JOHNSONIA |.
Published by
THE DEPARTMENT OF MOLLUSKS Museum of Comparative Zoology, Harvard University
Cambridge, Massachusetts
MAY 25, 1972
SEMELE
VOL. 5, NO. 49*
THE GENUS SEMELE IN THE WESTERN ATLANTIC
(Semelidae; Bivalvia)
BY
KENNETH J. Boss
ABSTRACT
The western Atlantic species of the mol- luscan lamellibranch genus Semele are re- viewed. Six species are recognized: Semele proficua, S. modesta, S. purpurascens, 8. bellestriata, S. casali, and S. nucoides.
Aspects of the zoogeography and_ the Tertiary history of these species are pre- sented, and a general discussion of the shell characters and of the anatomical attributes of the genus is included.
Semele is subdivided into the nominate subgenus wich five species and the subgenus, Semelina, with a single species. A description and discussion of the superspecific taxa are given.
A synonymy of each species is provided along with a discussion of the important aspects of nomenclatural history. Biological and paleontological data are included, and the bathymetric and geographic range of each species is established on the bases of exami- nation of museum specimens and upon refer- ence to literature.
INTRODUCTION
Semele is the largest genus in the tellina- cean bivalve family Semelidae and is widely distributed in the warm temperate and tropi- cal waters of the world. The genus is con-
spicuously rich in number of species in the Eastern Pacific; Keen (1958) noted 28 and Olsson Gio Gim) wlisted! 21 especies) Ini the Atlantic and Indo-Pacific regions, the genus is not as highly developed. Certain other semelid genera, /acra, Theora, and Montrou- sieria, for example, are limited to the Indo- Pacific region whereas still others, Cumingia, Abra, and Leptomya, are of wider distribu- tion and not limited to a single oceanic basin. The genus Scrobicularia is similar to Semele in many respects but differs in its lack of right lateral dentition and in having smoo and homorhabdic gills. Representatives of the Scrobicularidae were at one time in- cluded in the Semelidae (Lamy, 1914) but the families have been separated (Newell, 1965).
The family Semelidae is a young one in the geological record and makes its appear- ance in the Eocene (Zittel, 1900). Numerous representatives, particularly of the genus Abra, have been recorded in the Eocene of the Paris Basin (Cossmann, 1886). Harris (1919) and Aldrich (1921) have described species of Semele in North American Eocene deposits. Stoliczka (1871) stated that there are no known species of the family from Mesozoic deposits, although he discussed
*Johnsonia, Vol. 5, starts with No. 49.
z JOHNSONIA, No. 49
Semele
some fossils of Mesozoic Age incorrectly re-.
ferred to the semelids, dmphidesma, La- vignon, and Abra.
During the Tertiary the genus had nu- merous representatives in the western Atlan- tic and Antillean fauna. Gardner (1928) listed 11 species in the Alum Bluff Forma- tion alone and stated that some 30 species occurred in eastern North American forma- tions. Some of the Tertiary species were conspicuously larger than any of the living species, and as Olsson and Harbison (1953) have pointed out, several relatives of these larger species persist today in the fauna along the Pacific coast of Panama and northern South America. Only six species of Semele are in the Recent fauna of the western Atlan- tic and two of these are of limited southern occurrence. The majority of the species have relatively well-documented fossil histories and can be traced back into the upper Maio- cene.
The widely distributed species of the Tertiary were the stem elements from which the modern fauna arose. The factors of geographic isolation and consequent allo- patric speciation are evident when the closest relatives of the western Atlantic species are considered. Of the six species, four have so- called analogous elements in the eastern Pacine, Mable 1 listsy thes Atlantic species: their ranges, and the Pacific species with which they are related. The four widely dis- tributed Atlantic species with occurrences in the Caribbean form species-pairs; the species modesta and casali, which have more re- stricted ranges, probably arose from autoch-
Table 1. Western Atlantic species of Semele, their ranges and their eastern Pacific analogs
Atlantic Eastern species Range Pacific analog proficua North Carolina to Argentina Jenticulare
purpurascens North Carolina to Uruguay = sparsilineata
bellestriata North Carolina to Brazil pacifica
nuculoides North Carolina to Brazil subquadrata modesta Brazil to Gulf of Guinea none casali Brazil to Argentina none
thonous Atlantic elements. Most of the Atlantic species are sympatric with each other, a situation which indicates that the species are “old” in a geological sense, an indication that is corroborated in the fossil record.
ACKNOWLEDGMENTS
I ackowledge the aid of the following persons: Drs. Joseph Rosewater and Harald Rehder of the United States National Museum for permission to study specimens in their charge; Dr. William Clench of the Museum of Comparative Zoology of Harvard University for the loan of specimens; Dr. A. Myra Keen of Stanford University for an ad- vance copy of her manuscript on the Semelidae for the Treatise of Invertebrate Paleontology; Dr. R. Tucker Abbott then of the Academy of Natural Sciences of Philadelphia for providing catalog num- bers of Say’s types; Mr. Norman Tebble and the ‘Trustees of the British Museum (Natural History) for permission to study specimens in their collec- tion; Drs. Frederick M. Bayer and Donald R. Moore of the Marine Laboratory of the Univer- sity of Miami for obtaining preserved specimens for dissection; Mrs. Mildred H. Carrington for inking the line-cut drawings; Mr. George Radwin for drawing my attention to McGinty’s description of S. bellestriata donovani; Dr. Joseph Rosewater, Dr. Daniel Cohen and Mr. Ralph Hile for critically
reading the manuscript. ABBREVIATIONS
ANSP — Academy of Natural Sciences of Phila- delphia
BMNH — British Museum (Natural History)
MCZ — Museum of Comparative Zoology
UMML — University of Miami, Marine Labora- tory
USNM — United States National Museum
SHELL MORPHOLOGY
The gross morphology of the shell of Semele is illustrated in Plate 1. The muscu- lar impressions on the internal surface of the valves reflect some of the anatomical characteristics of the animal. The shape of the pallial sinus and its position in relation to the adductor muscle scars have diagnostic value for the identification of some of the
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JOHNSONIA, No. 49.
species. On the other hand, the scars of the cruciform muscles are obscure or poorly im- pressed and, because of their relative irregu- larity or placement, are of inconsequentia] diagnostic value.
The microscopic structure of the shell of representatives of the Semelidae was studied
by Boggild (1930) and Oberling (1964) ;
cardinal tooth and of a thin laminate pos- terior cardinal tooth. Anterior and posterior lateral teeth are present and situated some distance from the umbo; they are weaker than the lateral teeth of the right valve and fit into sockets above the right lateral teeth. In the right valve the cardinal complex con- sists of a posterior sub-bilobate cardinal tooth
Plate 1. Diagram of an internal view of the right valve of Semele to show the morphological features. A —umbo;
B—- cardinal complex; C— anterior lateral tooth; D—anterior adductor muscle scar; E—pallial line; F— cruci-
form muscle scars; G— pallial sinus; H — posterior adductor muscle scar; I— posterior lateral tooth; J — internal
element of the ligament or resilium; K— external element of the ligament.
the latter introduced a new nomenclature for the specific shell layers. In Semele the ovter layer or ectostracum is prismatic, the middle layer or mesostracum is cross-lamellar, and the inner layer or endostracum is complex. The dentition of Semele consists of differ- entiated lateral and cardinal elements (Plate 2). In the left valve the cardinal complex consists of a sub-bilobed or bifid anterior
of varying strength and of a thin to subdel- toid laminate anterior cardinal tooth, which is incorporated or coalesced into the floor of the lunule. The lateral dentition, consisting of anterior and posterior teeth, is socketed above, relatively well developed, and up- curled. In many specimens the exact nature of the cardinal dentition is obscured by the breakage and loss of the teeth. The positions
4 JOHNSONIA, No. 49
Semele
of the right lateral teeth relative to the cardi- nal dentition may be important as_ specific identifying characteristics.
The ligament of Semele is opisthodetic and consists of a thin, elongate external portion and of a well-developed internal element or resilium which is supported by a calcareous chondrophore. ‘The fine structure of the ligament of the Semelidae was discussed by
Plate 2. Diagram of the hinge structure of Semele.
umbo; B—-lunule; C— external portion of the ligament;
sess a different sculptural pattern and it is this character that is fundamentally diag- nostic. ANATOMICAL NOTES
The following résumé of the anatomical characteristics of Semele is based largely on a dissection of Semele purpurascens. The purpose of this discussion is to review the general gross anatomical features of Semele;
Upper figure, right valve; lower figure, left valve. A —
D —- internal element of the ligament or resilium; E—
anterior lateral tooth; F— posterior lateral tooth; G—anterior cardinal tooth; H— posterior cardinal tooth.
Trueman (1953) who worked on Scrobi- cularia plana and Abra alba.
The most important species-specific con- chological trait is the exact nature of the external sculpture. No doubt the sculpture of the valves has adaptive significance, al- though we are unable to explain the appear- ance and evolution of peculiar types of sculp- ture. All of the species treated herein pos-
it is meant to serve as a guide to anyone pur- suing physiological or other specialized studies on members of the genus and is not intended to be a thoroughly detailed treat- ment. Plate 3 illustrates the general anatomy.
The mantle is thin and transparent over most of its surface. It is united dorsally and fused posteroventrally at the cruciform muscle and anteriorly at the anterior adduc-
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JOHNSONIA, No. 49
| Un
tor muscle. Dorsally the mantle is modified in the region subtending the resilium. The pedal gape is large and extends ventrally from the anterior adductor to the cruciform muscle. The mantle is thickened ventrally where its edges are differentiated into outer, middle, and inner lobes. Along the margins short tentacles are developed on the middle lobe. Posteriorly, separate ventral incurrent and dorsal excurrent siphons are developed. The foot is large, pointed anteriorly, and compressed laterally. The byssal gland 1s vestigial and no byssus is developed (Barrois, 1885). Both the siphons and the foot are active and capable of considerable extension. Yonge (1949) discussed the intrinsic muscu- lature of the siphons in regard to their flexi- bility and extensibility.
The general muscular system of Scrobic- ularia plana and Semele solidum has been described by Graham (1934) and Schroder (1916), respectively. The muscular system consists of the elongate and _ semilunate anterior adductor muscle and the more or less subcircular posterior adductor muscle. The well-developed extrinsic pedal muscula- ture consists of bilateral pairs of anterior and posterior pedal retractors and of an anterior pedal protractor. The anterior pedal retrac- tor is attached to the shell immediately dorsal to the anterior adductor muscle along the an- terior dorsal margin of the valve; this re- tractor courses posteroventrally and inserts deeply into the foot. The posterior pedal retractor attaches to the shell along the posterior dorsal margin just dorsal to the posterior adductor muscle. It courses antero- ventrally through the kidney and_ inserts superficially into the foot. The pedal pro- tractor attaches to the shell within the circum- muscular tissue on the posterior ventral surface of the anterior adductor muscle. Contrary to Schréder’s (1916) statement, an elevator pedal muscle does not appear to be present. The siphonal muscles splay out into the mantle laterally; they leave a scar on the shell which defines the pallial sinus. Two
heads of this muscle are attached to the bases of the incurrent and excurrent siphons, respectively. The cruciform muscle with its slit-like specialized sensory pit is found pos- teriorly, where the ventral portion of the siphonal retractor attaches to the muscular lobe of the mantle.
The labial palps are rather elongate, sub- triangular, plicate on their entad surfaces, and much smaller than the ctenidia; they are capable of considerable contraction.
The gill is similar to that of Tellina; it consists of an inner ventral demibranch which is complete in having both inner and outer lamellae. The outer demibranch is smaller, upturned, and reduced to only the inner lamella. The combined demibranchs are united distally along the ventral surface of the pedal retractor muscles. The demi- branchs of Semele are plicate and_hetero- rhabdic while those of Scrobicularia are smooth and homorhabdic (Rice, 1897). Ac- cording to Ridewood (1903) each plica con- tains 32-35 filiaments in Semele.
The ciliation of the gills has been de- scribed for Semele decisa by Kellogg (1915 ) and for Scrobicularia plana by Atkins (1937) and Yonge (1949). Particulate material from substrate detritus is sucked into the mantle cavity by the incurrent siphon, then swept up over the gills which direct it ven- trally to the margin of the inner demibranch and thence to the labial palps and the mouth. There is no forward-running current along the gill axis in Semele as there is in Scrobic- ularia. Pseudofaeces are collected ventrally in the vicinity of the cruciform muscle. Specialized siphonal and parasiphonal organs are not present in Semele. In addition, there is no definite ventral mantle fold or ridge that creates a ventral channel, as is typical of tellinids (Boss and Kenk, 1964).
The structure of the alimentary canal is similar to that of Scrobicularia plana as de- scribed and figured by Graham (1934). The mouth is a narrow slit-like aperture formed by the medial portions of the labial palps.
6 JOHNSONIA, No. 49
Semele
A short straight esophagus leads directly to the stomach, which is surrounded by the digestive gland. The combined style sac and midgut leave the stomach posteroventrally. The intestine is long and greatly convoluted in the viscera. The rectum extends through the pericardial cavity and is enveloped by the ventricle; it passes posteriorly around the outer curvature of the posterior adductor muscle and terminates at the anus near the opening of the excurrent siphon. The intes- tine and the rectum generally contain com- pacted fecal pellets.
The heart is in the elongate pericardium, which extends between the posterior retractor muscles and the posterior wall of the viscera; it is partially covered by the upturned inner lamella of the outer demibranch. An in- distinct pericardial gland has been reported along the anterodorsal portion of the peri- cardial walls (White, 1942). The bilaterally paired auricles are thin walled and small relative to the rather extensive, subtriangular, thick-walled median ventricle which sur- rounds the rectum. A_ so-called bulbus arteriosus (Schréder, 1916) may be present, investing the rectum in the posterior portion of the pericardium.
The kidneys are granular and compacted structures beneath the pericardium; the reno- pericardial connection is an elongate and slit- like structure on the posterior dorsal surface of the kidney which communicates directly to the pericardial cavity (Odhner, 1912). The kidneys empty via the nephroproct externally and separately from the gonads in a common lateral urogenital sinus.
The structure of the nervous system of Semele solidum has been thoroughly dis- cussed by Schréder (1916). In its general pattern the nervous system is very much like that of Psammobia vespertinalis (Duvernoy, 1853) and Gari tellinella (Graham, 1934). Anteriorly on the entad surface of the an- terior adductor muscle are the paired cere- bropleural ganglia which are united by a dorsal commissure and which give rise to the
anterior pallial nerves as well as to the branches which innervate the anterior adduc- tor muscle. From the medial posterior portions of the cerebropleural ganglia, the lateral cerebropleural-pedal connectives arise and course posteroventrally to the united pedal ganglion in the foot. Numerous branches of nerves from the pedal ganglion innervate portions of the pedal retractors, pedal protractors, and pedal intrinsic muscu- lature, as well as the ventral portion of the viscera. From the posterolateral part of the cerebropleural ganglia, the bilaterally paired cerebropleural visceral connectives lead pos- teriorly to the visceral ganglion on the entad surface of the posterior adductor muscle. The visceral ganglia are united or compacted into a single bilobate ganglion. Extending anterolaterally from the visceral ganglion are the branchial and nephridial nerves. Postero- ventrally the visceral ganglion gives rise bilaterally to the posterior adductor nerve, the siphonal nerves, and the posterior pallial nerve.
Semele is dioecious. The gonad is em- bedded in the dorsal portion of the foot and surrounds much of the style sac and midgut. A genital tube opens into the suprabranchial chamber in the vicinity of the nephroproct in a common urogenital sinus. The repro- ductive biology of Cumingia tellinoides, a member of the Semelidae, has been studied im detail (Grave, 02 74uCostelloymchaal: 1957). Complete metamorphosis takes 16- 24 days in that species, and swimming veli- gers develop within 2 days after fertilization. Species of Semele probably exhibit a similar embryological pattern although no specific data relating to Semele itself are available.
SYSTEMATIC TREATMENT Superfamily Tellinacea Family Semelidae Stoliczka 1871 Genus Semele Schumacher Semele Schumacher 1817. Essai Nouv. Syst. Habit. Vers testaces, pp. 53, 165, 277, pl. 18, fig. 2 (type-species
by monotypy, Tellina reticulata ‘Linnaeus’ Spengler 1795, non Linnaeus 1767 [ = Tellina proficua Pulteney, 1799]).
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JOHNSONIA, No. 49
Western Atlantic
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8 JOHNSONIA, No. 49
Semele
Amphidesma Lamarck 1818. Anim. s. Vert. 5: 489° (type-species, by subsequent designation, Children, 1823, p. 301, Amphidesma variegata Lamarck 1818 [ — Venus purpurascens Gmelin 1791]).
Elegantula de Gregorio 1884, Bull. Soc. Malac. Ital., 10: 317 (type-species, by monotypy, Semele fazisa de Gregoria 1884 [ — Amphidesma striata Reeve 1853], teste Lamy 1914, p. 316).
The shells of species of Semele tend to be elongate-ovate to subcircular, subequilateral, and more or less equivalve. The ligament is divided into a small, obscure, elongate ex- ternal element and a strong, developed in- ternal element situated in a chondrophere. Both cardinal and lateral dentition is de- veloped; two cardinal teeeth and two lateral teeth are in each valve; the lateral dentition of the right valve is more strongly developed than that of the left. The pallial sinus is large, extensive, frequently reaching beyond the center of the valves, rounded anteriorly, and usually not confluent with the pallial line below. The sculpture is radial, concentric, acentric, or a combination thereof.
The group named Syndesmyella by Sacco (1901), with S. pliovoides Sacco as type- species by monotypy, was included in the synonymy of Semele by Dall (1900) ; how- ever, the configuration of the right lateral dentition shown in the figures given by Sacco indicate that this name may be better con- strued as a synonym of dbra Lamarck.
Semele may be divided into two groups, Semele s.s. with shells of larger size and stronger lateral dentition and Semelina, with shells that are smaller and with weaker lateral dentition, particularly in the left valve.
Once considered a _ western Atlantic Semele, the Amphidesma transversum Say (U8igie Amers our) Concheiai2.on pleas middle) from the coast of Georgia is the European Scrobicularia plana, The locality has been shown to be in error (Dall, 1900).
Semele proficua (Pulteney)
Plate 4, fig. A; Plate 5, fig. A; Plate 7, fig. A; Plate 8, fig. A; Plate 10, fig. A; Plate 12, figs. A, B, C, D, F.
Tellina reticulata “Linnaeus’ Spengler 1798. Skrivter af Naturhistorie Selkskabet, K@benhayvn, 4(2): 115, non Linnaeus 1767.
Tellina proficua Pulteney 1799. Catalogues of the birds, shells . . . of Dorsetshire [in] Hutchin. History of Dorset, p. 29, pl. 5, fig. 4 (type-locality, on the sands at the North Shore, Poole and at Waymouth, here cor- rected and restricted to St. Thomas, Virgin Islands; types not known).
Tellina decussata Wood 1815. General Concholegy, p. 190, pl. 43, figs. 2-3 (type-locality not given; here designated as St. Thomas, Virgin Islands; types, “Lin- naean Society’s Cabinet’’).
Amphidesma orbiculata Say 1822. Jour. Acad. Nat. Sci. Philadelphia, ser. 1, 2: 307 (inhabits the coast of Georgia; possible syntypes, ANSP 53267).
Amphidesma radiata Say 1826. Jour. Acad. Nat. Sci. Philadelphia, ser. 1, 5: 220 (southern shores of East Florida . . . on the coast of Georgia; syntypes, ANSP 53283), non Reeve 1853.
Amphidesma subtruncatum Sowerby 1833. Catalogue Amphidesma, Conch. Ill. (West Indies; zomen nudum) ; Reeve 1853, Conch. Icon. vol. 8, Amphidesma, fig. 11 (Island of Nevis, West Indies, in sandy mud at 6 fathoms; holotype, BMNH).
Amphidesma jayanum C. B. Adams 1845. Proc. Boston Soc. Nat. Hist., 2: 10 (Jamaica; lectotype, selected and figured by Clench and Turner, 1950, Occ. Papers Har- vard, 1(15): 298, pl. 43, figs. 3-4, MCZ 186109).
Lucina icterica Reeve 1850. Conch. Icon., vol. 6, Lucina, pl. 10, figs. 60 a-b (type-locality not given, here designated as St. Thomas, Virgin Islands; syn- types, BMNH) 1853. Conch. Icon., vol. 8, Amphidesma, sp. 36.
Amphidesma duplicata Reeve 1853. Conch. Icon., vol. 8, Amphidesma, pl. 3, fig. 14 (Antigua; types not known).
Amphidesma decora Reeve 1853. Conch. Icon., vol. 8, Amphidesma, pl. 3, fig. 15 (type-locality not given; here designated as St. Thomas, Virgin Isalnds; syn- types, BMNH).
Amphidesma luteola Reeve 1853. Conch. Icon., vol. 8, Amphidesma, pl. 6, figs. 42 (type-locality not given; here designated as St. Thomas, Virgin Islands; holo- type BMNH).
Amphidesma compta Reeve 1853. Conch. Icon., vol. 8, Amphidesma, pl. 7, fig. 51 (type-locality not given; here designated as St. Thomas, Virgin Islands; holo- type, BMNH).
Amphidesma amoena Reeve 1853. Conch. Icon., vol. 8, Amphidesma, pl. 7, fig. 52 (type-locality not given; here designated as St. Thomas, Virgin Islands; holo- type, BMNH).
Amphidesma australe ‘Sowerby’ Hanley 1856. Rec. Shells., p. 342, pl. 12, fig. 8, 20m Sowerby 1833.
Semele carolinensis Conrad 1867. Amer. Jour. Conch., 3(1): 14 (Waccamaw, South Carolina; types, missing, teste Moore, 1962, p. 47).
Western Atlantic
Semele phryne Angas 1879. Proc. Zool. Soc. London (1878), pt. 4, p. 860, pl. 54, fig. 4 (type-locality not given; here designated as St. Thomas, Virgin Islands; holotype, BMNH).
Semele mediamericana Pilsbry and Lowe 1932. Proc. Acad. Nat. Sci. Philadelphia, 84: 92, pl. 12, figs. 1, la, 2 (Nicaragua; holotype, ANSP 53295).
Semele aurora Tursch and Pierret 1964. Veliger, 7(1): 35, figs. 1-3 (off Rio de Janeiro, in 30 fathoms; holotype, Stanford Univ. Paleo. Type Coll., no. 9736).'
JOHNSONIA, No. 49 9
Description. Shell extending to 47 mm in length and to 42 mm in height, suborbicular, subsolid, nearly equilateral, equivalve, with a flexure to the right posteriorly. Umbos centrally located, somewhat inflated, slightly prosogyrous, often with concentrations of reddish or yellowish coloration. Anterior and. ventral margins broadly and_ evenly
Plate 4. A—external view of the right valve of Semele proficua, USNM 83350, Bermuda (length 25.2 mm.); B— external view of the right valve of Semele modesta, MCZ 232214, Ascension Island (length 38.8 mm.) ; C — external view of the left valve of Semele casali, MCZ 258310, off Bermeja Head, Argentina (length 20.9 mm.); D— external view of the right valve of Semele casali, USNM 170212, off Rio de la Plata (length 19.6 mm.).
‘Subsequent to this description, Klappenbach (1968), followed by Figueiras and Sicardi (1968), placed aurora in the synonymy of martinii Reeve, which is herein con- sidered a synonym of modesta Reeve. The type-speci- mens of both modesta and martinii possess the charac- teristic heavy rib-like concentric sculpture; aurora is characterized by its bright colored, radial strips, a feature so widespread in proficua populations that Say erected his species radiata for such specimens.
rounded; posterior margin irregularly and weakly convex with slight postventral inden- tations more noticeable in right valve; an- terior dorsal margin short and very weakly concave; posterior dorsal margin longer, sharply descending, and slightly convex. De-
IO JOHNSONIA, No. 49
Semele
pending on convexity or posterior margin, outline of shell with broad, blunt, posterior truncation. Concentric sculpture. consisting of regular raised lirations, spaced equidis- tantly (about 0.3-0.6 mm apart), stronger peripherally, and often stronger on right valve. Radial sculpture consisting of slightly irregular, weak, and slightly raised lirations (about 8-12 per mm) crossed by stronger concentric sculpture, producing minute can- cellate pattern. Concentric growth lines present and becoming more numerous and more closely spaced peripherally. Extremely weak biangulate ridges posteriorly, associated with posterior flexure. Area between weak ridges convex in left valve, concave in right. Weak ridges radiating from umbo along anterior and posterior dorsal margins. Liga- ment opisthodetic, consisting of internal oblique resilium in elongate chondrophore and of obsolete elongate, thin, external por- tion. Weak elongate escutcheon in left valve. Lunule conspicuous, though variable, elon- gate, cordiform, and generally stronger in right valve. Hinge line well developed. Left cardinal complex consisting of developed, moderately strong, anterior cardinal tooth and of thin, elongate posterior cardinal tooth, often lost, broken, or coextensive with anterior margin of resilium. Slightly pro- tuberant left anterior lateral tooth closer to umbo and more strongly developed than distal, weak posterior lateral tooth. Right cardinal complex consisting of thickened an- terior cardinal tooth coalesced with base of lunule and of elongate, thin, dorsoventrally rectangular posterior cardinal tooth, often broken or lost. Right anterior lateral tooth subproximal, strong, protuberant and_pos- terior lateral tooth distal, laminate, and slightly upcurcled. Muscle scars generally poorly impressed and internal surface of valves highly polished. Pallial sinus nar- rowed, obliquely ascending, free from pallial line ventrally, a little more extensive in right valve and often with fan-shaped pallial re-
tractor muscle scars evident. Interior of
valves irregularly pitted by mantle muscula- ture. Whitish externally and internally with sutfusions of yellow internally and/or blotches of brownish red; sometimes yellow, pink, or red umbonal concentrations of color and rarely reddish or pink radial rays.
length height width
46.3 mm 42.0 mm 18.5 mm St. Thomas
39.0 35.4 17.0 Veracruz, Mexico
35.0 32.5 — Murrell’s Inlet, South Carolina
33.4 29.3 19.4 lectotype of Amphidesma jayanum C. B. Adams
24.9 22.4 11.1 Apalachicola, Florida
19.0 16.4 7.8 St. Thomas
9.8 8.4 3.4 Half Moon Reef, Texas
3.8 3.3 1.5 Half Moon Reef, Texas
Remarks. Tellina reticulata Linnaeus
1767 is based upon plate 43, figure E, of Rumphius’ Amboinsche Rariteitkamer.' This species was called Chama_ scobinata by Rumphius and he noted that it did not occur in Amboina. Linnaeus (1767) gave the locality ‘In India’ upon the authority of Tesdorf. Dodge (1952) has shown that the figure of Rumphius, the description of Lin- naeus, the cited locality, and the absence of an authoritative specimen in the Linnaean col- lection all support the thesis that this named entity is unidentifiable and that the specimen was oriental in origin and not from the West Indies.
It is neecssary to note that Linnaeus (1758) cited exactly the same figure of Rumphius for his Tellina scobinata as well as plate 76, figure E of Gualtieri’s Index Testarum Conchyliorum (1742). In_ the 12th edition of the Systema (1767), Lin- naeus moved the reference to Rumphius from scobinata to reticulata. Clearly he was dif- ferentiating the species represented by the figures of Gualtieri and Rumphius. The shell figured by Gualtieri represents Tellina scobi- nata Linnaeus 1758, as presently understood,
*Not plate 42 as cited by Dodge (1952). The plates 42 and 43 of Rumphius’ 1705 ediiton were reversed in the 1741 edition and plate 42 (1705) was incorrectly renumbered plate 43.
Western Atlantic
JOHNSONIA, No. 49 11
and his illustration should be construed as the type-figure of that species. The figure given by Rumphius represents an unidentihable lucinid, probably a Codakia as suggested by von Martens (1902). ‘This is not the species Semele proficua (Pulteney), the Tel- lina reticulata “Linnaeus” of post-Linnaean authors.
Chemnitz (1782), in his non-binomial work, used Tellina reticulata Linnaeus and stated that it came from the West Indian Sugar Islands (Virgin Islands); Spengler (1798) also followed this interpretation of the Linnaean species; Schumacher (1817), in establishing the generic name Semele, used this interpretation for the type-species. Even Pulteney, who first described proficua, used reticulata in 1813.
The names amoena, compta, luteola, and decora were introduced by Adams at the July 1853 meeting of the Zoological Society of London, but they were not formally pub- lished in the Proceedings until 25 July 1854. In the Conchologia Iconica, Reeve cites Adams as their author, but an interpretation of priority requires the citation of Reeve as author.
Semele carolinensis Conrad 1867 is based upon the interpretation of dmphidesma orbiculata Say of ‘Tuomey and Holmes (1856) and their figure 4 of plate 23; the type-specimen can not be found in the Tuomey and Holmes collection at the Ameri- can Museum of Natural History, New York. As Olsson (1961) has pointed out, Semele medi-americana Pilsbry and Lowe 1s not from the Pacific coast of Nicaragua and is, in fact, proficua.
Ample historical synonymies of S. proficua are presented by Lamy (1914) and Weis- bord (1964).
One of the important variations in S. pro- ficua is distribution of coloration within the shell. Externally most specimens are a dirty grey-white while internally they are white with central suftusions of yellow; the internal surface of the valves is highly polished and
its periphery is almost always white. The degree of yellow suffusion is variable, and while some specimens have only a vague indi- cation of yellow coloration internally, others are bright canary yellow. Irregular brownish, reddish, or purplish blotches may supplement the yellow interior of the valves; specimens of this kind were pictured by Wood (1815, pl. 43, figs. 2-3) as Tellina decussata. Um- bonal concentrations of reddish orange or pink are often coupled with similarly colored radiations which are visible externally and internally; the synonyms radiata Sowerby and aurora Tursch and Pierret appear to have been founded on this particular color varia- tion. In addition, some reddish coloration may be concentrated along the concentric growth rings.
Specimens in the early lineage of S. pro- ficua from the upper Miocene of the Chocta- whatchee formation of Florida were named as a subspecies, harveyensis, by Mansheld (1932); they are distinct from typical Re- cent proficua in their much greater size. In the Phocene, S. proficua occurs in the Caloosahatchee marl of Florida, the Wacca- maw formation of South Carolina, and the lower Mare formation of Venezuela (Tuo- meys, and» Idlolmes; = 1856; Dall, 1900; Weisbord, 1964). There are numerous Pleistocene localities, including South Caro- lina, Florida, Cuba, Venezuela, Brazil, and Argentina (Holmes, 1858; Dall, 1900; Aguayo, 1938; Weisbord, 1964; von lher- iIngyw1Oo7 Cancelles, 1944).
(Sowerby), which ranges from Panama southward to Peru, 1s the eastern Pacific analog of Semele proficua. Olsson (1961) stated that the principal dis- tinguishing characteristic is one of size; 8. lenticulare is smaller than S. proficua. Semele cordiformis Holten [= S. sinensis (Adams) ] of the Philippines and adjacent areas of the South China Sea appears to be an Indo- Pacific analog of S. proficua (Hidalgo, 1903; Skarlato, 1965). It is most probable that all three of these forms arose from a widely
Semele lenticulare
12 JOHNSONIA, No. 49
Semele
distributed cosmopolitan Tethyan ancestor. Having become geographically _ isolated, separate populations gave rise to distinct biological species which have been treated separately taxonomically and which are very similar morphologically.
Semele proficua normally inhabits shallow water and prefers sand or sandy mud sub- strates in which it lies buried, on its left side. Various depths have been cited in the litera- ture. Off the coast of West Florida, S. pro- ficua has been found in 3-6 fathoms by Perry and Schwengel (1955) and in 16 fathoms by Adams and Kendall (1891). Parker (1956; 1959) has reported it in the upper sound of the Mississippi Delta and, as an indicator species, in the open high-salinity bays and sounds of the Taxas coast. A curi- ous and, no doubt, unusual habitat was re- corded by Moore (1961) who found S. pro- ficua living several feet above the bottom in dead oyster shells which were attached to a submerged wreck on the north side of Ship Island, Mississippi. Stanley (1970) noted that S. proficua was a rapid burrower in- habiting shallow water grass flats; he also suggested that the species might be a sus- pension feeder.
Range. The southernmost locality from which this species has been recorded is that noted by Carcelles (1944) who found it as far south as Isla Leones in the Bahia Busta- mante along the northern shores of the Golfo San Jorge, Argentina, at 45°00’S, 65°30’W. I have not been able to obtain specimens from that far south but have seen them from the Golfo San Matias. The northernmost occur- rence of S. proficua is at Beaufort, North Carolina, where it is found commonly in the sound (Hackney, 1944). However, a single lot in the U. S. National Museum is ques- tionably indicated as being from Virginia, and many of the published ranges of the species include this lot (Dall, 1903; Maury, 1920). The species is widely distributed in the temperate and tropical waters of the
western Atlantic, from North Carolina
through the Gulf of Mexico and Caribbean Sea along the coast of South America to the Golfo San Jorge in Argentina. This species lives in depths to 30 fathoms (55 m).
Specimens examined. VirGINIA: ? (USNM). Nortu CAROLINA: Fort Macon, Beaufort (USNM); Pivers Island (USNM; MCZ); Bogue Sound (USNM); Wrightsville Beach; Southport (both MCZ). Souru CAROLINA: Myrtle Beach; Murrell’s Inlet; Charleston (all USNM). Froripa: St. Augustine (USNM); Cape Canaveral (MCZ); Lake Worth; off Miami, in 20-30 fathoms; off Government Cut, Miami, in 3-30 fathoms (all USNM); Virginia Key (MCZ); off Bear’s Cut, in 18-20 fathoms; off Fowey Light, in 6-25 fathoms (both USNM); Turtle Harbor, in 6 fathoms; Long Key; Pirates Cove, Sugarloaf Key; off American Shoals (all MCZ) ; Hawk Channel, in 3-20 fathoms (USNM); Key West; Boca Grande (both MCZ); Tortugas; Cape Sable, in 1% fathoms (both USNM); Pavilion Key; Shell Island, Cape Romano; Horse Key; Marco; Naples (all MCZ); Bonita Beach; Fort Myers; Punta Rassa; Sanibel, in 6-15 feet; Captiva; Charlotte Harbor; Grove City; Gasparilla Key; Sarasota Bay; Egmont (all USNM); Mullet Key; Pinellas Point; Pass-a-Grille; Madeira Beach (all MCZ); Cedar Keys; Indian Pass, Apalachicola; Panama City (all USNM). Louisiana: Grande Isle; Grand Lake, Cameron County (both USNM). Texas: Galveston; Pass Cabello; Half Moon Reet, Matagorda Bay; Caranahua Bay (all USNM); Port Aransas (MCZ). Mexico: Tuxpam; 15 miles N of Tecolutla; Tecolutla; Veracruz; Alvarado (all MCZ). BririsH Honpuras: E. side of Sittee Island (16°48'35”N; 88°15'00”"W); Seine Bight, Placoneia Lagoon (16°35'10”N; 88°22'15”W) (both ANSP). Honpuras: Ruatan Island (USNM). PANAMA: Colon (MCZ). BreErMuDA: Castle Roads, Castle Harbour; Har- rington Sound; Hungry Bay; Agars Island (all MCZ). BaHAMA ISLANDS: Dick’s Point, Nassau, New Providence; Sandy Point, Savannah Sound, and Governor’s Harbour, Eleuthera Island; Orange Creek and Arthurstown, Cat Island; Simms, Long Island; Matthew Town, Great Inagua (all MCZ). Cusa: Arroyos; Santa Lucia, in 2 fathoms; Esperanza, in 2-3 fathoms (all USNM); Morrillo Beach, Bahia Honda (MCZ) ; Cabanas Harbor, in 2-3 fathoms (USNM); Cayo Frances (MCZ); Cien- fuegos Harbor (USNM) ; Caleton de Don Bruno; Rancho Aluna, Punta de los Colorados; Nicaro, Mayari; Guan- tanamo (all MCZ). Jamarca: Green Island Harbour; Rockfort; Port Maria; Robins Bay; Harboreale; Black River; Great Pedro Bay; Old Harbor; Hunt’s Bay; Port Royal; Kingston Harbor; Palisades (all USNM). Hispaniola: Haiti: Cape Hatian; Bizoton (both USNM); Miragoane (MCZ); Tiburon; Damassins; Port Salut; Torbeck; Les Cayes (all USNM); Aquin (MCZ); Baie Anglaise; Saltrou (both USNM). SANTO Dominco: Monte Cristi (MCZ) ; Maimon Bay (USNM) ; Santa Barbara de Samana (MCZ). Puerto Rico: Bahia de Afasco; Punta Guanajibo (both MCZ) ; El Desecheo Island, Mayaguez (USNM); Guanica (MCZ). VirRGIN
IsLANDS: Anegada (ANSP); Tortola; St. Johns; St. Thomas (all USNM). Lesser ANTILLES: Basseterre, St. Kitts (ANSP); Antigua; Post Castres and Marigot Harbor, St. Lucia (both MCZ); Villa, St. Vincent (USNM); Barbados (MCZ); Bathsheba and St. Law- rence, Barbados (USNM); Little Bacaye Harbor and Hardman Bay, Grenada (both ANSP); Dry Rocks, E
side of Buccoo Reef, Tobago; Point a Pierre and Saline
JOHNSONIA, No. 49 13
MCZ); Ilha Grande, Districto Federal; Sao Sebastiao;
Sao Paulo; Sao Francisco; Florianopolis (all USNM).
UruGuay: Lobos Island; Puerto La Paloma _ (both
USNM). ARGENTINA: Albatross I Station 2765, off Rio de la Plata, 11 fathoms; Albatross I Station 2766, off Rio de la Plata, 11 fathoms (both USNM); Hassler Sta- tion, 41°40'S, 63°13’W, Golfo San Matias, in 30 fathoms (MCZ); Puerto Madryn, Golfo Nuevo (ANSP).
Plate 5. Internal view of the right valve.
A—Semele proficua, USNM 441153, Port Maria, Jamaica (length 29.0
mm.); B—Semele modesta, MCZ 232214, Ascension Island (length 21.4 mm.); C—Semele casali, MCZ 258310,
off Bermeja Head, Argentina 21.7 mm.).
’
Bay, Trinidad (both MCZ). CarippEan IsLANnps: Curacao (USNM). CoLomsia: Cartagena; Puerto Co- lombia (both USNM). VENEZUELA: Barcelona (USNM) ; Margarita Island (MCZ). Brazit: Belém (MCZ) ; Ceara; Bahia (both USNM); Ilha de Maré, Todos Santos Bay, in 5-6 fathoms; Santo Antonio and Man- guinhos, Ilha de Itaparica; Ilheos; Praia de Boa Viagem,
Nictheroy; Ilha de Guanabara; Rio de Janeiro (all
(length 21.5 mm.); D—Semele purpurascens, USNM 53666, Key West, Florida (length
Semele modesta (Reeve )
Plate 4, fig. B; Plate 5, fig. B; Plate 7, fig. B; Plate 8, fig. B; Plate 10, fig. B.
Amphidesma modesta Reeve 1853. Conch. Icon., vol. 8, Amphidesma, pl. 6, figs. 35a-b (Cape Palmas, West Africa; syntypes, BMNH).
14 JOHNSONIA, No. 49
Amphidesma martinii Reeve 1853. Conch. Icon., vol. 8, Amphidesma, pl. 6, fig. 43 (Rio [de Janeiro]; holotype, BMNH).
Semele modesta Reeve. Adams 1854. Proc. Zool. Soc. London (1853), p. 95 (Cina Seas [in error]).
Semele martini Reeve. Adams 1854. Proc. Zool. Soc. London (1853), error for martinii Reeve.
Description. Shell extending to 31 mm in length and about 30 mm in height, suborbic- ular, subsolid to solid, nearly equilateral, nearly equivalve with right valve slightly more convex and inflated and with posterior flexure to right. Umbos central, elevated, blunt, and prosogyrous. Anterior margin gen- erally evenly and broadly rounded; ventral margin straight to slightly convex and rising behind at postbasal arcuation; anterior dorsal margin short, straight to concave; posterior dorsal margin longer, straight to weakly con- vex; posterior margin straight to broadly rounded and convex. Sculpture consisting of strong raised concentric ribs, 0.2-0.3 mm broad and about 1 mm apart. Weak radial lirations (12-15 per mm) on intercostal depressions and particularly evident in immature stages on disc. Weak posterior ridge coincident with postbasal arcuation. Ligament consist- ing of external, obsolete opisthodetic portion and of strong, yellow, internal resilium. Lunule subcordiform, often reddish and more extensive in right valve; escutcheon obsolete, narrow and lanceolate. Hinge line well developed. Left cardinal complex con- sisting of single, subsolid anterior tooth and of subobsolete, narrow posterior tooth, often lost, broken, or coalesced with resilial ele- ment. Anterior lateral tooth subproximal and more or less equal in strength to distal posterior lateral tooth. Righ cardinal com- plex consisting of single thickened, subdel- toid, anterior tooth often coalesced with floor of lunule, and of single strong posterior tooth. Anterior lateral tooth upcurled, closer to umbonal area and stronger than distal posterior lateral tooth. Muscle scars generally poorly impressed. Anterior ad- ductor muscle scar elongate-subquadrate ; pos- terior scar irregularly subquadrate. Pallial
Semele
sinus arising gently and narrowly rounded in front. Shell dirty white to yellowish ex- ternally; rarely with apricot suffusions intern- ally; polished and shining internally; lunule. often reddish; additional reddish