Subitaneous and diapause eggs in Mediterranean populations ofPontella mediterranea (Copepoda: Calanoida): A morphological study

Abstract

Transmission electron microscope studies on the morphology of subitaneous and diapause eggs in the neustonic copepod Pontella rnediterranea, collected in coastal waters of the Gulf of Naples from May to December 1986, revealed striking structural differences between the two egg types and the existence of a third egg type that was morphologically similar to a diapause egg but which hatched within 2 to 3 d. In smooth, subitaneous eggs the plasma membrane was surrounded by a thin outer chorion as compared to the thick and highly complex four-layer structure enveloping subitaneous eggs with short spines, and diapause eggs. This coat may be assembled just prior to or after deposition since the morphology of developing oocytes was similar in females laying either subitaneous or diapause eggs. The only other major structural difference between the two egg types was the presence of numerous, disc-like bodies in the ooplasm of diapause eggs. Development was arrested for at least 3 mo, prior to the initiation of the first cleavage, suggesting that these eggs were kept dormant by some endogenous and, possibly, structural mechanism preceeding the termination of diapause.

Differences in the density, sinking rate and biochemical composition of Centropages tenuiremis (Copepoda: Calanoida) subitaneous and diapause eggs

“…So it is not surprising that a complex egg structure capable of withstanding unfavorable environmental conditions and a large storage capacity are necessary for these eggs to survive for such long periods of time, which may result in the high dry weight of diapause eggs compared to that of subitaneous eggs. One of the morphological differences between diapause and subitaneous eggs of copepods is the shell structure, diapause eggs generally having a thick, multilayered shell, while subitaneous eggs have a thin, single-layered shell (Hairston & Olds 1984, Santella & Ianora 1990, Couch et al 2001. The presence of the chorion or external layer composed of lipoprotein impregnated with chitin and hematin was the major reason for the high protein content of diapause cysts of Artemia (García-Ortega et al 1998).…”

“…In many calanoid copepods, however, it is difficult to distinguish 2 egg types only using a light microscope (Hairston & Olds 1984, Chen & Marcus 1997. The most common difference is in the shell structure, since there is generally a thick and multilayered shell around the embryo of diapause eggs, whereas subitaneous eggs have only a thin and singlelayered shell (Hairston & Olds 1984, Santella & Ianora 1990, Ianora & Santella 1991, Couch et al 2001.…”

New observations of the ornamented Doushantuo embryo fossils from the Ediacaran Weng’an Biota, South China

“…Diapause is a common physiological state for embryos in a number of extant invertebrates (Belmonte et al 1997, Cáceres 1997, and even some vertebrates (Murphy & Collier 1997, Hrbek & Larson 1999. Diapause embryos are generally characterized by the following features: 1) thick and multilayered diapause cysts directly outside of the plasma membrane (Santella & Ianora 1990, Belmonte & Puce 1994, Marcus 1996, Castro-Longoria 2001, Couch et al 2001; the cyst consists of at least the cortical and alveolar layers (Gilchrist 1978, Blades-Eckelbarger & Marcus 1992, Dharani & Altaff 2004, Liu et al 2009); 2) taxon-specific ornamentation pattern on the outer surface of the diapause cyst (Gilbert & Wurdak 1978, Belk 1989, Shen & Huang 2008; and 3) diapause only occurs at a specific developmental stage for each species (Ianora & Santella 1991). The multilayered envelope and diverse ornamentation patterns of the A-type fossils are comparable to those known from extant diapause embryos.…”

“…annelids, molluscans, and arthropods (Santella & Ianora 1990, Conn 1991, Castro-Longoria 2001. The B-type fossils with a single capsule also resemble extant mature subitaneous eggs (Santella & Ianora 1990, Conn 1991, Ianora & Santella 1991, Couch et al 2001. In addition, the outer capsule, which shows elongated cell structure in some specimens (Fig.…”

Diapause egg production inAcartia (Paracartia) latisetosa(Crustacea, Copepoda, Calanoida)

“…Some recent indications confirm the existence of more than two types of eggs in calanoid copepods (Santella & Ianora, 1990); however it is impossible to explain why there are two morphologies for a subitaneous strategy.…”