Xyloplax medusiformis

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Xyloplax medusiformis
Status NZTCS DD.svg
Data Deficient (NZ TCS) [1]
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Echinodermata
Class: Asteroidea
Order: Peripodida
Family: Xyloplacidae
Genus: Xyloplax
Species:
X. medusiformis
Binomial name
Xyloplax medusiformis
Baker, Rowe & Clark, 1986 [2]

Xyloplax medusiformis is a sea daisy, a member of an unusual group of marine taxa belonging to the phylum Echinodermata. It is found at bathyal depths in waters around New Zealand. It was first described in 1986 by Baker, Rowe and Clark and is the type taxon of the genus Xyloplax . [2] Its generic name derives from the Greek "xylo" meaning wood and its specific name was chosen because its morphology superficially resembles that of a cnidarian medusa. [3]

Contents

Discovery

Specimens of Xyloplax medusiformis were first discovered by accident when a submersible craft was being used to collect samples of wood on the deep sea bed in the South Pacific near New Zealand. Nine individuals were discovered from five locations. At the time these specimens puzzled researchers because of their lack of close affiliations to other echinoderms. Since then further members of the genus Xyloplax have been discovered on wood at bathyal depths, Xyloplax turnerae in the Atlantic Ocean off the Bahamas and Xyloplax janetae in the central Pacific Ocean. [4]

Taxonomy

Xyloplax medusiformis was the first sea daisy to be described. It was clearly an echinoderm but at first it was considered to be sufficiently different from starfish, class Asteroidea, as to warrant it being placed in a new class of its own, the Concentricycloidea. The main difference was that the water vascular system of asteroids has a single ring canal circling the mouth connected to radial arms with short lateral side arms while that of the sea daisy had two ring canals surrounding the mouth, linked by five inter-ring canals. The concentric arrangement of plates on the surface of the sea daisy was novel and it had a single row of podia (tube feet) rather than the two rows typical of asteroids. [3] [5]

DNA sequencing was done on Xyloplax medusiformis and on a range of about twenty other varied species of echinoderm. It was found that X. medusiformis was indubitably a member of class Asteroidea and was a sister taxon to Rathbunaster in the order Forcipulatida. It is considered that X. medusiformis may be paedomorphic, retaining larval characteristics into adulthood. [5] Later it was confidently placed in Velatida (Molecular Phylogenetics and Evolution 115 (2017): 161–170).

Description

Xyloplax medusiformis is a small, flattened disc or umbrella-shaped invertebrate growing to a diameter of about 9 millimetres (0.35 in). The aboral (upper) surface is covered with flat plates arranged in concentric rings and there are short marginal spines projecting from the periphery. Internally the water vascular system consists of two super-oral rings and no radial canals. There is no stomach, gut or anus and it is thought that the velum (membrane) that covers the oral (lower) surface is equivalent to an everted stomach. There are five pairs of gonads, each associated with a fluid-filled sac. [6]

Distribution and habitat

Xyloplax medusiformis is known from deep waters around New Zealand. It is found on pieces of decaying timber that have sunk to the seabed and are at least 1,000 metres (3,300 ft) beneath the surface. It is believed that it may feed on bacteria or the products of wood decay but very little is known of the biology of this echinoderm. [6] [7] Similar numbers of males and females have been discovered and it appears that there is a long phase of embryonic development during which time the females brood the embryos in their ovaries until they are nearly ready to undergo metamorphosis into juveniles. [4]

Related Research Articles

<span class="mw-page-title-main">Echinoderm</span> Exclusively marine phylum of animals with generally 5-point radial symmetry

An echinoderm is any deuterostomal animal of the phylum Echinodermata, which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as larvae, as adults echinoderms are recognisable by their usually five-pointed radial symmetry, and are found on the sea bed at every ocean depth from the intertidal zone to the abyssal zone. The phylum contains about 7,600 living species, making it the second-largest group of deuterostomes after the chordates, as well as the largest marine-only phylum. The first definitive echinoderms appeared near the start of the Cambrian.

<span class="mw-page-title-main">Starfish</span> Class of echinoderms, marine animal

Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea. Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish are also known as asteroids due to being in the class Asteroidea. About 1,900 species of starfish live on the seabed in all the world's oceans, from warm, tropical zones to frigid, polar regions. They are found from the intertidal zone down to abyssal depths, at 6,000 m (20,000 ft) below the surface.

<span class="mw-page-title-main">Sea cucumber</span> Class of echinoderms

Sea cucumbers are echinoderms from the class Holothuroidea. They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. They are found on the sea floor worldwide. The number of known holothurian species worldwide is about 1,786, with the greatest number being in the Asia-Pacific region. Many of these are gathered for human consumption and some species are cultivated in aquaculture systems. The harvested product is variously referred to as trepang, namako, bêche-de-mer, or balate. Sea cucumbers serve a useful role in the marine ecosystem as they help recycle nutrients, breaking down detritus and other organic matter, after which bacteria can continue the decomposition process.

The water vascular system is a hydraulic system used by echinoderms, such as sea stars and sea urchins, for locomotion, food and waste transportation, and respiration. The system is composed of canals connecting numerous tube feet. Echinoderms move by alternately contracting muscles that force water into the tube feet, causing them to extend and push against the ground, then relaxing to allow the feet to retract.

<span class="mw-page-title-main">Brittle star</span> Echinoderms, closely related to starfish

Brittle stars, serpent stars, or ophiuroids are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomotion. The ophiuroids generally have five long, slender, whip-like arms which may reach up to 60 cm (24 in) in length on the largest specimens.

<span class="mw-page-title-main">Sea daisy</span> Genus of echinoderms

Sea daisies make up an unusual group of deep-sea taxa belonging to the phylum Echinodermata, with three species described in the genus Xyloplax. Intestine and anus are absent.

<span class="mw-page-title-main">Echinasteridae</span> Family of starfishes

The Echinasteridae are a family of starfish in the monotypic order Spinulosida. The family includes eight genera and about 133 species found on the seabed in various habitats around the world.

<span class="mw-page-title-main">Common sunstar</span> Species of starfish

The common sunstar is a species of sea star belonging to the family Solasteridae. It is found in the northern parts of both the Atlantic and the Pacific Oceans.

<i>Asterina</i> (starfish) Genus of echinoderms

Asterina is a genus of asteroideans in the family Asterinidae.

<span class="mw-page-title-main">Forcipulatida</span> Order of sea stars

The Forcipulatida are an order of sea stars, containing three families and 49 genera.

<span class="mw-page-title-main">Brisingida</span> Order of starfishes

The Brisingids are deep-sea-dwelling starfish in the order Brisingida.

<span class="mw-page-title-main">Asterozoa</span> Phylum of marine invertebrates

The Asterozoa are a subphylum in the phylum Echinodermata. Characteristics include a star-shaped body and radially divergent axes of symmetry. The subphylum includes the class Asteroidea, the class Ophiuroidea, and the extinct order Somasteroidea.

<i>Henricia</i> Genus of starfishes

Henricia is a large genus of slender-armed sea stars belonging to the family Echinasteridae. It contains about fifty species.

<i>Xyloplax janetae</i> Species of echinoderm

Xyloplax janetae is a Xyloplax of the family Xyloplacidae. It lives on the surface of wood sunken to abyssal depths.

Xyloplax turnerae is a sea daisy, a member of an unusual group of marine taxa belonging to the phylum Echinodermata. It has been found living on decaying timber in a deep oceanic trench in the Bahamas.

<span class="mw-page-title-main">Freyellidae</span> Family of starfishes

The Freyellidae are a family of deep-sea-dwelling starfish. It is one of two families in the order Brisingida. The majority of species in this family are found in Antarctic waters and near Australia. Other species have been found near New Zealand and the United States.

<i>Fromia indica</i> Species of starfish

Fromia indica, commonly called Indian sea star or red starfish, is a species of marine starfish belonging to the family Goniasteridae.

<i>Neoferdina cumingi</i> Species of starfish

Neoferdina cumingi, also known as Cuming's sea star, is a species of starfish in the family Goniasteridae. It is native to the tropical Indo-Pacific region.

Helen Elizabeth Shearburn Rotman was a New Zealand expert on echinoderms, specifically starfish.

References

  1. ↑ Funnell, Greig; et al. (January 2023). Todd, Amanda (ed.). Conservation status of indigenous marine invertebrates in Aotearoa New Zealand, 2021 (PDF) (Report). New Zealand Department of Conservation. p. 16. ISBN   978-1-99-118365-1 . Retrieved 27 September 2024.
  2. 1 2 Mah, Christopher (2012). Mah CL (ed.). "Xyloplax medusiformis Baker, Rowe & Clark, 1986". World Asteroidea database. World Register of Marine Species . Retrieved 2013-02-01.
  3. 1 2 Baker, Alan N.; Rowe, Francis W. E.; Clark, Helen E. S. (1986). "A new class of Echinodermata from New Zealand". Nature. 321: 862–864. doi:10.1038/321862a0.
  4. 1 2 Voight, Janet R. (2005). "First Report of the Enigmatic Echinoderm Xyloplax from the North Pacific". Biological Bulletin. 208 (2): 77–80. doi:10.2307/3593115. PMID   15837956.
  5. 1 2 Janies, Daniel; Mooi, Rich (1998). "Xyloplax is an asteroid" (PDF). Echinoderm Research. Retrieved 2013-02-01.
  6. 1 2 Dorit, R. L.; Walker, W. F.; Barnes, R. D. (1991). Zoology . Saunders College Publishing. pp.  792–793. ISBN   978-0-03-030504-7.
  7. ↑ Chrism (2008-09-30). "Xyloplax pt. 2: Conundrums & Controversies". Echinoblog. Retrieved 2013-02-01.
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