Molgula oculata

Molgula oculata, commonly known as the sea grape, is a species of solitary tunicate in the family Molgulidae. It is native to the north eastern Atlantic Ocean and the North Sea. The specific name oculata means "having eyes";[2] the species has orifices which "seem like dark eyes within a spectacle-formed frame".[3]

Not to be confused with Molgula occulta.

Sea Grape
Molgula oculata
a) oral siphon; b) atrial siphon
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Subphylum:
Tunicata
Class:
Ascidiacea
Order:
Stolidobranchia
Family:
Molgulidae
Genus:
Molgula
Species:
M. oculata
Binomial name
Molgula oculata
Forbes, 1848[1]
Synonyms[1]

Anurella oculata (Forbes, 1848)

Description

Molgula oculata is nearly spherical in shape and is about 2 to 3 in (5 to 8 cm) in diameter. It has a sac-like body with a leathery covering known as its tunic, with two siphons on the upper surface. Water is drawn into the body cavity through a six-lobed oral siphon and expelled through a four-lobed atrial siphon. The oral siphon is surrounded by a ring of branched tentacles, the function of which is to prevent large particles being drawn into the pharynx with the water current. This tunicate is very well camouflaged. It is a sandy brown colour and is partially buried in the sediment on the seabed with the two siphons projecting. Sand grains and shell fragments adhere to its tunic, completely covering the surface apart from a small area in the immediate vicinity of the siphons. This bare patch helps to distinguish it from the closely related Molgula occulta which is completely coated in particles.[4][5]

Distribution and habitat

Molgula oculata is found in the north eastern Atlantic Ocean and North Sea. Its range extends from Norway and the Shetland Islands southwards to the Bay of Biscay. It is found unattached but nearly submerged in the sandy or gravelly seabed with only its siphons protruding.[6] It occurs from low tide level down to depths of 80 metres (260 ft).[1][5]

Biology

Molgula oculata is a suspension feeder, filtering planktonic particles and bacteria from the water which is pumped continually through its body.[7] Like other tunicates, it is a hermaphrodite and at breeding time, sperm and eggs are liberated into the sea where fertilisation takes place. The larva of a tunicate is known as a tadpole larva because of its resemblance to an amphibian tadpole. It has such chordate characteristics as a notochord and a primitive nerve system, and also has a tail with which it can swim.[8][9] At metamorphosis, it attaches itself to a hard surface with a sucker, the tissues are extensively reorganised and it loses all these features.[9] The closely related species Molgula occulta does not have a tail (occulta means "tailless").[10] Nor does it have an otolith, a sensory organ connected with balance, which the former possesses. In the laboratory, the two have been hybridised and it was found that the larval offspring of the occulta x oculata hybrid possessed a half length tail and an otolith. The researchers hypothesized that both species were descended from a common ancestral line but that at some stage, M. occulta had lost part of its genome.[10]

References
  1. Sanamyan, Karen (2013). "Molgula oculata Forbes, 1848". WoRMS. World Register of Marine Species. Retrieved 2013-06-04.
  2. Charlton T. Lewis, Charles Short, A Latin Dictionary
  3. 1853, Edward Forbes, Sylvanus Hanley, A History of British Mollusca and their Shells, page 36
  4. Barrett, John; Yonge, Charles Maurice (1958). Collins Pocket Guide to the Sea Shore. Collins & Co. p. 188. ISBN 0002193213.
  5. "Molgula oculata". Macrobenthos of the North Sea: Tunicata. Marine Species Identification Portal. Retrieved 2013-06-04.
  6. Picton, B.E. & Morrow, C.C. (2015). Molgula oculata Forbes, 1848. [In] Encyclopedia of Marine Life of Britain and Ireland. Accessed on 2015-12-29
  7. Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th edition. Cengage Learning. pp. 940–956. ISBN 81-315-0104-3.
  8. Cavanihac, Jean-Marie (2000). "Tunicates extraordinaire". Microscope UK. Retrieved 2013-06-07.
  9. "Introduction to the Urochordata". 2000. Archived from the original on 2009-04-21. Retrieved 2013-06-07.
  10. Brown, C. Titus (2010-08-30). "Evolution of chordate features: looking at the Molgula". Retrieved 2013-06-04.
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