Crepidula plana Say, 1822

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 : 13-17

Crepidula plana Say, 1822

(Figs. 1, 2, 28, 29, 52–67)

Synonymy part in Hoagland (1977: 389). Complement:

Crepidula plana: Collin 2000: 1500–1512 (figs. 1, 2, 3A–B, 4, 5A, D, 6 left); 2001 (fig. 5).

Type: Neotype ANSP 19186 (designed by Collin [2000]); UNITED STATES OF AMERICA, Massachusetts, Woods Hole , 41º30'N 70º40'W.

Differential Diagnosis: Shell (Figs. 1, 2): Wide and flat, convex or concave, outline oval. Color white. Outer surface smooth except for weak growth lines. Septum deep and bulged ventrally; anterior edge with a broad median notch and others in each side, just in insertion in the remaining shell. Other details in Collin (2000).

Head­foot (Figs. 53, 58, 63): Tip of tentacles simple. Eyes dark, small, located on very small ommatophores between basal and middle third of tentacles lateral margin. Left neck lappet (nuchal lobe) broader than right one; right lappet brings low food groove along its dorsal limit with head; sperm groove of males (described below) running externally along food groove (Fig. 63). Foot occupying about 3/4 of shell concavity. Columellar muscle very small, contouring anterior border of shell septum, more concentrated at right (Figs. 53, 63) in smaller specimens and almost absent in larger ones.

Mantle organs (Figs. 52, 54–57): Mantle border thick, slight hollow due broad collar sinuses (Fig. 56). Mantle border without appendages, but entirely surrounded by series of minute repugnatorial glands; these glands arranged in elliptical form. Mantle border with special arrangement of folds in middle region of pallial cavity opening, a broad fold located from gill anterior end running towards left, decreasing and disappearing suddenly at level of osphradium; its broader region possessing a central furrow, its posterior edge expanding beyond mantle border covering ventrally anterior region of gill, its anterior edge slightly projecting outside (Fig. 57); a central, low fold, beginning in median region of above described fold, appearing gradually, becoming gradually weak at level of osphradium, producing a narrow furrow with posterior edge of main fold. Dorsal shell muscle well developed (Fig. 52: dm), origin small, in about middle­right region of shell, just anterior to septum; its fibers run anteriorly like a fan, insertion in adjacent anterior region of dorsal surface of pallial cavity. Lateral shell muscle (Fig. 52: lm) very small, fanlike, located close to mantle border right side, just in region where pallial cavity penetrates shell septum chamber.

Pallial cavity aperture occupies about 2/3 of anterior half of shell border 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. 54). Pallial cavity length about 2/3 of total length of animal (Figs. 52, 55). 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. 54, 55, 57). Osphradium length little more than 1/10 of pallial aperture length, in form of a small fold, attached to mantle, separated from gill structures. Osphradium leaflets rounded, close to each other, somewhat thick and tall, varying around 8 in number (Fig. 57). Osphradium ganglion narrow. Gill filaments triangular in their base and with very long, almost straight, narrow, stiff rod turned to right (Fig. 56); rods extend about three times longer than their triangular, membranous base; these rods begin in ctenidial vein region, in left margin of cavity roof and touches food groove of head­foot, in right margin of cavity floor; rod apex rounded and preceded by thicker region. Ctenidial vein narrow, with uniform width along its length. Endostyle (Figs. 55, 57: en) yellowish, in form of somewhat narrow glandular ridge located in middle level of ventral surface of ctenidial vein all along its length. Endostyle divided along its length by a narrow, middle furrow, into 2 similar ridges (Fig. 57). Hypobranchial gland whitish, thin, weakly developed, surface smooth; occupies area between gill and visceral mass. About 1/3 of visceral mass encroaches in pallial cavity roof (Fig. 55), occupying about 1/3 of this area in posterior­right region; pericardium and kidney posteriorly; a long intestinal loop, anus and pallial oviduct anteriorly (described below).

Visceral mass (Figs. 52, 54, 55): Morphological attributes similar to those of C. margarita , proportionally longer only.

Circulatory and excretory systems (Fig. 59): Pericardium very long, situated oblique to longitudinal axis of animal (Fig. 52); begins very narrow, just in posterior extremity of gill, in posterior­left end of pallial cavity; runs edging anterior margin of visceral mass part encroached in pallial roof, gradually enlarges; finishes in about middle level of this region of visceral mass, near median line. Auricle thin walled and very long, runs all along pericardium length attached to its anterior and dorsal inner surfaces (Fig. 59); connecting with ventricle approximately between its middle and right third parts; auricle has, then, broad portion beyond ventricle connection (Fig. 59: ab). Kidney occupying about half of area of visceral mass within pallial cavity (Figs. 55, 59). Kidney central region hollow, with single, irregular lobe (Fig. 59). Kidney lobe rich in transversal, folds not uniform in size, covering entire intestinal region passing through kidney chamber, and about half 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. Nephrostome a very small slit in left region of ventral wall (Fig. 59), in middle region of hollow portion of kidney; no inner glandular folds close to it. Adrectal sinus narrow, edging externally intestine loop exposed in pallial cavity, becoming slightly broader towards posterior; connecting directly to kidney chamber anterior­left edge.

Digestive system (Figs. 60–62): Buccal mass very large, occupying most of proboscis inner space and about 1/3 of haemocoel posterior to it. Jaw plates thinner. Pair of dorsal folds broad and tall. Odontophore muscles (Figs. 60, 61): mj) jaws and peribuccal muscles, somewhat thick, surround lateral and dorsal wall of buccal mass, origin around mouth, insertion in middle level of lateral and dorsal wall of odontophore; m10) pair of ventral protractor muscles of odontophore, forming median edge of mj and fused with these; m14) pair narrow and thin. Radula short, little more than odontophore length. Radula (Fig. 28, 29): rachidian tooth secondary cusps vary from 3 to 6 pairs, considerably smaller than central cusp; lateral tooth with about 12 triangular cusps, fifth cusp very larger; inner marginal tooth with about 8 cusps in its inner­subapical margin and 4–6 in its outer­subapical margin; outer marginal tooth with about 4 small cusps in inner margin. Salivary glands long, slender, coiled (Fig. 58), with about 2/3 of haemocoel length, do not pass through nerve ring. Ducts of salivary glands broad, running in dorsal surface of buccal mass, penetrating in adjacent buccal mass wall in short distance, apertures small in middle region of dorsal folds of buccal mass. Esophagus (Figs. 54, 58, 62, 65) narrow, long and coiled; anterior esophagus inner surface with pair of broad folds as continuation of those of buccal mass dorsal wall, located in opposite side from each other. Middle and posterior esophagus inner surface with only 4–5 longitudinal, narrow, similar sized folds. Stomach (Figs. 62, 65) somewhat slender. Anterior duct to digestive gland about in middle region of stomach ventral surface; highly dichotomic. Stomach gradually narrowing towards anterior and left, arriving close to left­posterior extremity of pallial cavity. Posterior duct narrow, strongly turned posteriorly. Stomach inner surface (Fig. 62) with square gastric shield located in right­posterior region, opposite to esophageal insertion; a narrow fold starts in right side of esophageal insertion and runs towards anterior, surrounding left and anterior edges of gastric shield; another fold, transversal, somewhat tall, located just anterior to posterior duct to digestive gland; this fold suddenly runs towards anterior in left gastric surface originating a pair of longitudinal folds dividing gastric surface into intestinal and style sac portions. No preserved crystalline style found. Digestive gland greenish brown in color, surrounding stomach except some areas in dorsal and ventral surfaces (Figs. 52, 65). Intestine narrow and sinuous (Fig. 62) differing by ampler middle loop, approaching first free portion of intestine from style sac, and renal portion from rectum. Anus small, siphoned, located in right region of pallial cavity close to mantle border.

Genital system. Development: See Collin (2000).

Male (Figs. 63–65, 67): Larger examined male with 9.7 mm. Testis pale yellow in color, located in anterior region of visceral mass (Fig. 65). Seminal vesicle convoluted, thick, broad, cream in color, located in anterior­right extremity of visceral mass, gradually narrows and becomes very slender tube that opens in right­posterior­ventral region of pallial cavity (Figs. 64, 65); in this portion, passing close to vestigial pallial oviduct. Shallow groove running from this aperture up to penis base, in pallial floor near right margin of head. Sperm groove more clear and deep anteriorly. Penis large (several times tentacle length and width), curved; suddenly narrows before tip producing a very long papilla (Figs. 63, 67), with about half of penis length and about 1/10 of its width. Penis duct opened (groove), running about in middle region of penis ventral surface until papilla tip. A small, somewhat spherical, incipient oviduct found in some males (Figs. 64, 65: vt), in region preceding aperture of visceral vas deferens in pallial cavity.

Female (Fig. 66): Ovary yellow, surrounding digestive gland, more concentrated in anterior region of visceral mass (Fig. 54). Visceral oviduct very narrow, running from left to right in anterior border of visceral mass. Gonopericardial duct well­developed, weakly broader than visceral oviduct; originating 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. 52, 55). Albumen gland long, slight broad, whitish, walls thick glandular; located in anterior­right extremity of visceral mass. About 5 seminal receptacles inserted in right side of albumen gland, successively larger towards anterior. Seminal receptacles duct broad and very short. Capsule gland broad, thick, occupying about half of pallial oviduct volume; walls thick glandular; inner duct narrow, flat, straight. Vaginal tube originating from anterior­left corner of capsule gland; running towards left, after a short distance suddenly twist and runs towards right, parallel to capsule gland; form somewhat thick and broad (about ¼ of capsule gland width); length about same of that of capsule gland. Genital papilla very tall, situated close to anterior region of albumen gland, at some distance from anus. Papilla with a pair of longitudinal folds along posterior surface; left fold longer, starts gradually in

papilla base, and finishes in a conspicuous fold situated parallel to pore; right folds short, starts as a low fold of middle region of papilla, finishes in posterior edge of pore. Genital pore a small, transversal, terminal slit.

Habitat: See Collin (2000), subtidal, in shells occupied by hermit crabs.

Distribution: East coast of North America, from New Brunswick ( Canada) to Georgia ( USA).

Measurements of shells (in mm) MZSP 36327 ♀ 1: 19.4 by 12.2; ♀ 2: 16.5 by 9.5; ♀ 3: 8.4 by 6.0 (immature); ♀ 4: 17.0 by 13.5; ♂ 5: 8.7 by 6.8; ♀ 6: 8.8 by 6.3 (mature); ♂ 7: 9.7 by 6.0; ♂ 8: 6.1 by 6.3; ♂ 9: 9.0 by 7.3.

Material examined: UNITED STATES OF AMERICA; Georgia; Saint Catherines Island , MZSP 36327 , 4♀, 5♀ (R. Collin col.) . South Carolina, ANSP 19495 . 3 shells (Mrs. Say col.)