Sipuncula

sipunculidpeanut wormpeanut wormssipunculid wormsipunculidsSipunculoideaSipunculidasipunculanSipunculanssipunculid or peanut worms
The Sipuncula or Sipunculida (common names sipunculid worms or peanut worms) is a group containing about 162 species of bilaterally symmetrical, unsegmented marine worms.wikipedia
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Annelid

Annelidaannelidsannelid worms
Traditionally considered a phylum, Sipuncula seems to be closely related to Myzostomida and Annelida, and may be a subgroup of Annelida, based on recent molecular work. Currently these two phyla have been included in a larger group, the Lophotrochozoa, that also includes the annelids, the ribbon worms and several other phyla.
In addition, the Pogonophora, Echiura and Sipuncula, previously regarded as separate phyla, are now regarded as sub-groups of polychaetes.

Sipunculus nudus

a kind of marine peanut wormmarine peanut worm
The Swedish naturalist Carl Linnaeus first described the worm Sipunculus nudus in his Systema naturae in 1767.
Sipunculus nudus is a cosmopolitan species of unsegmented marine worm of the phylum Sipuncula, also known as peanut worms.

Echiura

spoon wormspoon wormsechiuran
Subsequent analysis of the mitochondrion's DNA has confirmed their close relationship to the Myzostomida and Annelida (including echiurans and pogonophorans).
In the mid-nineteenth century Echiura was placed, alongside Sipuncula and Priapulida, in the now defunct class Gephyrea (meaning a "bridge") in Annelida, because it was believed that they provided a link between annelids and holothurians.

Phylum

phyladivisionsuperphylum
Traditionally considered a phylum, Sipuncula seems to be closely related to Myzostomida and Annelida, and may be a subgroup of Annelida, based on recent molecular work.

Phascolosomatidea

The mouth is located at the anterior end of the animal; in the class Sipunculidea, the mouth is surrounded by a mass of 18 to 24 ciliated tentacles, while in the class Phascolosomatidea, the tentacles are arranged in an arc above the mouth, surrounding the nuchal organ, also located at the tip of the introvert.
Phascolosomatidea is a class of peanut worms containing two orders:-

Hemerythrin

haemerythrin
Fluid transport and gas exchange are instead accomplished by the coelom, which contains the respiratory pigment haemerythrin, and the separate tentacular system, the two being separated by an elaborate septum.
Hemerythrin (also spelled haemerythrin;, ) is an oligomeric protein responsible for oxygen (O 2 ) transport in the marine invertebrate phyla of sipunculids, priapulids, brachiopods, and in a single annelid worm genus, Magelona.

Aspidosiphon elegans

Both asexual and sexual reproduction can be found in sipunculans, although asexual reproduction is uncommon and has only been observed in Aspidosiphon elegans and Sipunculus robustus.
Aspidosiphon elegans is a species of unsegmented benthic marine worm in the phylum Sipuncula, the peanut worms.

Sipunculus robustus

Both asexual and sexual reproduction can be found in sipunculans, although asexual reproduction is uncommon and has only been observed in Aspidosiphon elegans and Sipunculus robustus.
Sipunculus robustus is a species of unsegmented benthic marine worm in the phylum Sipuncula, the peanut worms.

Blood

human bloodhematologicaloxygen consumption
Sipunculans do not have a vascular blood system.
Hemerythrin is used for oxygen transport in the marine invertebrates sipunculids, priapulids, brachiopods, and the annelid worm, magelona.

Themiste pyroides

In at least one species, Themiste pyroides, swarming behaviour occurs with adults creating compact masses among rocks immediately before spawning.
Themiste pyroides is a species of unsegmented benthic marine worm in the phylum Sipuncula, the peanut worms.

Nemertea

ribbon wormnemerteannemertean worm
Currently these two phyla have been included in a larger group, the Lophotrochozoa, that also includes the annelids, the ribbon worms and several other phyla.
However, multiciliated epidermal cells and epidermal gland cells are also found in Ctenophora, Echiura, Sipuncula, Annelida, Mollusca and other taxa.

Thysanocardia procera

One species, Thysanocardia procera is thought to be carnivorous, gaining entrance in some way to the interior of the sea mouse Aphrodita aculeata and sucking out its liquefied contents.
Thysanocardia procera is a marine invertebrate belonging to the phylum Sipuncula, the peanut worms.

Trochophore

trocophore
Although some species hatch directly into the adult form, many have a trochophore larva, which metamorphoses into the adult after anything from a day to a month, depending on species.
Trochophores exist as a larval form within the trochozoan clade, which include the entoprocts, molluscs, annelids, echiurans, sipunculans and nemerteans.

Themiste (worm)

ThemistidaeThemiste
In the family Themistidae the tentacles form an elaborate crown-like structure, the members of this group being specialized filter feeders, unlike the other groups of sipunculans which are deposit feeders.
Themiste is a genus of peanut worms.

Lecthaylus

An unnamed sipunculid worm from the Cambrian period has been discovered in the Burgess Shale in Alberta, Canada, and Lecthaylus has been identified from the Granton Shrimp Bed, near Edinburgh, Scotland, dating to the Silurian period.
Professor Weller described this worm, which was abundant in the deposits, as being "manifestly related to Serpulites or Conularia; however, further examination by Sharat Kumar Roy determined that this was not the case, and that the worms were more likely members of Sipunculoidea, and this is now the accepted position.

Hyolitha

Hyolitheshyolithhyoliths
Some scientists once hypothesized a close relationship between sipunculans and the extinct hyoliths, operculate shells from the Palaeozoic with which they share a helical gut; but this hypothesis has since been discounted.
Their grade of organization was historically considered to be of the 'mollusc-annelid-sipunculid' level, consistent with a Lophotrochozoan affinity, and comparison was primarily drawn with the molluscs or sipunculids.

Trace fossil

Ichnologytrace fossilsichnofossil
Trace fossils of burrows that may have been formed by sipunculans have been found from the Paleozoic.

Species

specificspecific epithetspecific name
The Sipuncula or Sipunculida (common names sipunculid worms or peanut worms) is a group containing about 162 species of bilaterally symmetrical, unsegmented marine worms.

Symmetry in biology

bilateral symmetryradial symmetrybilaterally symmetrical
The Sipuncula or Sipunculida (common names sipunculid worms or peanut worms) is a group containing about 162 species of bilaterally symmetrical, unsegmented marine worms.

Segmentation (biology)

segmentssegmentsegmentation
The Sipuncula or Sipunculida (common names sipunculid worms or peanut worms) is a group containing about 162 species of bilaterally symmetrical, unsegmented marine worms.

Sea

maritimemarineat sea
The Sipuncula or Sipunculida (common names sipunculid worms or peanut worms) is a group containing about 162 species of bilaterally symmetrical, unsegmented marine worms.

Genus

generageneric namegeneric
The name Sipuncula is from the genus name Sipunculus, and comes from the Latin siphunculus meaning a "small tube".

Myzostomida

Myzostoma cirriferummyzostomidMyzostomides
Traditionally considered a phylum, Sipuncula seems to be closely related to Myzostomida and Annelida, and may be a subgroup of Annelida, based on recent molecular work. Subsequent analysis of the mitochondrion's DNA has confirmed their close relationship to the Myzostomida and Annelida (including echiurans and pogonophorans).

Anatomical terms of location

ventraldorsalanterior
The body is divided into an unsegmented, bulbous trunk and a narrower, anterior section, called the "introvert", which can be retracted into the trunk.