''Waminoa brickneri'' is a newly discovered

acoel Acoela, or the acoels, is an order of small and simple invertebrates in the subphylum Acoelomorpha of phylum Xenacoelomorpha, a deep branching bilaterian group of animals, which resemble flatworms. Historically they were treated as an order of ...

species from the

coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. C ...

s near Eilat (

Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; ...

) and the second described species in the genus (the first is '' Waminoa litus'').

Characteristics

''Waminoa brickneri'' is discoid to obcordate in shape, flat, 3–4 mm in diameter and 1 mm thick. Its bronze color with small white speckles is derived from the abundant dinoflagellate endosymbionts and the scattered white pigment spots. There are two distinct types of dinoflagellate

endosymbiont An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship. (The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within ...

s that lay scattered throughout the parenchyma of the animal: small symbionts of the genus ''

Symbiodinium : ''This is about the genus sometimes called Zoox. For the company, see Zoox (company)'' ''Symbiodinium'' is a genus of dinoflagellates that encompasses the largest and most prevalent group of endosymbiotic dinoflagellates known. These unicell ...

'' and larger symbionts of the genus '' Amphidinium''. The epidermis is transparent, fully

ciliated The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike project ...

, and glandulous. The dorsal body wall and lateral sides are especially abundant with rhabdoid glands, while the ventral body wall is abundant with

mucous gland Mucous gland, also known as muciparous glands, are found in several different parts of the body, and they typically stain lighter than serous glands during standard histological preparation. Most are multicellular, but goblet cells are single-cel ...

s; the mucous glands also occur scattered in the dorsal body wall, but there are no rhabdoid glands on the ventral side. The mouth is ventrally located, somewhere in the posterior third of the body length, and opens directly into the digestive

syncytium A syncytium (; plural syncytia; from Greek: σύν ''syn'' "together" and κύτος ''kytos'' "box, i.e. cell") or symplasm is a multinucleate cell which can result from multiple cell fusions of uninuclear cells (i.e., cells with a single nucleu ...

. Newly hatched juveniles possess a

statocyst The statocyst is a balance sensory receptor present in some aquatic invertebrates, including bivalves, cnidarians, ctenophorans, echinoderms, cephalopods, and crustaceans. A similar structure is also found in '' Xenoturbella''. The statocyst c ...

and paired eyes but mature individuals lack both. They also lack a frontal organ. The

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a ve ...

is bilobed and lies just beneath the epidermis close behind the anterior tip of the body; the two main masses consist of a central neuropile and nucleated rind and are connected by a short medial

commissure A commissure () is the location at which two objects abut or are joined. The term is used especially in the fields of anatomy and biology. * The most common usage of the term refers to the brain's commissures, of which there are five. Such a commi ...

. Like other acoelomorphs, ''Waminoa brickneri'' is a simultaneous hermaphrodite. The

reproductive organs A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...

produce a slightly thickened ridge medially in the terminal quarter of the body. A pair of ventrally situated

ovaries The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...

extends from about the second quarter of the body length posteriorly behind the mouth. The female pore is prominent and opens to a ciliated vagina located on the ventral body wall immediately anterior to the male gonadopore. Dorsally and laterally to the ovaries lies a pair of

testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoste ...

, which lead posteriorly to the

seminal vesicle The seminal vesicles (also called vesicular glands, or seminal glands) are a pair of two convoluted tubular glands that lie behind the urinary bladder of some male mammals. They secrete fluid that partly composes the semen. The vesicles are 5� ...

. The seminal vesicle, which lies just in front of the posterior notch in the body margin, is most prominent, and appears white from contained sperm. It is well-developed and walled by thin, loosely concentric muscles and reaches to a penis papilla. Flanking the seminal vesicle are prominent false seminal vesicles continuous with the tracts of sperm descending from the testes. There is a seminal bursa with 2 or more (2–8) bursal nozzles. Sperm cells are elongated and

biflagellate A flagellate is a cell or organism with one or more whip-like appendages called flagellum, flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes ...

Habitat

''Waminoa brickneri'' is an

epizoic An epibiont (from the Ancient Greek meaning "living on top of") is an organism that lives on the surface of another living organism, called the basibiont ("living underneath"). The interaction between the two organisms is called epibiosis. An ep ...

organism living on

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and ...

s in the

Gulf of Eilat The Gulf of Aqaba ( ar, خَلِيجُ ٱلْعَقَبَةِ, Khalīj al-ʿAqabah) or Gulf of Eilat ( he, מפרץ אילת, Mifrátz Eilát) is a large gulf at the northern tip of the Red Sea, east of the Sinai Peninsula and west of the Arabia ...

. It occurs in groups of non-overlapping individuals, causing the corals it inhabits to appear spotted. It has been detected on 13 species of stony corals, and on one species of soft coral. It can be found at depths of 2 to 50 meters. The presence of ''Waminoa'' species on live corals brought about several hypotheses about the nature of this coral-acoel association, one of which was that the acoels feed on the coral's

mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It ...

. A recent study by Naumann et al. (2010) corroborated this hypothesis.

References

{{Taxonbar, from=Q3373537 Acoelomorphs