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7 animals that lay the most unusual eggs
Almost all animals begin life as a fertilized egg, or ovum. Females (or female-gamete-producing hermaphrodites) of most invertebrates and all vertebrates that we commonly encounter produce, and in many cases lay, eggs. These eggs as well as their coverings or cases vary remarkably in size, shape, structure, and shade. The list below takes a closer look at seven of the most unusual eggs (and egg cases) in the animal world and the creatures that produce them.
Underwater ribbons of nudibranchs
The fertilized eggs of nudibranchsâsoft-bodied marine gastropod mollusks also called sea slugsâare laid in flattened gelatinous masses that remain anchored to the ocean floor, or other suitable substrata, while floating in the current and typically resemble ribbons or strings. They may also look like folded scrunchies or soft spiral corals and come in a whole range of shades: from white to muted pastels to bright red. These egg masses contain embryos, which hatch into a larval or a juvenile form depending on the nudibranch species. The number of eggs, and therefore embryos, in each such ribbon can number into the thousands. One study found a 4-cm-long ribbon to contain about 60,000 eggs.
Spiral necklaces of whelks
The pale, disc-shaped egg capsules or cases of whelksâmarine snails of the family Buccinidaeâare often strung together in long, twisting series, forming structures commonly called âmermaidâs necklacesâ because of their appearance. The whelk egg capsule is a protein-rich covering that forms around growing embryos while they are inside the female reproductive tract. The initially soft capsule is further processed in a specialized structure called the ventral pedal gland near the muscular foot of the whelk, which cross-links the capsule proteins and hardens the structure before it is laid. Whelks typically produce strings of 50 to 175 capsulesâthe resulting ânecklacesâ measure more than 61 cm (2 feet) in lengthâwith each capsule containing as many as 200 eggs. Historians believe that sailors may have used these elastic egg capsules as sponges.
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Curtain strands of octopuses
Giant Pacific octopuses (Enteroctopus dofleini) live for only three to five years. As they near the end of their lives, they mate, after which the female produces a large number of rice grainâsized eggsâsometimes up to 100,000. She attaches these eggs in long, curtainlike strands to the roof of an underwater rocky den that she has selected as her nesting site. She remains there for the rest of her life, tending and protecting her eggs until they hatch. The female dies soon after, having starved for the entire duration of her vigil over the developing eggs.
Stalked balloons of lacewings
To some, the eggs of green lacewings (insects of the family Chrysopidae) may appear as tiny pearls or drops attached to the tips of silken, hairlike stalks. They were even thought to be the fruiting bodies of a fungus that got its own scientific nameâAscophora ovalisâbefore the French scientist RenĂ©-Antoine Ferchault de RĂ©aumur found out their true nature in 1737. The characteristic hairlike silken strands of lacewing eggs play an important function: They prevent the newly hatched larvae from snacking on their unhatched siblings.
Marine corkscrews of sharks
The horn shark (genus Heterodontus) is a sluggish animal that crawls the ocean floor between central California in the U.S. and Baja California, Mexico. Female horn sharks lay eggs encased in corkscrew-shaped casesâeach case bearing a single baby shark. These egg cases range from 7.5 to 14.5 cm (3 to 5.7 inches) in length and 3.7 to 5.8 cm (1.5 to 2.3 inches) in maximum girth. A pair of flaplike flanges, or keels (anchoring structures), spiral along the sides of each case in 0.75 to 4 rotations, giving it a corkscrewlike appearance. This specific shape allows the female to insert the egg into small gaps on the ocean floor, where the embryo can grow without being swept away by currents until itâs time to hatch. Egg cases of some horn sharks also bear tendrils, which are long, sticky, filamentous structures that help anchor the egg.
Algal hosts of salamanders
Symbiosis refers to a close association between two dissimilar organisms that may benefit or harm one or both organisms. An example of a mutually beneficial symbiotic relationship is the association between coral and the algae that live in coral tissues. This type of symbiotic relationship is common in the invertebrate and plant worlds but rare among vertebrates. A notable exception is the spotted salamander (Ambystoma maculatum) endemic to North America. The eggs of these tail-bearing amphibians harbor a green alga (Oophila amblystomatis), which gives the eggs a green color. Although the precise benefits of this association remain unclear, researchers generally think that the salamander embryo benefits from the oxygen produced by the alga while the alga benefits from the nitrogenous waste of the growing embryo.
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Speckled cones of murres
The common murre (Uria aalge) is a large seabird with an unusual nesting habit. It lays its eggs on narrow rocky ledges and cliffs along the northern Pacific and Atlantic oceans. The eggs vary in colorâfrom white to blue to brownâwith speckles, blotches, and other markings and are also distinctive in shape. One end tapers, giving each egg a conical, almost pearlike appearance. Several theories have been proposed to explain this shape, including morphological adaptations for flight that might result in this shape. The most widely accepted theory suggests that a conical shape prevents the eggs from rolling off steep ledges. It likely stabilizes the eggs by keeping more of their surface in contact with the ground. But what explains the wide variation in egg color? Each year, every female lays eggs with a consistent base color and similar markings, which vary between individuals. One theory suggests that each set of parents can recognize these patterns, which helps them to identify their own eggs.