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The larvae are often planktonic, but in some species the eggs are retained inside the female, while in some the female broods the larvae. [ 73 ] [ 74 ] The larvae pass through several stages, which have specific names derived from the taxonomic names of the adults or from their appearance.
Sea urchins or urchins (/ ˈ ɜːr tʃ ɪ n z /) are typically spiny, globular animals, echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal to 5,000 metres (16,000 ft; 2,700 fathoms). [1]
The name dipleurula, two-sided, was given to stress the fact that the larva of the typically five-rayed, (approximately) radially symmetric adults show a bilateral structure. It was this bilateral structure of the larvae that identified echinoderms as bilaterian animals. The original doliolaria schema shows a benthic, crawling, larva. However ...
The larvae of several species of starfish can reproduce asexually before they reach maturity. [50] They do this by autotomising some parts of their bodies or by budding . [ 51 ] When such a larva senses that food is plentiful, it takes the path of asexual reproduction rather than normal development. [ 52 ]
The larva's free-swimming period lasts for only a few days before it settles on the bottom and attaches itself to the underlying surface using an adhesive gland on its underside. The larva then undergoes an extended period of metamorphoses into a stalked juvenile, becoming radially symmetric in the process. Even the free-swimming feather stars ...
Holothurians appear to be the echinoderms best adapted to extreme depths, and are still very diversified beyond 5,000 metres (16,000 ft) deep: several species from the family Elpidiidae ("sea pigs") can be found deeper than 9,500 metres (31,200 ft), and the record seems to be some species of the genus Myriotrochus (in particular Myriotrochus ...
This form of reproduction allows certain species to enhance their survival. And lastly, larval development, following fertilization, brittle star larvae undergo various developmental stages before transitioning into adulthood. In some species, larvae may remain attached to the parent until they can sustain themselves.
Many species brood developing larvae in the bursae, effectively giving birth to live young. A few, such as Amphipholus squamata, are truly viviparous, with the embryo receiving nourishment from the mother through the wall of the bursa. However, some species do not brood their young, and instead have a free-swimming larval stage.