Crepidula margarita, Simone, 2006

Simone, Luiz Ricardo L., 2006, Morphological and phylogenetic study of the Western Atlantic Crepidula plana complex (Caenogastropoda, Calyptraeidae), with description of three new species from Brazil, Zootaxa 1112 (1), pp. 1-64 : 7-13

Crepidula margarita new species

(Figs. 10–12, 26, 27, 35–51)

Crepidula aplysioides, Hoagland 1977: 369 ; Simone et al. 2000: 140. (non Reeve, 1859).

Types: Holotype MZSP 36329 ♀ . Paratypes: MZSP 50892 , 11 specimens from type locality .

Type locality: VENEZUELA; Nueva Esparta State; Margarita Island; La Restinga lagoon, 64 02'– 64 12'W 10 90'– 11 02'N (P. Penchaszadeh col.).

Description:

Shell (Figs. 10–12): Wide, somewhat flat, concave, outline oval; walls thin, transparent. Color cream, with pale brown, narrow, irregular spiral, radial bands. Periostracum absent, except very narrow portions in shell edges. Outer surface with weak growth lines. Anterior edge of septum with broad and shallow central notch, with edges almost straight, and another shallow notch in left end, narrower (Fig. 11). Inner surface glossy.

Head­foot (Figs. 36, 42): Head differentiated, preceded by long, dorso­ventrally flattened, neck region, about half as long as foot. Proboscis short, cylindrical, can be entirely retracted within haemocoelic cavity (Fig. 36). Tentacles long, stubby, apex somewhat bifid. Eyes dark, small, located on very short ommatophores in basal region of tentacles lateral margin. Neck with pair of lateral, flattened lappets (nuchal lobes); left expansion narrower than right one; right expansion bringing low food groove along its dorsal­medial limit (Fig. 36: fg). Foot wide (occupies about 3/4 of shell ventral area, dorso­ventrally greatly flattened, thin; distinct longitudinal inner sinus runs in median line; shell septum as dorsal foot limit. Mantle fuses with dorsal surface of foot and protrudes beyond its borders. Furrow of pedal glands transverse, in anterior margin of foot; this anterior margin of foot covered dorsally by posterior region of neck ventral surface. Columellar muscle reduced, very small, contours anterior border of shell septum, more pronounced on right (Fig. 36: cm) in smaller specimens and almost absent in larger ones. Inner haemocoel cavity narrow, running approximately in center of neck region. Inner space almost all filled by great quantity of transverse, very slender muscular fibers; these fibers connect ventral surface of dorsal haemocoel wall with dorsal surface of its ventral wall, contouring salivary glands and esophagus (Fig. 42: tm). No vestiges of operculum even in very young specimens (smaller than 1 mm) inside egg capsules.

Mantle organs (Figs. 35, 37–40): Mantle border thick, slightly hollow due broad collar sinuses (Fig. 40). Mantle border surrounds entire ventral margin of shell, free in anterior third and attached to foot margins in posterior 2/3, situated slightly away from foots edge, connected to it by a thin, semi­transparent portion. Mantle border without appendages, but filled entirely by series of minute repugnatorial glands, aligned inside mantle edge. Mantle border with special arrangement of folds in middle region of opening of pallial cavity, broad fold starting at anterior end of gill, running towards left, decreasing in width, disappearing abruptly at level of osphradium; its broader region possesses a central, broad furrow, its posterior edge expands beyond mantle border covering ventrally anterior region of gill, its anterior edge slightly projected outside (Fig. 37). Dorsal shell muscle well developed (Fig. 35: dm), origin small, in about middle­right region of shell, just anterior to septum; their fibers run fan­like anteriorly, insertion in adjacent anterior region of dorsal surface of pallial cavity. Lateral shell muscle (Figs. 35: lm) very small, fan­like, located close to mantle border on right side, just in region where pallial cavity penetrates shell septum chamber. Opening of pallial cavity occupies about 2/3 of anterior half of shell margin turned to right (if shell compared with a clock, in dorsal view and with head occupying 12 oclock, pallial aperture begins in 10 and finishes in 2 oclock) (Fig. 38). Pallial cavity deep, broad, triangular, arched and dorso­ventrally flattened. Anterior extremity of pallial cavity slightly larger than its opening due to closure in left and right extremities produced by fusion of mantle and foot (Figs. 38, 39: ml). Gradually, pallial cavity narrows towards posterior, extending at left of visceral mass (described below); cavity length about 2/3 of total length of animal (Figs. 35, 38, 39). Osphradium very small, monopectinate, located between anterior half of gill and mantle border, at some distance from gill anterior end, located about in left region of pallial aperture somewhat perpendicular to longitudinal axis of animal body (Figs. 38). Length of osphradium slightly more than 1/6 of length of pallial opening, shaped like a small fold, attached to mantle, separated from gill structures. Osphradium leaflets cylindrical, separated from each other, somewhat thick and tall, approximately 9 in number (Fig. 37). Osphradial ganglion narrow. Gill very large, its base somewhat narrow, surrounding anterior and left margin of pallial cavity [almost entire length of this cavity; anterior tip of gill in rightanterior region of opening of pallial cavity, close to its right limit, on thick mantle border; posterior margin of gill in posterior end of pallial cavity (Fig. 39). Basal region of gill filaments triangular, with very long, almost straight, narrow, stiff rod turned to right (Fig. 40); rods about three times as long as their triangular, membranous base; rods begin in ctenidial vein region, in left margin of cavity roof, touching food groove of head­foot, in right margin of cavity floor; rod apex rounded and preceded by thicker region. Gill filaments stay connected with each other by cilia, mainly of their thicker apical region, maintaining them in somewhat firm position. Gill filaments longer in central gill region, shortening gradually in both extremities; anterior tip of gill, with short filaments, suddenly turning forwards, located on mantle border (Figs. 37–39). Ctenidial vein narrow, of uniform width along its length. Endostyle well­developed (Figs. 37, 39: en), yellowish, in form of broad and flat glandular ridge located in middle level of ventral surface of ctenidial vein all along its length. Hypobranchial gland whitish, thin, weakly developed, surface smooth; occupies area between gill and visceral mass. About 1/3 of visceral mass encroaching on pallial cavity roof (Fig. 39), occupying about 1/3 of this cavity in posterior­right region; pericardium and kidney posteriorly; intestinal loop long, anus and pallial oviduct anteriorly (described below).

Visceral mass (Figs. 35, 38, 39): Dorso­ventrally flattened, cone­shaped, housed in shell chamber produced by thin calcareous septum (Fig. 35); separating visceral mass from dorsal surface of foot. Left and anterior region of visceral mass occupied by pallial cavity (Figs. 35, 39). Remaining regions of visceral mass with stomach as central structure, immediately surrounded by digestive gland (except in some ventral and dorsal areas). Gonad surrounds externally digestive gland, more concentrated anteriorly. All structures described in more details below. Visceral mass also lies on right­posterior region of pallial cavity roof as described above, and possesses another ventral flap forming floor of pallial cavity. Anterior extremity of visceral mass ventral flap stays just in shell septum anterior border, covering columellar muscle (Figs. 38, 39).

Circulatory and excretory systems (Figs. 39, 41): Pericardium somewhat triangular and broad, situated obliquely to longitudinal axis of animal (Fig. 35: pc). Left region of pericardium very narrow, forming a vein connecting gill with auricle, beginning just at posterior end of gill, in posterior­left end of pallial cavity; running along anterior margin of visceral mass (its portion in pallial roof), about in middle level of this region of visceral mass it connects to auricle, near median line. Remaining pericardium limits: 1) anterior and ventral pallial cavity; 2) posterior visceral mass (gonad generally); 3) dorsal mantle; 4) right kidney. Auricle thin­walled, long, narrow, runs all along broader region of pericardium, attached to its anterior and dorsal inner surfaces (Fig. 41); connecting with ventricle approximately in its middle portion; auricle having broad portion beyond ventricle connection as blind sac (Fig. 41: ab), bearing orifice to nephridial gland. Ventricle elliptical, very muscular; its connection with auricle located about in middle region of its anterior surface; on opposite side bears origin of aortas. Anterior aorta broad, running towards opposite side than posterior aorta. Anterior aorta running towards right, adjacent to posterior inner pericardium surface; penetrating head haemocoel. Kidney occupying about half of visceral mass within pallial cavity (Figs. 39, 41). Kidney limits: 1) dorsal mantle; 2) ventral pallial cavity; 3) posterior­right visceral mass (gonad generally); 4) posterior­left pericardium; 5) anterior an intestinal loop; 6) lateral­right intestine and oviduct (when present). Kidney central region hollow, with single lobe (Fig. 41). Kidney lobe slightly uniform, covers dorsal surface, intestinal region passing through kidney chamber, and about 1/4 of inner space of kidney adjacent to intestine. Nephridial gland in renal limit with pericardium, very small, presenting a series of triangular, transversal, narrow folds connected with dorsal renal lobe (Fig. 41: ng). Nephrostome a very small slit in left­anterior region of ventral wall (Figs. 39, 41), in anterior region of hollow portion of kidney; no inner glandular folds close to it. Adrectal sinus very broad, adjacent to externally intestine loop exposed in pallial cavity, connected to main kidney chamber by a narrow region presenting a branch of renal lobe; this branch runs a short distance inside adrectal sinus (Fig. 41).

Digestive system (Figs. 42–49, 51): Proboscis short and broad, with capacity of retraction inside haemocoel in small rhynchocoel (Figs. 36, 42), but a short snout remains. Pair of narrow ventral proboscis retractor muscles very thin, immersed in proboscis wall. Mouth longitudinal, in center of anterior proboscis surface. Buccal mass very large, occupying most of proboscis inner space and short portion of haemocoel posterior to it. Jaw plates in dorsal wall of buccal mass, thin, almost vestigial, broad laterally, short longitudinally (Fig. 44). Pair of dorsal folds broad and tall, begin at some distance posterior to jaws; dorsal chamber between both folds shallow. Odontophore occupying about 1/4 of haemocoelic space, and most of buccal mass volume. Odontophore muscles (Figs. 43, 45–49: m1) jugal muscles, several very narrow muscles connecting buccal mass with adjacent wall of snout, more concentrated anteriorly around mouth; m1a) pair of dorsal protractor muscles, narrow, thin and superficial, origin in anterior­dorsal region of mouth, close to median line, inserting in posterior­dorsal­lateral region of odontophore; m2) pair of retractor muscle of buccal mass (retractor of pharynx), broad, origin in lateralventral region of haemocoel just posterior to snout, run towards anterior, insertion in lateral­posterior­dorsal region of odontophore cartilages; m2a) pair of dorsal tensor muscles of radula, continuation of m2 after insertion in cartilages, run towards anterior, insertion in subradular cartilage in middle region of its dorsal inner surface; mt) dorsal transversal muscle or approximator muscle of cartilages, connects dorsally both posteriordorsal­lateral surfaces of cartilages, lies between superficial membrane which covers odontophore and tissue on middle region of radula (to); m4) pair of median dorsal tensor muscle of radula, very large and thick, origin in ventral­middle­posterior region of odontophore cartilages, run towards medial, contours medial­ventral surface of cartilages, run on their dorsal surface, insertion in subradular cartilage dorsal­posterior­medial extremities; m5) pair of median radular tensor muscle, thick, origin in median­posteriordorsal region of odontophore cartilages, just by side of m2 insertion and m2a origin, cover perpendicularly m4 middle region, run towards medial, insertion along radular sac in its both sides (each m5 branch covers a side of radular sac, medially and dorsally); m6) horizontal muscle, very thin, unites anterior half of odontophore cartilages, inserting on their dorsal margin; m7) pair of ventral tensor muscle of radula, thin and narrow, origin inside radular sac ventral surface close to each other, run towards anterior separating gradually from each other, insertion in radula ventral border; m8) pair of strong muscles origin in posterior­dorsal­lateral regions of odontophore cartilages just by side of insertion of m2, run attached to dorsal margin of odontophore cartilages, insert in their anteriordorsal region close to horizontal muscle (m6); m9) pair of dorsal­medial tensor muscle of radula, broad and thin, origin along dorsal­median surface of radular sac (in its region internal to odontophore), cross to dorsal surface, insert in dorsal­ventral border of subradular cartilage; mj) jaws and peribuccal muscles, of moderate thickness, surround lateral and dorsal wall of buccal mass, origin around mouth, insertion in middle level of lateral and dorsal wall of odontophore; m11) absent; m14) pair broad and thin, origin in posterior­dorsal region of odontophore, close to m2 and m5 origins, runs towards ventral and anterior, insertion in snout inner ventral surface in about middle level of odontophore; to) tissue covering middle region of radula within odontophore, in its dorsal surface. Radula short, little longer than odontophore. Radula (Figs. 26, 27): rachidian tooth tall, narrow, strongly curved inwards, central cusp large and sharp, 3 to 4 similar sized pairs of secondary cusps, pair of lateral reinforcements on its borders somewhat weak; lateral tooth about 3 times as broad as rachidian, curved internally, with about 12 triangular cusps, fifth cusp larger, apical, turned towards median, cusps decrease towards lateral, disappear about in middle region of tooth, remaining a slight thick and arched border; inner marginal tooth long, curved, tall, tip sharp pointed, about 9 sub­terminal cusps along its inner­apical margin and up to 6 very small cusps along outer margin; outer marginal tooth similar to inner marginal tooth, except in being slender, and with 2–3 small cusps along its inner margin only. Pair of buccal ganglia large, close with each other near median line (Fig. 43), located between buccal mass and adjacent esophagus. Salivary glands narrow, slender, long; length about half of that of haemocoel (Figs. 42). Salivary glands do not pass through nerve ring. Ducts of salivary glands broad, run in dorsal surface of buccal mass, penetrate in adjacent buccal mass wall a short distance, openings small in anterior region of dorsal folds of buccal mass (Figs. 44). Esophagus (Figs. 42, 43, 51) narrow, long and somewhat coiled; inner surface of anterior esophagus with pair of broad folds. Stomach (Fig. 51) slightly conical, large, occupying about half of visceral mass size; esophagus inserting in left side of its posterior­left region, close to shell apex. Anterior duct to digestive gland about in middle region of stomach ventral surface; highly branched. Posterior duct to digestive gland very narrow, located in ventral region of stomach posterior end, turned posteriorly. Stomach gradually narrowing towards anterior and left, arriving close to left­posterior extremity of pallial cavity. Stomach inner surface with pair of longitudinal folds, posterior to esophagus insertion, separating intestine from style sac region of stomach. Digestive gland pale brown in color, surrounding stomach except some areas in dorsal and ventral surfaces. Intestine narrow and sinuous (Fig. 51); running along anterior border of visceral mass from left to right, initially in its ventral region, slightly near median line cross to its dorsal region and runs up to right­anterior extremity of visceral mass (Fig. 51); running towards left in this region, becoming broader and exposed in pallial cavity, surrounds right and anterior border of kidney, suddenly runs towards right in a U­shape, parallel to preceding loop. Anus small, siphoned, located in right region of pallial cavity close to mantle border. Intestine last loops replete of several somewhat small, elliptical fecal pellets.

Genital system: Development: Protandric hermaphrodite, further details in Miloslavich & Penchaszadeh (2001). No male examined herein.

Female (Fig. 50): Ovary yellow, surrounds digestive gland, more concentrated in anterior region of visceral mass (Fig. 38). Visceral oviduct formed by gradual decrease from right­anterior end of ovary. Gonopericardial duct narrow; origin in right­ventral extremity of pericardium, running ventral to visceral glands encroached in pallial cavity, inserting in posterior extremity of pallial oviduct joined with insertion of visceral oviduct. Pallial oviduct relatively small, located in right­anterior end of pallial cavity (Figs. 35, 38). Visceral oviduct preceding pallial oviduct somewhat broad. A pair of seminal receptacles located in right side of last portion of visceral oviduct; each one as a small sac; duct very narrow and long; their insertion preceding albumen gland, in right surface. Albumen gland long, narrow, whitish, walls thick glandular; located in anterior­right extremity of visceral mass. Capsule gland as continuation of albumen gland, broad, spherical; walls thick glandular, pale brown; inner duct narrow, U­shaped. Genital pore in form of tall, long papilla close to mantle border and at right of anus. This papilla has a broader base and a somewhat conical form; a pair of low folds runs close to each other along its posterior side; both start gradually in papilla base and finish at some distance from pore; right fold slightly longer than left one.

Habitat: Attached to the mangrove oyster Crassostrea rhizophorae (Guilding, 1828) , that is attached to mangrove roots of Rhizophora mangle Linné, 1753 , from 0.5 to 1.0 m depth.

Distribution: Venezuela.

Measurements of shells (in mm): MZSP 36329, ♀: 1: 17.8 by 12.0; ♀ 2: 16.3 by 10.6.

Material examined: types.

Discussion: Crepidula margarita was previously identified as C. aplysioides Reeve, 1859 in some previous papers ( Hoagland, 1977; Simone et al. 2000; Miloslavich et al. 2001, 2003). However, further examination of the type specimens of C. aplysioides at BMNH revealed some important conchological differences. They share the external fashion, flat, wide, with terminal apex (Figs. 119–121). However, C. aplysioides type specimens (Figs. 119–122) possess a large muscle scar just dorsal to the right insertion of the septum (Figs. 119, 122 arrow). This feature is not found in the Crepidula plana complex, with normally has this muscle scar small and inconspicuous. Larger dorsal muscle scars are found in the western Atlantic species only in C. convexa (commented below) and Bostrycapulus aculeatus that I have examined. C. margarita additionally differs from C. aplysioides in having longitudinal colored bands, by apex closer to the posterior shell edge, and by loss of periostracum.

The type locality of C. aplysioides is Rio de Janeiro. However, the imprecision of the South American localities in the middle of 19th century is well known, and “ Rio de Janeiro ” can be any city located in Atlantic coast of that mainland. Hoagland (1977) had commented on the systematic problems related to C. aplysioides , but she could not resolve them because of the absence of the types. Anyway, based on the description, the examined species of that paper appears to be of C. margarita .

C. aplysioides has the shell apex somewhat projected posteriorly and slightly away from the shell base, which approaches it from C. convexa (see below). On the other hand, C. aplysioides has a well developed beige periostracum, that show some similarity with C. carioca and C. pyguaia described below.