, 4A). Minute drop-shaped papillae in single rows parallel to segmental folds dorsally in segments 1–3. Body damaged ventrally on segments 3–4 with oesophagus protruding (Figs 1, 2C, 3A). Gonopodial lobes small, digitiform, protruding ventrolaterally from intersegmental groove between segments 5 and 6 (Figs 1, 4 A–B).

ANTERIOR ABDOMEN (PRE- SHIELD REGION). Comprising eight segments. Body papillae minute, round, forming single rows close to intersegmental folds, sometimes obscured by sediment particles (Figs 1, 4B). Most pre-shield segments of holotype with smooth median surface on ventral side, possibly abraded, and few, short, filamentous papillae on lateral sides; in paratype median surface papillated (Figs 1, 4A). Few filamentous papillae among adhering sediment particles on segments anterior to branchial plates.

VENTRO- CAUDAL SHIELD. Densely covered by fine, firmly adhering sediment particles. Shield colour light brown, obscured by dense cover of sediment. Colour most intense around anterior end of median suture (sediment abraded in holotype, not abraded in paratype) (Figs 3B, 4A). No structures (ribs, concentric rings) visible due to sediment cover. Anterior margins slightly rounded, anterior depression shallow, covered by sediment; anterior keels faintly visible (Fig. 3B), not exposed. Lateral margins rounded, strongly bent towards dorsal side, not forming free, stiff or pliable margins, but rather merging into integument. Posterior fan and lateral notch not discernible due to sediment cover; shallow median notch (more pronounced in paratype (Fig. 4A, C)). Suture defined in anterior ¼ of shield, moderately deep with distinct lateral borders (Figs 3B, 4A).

MARGINAL SHIELD CHAETAE. Yellow; 20 lateral fascicles, i.e., 9–11 fascicles per side, with 4–6 capillary chaetae each. Chaetae arranged in oblique rows, increasing gradually in length posteriorly within each fascicle and among fascicles (Figs 2C, 3C, 4 B–C); chaetae of posteriormost lateral fascicle very long, equalling body length (Figs 2C, 3D). Six pairs of fascicles posterior to shield (i.e., posterior shield chaetae), each with 1–3 (mostly 2) yellow capillaries of varying length and different strength (Figs 3B, 4A, C); lateralmost longest, equalling length of shield. Peg chaetae absent.

BRANCHIAL FILAMENTS. Numerous, increasing in length posteriorly, opaque, coiled to various extent.

BRANCHIAL PLATES. Brownish, forming ovoid to trapezoidal region, densely covered by filaments, filamentous papillae and sediment grains (Fig. 3C).

Distribution

Northeast to Southeast Atlantic, from off Mauritania to Angola, in deep-sea mud, in depths of 2700– 4400 m.

Remarks

Mauretanaspis longichaeta gen. et spec. nov. can be distinguished from all other known species of Sternaspidae by the following combination of characters: introvert hooks tapering, tips transparent; pre-shield region with eight segments; ventro-caudal shield densely covered with fine, firmly adhering sediment obscuring shield structures except median suture. Mauretanaspis longichaeta gen. et spec. nov. is the only sternaspid with chaetae in posteriormost lateral fascicles equalling body length. In one specimen collected off Angola (MNCN 16.01/18763), posteriormost lateral chaetae even measure about 4× the length of the body.

Several specimens from off Angola (SMF 28062, MNCN 16.01/18762, MNCN 16.01/18763, DBUA0002349.01) show black pigment presumably from surrounding sediment included in sediment cover and among sand grains in the branchial region. Black particles are scattered on the shield forming spots of different sizes.

We compared our material to a specimen collected off Northwest Africa in 1320 m depth and identified as Sternaspis scutata (Ranzani, 1817) by Kirkegaard (2001: 396). The specimen, deposited in the collections of the Natural History Museum of Denmark (NHMD 662048), was not available for study, but pictures of it were kindly made available to us by S. Salazar-Vallejo. Unfortunately, the animal is in very bad condition: anterior hooks tapering to fine tips, number of pre-shield segments and gonopodial lobes not distinguishable, shield completely covered by fine sediment obscuring surface structures, shield without free margins, length of lateral and posterior shield chaetae indeterminable. It remains uncertain whether the sediment can be removed from the shield without damaging it, but with regard to shield characters visible in the pictures available, the specimen appears incorrectly identified as Sternaspis scutata. However, due to its bad condition we cannot identify it any further.

Identification key to Sternaspidae with sediment particles firmly attached to ventro-caudal shield ( Caulleryaspis (in part) and Mauretanaspis gen. nov.) (adapted from Salazar- Vallejo 2017)

1. Shield with anterior depression deep; peg chaetae robust................................................................ 2

– Shield with anterior depression shallow; peg chaetae absent........................................................... 3

2. Shield with anterior margins angular; peg chaetae forming thick, large spines.......................................................... Caulleryaspis gudmundssoni Sendall & Salazar-Vallejo, 2013 (N Atlantic, Iceland)

– Shield with anterior margins rounded; peg chaetae forming thin, small spines..................................... Caulleryaspis fauchaldi Salazar-Vallejo & Buzhinskaja 2013 (NE Pacific, Oregon to California)

3. Seven pre-shield segments; chaetae in posteriormost lateral fascicles about length of shield............................................... Caulleryaspis laevis (Caullery, 1944) (Indo-Pacific, Indonesia)

– Eight pre-shield segments; chaetae in posteriormost lateral fascicles equalling body length.......................... Mauretanaspis longichaeta gen. et spec. nov. (NE and SE Atlantic, Mauritania to Angola)