The impact of starvation on larvae of Ivory shell Babylonia formosae habei was studied in a laboratory experiment. Newly hatched veligers showed considerable tolerance to starvation due to their endogenous yolk material, and time to the point-of-noreturn (PNR; the threshold point during starvation after which larvae can longer metamorphose even if food is provided) was calculated to be 104.5h. However, starvation still affected larval growth, survival, and metamorphosis. Mean shell length of larvae increased 49.77 Am day 1 for nonstarved, but only 11.13 Am day1 for larvae starved for 108h. After larvae began feeding, their growth rates rapidly recovered to the level of the nonstarved following short periods of starvation (less than 48h), but were inhibited and unable to ever reach the level of the nonstarved when being starved beyond 48h. Percent metamorphosis was 53.75% for the nonstarved, but all larvae died before 10 days for those starved for 108h. Starvation not only affected larval time to reach metamorphosis, but also caused the delay in the time to metamorphosis. For the nonstarved, larvae took only 11.5 days to reach spontaneous metamorphosis, but they took 20 days to reach spontaneous metamorphosis when starved for 96h, and this duration of delayed metamorphosis reached 8.5 days. Furthermore, the importance of yolk material for maintaining larval survival of B. formosae habei during starvation periods is also discussed.

The development of embryos and larvae of Babylonia formosae habei living along the southeast coast of China is observed under laboratory conditions. The egg masses are laid by females on hard substrate at night and each capsule contains 100-500 eggs. Each egg is 250-280mm in diameter. The first two cleavages of the embryo are meridional and equal, and a polar lobe is produced, larval kidney, which only consists of a single ceil, appears during the gastrula stage on each side of the embryo. The right tentacle develops prior to the left one. At 25-27℃, an intracapsulate veliger stage is reached about 4.5d after deposition. The larvae hatch on the fifth day as swimming veligers with a shell length of 360～500mm. The newly hatched larva can ingest suspended algal cells from the water column and remains in the pelagic stage for 8～10d. The newly settled juveniles are 900-1200mm in shell length.

The morphological characters on different developmental phases of embryo and larva and the schedule of the whole early developmental process in Styela canopus were observed and described. The types of reproduction and early development as well as the morphology of egg and larva in different ascidian species were compared. Styela canopus is oviparous. Its egg, 230.4～336.0μm in diameter, is equipped with extraembryonic cell layers measured 43.2～63.0μm thick. The early development of Styela canopus is typical urodele development, including fertilization, cleavage, gastrulation, tadpole in membrane, tadpole, initiating metamorphosis and juvenile. The tadpole of Styela canopus, with a length of 0.6～0.9mm, consists of trunk and tail. There are obvious notochord, ocellus and adhesive papillae in the tadpole. Under the water temperature of (25±0.5)℃ and the salinity of 27.0, the larva was hatched after 9.5～11.0h since the fertilization

The larvae of Styela canopus show the highest rates of settlement and metamorphosis when treated with 40mM KCl-elevated seawater at 25℃ in temperature and 27.0 in salinity. Induced by 40 mM KCl-elevated seawater, it took Styela canopus larvae approximately 3h after hatching to develop competence to settle and metamcamorphose. The present experiment shows that Styela canopus larvae is an ideal model organism for examining the efficiency of antifouling substance.

We examined trace metal ingestion and as-similation (Cd, Se, Zn) by the green mussel Perna viridis in a mixture of diatoms and sediment at concentrations below and above the pseudofeces production levels. Dual gamma radiotracers (109Cd, 65Zn) were used to investigate particle selection on marine diatoms and sediments. The diatom (Thalassiosira weissflogii) was radiolabeled with 109Cd, and the natural sediment was radiolabeled with 65Zn. By comparing the ratios of 09Cd: 65Zn in the particle mixture, mussel tissues and pseudofeces within a short-term exposure period (35min), the results demonstrated that the green mussels were able to selectively ingest the diatom particles at a high particle load. Efficiency of selection for nutritious particles (e.g. diatoms) increased with increasing ratio of sediments in the particle mixture. Pseudofeces contained a higher ratio of sediments relative to that in the feeding suspension. No major particle selection was observed at concentrations below the level for pseudofeces production. The assimilation of Cd, Se and Zn by the green mussels was quantified using a pulse-chase feeding technique. The assimilation of Se and Zn by the green mussels from ingested diatoms was reduced with the presence of sediment within the mussel gut, presumably due to the resorption of metals onto the sediment, leading to a quicker passage of metals through the digestive tract and a lower proportion of metals subjected to intensive digestion. In contrast, the presence of diatoms did not significantly affect metal assimilation from ingested sediment. A significant correlation between metal assimilation efficiency and metal gut passage time was also observed. Metal assimilation by the green mussels appeared to be little dependent on the particle concentration in seawater. Our study suggests that particle selection may potentially alter metal influx from ingested food sources, particularly at high particle concentrations. Selective feeding of nutritious particles, coupled with a high assimilation efficiency from these ingested particles, may increase metal influx into mussels from the dietary phase.