Peronella lesueuri - a beautiful sand dollar of importance in coastal ecosystem processes
The striking Peronella lesueuri (Clypeasteroida - Laganidae), is a large sand dollar up to 15 cm in diameter, with a wide Indo-Pacific distribution. The most noticeable and amazing feature of this species is its bright pink when alive, hence its common name of Pink sand dollar.
It is a shallow burrower and occurs at densities which may influence surface sediment chemistry and community dynamics. Therefore, knowledge of seasonal and diet movement rates and rhythms of this species are a key of interest in understanding coastal sediments biogeochemical dynamics.
Bristly but benign! These spiny brittle stars stretch out an arm or two to catch drifting bits of food, burying the rest of their bodies in the sand for protection. If a curious fish takes a nibble, the star can leave the arm behind and grow a new one!
It may not seem much an apple, nor a cucumber, but these are colorful sea cucumbers commonly known as Sea Apples belonging to the species Pseudocolochirus violaceus (Holothuroidea - Dendrochirotida - Cucumariidae), which occurs in the Indian Ocean and the western part of the Pacific Ocean.
Sea apples are about 18 cm long. They usually are purple, but also can be blue, red, white, and yellow. Three rows of tube feet run along the bottom side of the animal. The top side has two rows of tube feet as well as small scattered tube feet. The body is curved so that the mouth and anus point upward. They have ten tentacles which are bushy purple to red and have white tips. The pieces of the body wall skeleton are rounded, smooth plates with a few holes.
When relaxed, the normal shape is short and sausage-like as with most other sea cucumbers. When stressed, however, it may inflate itself into a large round ball.
Sea apples live partly hidden to fully exposed with tentacles expanded, even during the day. They feed continuously, capturing large food particles with outstretched branching tentacles that are lightly coated in mucus.
These beautiful sea cucumbers unfortunately are harvested for the aquarium trade. Ironically, they do not make good aquarium specimens as they are often toxic to their tank mates.
…a species of temenopleurid urchin that is distributed throughout the Indo-Pacific. Like many other urchins this species is mainly active at night and will graze on algae under the cover of darkness. During the day it can be found lodged in between rocks and crevices. This species, like others, will engage in covering behavior and will ‘place’ shells. algae, sponges, and other items onto itself to make itself less noticeable to predators.
California sea cucumber, Parastichopus
Sea cucumbers and their kin are sometimes called the “earthworms
of the sea,” as they cultivate the seafloor in much the same manner as
earthworms cultivate the soil. The cylindrical design of their squishy bodies
is similar to that of earthworms, too, with a mouth at one end and anus at the
other and a long, branched tube in between.
Most species live on or near the seafloor, sometimes partially buried beneath, and are found in habitats from coastal
tide pools to the deep sea, where “herds” can move together, hunting for food. Five
rows of tiny tube feet create locomotion. While they don’t move fast, they can travel about 12 feet a day in search of food
Sea cucumbers serve a useful role as they help recycle
nutrients in the marine ecosystem, breaking down detritus and other organic
matter after which bacteria take over the degradation process.
A sea cucumber’s mouth contains a bloom of about 20 anemone-like
sticky tentacles that trap food particles sucked up from the seafloor’s sediment and mud,
or as they float by on a current. The tentacles retract, funneling the morsels
inside and breaking them down even more, eventually becoming fodder for bacteria.
Despite a tendency to be toxic, they themselves are food for
larger invertebrates including some molluscs and crabs, and sometimes triggerfish
and pufferfish. When attacked, sea
cucumbers eviscerate themselves, spewing out their internal organs. The sticky organs may
entangle and distract or provide a meal for the predator while the sea cucumber
escapes; the organs eventually regenerate.
Sea cucumbers are harvested commercially for consumption by
humans as meals and medicine. California sea cucumbers are abundant across a
wide range and harvested sustainably for their muscles and skin. In the 1980s their
populations started to decline, but restrictions on harvesting have allowed
this species to recover.
You can see a variety of sea cucumbers in many exhibits in our
Ocean’s Edge galleries, including the Kelp
Forest, and even tap them in our touch pools.
Tosia magnifica (Valvatida - Goniasteridae) is a beautiful, large biscuit sea star with up to 16 cm. It is native to Australia, living on sub-tidal rocks and sediment, to depth of 200 m. It is rarely seen and little is known of its biology.
…a species of basket star (echinoderms related to brittle stars) found throughout the Caribbean Sea and the Gulf of Mexico. Like all basket stars A.muricatum uses its many branched arms, which are lined with tentacles, to capture passing plankton and small marine invertebrates. During the day the giant basket star will retract its fragile arms and curl into a ball for defense, at night it will extend them to feed.
Sea cucumbers are echinoderms—like starfish and sea urchins. There are some 1,250 known species, and many of these animals are indeed shaped like soft-bodied cucumbers. All sea cucumbers are ocean dwellers, though some inhabit the shallows and others live in the deep ocean. They live on or near the ocean floor—sometimes partially buried beneath it.
Sea cucumbers feed on tiny particles like algae, minute aquatic animals, or waste materials, which they gather in with 8 to 30 tube feet that look like tentacles surrounding their mouths. The animals break down these particles into even smaller pieces, which become fodder for bacteria, and thus recycle them back into the ocean ecosystem. Earthworms perform a similar function in terrestrial ecosystems.
Sea cucumbers, particularly eggs and young larvae, are prey for fish and other marine animals. They are also enjoyed by humans, especially in Asia, and some species are farmed as delicacies.
When threatened, some sea cucumbers discharge sticky threads to ensnare their enemies. Others can mutilate their own bodies as a defense mechanism. They violently contract their muscles and jettison some of their internal organs out of their anus. The missing body parts are quickly regenerated.
Sea cucumbers can breed sexually or asexually. Sexual reproduction is more typical, but the process is not very intimate. The animals release both eggs and sperm into the water and fertilization occurs when they meet. There must be many individuals in a sea cucumber population for this reproductive method to be successful. Indeed, many parts of the deep ocean host large herds of these ancient animals, grazing on the microscopic bounty of marine waters.
The Shingle urchin, Colobocentrotus atrata (Echinometridae), has a peculiar limpet-life morphology, unique among the regular echinoids.
The aboral spines of Colobocentrotus atrata (on the opposite side to the mouth) are extremely reduced, forming a smooth pavement or plates, and the adoral part (situated near the mouth) is surrounded by a basal skirt of flattened spines. These two features improve the adhesive capacities of the animal and are adaptations to life in areas of extreme wave exposure throughout the Indo West Pacific where this sea urchin lives.
…a species of synaptid sea cucumber that is widely distributed throughout the Indo-Pacific. Like other synaptids this species lacks tube feet, retractor muscles and tentacle ampullae it moves by waves of peristaltic contractions. E. godeffroyi is benthic and a deposit feeder, feeding on particles suspended in soil.
…is a very small (< 2cm) species of Asterinid starfish which was first discovered at Reunion Island, and was then later identified across the Mascarene Islands. Aquilonastra conandae individuals often have around seven or eight arms, which are often irregular in length. This is most likely due to regeneration.