Coccodentalium carduus ( Dall, 1889 )

Simone, Luiz Ricardo L., 2009, Comparative morphology among representatives of main taxa of Scaphopoda and basal protobranch Bivalvia (Mollusca), Papéis Avulsos de Zoologia 49 (32), pp. 405-457 : 409-412

Coccodentalium carduus ( Dall, 1889)

( Figs. 1-9 , 47-64 )

Dentalium carduus Dall, 1889: 423 (pl. 27, fig. 3); Pilsbry & Sharp, 1897: 30 (pl. 7, fig. 6); Henderson, 1920: 33 (pl. 3, figs. 4, 5, 7); Steiner & Kabat, 2004: 573-574.

Dentalium (Fissidentalium) floridense Henderson, 1920: 64-65 (pl. 10, figs. 1, 2, 6, 7) [off Sand Key, Florida (Eolis sta. 301, 173 m depth]; Penna-Neme, 1974: 113; Scarabino, 1975: 184 (pl. 59, fig. 902); Steiner & Kabat, 2004: 591.

Dentalium (Coccodentalium) carduus : Emerson, 1952: 2.

Dentalium (Dentalium) carduum : Turner, 1955: 311.

Dentalium (Coccodentalium) carduum : Abbott, 1974: 384 (fig. 4497).

Dentalium (Fissidentalium) amphialum : Penna-Neme, 1974: 113 (non Watson, 1879).

Fissidentalium floridense : Scarabino, 1985: 199 (pl. 72, fig. 1021); Emerson in Turgeon, 1988: 50; 1998: 54, 200; Sumida & Pires-Vanin, 1997: 781.

Fissidentaliumcarduum: Scarabino,1994: 306 (pl. 106, fig. 1509); Steiner & Kabat, 2001: 444.

Coccodentalium carduum : Steiner, 1998: 81.

Fissidentalium carduus : Steiner & Kabat, 2004: 574.

Coccodentalium carduus : Caetano et al., 2006: 18 (figs. 33-38); Caetano, 2007: 94-97 (figs. 73-83).

Types: lectotype MCZ 7692 (designed by Henderson, 1920: 30); paralectotypes: USNM 95321 , 1 shell; USNM 95322 , 1 shell; MCZ 7691 , 1 shell. D. floridense : Holotype USNM 314457 (examined).

Type locality: Lesser Antilles , 13°50’N 61°03’W, off St. Lucia, 211 m depth (Blake sta. 220) .

Description

Shell ( Figs. 1-5 ): Size about 80 mm, walls thick, color white, weakly curved, section circular ( Fig. 4 ). Color yellowish. Relatively abrupt widening (tax of increase about 0.145 mm /mm of length). Sculpture six longitudinal, equidistant primary ribs close to posterior aperture; gradually secondary ribs appearing between primary ribs towards anterior, about 30 similar-sized ribs close to anterior aperture ( Figs. 2-3 ); each longitudinal rib spaced from neighboring ribs by space equivalent to is width, this space filled by transverse, uniform threads, located close to each other (space about half their width), each thread about three times smaller than longitudinal ribs, transversely aligned, producing uniform reticulate effect. Posterior aperture with narrow slit in ventral surface ( Fig. 5 ), from 3 to 8% of shell length.

Main muscle system ( Figs. 47-50 ): Pair of longitudinal muscles originated in ventral side of base of apical flap of posterior aperture ( Fig. 49 ), occupying about half of this base. Both longitudinal muscles running straight towards anterior, gradually crossing from ventral to lateral, coming away from one another ( Figs. 47, 48 ). Posterior half of each muscle incompletely divided longitudinally in two portions of equivalent sizes. Thinness of both longitudinal muscles equivalent to that of shell wall, gradually becoming slightly thicker anteriorly. Both longitudinal muscles bifurcating between middle and anterior thirds of animal’s body; external branches splaying like a fan in anterior pallial wall up to anterior 1/6, where both muscles touch each other along medial line, thickness about half of that of shell wall, both muscles ending in anterior mantle edge; internal branches splaying in foot base as longitudinal layer of foot retractors, thickness equivalent to that of shell wall. Thin internal layer of circular muscles surrounding posterior half of foot, with thickness about half of external layer of longitudinal muscles. Longitudinal pedal muscles becoming thicker in anterior pedal half, forming two distinguishable thick layers, a dorsal layer covered by integument, another ventral layer running laterally, forming lateral walls of visceral mass, in direction of bifurcation of longitudinal muscles ( Fig. 53 ). Posterior mantle flap with a very thin layer of longitudinal muscles inserted in a ring of entire flap base, just posterior to longitudinal muscles origin in ventral half.

Foot ( Figs. 47, 52-54 ): Solid in anterior half, surrounding visceral mass in posterior half; total length approximately 1/3 of total shell length; width about 2/3 of adjacent shell width. Proximal 3/4 somewhat cylindrical, abruptly expanding in distal tip as an umbrella, about 1/3 wider. This umbrella-like edge surrounding a central elevation, tall, with about half of foot width and 1/6 of its length; tip rounded. Foot edges producing a concavity turned anteriorly, uniform, except for a ventral notch becoming a longitudinal furrow, running along ventral side of central projection. Basal portion of foot divided by a pair of muscular bundles, one ventral and another dorsal to visceral mass, both gradually converging to longitudinal muscles.

Mantle ( Figs. 47-49 ): Very thin, translucent, with anterior aperture about 4 times wider than posterior aperture. No pigment. Anterior edge very thick ( Figs. 47, 48 ), a pair of folds; outer fold relatively narrow, thickness equivalent to that of shell wall; inner fold 5-6 times wider and taller than inner fold, positioned inward. Posterior mantle flap tall, about 1/7 of shell length; aperture with ventral notch very deep ( Figs. 47, 49 ), almost reaching flap base; posterior region of aperture wider; edges simple and thin. Posterior aperture preceded by wide notch, occupying almost entire ventral length; edges thin, simple; length of notch about 1/7 of total shell length.

Pallial cavity: Compressed by pedal and visceral structures, with approximately 1/3 of internal shell space. Mantle with about 7-8 transverse folds present in basal level of foot, uniform, very narrow (width equivalent to mantle thickness), spaced by equivalent width (of folds); surrounding entire mantle; length about 1/20 of shell length ( Fig. 47 : pf). Glandular area located just posterior to folds, area about 3 times longer than folds, composed by irregular, yellow acini, very low, plane, close to each other ( Fig. 47 : pl).

Visceral mass ( Figs. 47, 48, 52 , 53, 55, 56 ): Elongated and conical as internal mould of shell. Anterior region (about 1/4 of shell length) located inside posterior half of foot; posterior region of foot bulged ventrally, containing almost exclusively digestive tubes (foregut and intestinal loops) ( Figs. 53, 55 ). Middle region with about 1/8 of shell length containing reno-pericardial structures, with about same width of posterior region of foot. Posterior region almost as long as anterior region, containing stomach in anterior half and gonad in posterior half ( Figs. 47, 52 ). All structures described below. Region preceding kidney and anus, continuous with foot, ventrally bulged; this form maintained by cruciform-like musculature of local wall of integument ( Fig. 50 : cm).

Circulatory and excretory systems ( Figs. 47, 50, 51 ): Pericardium a simple hollow chamber located in center of reno-pericardial ventral surface (pc). Dorsal surface touching stomach centro-anterior region; ventral surface bulging inside pallial cavity; anterior and a portion of dorsal surface touching kidney. No detectable heart. Kidney solid, pale beige, triangular, occupying about 3/4 of reno-pericardial area. No detectable inner folds or chamber. Nephropore a pair of slits as lateral ends of kidney; apparently lacking sphincter, protected by pair of low flaps, one anterior and another posterior. Anterior third of kidney surrounding rectum.

Digestive system: Enormous quantity of captacula ( Figs. 47, 52 ). Conjunct of captacula about 4-5 times shell thickness. Base of captacula as curve flap located surrounding base of oral tube ( Figs. 52 , 54 : cb), a distance equivalent to 1/5 of local visceral width from base of oral tube and restricted to ventral and lateral sides. Oral tube ( Figs. 52-55 : ot) wide, thin-translucent walled; length and width about 1/3 those of foot; base rounded, located somewhat equidistant from that of foot (dorsally) and of captacula (laterally and ventrally). Oral tube inner surface with pair of longitudinal folds ( Fig. 55 : of); each one U-shaped (opened anteriorly), located on each lateral side, dividing inner oral tube volume in three approximately equivalent chambers; tallness of each fold with about 1/4 of oral tube width; anterior ends of each fold gradual, distant from edge about 1/8 of oral tube length. Oral tube edge simple, undulating. Mouth located at base of oral tube ( Figs. 53-55 : mo), elliptic, simple, lacking apparent sphincter. Odontophore located on dorsal surface of esophagus, at about 1/20 of shell length posterior to mouth ( Figs. 53, 55 : od). Connection between esophagus and odontophore a small orifice with about half of local esophageal width, lacking sphincter ( Figs. 57, 58 : on). Odontophore spherical, with about 1/5 of visceral mass volume. Except for connection with esophagus, no other structure connecting odontophore with neighboring structures. Odontophore muscles ( Figs. 57-62 ): mj, pair of thin protractor muscles ( Figs. 57, 58 ), located immersed in halls connecting odontophore and esophagus, more concentrated laterally, becoming thinner ventrally (dorsal wall free from muscular tissue); originating in orifice with esophagus, inserting in odontophore cartilages lateral and ventral edges; m3, single muscle connecting dorsal edges of both odontophore cartilages ( Figs. 59-62 ), about as wide as odontophore, with about 1/4 of odontophore thickness; m4, main pair of dorsal tensor muscles ( Figs. 57-62 ), strong and wide, originating on outer edge of anterior surface of odontophore cartilages, running posteriorly covering cartilages posterior edges, after running medially towards anterior, inserting in radular sac along its internal portion inside odontophore, origins almost as wide as cartilages, medial region with muscular fibers coming from each muscle imbricating, about half thick of m3; m6, single muscle of approximator of cartilages ( Figs. 59-62 ), uniting medial-ventral edges of both odontophore cartilages, mainly in internal edges, with about half of cartilages length, posterior region with about 1/4 of each cartilage width, graduating becoming wider, anterior region with about double of posterior region, about half thick as m3; m7, pair of small muscles located inside radular sac lateral walls ( Fig. 60 ); each with about 1/4 of radular sac wall width, originating in insertion of m4 pair, running towards posterior, gradually disappearing along radular sac lateral walls. Odontophore cartilages (oc) somewhat squared (with rounded vertices) ( Figs. 61, 62 ), weakly curved and concave internally; thickness about 1/5 of that of odontophore; anterior edge about 85% shorter than posterior edge. Subradular cartilage expanding about 20% beyond radula in exposed (in use) region of odontophoral chamber connected to esophagus, performing a circular protective layer covering entire odontophore exposition inside this chamber ( Figs. 6, 7 ). Radula relatively short, about 50% longer than odontophore length ( Figs. 57, 58 ); color uniform pale brown; about half of radula located inside radular sac, possessing about same length of odontophore, positioned approximately in its center, and surrounded by pair of m4 muscles ( Figs. 59, 60 : rs); distal half or radula expanded, covering exposed portion of odontophore; about 20 rows of radular teeth along its length ( Figs. 6, 7 ). Radular teeth ( Figs. 6, 8, 9 ): rachidian (central) tooth almost rectangular, weakly curved; with about 1/4 of total radula width and about three times wider than long; no cusps or projections; distal edge shallowly concave and encased in preceding tooth, distal edge slightly thicker and shallowly convex. Pair of lateral tooth sigmoid, marginal half thinner and located at a position more distal than at medial half; width about 70% that of rachidian; medial half flattened, with rounded, relatively thick proximal edges, located approximately in same level of rachidian; lateral half with strong, subterminal concavity in proximal edge with about 1/3 of tooth’s width, located approximately at level of following distal rachidian; proximal-marginal vertex marked by small cusp turned proximally. Pair of marginal teeth similarly shaped to rachidian, except in being flatter and obliquely positioned (approximate angle of 55° in relation to longitudinal axis of radula); medial edge thicker than lateral edge; medial edge articulating with lateral edge of lateral tooth. Esophagus running directly towards posterior ( Figs. 53, 55, 56 : es), flattened dorso-ventrally; length slightly longer than 1/3 of that of shell, width about 1/3 of local visceral width in anterior half, and gradually about half of that in posterior half. Esophageal insertion simple, on right side of stomach middle-dorsal region. Stomach ( Figs. 47, 52 , 53, 55 : st) constituted by central chamber, with about 1/7 of total shell length, somewhat flattened dorso-ventrally, smooth, simple inner surface; and marginal digestive diverticles in lateral edges; about 20 pairs of similar-sized diverticles, each pair of diverticles performing lateral, flat expansions like wings, being slightly longer posteriorly ( Figs. 50 , 53, 55 : dg); diverticles staying somewhat aligned in a virtual longitudinal line, directed externally, located immersed in lateral walls of visceral mass and part exposed in middle region of pallial cavity, each conjunct of diverticles with about 1/5 of shell length and about same width of stomach; surrounding animal walls towards ventral, performing, both conjunct of diverticles and ventral concavity. Each digestive diverticle with rounded tip; walls thin, translucent; performing an undulating cylinder with about 1/4 of local shell width; inner region hollow and continuous with stomach inner surface. Intestine originating in dorsal gastric wall just at left of esophageal insertion ( Figs. 55, 56 ); both situated side by side and of equivalent size (about 1/4 of gastric main chamber). Intestine running direct towards anterior at a distance equivalent to 1/6 of shell length, up to visceral region just posterior to odontophore; in this region intestine performing a complex set of loops as shown in Fig. 55 . Intestine with thin, translucent walls, with uniform width along its length, average width approximately 1/10 of local shell width. Rectum marked by gradual diminishment of width, crossing through kidney ( Figs. 55, 56 ). Anus a small papilla, projected ventrally, edges somewhat expanded and thicker than preceding intestinal walls; located approximately at middle level of pallial cavity, on median line ( Figs. 47, 50 , 55 : an).

Genital system: Gonad somewhat elliptical, with about 1/4 of shell length; about 4 times longer than wide ( Figs. 47, 50 ); located in posterior limit of visceral mass, lying ventrally to posterior half of longitudinal muscles, and with ventral surface exposed in pallial cavity; color pale beige; gonad acini normally distributed in transverse rows connected in longitudinal furrow running along center. Anterior end of gonad continuously connected to gonoduct, very thin walled ( Figs. 56 : gd), transparent. Gonoduct running towards anterior, between stomach and mantle, gradually running obliquely, from median line to right, crossing esophageal insertion; insertion on dorsal-right surface of kidney, just by side of local portion of esophagus.

Central nervous system ( Figs. 53 , 63, 64 ): Pair of cerebral ganglia located just dorsal to mouth (between bases of captacula and oral tube); each cerebral ganglion spherical, with approximate diameter equivalent to 1/15 that of anterior shell aperture; both ganglia located very close to one another and to median line; cerebral commissure very short, narrow, located in middle region of ganglia median surface; two pairs of large anterior nerves. Pair of pedal ganglia of equivalent size than cerebral ganglia, located on foot base at same level of cerebral ganglia, on opposite side of mouth; staying attached to ventral surface of pedal musculature; form of each ganglion roughly spherical, except for low expansions correspondent to each main nerve, being two anterior pairs and another pair postero-lateral. Pedal commissure short, very narrow, located in anterior region of medial surface of both ganglia. Pair of statocysts located just posterior to pedal ganglia, closer to median line; volume of each statocyst about 1/5 of each pedal ganglion; internally several statoconia. Visceral ganglia not seen. Pair of buccal ganglia very small (each ganglion about 1/100 of odontophore), located in ventral wall connecting odontophore to esophagus; distance between both buccal ganglia equivalent to 1/4 of odontophore width; a pair of anterior nerves and two pairs of posterior nerves.

Measurements (respectively antero-posterior length, dorso-ventral maximal lateral inflation in mm; finally tax of increase in mm/mm of length): MZUSP 32977: #1: 80.2 by 11.4, 0.142; #2: 74.5 by 11.0, 0.147; MZUSP 47189: 52.3 by 8.1, 0.154.

Distribution: From North Carolina, USA, to Rio Grande do Sul, Brazil.

Habitat: Sandy bottoms, from 40 to 1980 m depth; living specimens from 180 to 270 m depth ( Steiner & Kabat, 2004; Caetano et al., 2006). Content of buccal tube several foranmifer testa and rarely small mollusks.

Material examined: UNITES STATES. Florida. Dry Tortugas, Sand Key, 174 m depth, USNM 314457 (holotype of Dentalium floridense ; Eolis sta. 301, 1915). BRAZIL. Rio de Janeiro. Off Cabo Frio , 350-400 m depth, MZUSP 32977 , 21 specimens (o.t.; C. Cunha col iv/2001) . São Paulo. Off Ubatuba , 320 m depth, MZUSP 47189 , 17 specimens (R.V.W. Besnard sta. 5365; 07/xii/1988) .

Figures

FIGURES 1‑15: Shell, radular and anatomical aspects of Dentaliidae: 1-9) Coccodentalium caduum; 1) Shell, whole right view, MZUSP 32977, length = 74.0 mm; 2) Detail of anterior aperture, profile, right view; 3) Detail of sculpture of middle region. 4) Anterior aperture, anterior view, animal still inside; 5) detail of posterior aperture, dorsal view, scale = 2 mm; 6) Radula in situ, anterior view, scale = 1 mm; 7) Radula removed from odontophore, ventral view, scale = 1 mm; 8-9) Radulae of 2 specimens in SEM, scale = 200 µm; 10-15) Paradentalium disparile; 10) Shell, whole left view, MZUSP 25589#1, length = 35.1 mm. 11) Same, detail of posterior aperture; 12) Shell, whole left view, MZUSP 25589#2, length = 31.5 mm; 13) Detail of dissected anterior region, central view, captacula deflected to show foot, scale = 2 mm. 14-15) Radulae of 2 specimens in SEM, scales = 100 µm.

FIGURES 47‑52: Coccodentalium caduum anatomy: 47) Whole ventral view, mantle opened longitudinally along median line and deflected; 48) Whole left view; 49) Detail of posterior region, dorsal-slightly right view; 50) Detail of middle and posterior region of pallial cavity roof, ventral view; 51) Anterior region of visceral mass, just posterior to haemocoel, transverse, semi-schematic section; 52) Foot and anterior region of haemocoel, left view. Scales = 2 mm.

FIGURES 53‑56: Coccodentalium caduum anatomy: 53) Whole ventral-slightly right view, haemocoel opened longitudinally exposing internal organs, stomach partially deflected, topology of some other structures also shown; 54) Detail of foot and anterior region of haemocoel, left view, captacula mostly extracted, except their base; 55) Digestive tubes, left view, foregut opened longitudinally, topology of some adjacent structures also shown, trajectory of intestine indicated in schematic representation at left; 56) Middle region of visceral mass, dorsal view, outer layer of structures, main mantle and longitudinal muscles, removed. Scales = 2 mm.

FIGURES 57‑64: Coccodentalium caduum anatomy: 57) Odontophore, dorsal view; 58) Same, ventral view; 59) Odontophore, anterior view, superficial layer of muscles and membranes removed, part of radula also removed (except portion inside radular sac); 60) Same, posterior view, radula completely removed, left portion of radular sac shown in situ, right m4 deflected; 61) Same, dorsal view, m3 transversally sectioned, both cartilages deflected; 62) Same, both m4 deflected downwards; 63) Cerebral ganglia, ventral view; 64) Pedal ganglia and statocysts, dorsal view. Scales = 0.5 mm.