AGE AND GROWTH OF LITHOPHAGA LITHOPHAGA (LINNAEUS, 1758) (BIVALVIA: MYTILIDAE), BASED ON ANNUAL GROWTH LINES IN THE SHELL

The life span of Lithophaga lithophaga was found to be >54 years when the annual growth lines in longitudinal shellsections were counted. The age determination was confirmed bya) length frequency histograms, b) the time taken for the formationof annual and reproduction rings and c) by determining the agein different parts of the shell. The age of individuals of thesame length varies, for example, individuals with a length of5.0 ± 0.2 cm range in age from 18–36 years. Theoldest individuals were found at depths of 1–5 m. Maximumgrowth (75%) was observed from the end of spring to the beginningof summer. The increase in length of the borehole, which was1.5 times greater than the length of L. lithophaga, was continuousand occurred at a faster rate in winter. Parameters, such as,shell length, age, axes, the occurrence of abnormal, white andpearlcontaining forms and wetflesh weight varied significantlywith depth. There was no variation in the ratio of boreholevolume/shell volume. On the basis of the above parameters, andalso the population density, each depth at which samples werecollected, was graded. Depths of 2–4 m were found to bethe most suitable for growth and habitation. Depths of 0–1m were most inhospitable due to strong wave action and the directeffect of the atmosphere. (Received 15 August 1994; accepted 17 March 1995)     

THE REPRODUCTIVE CYCLE AND SEXUALITY OF THE GREEN MUSSEL PERNA VIRIDIS (L.) (BIVALVIA: MYTILACEA) IN VICTORIA HARBOUR, HONG KONG

The reproductive cycle and sexuality of the green mussel Pernaviridis (L.) in Victoria Harbour, Hong Kong, were investigatedfrom July 1982 to May 1984. Histological studies showed thatthe cyde could be divided into 4 stages occurring in a highlyseasonal pattern. The very low (<0.1%) occurrence of functionalhermaphrodites indicates that P. viridis is gonochoristic. Pastreports of protandric rhythmic hermaphroditism may have resultedfrom reliance on fluctuations in sex ratio and sex identificationby gonad colour. These criteria are, however, considered invalidfor P. viridis because differences exist between the developmentalpatterns of the male and female gonads and, further, colourof the female gonad at the early proliferation stage resemblesthe male. Temperature was found to correlate positively withgonad development and with the lower threshold at 24°C.Temperature was not, however, limiting at some sites in HongKong. A joint Principal Component Analysis-Stepwise multipleregression procedure suggested that hypertrophication mightinhibit gonadal development in Victoria Harbour (Received 2 November 1987; accepted 30 December 1987)     

BROODING AND NON-BROODING DACRYDIUM (BIVALVIA: MYTILIDAE): A REVIEW OF THE ATLANTIC SPECIES

The Atlantic species of the marine bivalve genus Dacrydium arereviewed, with particular emphasis on their hinge and protoconchcharacters. The basic groundplan of a Dacrydium comprises afunctional primary ligament, a paired series of primary teeth,and a posterior row of secondary teeth separated from the latterby a secondary ligament; this can be transformed into a singleseries either by loss of the secondary ligament and mergingprimary and secondary teeth, or by loss of secondary teeth andligament through paedomorphosis. Twelve species are recognized, of which eleven are illustrated.One abyssal species is not separable morphologically from theIndian Ocean D. speculum Poutiers, 1989 and is new to the Atlantic;four new species (D. wareni, D. dauvini, D. filiferum and D.balgimi) are described; a Caribbean form which is hardly distinctfrom the Eastern Pacific D. elegantu-lum Soot-Ryen, 1955, isdescribed as a new subspecies D. e. hendersoni. The larvae are brooded in D. hyalinum (Mon-terosato, 1875),D. viviparum Ockelmann, 1983 and D. balgimi. The brooding specieshave larger larvae (protoconch 210 to 315 µm long) thanthe non-brooding (protoconch 120 to 150 µm long), andreach a smaller adult size (1.4 to 3 mm instead of 4.5–5mm). A phylogenetic reconstruction is attempted using parsimonyanalysis of hinge and shell characters as well as the brooding/nonbrooding character. (Received 22 October 1996; accepted 28 November 1996)     

INITIAL SETTLEMENT BEHAVIOUR AND SURVIVORSHIP OF LITHOPHAGA BISULCATA (d'ORBIGNY) (MYTILIDAE: LITHOPHAGINAE)

Although infaunal associates of living reef building coralsindude numerous phyla, initial settlement on the coral hosthas never been described. Experiments described here includedraising the larvae of a common Caribbean coral-boring mussel,Lithophaga bisulcata to observe their behaviour in the presenceof a variety of settlement substrates. On Stephanocoenia michelini,the most common host, larvae moved about the coral surface withimpunity, exploring the surface with the foot. On this coralspecies, competent pedi-veligers were ingested by the coralbut not necessarily digested. Penetration of the coral is initiatedby entering the coelenteron, where metamorphosis will presumablytake place. On species which L. bisulcata rarely inhabits, thelarvae appeared to be stung by nematocysts and withdrew thefoot rapidly from contact with the tissue Habitation of a living coral substrate appeared to be beneficialto the bivalve. Although L. bisulcata inhabits both riving anddead coral, there is evidence that survival, longevity and reproductiveoutput are enhanced when the mussel is surrounded by livingcoral tissue (Received 9 June 1987;     

REPRODUCTIVE CYCLE, MANAGEMENT AND CONSERVATION OF PAXYODON SYRMATOPHORUS (BIVALVIA: HYRIIDAE) FROM THE TOCANTINS RIVER, BRAZIL

The reproductive cycle of a population of Paxyodon syrmatophorus(Meuschen, 1781), a mussel exploited for its shells in the lowerTocantins River, Brazil, was studied between September 1997and August 1998. Monthly examination of gonad sections and inspectionof the demibranchs of females showed that gametogenesis takesplace all year round and that spawning occurs during the months ofthe dry season. Gravid females were found throughout the period betweenFebruary and September. Sexually mature mussels as small as 23mm in length were found and the smallest gravid female was 32mm in length. The implications of the findings are discussedin relation to the conservation and management of exploitedfreshwater mussel populations in the region. ³ Author for correspondence. Telefax: +55-91-8251209. Email: beasley{at}eletronet.com.br ⁴ Current address: UPIS, Sep/Sul EQ. 712/912 Conjunto "A" Brasília70390-125, DF Brazil (Received 20 September 1999; accepted 13 January 2000)     

EFFECTS OF TEMPERATURE ON CHRONIC HYPOXIA TOLERANCE IN THE NON-INDIGENOUS BROWN MUSSEL, PERNA PERNA (BIVALVIA: MYTILIDAE) FROM THE TEXAS GULF OF MEXICO

Effects of temperature (15°, 20° and 25°C), O₂ partialpressure (P_O2=0, 1, 2, 4, and 6 kPa), and individual size(12–79 mm shell length; SL) on survivorship of specimensof the non-indigenous, marine, brown mussel, Perna perna, fromTexas were investigated to assess its potential distributionin North America. Its hypoxia tolerance was temperature-dependent,survivorship being significantly extended at lower temperaturesunder all tested lethal P_O2. Incipient tolerated P_O2 was 4 and6 kPa at 15 and 20°C, respectively, with >50% mortalityoccurring at 25°C at all tested levels of hypoxia. P_O2 hadless of an effect on survival of hypoxia than temperature. At25°C, survivorship was not different over a P_O2 range of0–2 kPa and increased only at 4 and 6 kPa. Survivorshipwas size-dependent. Median survival times increased with increasingSL in anoxia and P_O2=1 kPa, but at 2, 4 and 6 kPa,smaller individuals survived longer than larger individuals.With tolerance levels similar to other estuarine bivalve species,P. perna should withstand hypoxia encountered in estuarine environments.Thus, its restriction to intertidal rocky shores may be dueto other parameters, particularly its relatively low temperaturetolerance. (Received 26 January 2004; accepted 31 March 2005)     

DISTRIBUTION, HABITAT AND MORPHOLOGY OF THE CARIBBEAN CORAL- AND ROCK-BORING BIVALVE,LITHOPHAGA BISULCATA (d'ORBIGNY) (MYTILIDAE: LITHOPHAGINAE)

Lithophaga bisulcata is the most common Caribbean and Atlanticlithophagine and is the only species of the genus known to occurfrequently in both living and dead coral. The abundance in livingcorals is non-random and variable. Most common hosts are Siderastereasiderea and Stephanocoenia michelini. The bivalves are moreabundant in their preferred hosts than in dead coral. Individualsfrom the two habitats are indistinguishable in shell shape,musculature and size of boring and posterior pallia! glands,indicating a single population. Boreholes differ in the twohabitats with respect to size and lining. Linings are formedat the "inactive" end of the burrow; therefore living coralinhabitants line the anterior end of the burrow and dead coralborers line the posterior end. Recruitment rates are unknownin dead coral but were very low in living coral (Received 9 June 1987;     

A NEW SPECIES OF LITHOPHAGA (BIVALVIA: LITHOPHAGINAE) BORING CORALS IN THE CARIBBEAN

A new species of Lithophaga is described as a small lithophaginemussel exclusively boring Madracis mir-abilis, M. decactis andM. formosa in Jamaica. The shell, musculature and pallial glandsshow modifications for live coral boring similar to those ofIndo-Pacific species of the genus. However, both the boringand posterior pallial glands are more primitive than other speciesexamined to date, interpreted as indicative of a more recentadaptation to life in a living coral habitat by this species. ^*Contribution No.359 of the Discovery Bay Marine Laboratory,University of the West Indies (Received 23 April 1985;     

LIFE CYCLE AND HABITAT SHIFT OF THE TROCHID SNAIL DILOMA SUAVIS (PHILIPPI) WITHIN INTERTIDAL MUSSEL ZONES

The life cycle of the trochid snail Diloma suavis (Philippi,1849),was studied on an intertidal rocky shore at Shirahama, WakayamaPrefecture,where two mytilid bivalves, Septifer virgatus(Wiegmann) andHormomya mutabilis (Gould), formed verticallycontiguous musselbeds in the upper-middle and lower zones,respectively. At lowtide in April, the snail density increased withdecreasing shoreheight and was greatest at the middle level of theH. mutabilisbed. Then, the density decreased towards thelower littoralfringe. Newly settled juveniles smaller than 2 mm inshell heightappeared abundantly in late summer and autumn withinalgal turfon the lower shore. As snails grew larger than 2 mm, theyappearedwithin the gaps of the H. mutabilis bed and theS. virgatusbed. They increased in size monotonically towardsthe next summer,but rate of growth in shell height tended to be greatin autumnand small in winter. Seasonal change in the density ofsnailsfound within the gaps of the mussel beds was remarkable duringathree year period, increasing from autumn to winter and thendecreasingtowards next summer. Reproduction occurred in summer, andadultsnails disappeared by September. It is thus suggested that thisspecieshas a one year lifespan and shows a habitat shift from algalturfto the gaps of the mussel beds with growth. (Received 12 October 1998; accepted 2 March 1999)     

ANNUAL REPRODUCTIVE CYCLE OF THE FEMALE HAWAIIAN MONK SEAL (MONACHUS SCHAUINSLANDI)

Abstract: The annual reproductive cycle is described for the adult female Hawaiian monk seal ( Monachus schauinslandi ) from data collected at Laysan Island (1982–1991) and Lisianski Island (1982–1983) in the Northwestern Hawaiian Islands. Pupping, lactation, weaning, and molting were directly observed, while mating was rarely observed and was, therefore, inferred from the occurrence of mounting injuries and from adult male and female association patterns. Pooled birth rates during the study period were 0.544 for all adult-sized females and 0.675 for females parous in earlier years. For parturient females, pupping peaked in late March and early April, weaning in May, mounting injuries in May and June, and molting in July. For non-parturient females, the median mounting injury and molting dates occurred 17 and 28 days earlier, respectively. Pupping date set the timing of subsequent events in the annual cycle, but the timing of those events was adjusted by loss of the pup or poor physical condition of the female. Individual pupping patterns varied widely. The mean interval for births in consecutive years was 381 days; females that pupped in consecutive years gave birth later each season. Conversely, females who skipped a year or more gave birth earlier their next pupping season.     

THE ANATOMY OF CALLOCARDIA HUNGERFORDI (BIVALVIA: VENERIDAE) AND THE ORIGIN OF ITS SHELL CAMOUFLAGE

Callocardia hungerfordi (Veneridae: Pitarinae) lives in subtidalmuds (220 to 240m C.D.) and is covered by a dense mat of mudthat, effectively, camouflages the shell. The periostracum is two layered. The inner layer is thick andpleated, the outer thin and perforated. From the outer surfaceof the inner layer develop numerous, delicate (0.5 mm in diameter),calcified, periostracal needles. These penetrate the outer periostracum.Mucus produced from sub-epithelial glands in the inner surfaceof the mantle, slides over the cuticle-covered epithelium ofthe inner and outer surfaces of the inner fold and the innersurface of the middle mantle fold to coat the outer surfaceof the periostracum and its calcified needles. Increased productionat some times produces solidified strands of mucus which bindmud and detrital material into their fabric to create the shellcamouflage. Calcified periostracal needles have been identified in othervenerids, including some members of the Pitarinae, but how theyare secreted and how the covering they attract is producedand, thus, how the whole structure functions, has not been explained. (Received 7 December 1998; accepted 5 February 1999)     

EVOLUTION OF THE TELLINACEA (BIVALVIA)

The suspension feeding Astartacea appear to be among the earliestheterodonts. These organisms may have given rise to the Carditaceaand the rest of the heterodonts including the Tellinacea. Paleontological evidence indicates that the earliest Tellinaceawere suspension feeders with members that lived vertically ina burrow in shifting sand. These conditions resemble those foundin species of modern Donax in the Donacidae. From a Donax-likestate of suspension feeding evolution most likely proceededto non-selective feeders. Extant organisms that resemble thisstage are found in the Solecurtidae. A later stage resemblessome of the extant Psammobiidae. The final stage in tellinaceanevolution is the acquisition of deposit feeding with its associatedmorphology. These stages are observed in the Scrobiculariidae,Tellinidae and a few members of the Semelidae. (Received 27 April 1981;     

THE ADDUCTOR AND RETRACTOR MUSCLES OF THE VELIGER OF PECTEN MAXIMUS (L.) (BIVALVIA)

In Pecten maximus (L.), retractor and adductor muscles becomefunctional in the early veliger larva. The twelve-day-old veligerhas four pairs of velar retractors, three pairs of retractorsattached to the posterior body wall and an anterior adductor.The pediveliger has in addition, pedal retractor muscles anda posterior adductor. The retractors consist of striated muscle:the adductors have both smooth and striated portions. The retractorsattach near the hinge, branch to a greater or lesser extent,then attach to specific areas of the velum, posterior body walland foot. Some features of the branching and of the dispositionof points of attachment form a pattern which exhibits mirrorsymmetry about the plane between the two shell valves. Thispattern is characteristic of the species. It is deduced thatretraction and protraction of the velum result from co-ordinatedsequences of muscle contractions. ^*Present address: Forest Products Research Centre, P.O. Box1358, Boroko, Papua New Guinea. (Received 15 June 1984;     

REPRODUCTIVE SYNCHRONY AND THE ESTIMATION OF MEAN DATE OF BIRTH FROM DAILY COUNTS OF NORTHERN FUR SEAL PUPS

Two methods for estimating the mean date of birth from daily counts of northern fur seal pups ( Callorhinus ursinus ) are presented and applied to data collected on the Pribilof Islands in 1951, 1962, 1963 and 1983. The mean date of birth over the four years was July 9. Reproduction is highly synchronized and consistent from one year to the next. Pupping occurs over a five week period with over 50% of the pups being born during the first two weeks of July.