Hanleya brachyplax Simone & Jardim, 2009

Jardim, Jaime A. & Simone, Luiz Ricardo L., 2010, Redescription Of Hanleya Brachyplax (Polyplacophora, Hanleyidae) From The South-Southeastern Brazilian Coast, Papéis Avulsos de Zoologia 50 (40), pp. 623-633 : 624-632

Hanleya brachyplax Simone & Jardim, 2009

( Figs. 1-32 )

Hanleya sp. Simone, 2009:446.

Hanleyia brachyplax Simone & Jardim in Rios, 2009:20 (fig. 39).

Types: Holotype – MZUSP 87263 ( Fig. 1-11 ) . Paratypes – BRAZIL; São Paulo; 25°44’S, 45°11’W, 400 m, off Cananéia , MZUSP 87264 , 1 specimen (REVIZEE Score Sul) ; Santa Catarina, off Cape Santa Marta, 250 m depth, MORG 18953 , 1 specimen .

Type locality: BRAZIL; São Paulo; 25°44’S, 45°11’W, off Cananéia , 408 m (sta. #1126, 18/IV/02) .

Diagnosis

Shell sculptured by randomly organized round- ed pustules; diagonal line weakly conspicuous on intermediate valves and inconspicuous on tail valve, jugal and pleural regions indistinct; head valve semielliptical, insertion plates with vertical furrows; intermediate valves with evident apex, wide and concave jugal sinus, and triangular apophysis; tail valve with central mucro; insertion plates well developed. Girdle wide, totally covered by solid dorsal spicules; marginal spicules similar to dorsal spicules, though slightly smaller; ventral surface covered by small, overlapping scales.

Description

Shell ( Figs. 1-11 ): Occupying about 60% of animal’s dorsal surface ( Figs. 1-2 ). Color white. Each valve twice as wide as long, and about twice as wide as tall; lateral edges rounded. All valves inserted laterally in girdle and medially in mantle; apophyses of head valve striated on outer surface ( Fig. 5 ), apophyses of remaining valves smooth ( Figs. 8, 11 ). Head valve ( Figs. 3-5 ) with pustules roughly arranged in rows in marginal region; inner surface glossy; muscle scar occupying about 60% of valve inner surface, flanking lateral and posterior edges ( Fig. 4 ). Insertion tooth of head valve about half as high as valve, located in anterior and lateral edges, shorter near median line; irregular longitudinal furrows on outer surface ( Fig. 5 ). Sculpturing of intermediate valves ( Figs. 6-8 ) similar to head valve; with rows of pustules parallel to anterior edge; anterior edge rounded, with small straight median edge between apophyses; posterior edge almost straight, with small projected apex; muscle scars occupying about half of interior surface, located close to lateral and posterior edges ( Fig. 7 ); apophyses flat, triangular, approximately same length as valve ( Figs. 6-8 ). Sculpture of tail valve ( Figs. 9-11 ) similar to head valve, except for concentric rows of pustules on central apex; mucro prominent, weakly projected posteriorly; muscle scars occupying about half of inner surface, more concentrated in lateral and middle regions ( Figs. 10 ); apophyses similar to those of intermediate valves, except about 30% shorter.

Girdle ( Figs. 1, 2, 12-15 ): Color cream. Dorsal surface totally covered by long cylindrical spines (measurements: 500 to 650 µm), 10-15 times longer than wide, apex pointed. Marginal spines shorter (measurements: 350 to 400 µm) ( Figs. 13, 14 ). Ventral surface with similar but much shorter spines (measurements: 90 to 260 µm) ( Figs. 12, 15 ).

Main muscle system ( Figs. 18, 19 ): Pair of straight muscles (ml), originating on second valve, in its anterior-ventral region at some distance from anterior edge and from median line, each scar equivalent to 0.5% of inner surface of valve; extending towards posterior flanking mantle surface, somewhat flattened dorso-ventrally, each muscle occupying about 0.5% of body width; after anterior insertion, in distance equivalent to 16% of second valve length, both muscles united with each other along median line; in anterior level of fourth valve, gradually both muscles diverge from each other, extending close to median line; insertion scar in anterior third of seventh valve, similar to origin scar; secondary insertions all along these muscles in anterior extremity of each valve (id), from third to seventh valves. Eight pairs of transverse muscles (mr), somewhat thick; each one originating in lateral region of foot, extending towards dorsal and medial valve surface, bordering dorsal surface of visceral mass; intermediate insertion along lateral edge of each valve; afterwards becoming oblique and triangular, with fibers directed medially and posteriorly; final insertion along anterior edge of middle portion of tail valve; these muscles relatively small in head valve and very narrow in tail valve. Muscles of head valve (cm) consisting of 4 bundles, originating from anterior edge of foot, running dorsally and anteriorly, aligned transversely in middle level of head valve. Seven pairs of lateral muscles (ma), with approximately same thickness as dorsal muscles; each muscle originating on lateral-anterior edge of each valve (except tail valve), just anterior to secondary insertion of transverse muscles, in an area equivalent to 0.33% of valve inner surface; running medially and posteriorly, narrowing gradually, in their anterior 1.5% edging inner border of transverse muscles, gradually crossing ventrally to this in posterior 3%; inserting on immediately posterior valve, close to median line, adjacent to secondary insertions of longitudinal muscles in an area equivalent to 1.5% of their origins. Insertion of lateral muscles (ma) and longitudinal muscles (ml) just posterior to insertion of transverse muscles (mr) on anterior edge of each valve.

Mouth and foot ( Figs. 2 , 19 , 22 ): Mouth wide, a transverse central slit in shape of inverted “U”, occupying about 16% of ventral surface. Anterior pair of folds flanking entire anterior region of mouth, narrow in median line, widening laterally; posterior-lateral end rounded. Posterior pair of folds elliptical, flanking almost entire posterior edge of mouth, except for short area on median line. Foot occupying about 80% of entire ventral surface; lateral edges of sole planar and uniform, extending slightly beyond its dorsal region, covering ventral region of pallial furrow; sole relatively thin along median line, thickening towards borders.

Pallial cavity ( Figs. 19 , 22 ): Pallial furrow extending along a narrow space between girdle and foot; particularly narrow around labial palp. Anterior and middle thirds about 25% as wide as girdle. Gradually and slightly widening posteriorly. Gills with about ten filaments restricted to posterior quarter, slightly longer laterally. Anterior and posterior filaments slightly shorter than middle filaments, ending at short distance from anus. Gill filaments triangular, relatively elongated, about three times larger than their base ( Fig. 21 ). Both edges relatively thicker on middle surface. Efferent vessel broader than afferent vessel. Pair of very small pores (nephridial and genital) in anterior level of gills, closer to outer edge. Anus located in medial line, near outer edge of mantle furrow.

Visceral mass ( Fig. 22 ): Buccal mass restricted to anterior region, about 16% of visceral mass. Digestive gland brown, occupying about 60% of inner space; intestinal loops immersed in digestive gland. Pair of gonads cream-colored, extending dorsally and laterally, occupying about 15% of visceral mass; pericardium and kidney confined to posterior quarter, pericardium dorsal and kidney ventral, with a flat portion of gonad and rectum between them.

Circulatory and excretory systems ( Figs. 19, 20 , 22 ): Pericardium lozenge-shaped, dorso-ventrally flattened, located in posterior and dorsal ends. Pericardial membrane thin, translucent. Efferent gill vessel and auricle separated by thick muscle wall; five relatively wide orifices connecting both chambers; one orifice isolated in anterior half, other four orifices more concentrated posteriorly. Pair of auricles symmetrical, walls thin, transparent; external region almost as long as gill, abruptly narrowing to ventricle. Two pairs of connections to ventricle, both restricted to anterior half of ventricle; one connection anterior and the oth- er posterior in same horizontal line; anterior end of both auricles somewhat bulging, rounded. Ventricle surrounding subterminal region of intestine, about half as long as auricles, ending at short distance from posterior haemocoel wall. Anterior aorta running along ventral surface of intestine. Kidney very flat, restricted to posterior half of haemocoel, constituted of branched, dark-brown nephridia flanking outer and dorsal inner surface of haemocoel. Gradually becoming more concentrated posteriorly and ventrally, covering ~2% of entire ventral surface of visceral organs. Pair of final nephroducts not seen in detail, but possibly as a pair of whitish tubes running obliquely through anterior edges of pericardium. Renal orifices in each side in anterior level of gill, between bases of first and second gill filaments.

Digestive system ( Figs. 22-31 ): Mouth wide, locat- ed ventrally at mid-region of labial palp. Oral tube thin-walled, connecting mouth to lateral and ventral regions of odontophore and to dorsal region of oral cavity ( Fig. 23 ). Pair of lateral buccal dilators (m1a) originating in lateral inner surface of haemocoel, at posterior level of labial palp; passing anteriorly and medially through nerve ring; inserting in lateral and slightly ventral sides of oral tube, close to mouth. Buccal sphincter narrow and inconspicuous, immersed in walls of oral tube, except for lateral thick muscle bundles ( Figs. 27, 28 : mj) inserted in outer surface of cartilages, between anterior and middle thirds ( Fig. 30 : mj). Pairs of dorsal retractor muscles of buccal mass (m1d) originating in 2-3 small portions of dorsal wall of haemocoel on each side, just dorsal to oral tube and close to median line; running ventrally and posteriorly, sometimes coalescent, at about same length as oral tube; inserting in lateral side of transition between oral tube and dorsal wall of buccal mass. Pair of ventral retractors of buccal mass (m1v) originating in lateral region of haemocoel, in mid-level of oral tube, from 3-4 small points on each side; running anteriorly and dorsally; inserting on lateral side of posterior region of oral tube ( Fig. 23 ). Odontophore occupying about 75% of buccal mass. Odontophore muscles: m2, pair of radular muscles or retractor muscles of odontophore, thick and strong, composed by several separate bundles; originating in second valve, each origin circular, occupying about 2% of valve inner surface, located close to median line, separated from each other by straight muscle ( Figs. 18, 19 : rm); extending in sigmoid fashion anteroventrally ( Figs. 25 , 27 ), flanking median line along half of buccal mass; inserting partly in posterior region of cartilages, in arched, narrow region ( Fig. 30 ), and partly in median-ventral surface of radular sac ( Fig. 25 ). Pair of dorsal protractor muscles of buccal mass (m3), somewhat thick and cylindrical, originating in latero-dorsal region of haemocoel, in posterior level of oral tube; extending posteriorly along entire length of buccal mass; inserting in lateral region of posterior end of cartilages ( Figs. 23-25 , 29 ). Pair of dorsolateral circular muscles (m3a), extending superficially covering dorsal wall of buccal mass, in its posterolateral region ( Fig. 23 ); inserting in posterolateral region of cartilages, just internally to insertion of m3. Main pair of dorsal tensor muscles of radula (m4) thick; originating in ventrolateral edge of cartilages ( Figs. 30, 31 ), along almost their entire edge; extending medially and dorsally, covering internal surface of cartilages ( Figs. 25 , 27 ); inserting in subradular cartilage along its entire portion crossing through odontophore, close to median line. Pair of secondary dorsal tensor muscles (m4a), small and short; originating in inner lateral surface of membrane covering odontophore; extending a short distance dorsally and medially; inserting in lateral region of subradular cartilage, in its middle level in odontophore ( Figs. 24, 25 ). Pair of medial dorsal tensor muscles of radula (m 4m) flattened and wide, about 33% as long as odontophore; originating in ventral edge of cartilages ( Fig. 27 ); extending dorsally over anteromedial surface of cartilages; inserting in subradular membrane, in its anterodorsal region. Pair of auxiliary tensor muscles of radula (m5) thickened; originating along dorsolateral edge of cartilages ( Figs. 30, 31 ), on nearly opposite side to m4 origin; extending towards median region, covering m4 pair ( Figs. 27, 28 ), becoming gradually narrower; inserting in subradular cartilage in anterolateral level of m4 insertion. Horizontal muscle (m6) connecting both cartilages along their anterior portion, occupying about 65%; inserting in both cartilages close to centrolateral surface ( Fig. 30 ), about as wide as long ( Figs. 28, 29 ). Pair of very narrow, long muscles (m7); originating in lateral and middle region of cartilages, extending superficially towards dorsal region, and after a distance equivalent to 33% of its length extending posteriorly, covered by expansions of subradular cartilage ( Fig. 24 ); inserting in subradular cartilage just posterior to its expanded region. Pair of protractor muscles of buccal mass (m10); originating ventrally at middle level of oral tube, close to median line; diverging from each other posteriorly and slightly dorsally; inserting on lateral side of posterior end of each cartilage ( Fig. 23 ). Pair of ventral tensor muscles of radula (m11) long and thin; originating on ventral surface of haemocoel, just posteriorly to buccal mass; extending towards dorsal region, penetrating into odontophore laterally at radular sac at a distance equivalent to odontophore length; inserting in subradular cartilage on its ventrolateral edge ( Figs. 27, 28 ). Pair of secondary ventral tensor muscles of radula (m11a) short, slightly thicker than m11; originating in anteroventral region of cartilages; extending medially and slightly anteriorly; inserting on ventral end of subradular cartilage, close to median line ( Fig. 28 ). Subradular cartilage extending along ventral surface of radula; with pair of wide rounded expansions in buccal cavity ( Fig. 16 ); each expansion half width of radula. Pair of cartilages claviform and flattened ( Figs. 27 , 30, 31 ); anterior third wide, half as wide as odontophore, with a blunt ventral projection; abruptly narrowing between anterior and middle thirds, middle and posterior thirds about half as wide as anterior third, length uniform, thickness about 33% of width; posterior end rounded. Dorsal wall of buccal mass ( Figs. 23 , 26 ) with pair of small chambers (dc) filled by mucus; each chamber about half as long and one-fourth as wide as buccal mass; medial edge with relatively tall, longitudinal fold (df); anterolateral edge bearing salivary gland (sg); remaining surface of dorsal wall and esophagus smooth. Esophagus short, wide and simple, about 33% as long as buccal mass ( Fig. 23 ). Stomach inconspicuous, marked only by wide duct to digestive gland ( Fig. 22 : dd); duct to digestive gland successively branched, with branches immersed in digestive gland. Digestive gland occupying about 60% of haemocoel, along its central region ( Fig. 22 : dg). Intestine initially as wide as esophagus, gradually narrowing distally ( Fig. 22 : in); with single loop surrounding digestive gland; inner surface simple, smooth. Rectum simple, very narrow, crossing through posterior chamber of kidney. Anus simple, short and with low papilla.

Genital system ( Figs. 20 , 22 ): Pair of gonads described above (visceral mass), connected posteriorly to each other, dorsally to kidney. Genital pores in pallial furrow visible as pair of very small orifices located near anterior end of gill ( Fig. 19 : gp), preceded by pair of genital ducts located anteriorly and dorsally to pericardium ( Fig. 19 : gd).

Central nervous system ( Fig. 32 ): Pair of cerebral ganglia weakly defined, about as wide as anterior region of oral tube. Cerebral commissure about half as wide as buccal mass; narrower region close to median line, about half as wide as cerebral ganglion; several pairs of secondary nerves along anterior and posterior edges of ganglia and commissure. Pair of buccal ganglia about half size of cerebral ganglia; located between oral tube and dorsal wall of buccal mass ( Fig. 26 : bg).

Measurements (respectively antero-posterior length, dorso-ventral height, and maximum lateral inflation, in mm): Holotype ( MZUSP 87263): 41.5 by 10.0 by 2.5; paratypes: MZUSP 87264: 51.0 by 14.0 by 27.7; MORG 18953: 73.0 by 12.2 by 26.0.

Distribution: SE and S Brazilian coast, from São Paulo to Santa Catarina.

Habitat: From 250 to 408 m depth, substrate unknown.

Figures

FIGURES 1‑17: Hanleya brachyplax, holotype, photos and SEM. 1, dorsal view, length = 416 mm; 2, right view; 3-5, head valve, dorsal, ventral, and right views; 6-8, fourth valve, dorsal, ventral, and right views; 9-11, tail valve, dorsal, ventral, and left views, scale = 5 mm; view 12, girdle, middle portion of right side, profile (ventral region at left); 13, same, view from edge; 14, same, higher magnification; 15, same, detail of ventral surface; 16, radula, anterior region; 17, radula, detail of a portion preceding buccal mass. Scales = 500 µm, except 4 = 200 µm.

FIGURES 18‑21: Hanleya brachyplax, anatomy. 18, whole dorsal view, valves removed, showing main muscle groups, scale = 10 mm; 19, whole ventral view, foot and visceral structures mostly removed, showing main muscle groups, scale = 10 mm; 20, pericardial region, ventral view, ventral wall of pericardium and adjacent structures removed, topology of some associated organs shown, scale = 5 mm; 21, isolated gill filament as in situ, scale = 2 mm.

FIGURES 22‑25: Hanleya brachyplax, anatomy. 22, whole ventral view, foot removed, visceral structures deflected, scale = 10 mm; 23, buccal mass, right view; 24, odontophore, right view, superficial layer of muscles and membranes removed; 25, same, dorsal view, most structures slightly deflected; scales (23-25) = 2 mm.

FIGURES 26‑29: Hanleya brachyplax, anatomy. 26, dorsal wall of buccal mass, ventral-inner view; 27, odontophore, dorsal view, both cartilages deflected, most left muscles also deflected, left m4m sectioned longitudinally; 28, odontophore, ventral view, superficial layer of membranes mostly removed, radular sac longitudinally sectioned; 29, same, superficial layer of membranes and muscles as in situ. Scale = 2 mm.

FIGURES 30‑32: Hanleya brachyplax, anatomy.30, right odontophore cartilage, medial view, muscle origins shown; 31, same, lateral view; 32, central nervous system, frontal-anterior view, topology of mouth shown. Scale = 2 mm.