Carlos S. Gallardo

DEVELOPMENTAL PATTERN AND ADAPTATIONS FOR REPRODUCTION IN NUCELLA CRASSILABRUM AND OTHER MURICACEAN GASTROPODS

1. Eggs of Nucella crassilabrum range from 204 to 293 µm in diameter (mean = 240 µm). Only 6.6 to 7.9% are fertile; the remaining are ingested as nurse eggs. 2. Embryos metamorphose before hatching. Pre-hatching time ranges from 55 to 80 days according to seasonal temperature fluctuations. 3. Hatching size varies from 0.82 to 1.3 mm, depending on number of nurse-eggs ingested per embryo (from 3 to 20). Number of fertile embryos per capsule (10 to 122) depends on capsule size. 4. Hatching type and hatching size shown by N. crassilabrum agree with those of other muricaceans living in similar habitat conditions. 5. Pre-hatching time and hatching size data of various muricaceans are analyzed to determine to what extent they influence embryonic mode of nutrition, namely the presence of nurse-eggs or alternatively large and fertile self-sufficient eggs. Provision of nurse-eggs for embryos is of common occurrence among intertidal muricaceans and this mode of nutrition seems to have been favored in such habitats to reduce developmental time. Providing the yolk as nurse-eggs seems also to contribute to a larger hatching size, as suggested by some subtidal muricaceans with such embryo support patterns.

Two modes of development in the morphospecies Crepidula dilatata (Gastropoda: Calyptraeidae) from Southern Chile

In Chinquihue Bay, a sheltered locality in Southern Chile, female Crepidula dilatata Lamarck brood egg masses which differ in intracapsular development. In some, all eggs develop and are hatched as free veliger larvae (indirect development). In others, only some of the eggs develop and hatch as young adults (direct development), the rest being consumed as nurse eggs. Two possible interpretations are considered: intrapopulation variation of developmental pattern in a species, and the coexistence of two sibling species. Stages of the intracapsular development are described and illustrated. Fecundity varies according to size of the female. For females brooding eggs with indirect development it is estimated at between 3840 and 85575 embryos per spawn; for females with eggs undergoing direct development, embryo production per egg mass is estimated at between 70 and 812. A comparison is made between females brooding the two kinds of egg masses. Minor differences exist in adult coloration, shape of egg capsules, egg diameters, spawning season and their abundance and distribution in the intertidal. Brooding females with eggs displaying indirect development are significantly larger than those with eggs of direct development. The latter females form chains subtidally but not intertidally as do females bearing eggs with indirect development. On these females with pelagic larvae, chains frequently include sedentary males which reach large sizes. On basal females with direct development, chains contain mostly other females, suggesting that matings are temporary and by errant males. These results are compared with existing information in the literature for other species both in this genus and in other marine invertebrates. It is concluded that two sympatric sibling species with different modes of development are present in the morphospecies C. dilatata Lamarck in Southern Chile.

Especies gemelas del genero Crepidula (Gastropoda, Calyptraeidae) en la costa de Chile; una redescripcion de C. dilatata Lamarck y descripcion de C. fecunda n. sp.

Abstract According to differences in pattern of development, which have been discussed in a previous paper, two sibling Crepidula species are reported from the coast of Chile. On this basis, a redescription of C. dilatata Lamarck is done, this species being characterized by a direct development; only some of the eggs contained in each ovicapsule develop, the rest being nurse eggs. C. fecunda n. sp. is distinguished from the former by an indirect type of development ending with the hatching of numerous free living larvae. Both species are sympatric at some localities; at these places, females of C. fecunda are significantly larger than those of C. dilatata Lamarck. Brief information about both species’ habitat, as well as localities at which they have been found is also given.

Imposex in Three Marine Gastropod Species in Chile and Potential Impact on Muriciculture

Abstract A survey of imposex was conducted between the Bay of San Vicente, Concepcion, Chile (36° 50′) and the Bay of Renocavi, Puerto Montt, Chile (41° 35′), to determine if imposex is occurring in an area of collection and cultivation of the gastropod, Chorus giganteus . Imposex was recorded in three chilean muricids C. giganteus, Xanthochorus cassidiformis and Nucella crassilabrum complex . Percentage of imposex in females sampled ranged from 0% to 100%. The degree of expression of imposex was not so severe as to elicit sterility in the individuals surveyed. Incidence of imposex was as high as 47% in areas of harvest of C. giganteus for reproductive and cultivation studies for commercial production of this species. A six percent incidence of imposex was observed in Nucella proximal to the facility for cultivation of C. giganteus . Gastropods of the genus Nucella are used in other countries to monitor incidence of imposex and have demonstrated sensitivity toward tributyltin (TBT), the associated causal agent. Since sex of individuals in muriciculture is determined by the presence or absence of a penis, imposex may lead to erroneous classification of males and females. The incidence and severity of imposex in C. giganteus and related species may have a negative impact on sustainable cultivation and harvest of gastropods in Chile.

Nutritive Egg Formation in the Marine Snails Crepidula dilatata and Nucella crassilabrum

Summary Both frequency and morphology of the nutritive eggs in the snails Crepidula dilatata and Nucella crassilabrum were analyzed. In both species, nutritive eggs constitute over 90% of the eggs deposited in each capsule. Marked differences in nutritive eggs exist between these species with respect to morphological and cytological characteristics. Nutritive eggs of C. dilatata remain uncleaved and in their cytological characteristics resemble oocytes whose development becomes arrested at the stage of germinal vesicle. Although the eggs of this snail are dimorphic in size, such dimorphism is not correlated with the fate of these cells. Nutritive eggs of N. crassilabrum typically abort their development at the stage of zygote cleavage divisions and anarchic cleavage occurs only in a small fraction of them (X = 5–6%). The nature of these food eggs is discussed. Our findings suggest that, at least in C. dilatata, the mechanisms of nutritive egg formation reside in properties of the oocyte.

Posturas y estadio de eclosión del gastropodo muricidae Chorus giganteus (Lesson, 1829)

Abstract According to ecological developmental patterns in muricids summarized by Spight (1977), Chorus gigahteus shows an intermediate Veliconcha hatching type. Egg size, hatching size and embryonic source of food are similar to those reported for Murex trapa; this last species also possesses a Veliconcha hatching type. Field observations reveal that Ch. giganteus inhabits on shallow water sand bottoms as predicted by Spight for muricid species with a Veliconcha hatching type. Egg mass structure of Ch. giganteus and field observations suggest a communal spawning as previously observed in other muricids. Some possible adaptations of Ch. giganteus in relation to its existence in sand bottoms are assumed and discussed. They specially refer to its hatching type and the availability of solid substrate for the attachment of egg capsules. According to information available for Chilean muricids, the developmental pattern of Ch. giganteus shows closer evolutionary affinities with that of Nucella crassilabrum than...

Embryonic and larval development of the muricid snail Chorus giganteus (Lesson, 1829) with an assessment of the developmental nutrition source

Abstract Chorus giganteus is a muricid snail of great commercial value in Chile. Preliminary estimates of size and number of their encapsulated eggs support the assumption of lecithotrophic development mediated by the provision of extraembryonic nurse eggs. To examine the validity of this hypothesis, the major objectives were: a) to analyze and describe prehatching ontogenetic stages, b) to determine the amount of extraembryonic food consumed and to assess, through laboratory experiments, whether the posthatched larvae relie on such reserves (lecithotrophy) during their free swimming stage and c) to establish the duration of intracapsular development and of the free swimming larval stage. We also confirm the occurrence of nurse eggs that are ingested by the early encapsulated embryos, indicating that the snails develop through a yolk-supported (lecithotrophic) type of development. Free swimming larvae reared in the absence of phytoplankton survived as well (P > 0.05) as those supplied with particulate foo...

Prey attack, food preference and growth in juveniles of the edible muricid snail, Chorus giganteus

Chorus giganteus is a marine snail with potential in aquaculture or sea-farming. Considering predictions of optimal foraging, the aim of this study was to identify the preferred prey and to determine the extent to which this preferred prey promotes a higher rate of growth. Prey handling mechanisms, prey preference and resulting growth were assessed by offering C. giganteus the mussels Semimytilus algosus and Perumytilus purpuratus as alternative prey items. Juvenile snails of two size classes were used to assess handling behaviour and prey preference. Experimental treatments included mixed (S. algosus–P. purpuratus) as well as pure diets. A tendency to drill the prey shell, instead of using pedal handling, was observed in smaller snails (6–8 mm), while among larger snails (10–12 mm), the handling mechanism depended upon the prey species offered. Shell drilling was used more frequently to feed on P. purpuratus; in contrast, pedal handling was clearly favored when feeding on S. algosus. S. algosus was significantly preferred as prey (Quade test, T=30.51; K1=1 and K2=8; P<0.01), and the growth thus obtained was significantly higher than with P. purpuratus as prey.

Ultrastructure of sperms in bivalve molluscs of the Mytilidae family

Summary The sperm structure of five external fertilizing bivalve molluscs pertaining to the Mytilidae family is compared. Apart from examining if such gamete structure conforms to the primitive sperm form of the type I predicted by Franen, a major aim of the study is to compare the development and structure of some organelles whose evolution among the bivalve sperms has also been associated with the style of fertilization (whether external or within brooding chambers where the retained eggs are fertilized). Observations are specially focused on examining the existence of the acrosome, its morphology and the way in which it develops as well as on the pattern of condensation of the nucleus. Finally, the morphology of the mitochondria, conforming the mid-piece, is also examined. The sperms studied conform to the primitive general type proposed for external fertilizing species as well to the morphological pattern presented by other free-spawning bivalve molluscs. A well developed acrosome is observed, support...

Crepidula philippiana n. sp., nuevo gastropodo Calyptraeidae de Chile con especial referencia al patron de desarrollo

Summary Crepidula philippiana n. sp., a new Calyptraeid gastropod from Chile with special reference to its development, A new species of Crepidula, C. philippiana n. sp., is described from the Southern coast of Chile. The species has been found attached to the inside of empty marine snail shells, generally inhabited by hermit crabs. C. philippiana is distinguished from other related marine species mainly by its reproductive strategy. The species shows direct development. Only one egg per capsule develops, the others remaining as nurse eggs; therefore this unique embryo consumes all the eggs contained in a capsule. In this way, few young snails are hatched per egg mass which attain a great size (3 mm) when passing to the extracapsular environment.