-

Page 378 THE Vol. 22; No. 4

Early Development of Mytilopsis leucophaeata

( : Dreissenacea )

BY

SCOTT E. SIDDALL

Rosenstiel School of Marine and Atmospheric science, University of Miami, Miami, Florida 33x49

(I Plate)

SEVERAL KEYS HAVE BEEN PUBLISHED for identification of to 3o’C (July), averaging 26’C during spatfall. In the bivalve larvae based on characters of the larval she& or spring of x976, sexually ripe adults exposed in the labora- (CHANLEY c ANDREWS, 1971; LKSANOFF, tory to 35’ C seawater (IO&) for 20 minutes spawned DAVIS k CHANLEY, x966). However, none describe Myth within one hour of treatment. Larvae were reared through lopsis [eucophaeata (Conrad, 1831), an estuarine species metamorphosis at three salinities (IO, 24 and 32sO) using distributed along the North American east coast from New techniques commonly applied in the culture of bivalve York to Florida and from Texas to Mexico (ABBCXT,x974; larvae ( LOOSANOFF QDAVIS, x963). Serial samples of both EMERSON 8 JACOBSON, 1977). The objective of the present naturally set larvae and juveniles (1975 material) and study was to describe the development of larval and juve- laboratory cultured larvae and juveniles (1976 material) nile Al. leucophaeata. were cleaned in a buffered sodium hypochlorite solution In early 1975, I monitored the abundance of bivalve (seeCARRIKER, 1979) then examined on an AMR-goo scan- larvae in a man-made embayment on Virginia Key, ning electron microscope. Miami, Florida, supporting a population of bivalves com- Though the effects of the three salinities were not sig- posed almost exclusively of Mytilopsis leucophaeata. No nificant on either the timing of, or the size at, metamor- other adult bivalves were observed and greater than 99% phosis (P > 0.05), it is interesting that these brackish water of all larvae collected and reared through metamorphosis bivalve larvae were capable of growth to metamorphosis in the laboratory were later identified as M. leucophaeata. at near-oceanic salinities (32%& Natural (filamentous algae) and artificial (cotton thread) Characteristics of the hinge line are used to differen- spat collectors were sampled for metamorphosing bivalves. tiate bivalve speciesboth as larvae and adults (REES, 1950; Tidal flushing was restricted with salinities decreasing LUTZ a JABLONSIU, 1978; SIDDALL, 1978). Serial develop from 227&, to 87&, after late spring rains. Heaviest set of mcnt of the hinge line in Mytilopti leucophaeatu is shown spat occurred two weeks after the onset of this annual in Figure I. Using the terminology of CHANLEY L rainy season. Temperatures varied from 13~ C (January) ANDREWS (rg;l), M. leucophaeatu develops “knobby”

Explanation of Figures z and 2

maximum shell dimension = 375~; e) 28 DAF: maximum Figurn I : SEM photomicrographs of hinge lines of Mylilopk ku- shell dimension = 500 qn; showing shelf under the cophorata at two times prior to nietarnorphosis: a) 2 days afkr Figure o: SEM microphotograph of juvenile Mytilopsis Icwophoc- fertilization (DAF); shell length = 74~; b) G DAF; shell length da (0.5cm maximum dimension) (a) with pits randomly dis- ZZ 18opn; and at three times subsequent to metamorphosis: per& anterior to pa&al line; and (b) a magrdkd view of pit 18 DAF: c) 11 DAF : maximum shell dimension = 270 q; d) (3)&m in diameter) TIIE VELIGER, Vol. 22, No. 4 [SIDDALL] Figures I and 2 Vol. 22; No. 4 THE VELIGER Page379 umboncs which became “skewed” anteriorly following (4 settlement of spat peaked 2 weeks after gamete re- metamorphosis. At 26’ C, larvae fed a mixed phytoplank- lease in natural populations; in the laboratory at 26“ ton diet (Zsochrysis galbana, Monochrysis lutheri and C, well fed larvae metamorphosed in 6 to 8 days; Tetraselmis sue&a) metamorphosed 6 to 8 days after fer- (3) Mytilopis leucophaeata larvae and post-larvae are tilization at a mean shell length (parallel to the hinge line) euryhaline, capable of development to metamorphosis of nropm (n=25). Neither larvae nor juveniles of M. at ro to 32gc; leucophaeata possess at any stage. The “tri- angular tooth” referred to in ABBOTT’S(1974) description (4) neither larvae nor older stages of Mytilopti Ieuco- of M. leucophaeuta is a projection of the shelf near the phaeata possesshinge teeth; , not to be confused with hinge teeth. Because the (5) shells of juvenile and older Mytilopsis leucophaeata adult is broad, the shell presumably does not are tubulate; tubules are restricted to the older shell require teeth for stabilization of the opening and closing regions bounded by the and do not pene- motion of the valvol. For the adult population sampled, trate the . mean maximum shell dimension was 2.2 cm (n - I 25). Figure 2 shows a typical juvenile (0.5 cm maximum shell dimension). Evenly dispersed and uniformly shaped tu- Literature Cited bules penetrate the inner calcareous crossed-lamellar layer typical of the Dreissenacca (KENNEDY, TAYLOR 8 HALL, As-, Rourr Toorn xg6ga). These tubules range in diameter from 3 to 5 p IS?& Amhun #sdds. s~cd.;669pp;&?mo+6g;pthl-~ (in color).Vsn Nostrand Reinhold CO.. New Yat and should not be confused with the very small tubule- auury, MXLSO- Ronurn like structure3 occurring in mytilids (an order of magni- 1979. u1pummhusl drect of Ckulin~ mouuaun shell with mdium tude smaller). The tubules of Mytilopsis Zeucophaeata are hyplxhbctc (Olomx). Ihe Nsutihr 9s (n-s): ,,-,g CEAHLSY, PAUL l JAYD. ANDLIW. uniformly distributed in, and restricted to, the older 1971. Aids for identihtion of bivalve I- of Vulipir logi* II (1): ,yrrg; 51 M figs. (8 OstobQH~ regions of the shell bounded by the pal&l line. This dis- Exxuow, W-Y KSITB& Mouxs KMLISAMNJAOOBSOM tribution suggests a secondary origin for the tubules ~976. Guide to sh.zUs. Nfied A. Knopf, Inc., New York, xviii+ (KENNEDY, TAYLORt HALL, 1g6gb). In their brief review 48s pp.; 97 plu [of which r6 colored]; 6 tat 6~s. KXNNKTJY, WILLIAM J~yas, JOHN Dlwrr, TAYLOR. ANTHONY HALI, of tubulate bivalve shells, KENNEDY et al. (xg6gb) state ,969~. Environmenul and biological controt on biwtve shell miner& that these tubules penetrate the periostracnm. Such was WY. Biol. Rev. 14: 4gg - 330 t96gb. ‘Ihe shell struchve and mixmralm of the. Bivalvia. Intiuctioa not the casein the material examined in the present study. - Nucuiaca - %+nua Bull. Brit Mu:. (N. H.) ZOOI. SuppI. The tubula of M. Ieucophaeata first appear in metamor- 3: I - rss; sg pier. maximum shell dimension) and LCCSANO~~, VICTOR LYON . I&mw CARL DAVIS phosed juveniles (0.5mm 1963. Rearing of bivalve mollusks. In: Ad- in msriw biolo(n. are seen in individuals of all Iarga sizes. I: I - r36; ,s text f$. I? S. Russell (cd.). Academic Press, London LUTZ, R. A. . D. JAE.LOHSKI 1978. CrcucuJur biislve lawse. Science rgg: &jg - MO To summa&c : RICES, C. B. 1950. The identification and clatsXcation of luaellihch IUV~O. (I) in the population of Mytilopti leucophucata studied, Hull Bull. Mu.. EcoIw~ S: ,g - noa gamete release consistently occurred as salinities de- SODALL, s. E. -- - 1978. The development of the hinge line in tmpiul musei I- of creased during the annual rainy season; the pwa Perno. Rot. National Shellfish. AISOC 68: 86