Most tusk shells live in fairly deep water, sometimes to depths of about 4, metres 13, feet ; many deep-sea species are cosmopolitan in distribution. Tusk shells eat microscopic organisms, especially foraminiferans fo-re-mi-NIH-fer-ehns , single-celled organisms that have a nucleus.
The nucleus is a structure that contains the genetic information. Other species feed on tiny crustaceans, as well as clams and their relatives. How do Scaphopods reproduce? Behavior and reproduction: They burrow into soft ocean bottoms, leaving only the tips of their shells exposed.
Males and females are required for reproduction. Both eggs and sperm are released into the water, where fertilization and development take place.
How many species of chitons are there? How do gastropods eat? Fossils show specimens 30 cm long. The scaphopod shell is open at both ends. The wider end of the shell where the head and foot extends out is the anterior end.
The posterior is the narrow end of the shell which usually is at or below the substrate. The shell surrounds a large mantle cavity, and wraps around the viscera to form a tube.
The mantle cavity goes along ventral side to a smaller opening at the other end. No ctenidia are present, and gas exchange is through the mantle surface. Cilia an currents move water thorugh posterior aperature.
Occasional muscular contractions expell water from the posterior end of the shell. The head is a short, conical projection probosicis with a mouth. Lobes on each side of the head have threadlike tentacles, called captacula, which are used to capture food. Barnes, ; Reynolds, ; Shimek, After fertilization, the egg develops into a free-swimming trocophore larvae, then a bilaterally symmetrical veliger. The veliger usually metamorphoses in days.
At this point it becomes benthic. Barnes, ; Jones and Baxter, Scaphopods are gonochoristic or dioecious. Eggs are released singly through the right nephridium. Sperm is also released through the nephridium.
Eggs are planktonic and fertilization is external. Barnes, There is no parental investment after release of gametes. Scaphopods burrow by projecting their foot into the substrate and contracting pedal retractor muscles to pull the animal downward. Extension of the foot may help with water intake, and the scaphopods probably use foot movements to expel wastes from the posterior opening. Individuals in the Gadilida burrow up to 30 cm in captivity and burrow this deep in the ocean.
The scapopod captacula may have tactile receptors, but this is unknown. Despite detailed monographic work from the late nineteenth and early twentieth centuries, however, the biology of scaphopods is today among the least understood of mollusks. To some extent, this is related to a significant departure from more typical molluscan organization inferred from studies of the larger classes. For example, the mantle cavity is elongate and restricted in space, and several associated organs are lost, including the osphradium and ctenidia; the latter is associated with the loss of auricles from the scaphopod heart.
There is also little record of ontogeny in the adult shell, as the older portion is periodically decollated to maintain the posterior aperture for passage of inhalant and exhalant currents. This and other constraints on scaphopod diversification are reflected in the range limits of shell shape within the class.
In contrast, the "Dentalium" egg has been a model system for experimental embryology, particularly in studies of cell lineage and early morphogenesis. TLittle hairs cilia along the tentacles move small food particles back to the mouth.
The tentacles retract to bring larger food to the mouth. The radula is used to grind their food which is digested in the stomach, then travels to the intestine before passing to the anus. Their predators are fish and crabs. The mantle tissue not only produces the shell, but also acts as gills ito get oxygen from seawater.
Scaphopods are simple animals lacking a heart, blood vessels and eyes.
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