Spawn and larval development of Pleuroploca aurantiaca ( Lamarck , 1816 ) ( Gastropoda : Fasciolariidae ) from northeast Brazil *

The gastropod family Fasciolariidae is represented by seven genera in Brazil: Colubraria Schumacher, 1817; Fasciolaria Lamarck, 1799; Fusinus Rafinesque, 1815; Latirus Montfort, 1810; Leucozonia Gray, 1847; Metula H. and A. Adams, 1853 and Pleuroploca Fischer, 1884 (MatthewsCascon et al., 1989; Rios, 1994). According to Matthews-Cascon et al. (1989), all fasciolariid species are predators that usually prey on other gastropods and bivalves. SCI. MAR., 69 (2): 199-204 SCIENTIA MARINA 2005


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Pleuroploca aurantiaca is common in the West Indies and Brazil (Rios, 1994), living upon coral and rocks with calcareous algae in shallow waters (Matthews-Cascon et al., 1989).In this work, the spawn mass and larval development of P. aurantiaca are described.

MATERIAL AND METHODS
Four egg masses of Pleuroploca aurantiaca were collected between September 2000 and November 2001 during low tide in the intertidal zone at Pacheco Beach (3º41'S, 38º37'W), located in Caucaia County, Ceará State, northeast Brazil.The material was maintained in an aerated, non-circulating seawater 60-litre tank at 26-28ºC and a salinity of 35 ppt.Another P. aurantiaca egg mass was spawned by a female in the laboratory.
Three aspects of the spawns were observed: number and size of egg capsules, number and size of eggs and time of egg development to hatching.Egg capsules were measured with a slide under a stereoscopic microscope.The eggs were measured with an ocular micrometer under an optical microscope.Development from egg to hatching was observed daily with a stereoscopic microscope.The terminology used in the capsule and development description was based on that used by D'Asaro (1970a) and Miloslavich and Penchaszadeh (1997).
The egg capsules were photographed with a camera linked to a stereoscopic microscope and the hatching stage juvenile's shell with a (SEM) PHILLIPS XL30 scanning electron microscope.

RESULTS
The reproductive period of Pleuroploca aurantiaca (Fig. 1A) at Pacheco Beach lasted from August to December with a peak in November.This site has a rocky substratum and the egg masses were found under beach rocks (Fig. 1B).
The five studied Pleuroploca aurantiaca egg masses were composed of 29 ± 3 vase-shaped capsules (Fig. 1C).Each capsule was linked by a peduncle to a common basal membrane.They measured 9 ± 1 mm (n = 30) in length and 4.5 ± 0.5 mm (n = 30) in width and showed a slightly concave side and a concave apical plate.Strong horizontal lines in the concave lateral side (from the peduncle area to the apical ridge) and strong horizontal and vertical lines in the total area of the convex lateral side (sometimes only from the apical ridge to about half the capsule length) (Fig. 1D).The exit plug (Fig. 1E) had a circular shape, was covered by a transparent concave membrane and was located on the apical area.It measured 2.5 ± 0.5 mm (n = 30) in diameter.
The number of eggs per capsule was 353 ± 59 (n = 10).The eggs were pink and measured 278 ± 11 (n = 15) µm in diameter (Table 1).Only 5 to 7 eggs became embryos in each capsule.The remaining eggs were nurse eggs used by the embryos as a food resource (Fig. 2A).By the sixth day, it was possible to see some changes in the embryos' shape: they had a kidney-like shape with a ciliated mouth.On the tenth day, the intracapsular veliger (Fig. 2B) stage was observed for the first time and it was possible to see it feeding on the nurse eggs.It had a translucent and not calcified shell and transparent and long velar lobes, with two large and thin lobes with small cilia (Fig. 2C).
By the twenty first day, the intracapsular pediveliger stage had been registered for the first time, when the individuals had a functional foot and reduced velar lobes.The orange shell had a small anterior siphonal canal.At the prehatching stage, reached by the twenty-fifth day, the foot and shell had a dark orange colour, a well-developed anterior siphonal canal and degenerated velar lobes.Five days later, on the thirtieth day, we observed the hatching stage, when the juvenile detached the exit aperture membrane.It had a well-calcified, light brown and smooth shell, with 1.75 to 2.0 whorls (Fig. 2D, 2E, 2F).The shell measured 3884.5 ± 354.2 (n = 15) µm in length (Table 1).The egg capsules that had 6 or 7 embryos showed hatching juveniles with smaller shells than the ones that had 5 embryos.The foot was dark orange and the operculum light brown and very thin.There was no remaining velar lobe.Only 1% of the eggs developed to the hatching stage (3-5 juveniles).P. aurantiaca has an intracapsular metamorphosis development type (Bouchet, 1989).Table 1 shows the duration of the developmental stages and embryo sizes.

DISCUSSION
According to Bouchet (1989), the non-planktotrophic development in mollusks is observed in two different situations: when the larva hatches as a SPAWN AND DEVELOPMENT OF PLEUROPLOCA AURANTIACA 201 swimming non-feeding veliger and metamorphosis will occur after a few hours to a few days in the plankton (lecithotrophic development), and when metamorphosis occurs before hatching (as we see in Pleuroploca aurantiaca), often improperly said to be direct.This terminology is embryologically incorrect (Fioroni, 1982), the term intracapsular metamorphosis being more suitable (Bouchet, 1989).
The egg capsule structure shows some variations within the Fasciolariinae.According to Pilkington (1974), bulliform egg capsules with an escape aper- ture are known for Glaphyrina.Fasciolaria and Pleuroploca have more or less conical vasiform capsules tapering to a narrow stalk (D'Asaro, 2000).
According to D'Asaro (2000), encapsulations produced by Fasciolaria spp.from Australia and the western Atlantic have species-specific apical ridges and show a variation in the structure of the escape aperture, but in Pleuroploca, he observed conical capsules with simple apical ridges and distinctive horizontal ridges on the sides (or without the horizontal ridges, resembling Latirus egg capsules).
Pleuroploca aurantiaca has a strong suture and associate ridges similar to the ones described by D'Asaro (2000) for P. gigantea (Kiener, 1840) and P. trapezium, but with more associations between horizontal and vertical lines.Those associations provide a new pattern shape for the egg capsule wall of Pleuroploca.
Comparing the egg mass material from Pleuroploca species, as we can see in Table 2, P. gigantea and P. trapezium (from Sri Lanka) have the highest numbers of capsules in the egg mass (34 to 140 and 110 to 140 respectively).P. aurantiaca and P. lugubris (Reeves, 1847) have the same number of embryos (6 to 7) but the former has the smallest dimensions of the capsule (L = 9.0 ± 1.0 mm and W= 4.5 ± 0.5 mm), like P. lignaria (Linnaeus, 1758) (L = 8 -11 mm and W= 5 mm).
We observed that embryos of P. aurantiaca use one of the adelphophagy mechanisms reported by Fioroni (1967).There is a rotation of the nurse eggs by the embryos with the help of the velum.This rotation, according to Fioroni (1967), detaches some particles from the egg that enter the stomodaeum by ciliary movements.We can see in Figure 2A that nurse eggs are bigger than the normal eggs.According to Fretter and Graham (1962), nurse eggs from some fasciolariids undergo cleavage resulting in a group of cells with haploid nuclei.
As Penchaszadeh and Paredes (1996) indicated for Fasciolaria tulipa hollisteri, there seems to exist an inverse relationship between shell size at hatching and the number of embryos per capsule for Pleuroploca aurantiaca, i.e. the lower the number of embryos, the larger the shell size of the hatching juvenile.According to the same authors, this could be related to the number of nurse eggs available for ingestion by an embryo.