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Early Development of Mytilopsis Leucophaeata

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Early Development of Mytilopsis Leucophaeata Page 378 THE VELIGER Vol. 22; No. 4 Early Development ofMytilopsis leucophaeata (Bivalvia : Dreissenacea) BY SCOTT E. SIDDALL Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida 33x49 (1 Plate) Several keys have been publishedfor identification of to 30o C (July), averaging 26° C during spatfall. In the bivalve larvae based on characters of the larval shell, orspring of 1976, sexually ripe adults exposed in the labora­ prodissoconch(Chanley & Andrews,1971 ; Loosanoff, tory to 350 C seawater ( io%0) for 20 minutes spawned Davis & C hanley,1966); However, none describeMyti­ within one hour of treatment. Larvae were reared through lopsis leucophaeata (Conrad, 1831), an estuarine species metamorphosis at three salinities (io, 24 and 32%«) 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(Abbott, 1974; larvae (L o o s a n o f f & D a v is , 1963). Serial samples of both Em erson & Jacobson,1977). The objective of the present naturally set larvae and juveniles (1975 material) and study was to describe the development of larval and juve­laboratory cultured larvae and juveniles (1976 material) nile M . leucophaeata. were cleaned in a buffered sodium hypochlorite solution In early 1975, I monitored the abundance of bivalve (see C a r r ik e r , 1979) then examined on an AMR-900 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 Mytilopsisof 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 asM . leucophaeata. at near-oceanic salinities (32%0). 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 species both as larvae and adults( R e e s , 1950; Tidal flushing was restricted with salinities decreasing L utz & Jablonski,1978; S id d a ll, 1978). Serial develop­ from 22%co to 8/0 after late spring rains. Heaviest set of ment of the hinge line in Mytilopsisleucophaeata is shown spat occurred two weeks after the onset of this annual in Figure i. Using the terminology ofC h a n l e y a rainy season. Temperatures varied from i3°C (January) A n d r e w s (1971), M. leucophaeata develops "knobby” Explanation of Figures / and 2 maximum shell dimension = 375 pm; e) 28 DAF: maximum Figure i : SEM photomicrographs of hinge lines ofMytilopsis leu­ shell dimension = 500 pm; showing shelf under the umbo cophaeata at two times prior to metamorphosis: a) 2 days after Figure a : SEM microphotograph of juvenileMytilopsis leucophae­ fertilization (DAF); shell length = 74 pm; b) 6 DAF; shell length ata (0.5 cm maximum dimension) (a) with pits randomly dis­ s, 1 Ho /un; and at three times subsequent to metamorphosis: persed anterior to palliai line; and (b) a magnified view of pit c) 13 DAF: maximum shell dimension = 270pm; d) 18 DAF: (3 pm in diameter) The Veliger, Vol. 22, N o. 4 [Siddall] Figures 1 and 0 Vol. 22; No. 4 THE VELIGER Tage. 879 umbones which became "skewed” anteriorly following (2) settlement of spat peaked 2 weeks after gamete re­ metamorphosis. At 26o C, larvae fed a mixed phytoplank­ lease in natural populations; in thelaboratory ata6° ton diet (Isochrysis galbana, Monochrysis lutheri and C, well fed larvae metamorphosed in 6 todays; 8 Tetraselmis suecica) metamorphosed 6 to 8 days after fer­ (3) Mytilopsis leucophaeata larvae and post-larvaearc tilization at a mean shell length (parallel to the hinge line) euryhaline, capable of development to metamorphosis of 210 pm (0=25). Neither larvae nor juveniles ofM. at io to 32%0; leucophaeata possess hinge teeth at any stage. The “tri­ angular tooth” referred to inA b b o t t ’s (1974) description (4) neither larvae nor older stages ofMytilopsis leuco­ of M. leucophaeata is a projection of the shelf near the phaeata possess hinge teeth ; beak, not to be confused with hinge teeth. Because the (5) shells of juvenile and olderMytilopsis leucophaeata adult ligament 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 palliai line and do not pene­ motion of the valves. For the adult population sampled, trate the periostracum. mean maximum shell dimension was 2.2 cm (n » 125). 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 Dreissenacea(K e n n e d y , T a y l o r & H a l l , Ab b o t t. R o bb x t T u o k s r 1969a). These tubules range in diameter from 3 to 5 pm 1974- American seashells. a»d ed.; 663 pp; 40O0+ 6g«.; phi. 1 ■ *4 (in color). Van Nostrand Reinhold Co., New York and should not be confused with the very small tubule­ Garriker, M elbourne Romaine like structures occurring in mytili ds (an order of magni­ 1979. Ultras tructural effect of cleaning moUuscan dreh with sodium hypochlorite (Clorox). The Nautilus 93 (2-3): 47-49 tude smaller). The tubules ofMytilopsis leucophaeata are Chanley, Paul a Jay D. Andrews uniformly distributed in, and restricted to, the older 1971. Aids for identification of bivalve larvae of Virginia. Malaco­ regions of the shell bounded by the palliai line. This dis­ logie r i (1 ): 45-119; 51 text figs. (8 October 1971) E m e r s o n, W il l ia m K e i t h a M o r b is K a r l m a n n J a c o b s o n tribution suggests a secondary origin for the tubules 1976. Guide to shells. Alfred A. Knopf, Inc., New York, xviii+ 482 pp.; 97 pits, [of which 16 colored]; 6 text figs. (K e n n e d y , T a ylor & H a l l , 1969b). In their brief review Kennedy, W illiam James, John David Taylor a A nthony H all of tubulate bivalve shells,K e n n e d y et al. (1969b) state 1969a. Environmental and biological controls on bivalve shell mineral­ that these tubules penetrate the periostracum. Such was ogy. Biol. Rev. 44: 499 - 530 1969b. The shell structure and mineralogy of the Bivalvia. Introduction not the case in the material examined in the present study. — Nuculacea — THgonacea. Bull. Brit. Mus. (N. H.) Zool. Stippi. The tubules of Af. leucophaeata first appear in metamor­ 3: i -125; 29 pits. L o o s a n o f f , V ic t o r L y o n a H a rr y C a r l D a v is phosed juveniles (0.5 mm maximum shell dimension) and 1963. Rearing of bivalve mollusks. In: Advances in marine biology. are seen in individuals of all larger sizes. 1: i -1 3 6 ; 43 text figs. E S. Russel] (ed.). Academic Press, London L u t z , R. A. a D. J a b l o n s k i 1978. Cretaceous bivalve larvae. Science 199: 439 - 440 To summarize: R e e s , C. B. 1950. The identification and classification of lamellibranch larvus. (1) in the population ofMytilopsis leucophaeata studied, Hull Bull. Mar. Ecology 3: 73-104 gamete release consistently occurred as salinities de­ Siddall, S. E. 197B. The development of the hinge line in tropical milnei tarv** of creased during the annual rainy season; the genusPerna. Proc. National Shellfish.Assoc. Ml M.
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