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Table 2 Morphological and Anatomical Features of Crassostrea gigas Larval Development Stages

From: Nervous system development in the Pacific oyster, Crassostrea gigas (Mollusca: Bivalvia)

Stagea Time of developmentb Morphological features
Early trochophore 20 hpf Spheroidal form, slightly conical at the basal region with two obvious invaginations (shell gland and presumptive mouth opening) and prototroch (Fig. 1a). Long cilia form an apical tuft that is present at the apical pole.
Middle trochophore 24 hpf Spheroidal form with one invagination (mouth). Shell gland everted (Fig. 1b).
Late trochophore 28 hpf Spheroidal form with well-developed prototroch and telotroch. Shell gland begins to secrete a shell (Fig. 1c). Locomotory organ—prototroch.
Early veliger (D-hinge-stage veliger) 36 hpf—72 hpf Two D-shaped shells surround the larval body. Digestive tract is complete and consists of mouth, esophagus, stomach, intestine, and anus. Elements of the muscular system (retractors) are well developed. Locomotory organ—velum (Fig. 1d).
Middle veliger 92 hpf-96 hpf Shells increase in size and are slightly elongated. Retractors and two adductors are well developed (Fig. 1e).
Late veliger after 5 dpf Right and left shells first demonstrate asymmetry (Fig. 1f). Velum is markedly larger than in the previous stage.
Pediveliger (umbo stage) after 28 dpf Umbo is distinguished as highest and most prominent part of each valve of the larval shell. Velum is markedly larger than at the previous stage.
  1. hpf hours post fertilization, dpf days after fertilization
  2. aOyster developmental stages were recognized by external morphological characteristics rather than based on exact determination of time after fertilization
  3. bThe data are for larval development at a temperature of + 20 °C and salinity of 28‰