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Glossary of Tunicate Terminology

How to cite this glossary: Rocha, R. 2011. Glossary of Tunicate Terminology.

Caribbean Phycology Resources

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Picture A - Z Definition - Spanish - Portuguese - French
A
Plate 2, fig. G Abdomen Present in colonial ascidians with two or three body regions. It is the part of the animal that includes the digestive tract. In some groups, also includes gonads and the heart. It is posterior to the pharynx.  
Plate 2, figs. H, I;
Plate 6, figs. C-E
Adhesive papillae Outer adhesive structures of a larval ascidian used to adhere to a substrate.
Plate 6, fig. D Ampullae Present in larval and adult colonial ascidians and some larvae of solitary ascidians, grown from the epidermus of the body and are used to attach the animal to the substratum. 
Plate 1, figs. C-E;
Plate 4, fig. E
Anal opening Terminal orifice of the intestine, with smooth or lobed margin.
Plate 1, figs. C-E;
Plate 4, fig. E
Anus Terminal orifice of the intestine, with smooth or lobed margin.
Ascending limb of gut loop Ascending limb of intestine, towards to anterior region of the body.
Plate 2, fig. G Atrial cavity Area between the wall of the branchial bag and the mantle.
Plate 1, fig. C;
Plate 4, figs. E, F
Atrial apperture The opening in the tunic through which water exits the ascidian. Also known as the exhalent aperature or clacal aperture. 
Atrial tentacles Simple tentacles at the base of the exhalent siphon, very rare.
Plate 1, figs. G, H;
Plate 3, figs. A, B, D, F, G;
Plate 6, fig. G
Atrial siphon The opening in the tunic through which water exits the ascidian. 
B
Blastozooid Zooid originating from division of oozooid (asexual reproduction).
Plate 1, figs. G, H;
Plate 2, fig. G;
Plate 3, figs. A, B, D, G;
Plate 4, fig. D;
Plate 5, figs. B, G;
Plate 6, fig. G
Branchial aperture Opening through the water into the animal. Also known as oral aperture or inhallant syphon. It indicates the anterior region of body.
Plate 1, figs. F, I Branchial fold The wall of the branchial sac that folds on itself longitudinally, increasing the filtering and breathing surface. Present only in the order Stolidobranchia.
Branchial formulae  The number of internal longitudinal vessels on and between the branchial folds (for species that have them) or the number of stigmatas between the longitudinal vessels. The count is conducted from the endostyle to the dorsal lamina on the right side, and in the opposite direction on the left.
Plate 1, figs. G, H; Plate 2, fig. G; Plate 3, figs. A, B, D, G; Plate 4, fig. D; Plate 5, figs. B, G; Plate 6, fig. G Branchial opening The same as the branchial aperature.
Plate 1, figs. G, H; Plate 2, fig. G; Plate 3, figs. A, B, D, G; Plate 4, fig. D; Plate 5, figs. B, G; Plate 6, fig. G Branchial orifice The same as the branchial aperature.
Plate 2, fig. B; Plate 4, figs. G, H Branchial papillae Expansions of the inner wall of the branchial sac, which support the internal longitudinal vessels. Present in Phlebobranchia.
Plate 2, fig. G; Plate 5, figs. F, G Branchial sac Perforated sac where respiration and food filtration occurs. It is equivalent to the pharynx in vertebrates.
Plate 1, fig. A; Plate 2, fig. A; Plate 3, figs. E, F; Plate 4, figs. B, C Branchial tentacles Flexible elongated expansions that exist in the internal margin of the oral syphon, next to the base. They could be simple or ramified.
Brood pouch Mantel expansion where the embryos developed.
Bud  Undeveloped or embryonic zooid that develops asexually.
Budding Type of vegetative reproductions; may occurs in different forms in ascidians.
C
Caecum A sac or invagination forming a curve from the stomach wall. It is common in Phlebobranchia and Stolidobranchia.
Plate 5, fig. C Calcareous spicules Calcareous structures present in the tunic of some tunicate species.  In Didemnidae and Polycitorella they are star-shaped or spherical while in the genre Cystodytes they are disc-shaped and in Pyuridae they are fusiform. 
Cerebral vesicle Sensory organ of the larva that contains a light sensitive eyespot and a gravity-sensitive otolith. It is also called sensorial vesicle.
Plate 1, fig. H Circular muscles Muscle bundles that are present around the siphons
Plate 3, fig. C; Plate 5, figs. B, E Cloaca  Opening of cloacal cavity or cloacal canals on the surface of the tunic of a colony.
Cloacal aperture The same as atrial siphon.
Plate 5, fig. B Cloacal canal A channel in the tunic linking the atrial openings of several zooids in a colony.
Cloacal cavity Cavity into which the atrial aperture of various zooids in a colony are opening.
Plate 2, fig. G Cloacal languet  Expansion of the upper wall of the exhalant siphon.
Plate 5, figs. B, D, E, H Colonial ascidian Ascidian with vegetative reproduction, and the individuals originated remain united through the tunic.
Colony Set of several zooids originating from a larva that remain united by the common tunic.
Plate 5, figs. B, D, E, H Compound ascidian The same as the colonial ascidian.
D
Descending limb of gut loop The descending part of intestine.
Plate 3, fig. G; Plate 5, figs. F, G Digestive tract Alimentary canal including the stomach, intestine and rectum.
Distal Anatomically located far from a point of reference, such as an origin or a point of attachment.
Plate 2, figs. C, D; Plate 4, fig. D Dorsal lamin A longitudinal membrane on the mid-dorsal side of the pharyngeal basket (opposite to endostyle).  It is a ridge curved to form a ciliated gutter which carries food from the pharynx to the esophagus.
Dorsal languets Tongue-shaped structures on on the mid-dorsal side of the pharyngeal basket. Function in the same manner as dorsal lamina
Plate 1, fig. A; Plate 2, fig. A; Plate 4, figs A, B, D Dorsal tubercle The dorsal tubercle is a ciliated funnel that protrudes above the pharyngeal lining, appearing as small slits or coiled opening(s). The funnel opens into a ciliated duct which connects to the neural gland. It is present in Stolidobranchia and Phlebobranchia.
E
Plate 6, fig. D Ectodermal ampullae Tubular projection in the anterior region of the larva, close to adhesive papillae.
Ectodermal vesicles Bubble-like membraneous structures in the larval trunk, which help in the fixation on the substrate.
Egg  Diploid cell resulting to the sexual reproduction.
Plate 6, fig. A Embryo The first stages in the larval development. Usually, solitaries ascidians has planktonic embryos while colonial ascidians incubate them.
Endocarp Evagination of the internal body wall forming globular or elongate structure. Blood vessels are present on the endocarp. They are present in Styelidae and Pyuridae.
Plate 2, fig. G; Plate 4, fig. D Endostyle A longitudinal ciliated groove of thyroid origin, on the ventral wall of the pharynx which produces mucus to gather food particles.
Epicardium The outermost layer of the heart wall.
Excretory vesicles Bubble-like membraneous structures involved in excretion. They are present in Phlebobranchia.
Plate 1, fig. G, H; Plate 3, figs. Ab, B, D, F, G; Plate 6, fig. G Excurrent siphon The same as atrial siphon.
G
Gastric caecum A sac or invagination forming a curve from the stomach wall. It is common in Phlebobranchia and Stolidobranchia.
Gastric reservoir Extra space to aid in digestion in the pyloric gland.
Gastrointestinal gland Set of tubes around the intestine, close to the stomach. The tubes are fusing in a duct in the area between the stomach and duodenum. Sometimes, this duct is expanded as a vesicle.
Plate 1, figs. D, G, H; Plate 3, fig. G; Plate 4, fig. F; Plate 5, fig. F Gonads Reproductive organs.
Gonochoric gonad  A gonad that is specifically either ovaries or testes and not both.
Plate 3, fig. G; Plate 4, figs. E, F; Plate 5, figs. F, G Gut Where digestion takes place; includes the esophogus, stomach and intestine.
Plate 3, fig. G; Plate 4, fig. F; Plate 5, fig. G Gut loop Curve formed by the intestine; might have one primary and one secondary loop.
H
Head  In pedunculated solitary ascidian, is the width region with the branchial sac. In colonies, it is the superior and globular part of the colony, where the zooids are.
Heart Tubular structure, located within or under the gut loop (posterior region of the body). It has two pacemakers so can move cells and fluid in vessels in both directions, alternately.
Hepatic gland Gland on the stomach in Pyuridae and Molgulidae.
Hermaphrodite gonad A gonad that has both eggs and sperm .
I
Incubatory pouch Expansion of the mantle, where embryo develops.
Plate 1, figs. G, H; Plate 2, fig. G; Plate 3, figs. A, B, D, G; Plate 4, fig. D; Plate 5, figs. B, G; Plate 6, fig. G Incurrent siphon The same as branchial siphon.
Infundibula  Each of the conical projections of the branchial sac facing the lumen of the branchial sac; appears in Molgulidae, some Agnesiinae and Corellinae, and in Hartmeyeria and Ctenyura.
Plate 3, fig. G; Plate 4, fig. F; Plate 5, fig. G Intestinal curvature Curve formed by the intestine; might have one primary and one secondary loop.
Plate 3, fig. G; Plate 4, fig. F; Plate 5, fig. G Intestinal loop  Curve formed by the intestine; might have one primary and one secondary loop.
Intestinal swelling  Enlargement of the posterior intestine.
Plate 1, fig. H; Plate 3, fig. G; Plate 4, figs. E, F; Plate 5, figs. F,G Intestine The portion of the alimentary canal extending from the stomach to the anus.
K
Kidney Closed sac in Molgulidae on the right side of the mantle. Excretory function.
L
Plate 2, figs. H, I; Plate 6, figs. A-E Larva (pl. Larvae) Stage of the life cycle that is an immature free-swimming form (natant).
Plate 2, figs. H, I; Plate 6, figs. A-E Larval tail  Tapered region that contains the notochord and dorsal nerve cord.
Plate 2, figs. H, I; Plate 6, figs. A-E Larval trunk  Body of the larva, excluding the tail.
Lateral organ Circular or elongated structure that appears in the mantle side, at chest. Present in Didemnidae
Liver diverticula  The same as hepatic gland, located around the stomach and occurs in Pyuridae and Molgulidae.
Plate 1, fig. F; Plate 2, fig. B; Plate 4, fig. I Longitudinal vessels  Blood vessels present in the inner wall of the branchial sac, arranged longitudinally. Present in Phlebobranchia and Stolidobranchia.
Plate 1, fig. H; Plate 3, fig. H Longitudinal muscles  Present in the mantle, muscle bundles radiating from the siphons toward the abdomen.
M
Plate 3, fig. G Mantle Membrane surrounding the animal, inside the tunic, composed of epithelial tissue, connective tissue, muscle and blood vessels.
Mesh Area of the branchial basket between four papillae or between two longitudinal vessels and two transverse vessels.
Plate 1, fig. H; Plate 3, fig. H Muscle bands Set of muscle bundles.
Muscular process  Muscular appendix, thin and long, used in fixing the zooid within the colony. In Didemnidae it is present in between the rear end of endostyle and posterior margin of the opening of the eosophagus.
N
Nerve ganglion A small oval structure, present in the dorsal body wall, between the bases of siphons.
Neural complex Association between the ganglion and neural gland.
Neural duct Duct of the hiponeural gland.
Plate 2, fig. F Neural gland Gland usually under the nervous ganglion, but dorsal to it in the Stolidobranchia order.
O
Plate 2, fig. H; Plate 6, figs. A, B Ocellus (pl. ocelli)  Light-sensitive pigment spots present in larvae.
Plate 1, figs. E, I; Plate 2, fig. D Oesophageal opening Opening of the esophagus from the pharynx located at the end or close to the dorsal lamina.
Plate 2, fig. G Oesophageal neck  Narrow region between the thorax and abdomen, formed by the esophagus and the rectum, only in colonial ascidians.
Plate 5, fig. F Oesophagus  Cylindrical tube connecting the pharynx and the stomach.
Platre 2, fig. I Oozooid  First zooid of a colony, originated from the metamorphosis of the larva fixed.
Plate 1, figs. G, H; Plate 2, fig. G; Plate 3, figs. A, B, D, G; Plate 4, fig. D; Plate 5, figs. B, G; Plate 6, fig. G Oral aperture  The same as oral or branchial siphon. It is the most anterior siphon.
Plate 3, fig. D Oral lobes Short expansions that extend from the margins of the oral siphon.
Plate 1, fig. A; Plate 2, fig. A; Plate 3, figs. E, F; Plate 4, figs. B, C Oral tentacles  The same as the branchial tentacles.
Plate 2, fig. H; Plate 6, fig. D Otolith Structure gravity-sensitive in larvae.
Ovary  Female gonad.
Plate 1, fig. E; Plate 3, fig. G Oviduct Duct that leaves the ovary and continues to the brood pouch or to the atrial opening.
P
Parastigmatic vessels  Transverse intermediate vessels that cross the gill slits, but do not interrupt them.
Plate 2, fig. G Peribranchial cavity  Cavity between the wall of the branchial basket and the mantle.
Plate 1, fig. A; Plate 2, fig. A; Plate 4, fig. B Peripharyngeal band  The same as prebranchial groove.
Peritubercular area  Area in the shape of a V around the dorsal tubercle, along the margin of peripharyngeal space.
Plate 2, fig. G; Plate 5, figs. F, G Pharyngeal basket  Also called the pharynx. It is a bag with many perforated slits used for respiration and filtration of food.
Post-stomach  Part of the intestine that follows the stomach and is divided by constrictions into separate regions.
Postabdomen  Part of the body situated behind the abdomen; presents the gonads and heart. Found only in Polyclinidae, some Distaplia and Hypsistozoa.
Plate 2, fig. A Prebranchial area Area between the ring of oral tentacles and peripharyngeal band.
Plate 1, fig. A; Plate 2, fig. A; Plate 4, fig. B Prebranchial groove  Ring structure similar  to the endostilo located at the anterior of the branchial sac.
Prestomach  Enlargement of the esophagus, found only in some species of the genus Clavelina.
Proximal Part of an organ or structure that is located closest to the base or point of attachment.
Pyloric gland Set of tubes around the intestine, close to the stomach. The tubes are fusing in a duct in the area between the stomach and duodenum. Sometimes, this duct is expanded as a vesicle.
R
Rectal valve  Two caeca, or folds, projecting back at the beginning of the rectum. Found in Distaplia, Hypsistozoa and Neodistoma.
Rectum Terminal portion of the intestine, whose opening is next to the opening of the atrial siphon.
Renal vesicle The same as renal sac.
Renal sac  Single, large, closed, bean-shaped sac in which waste matter is gradually added and stored. Found in Molgulidae.
Retropharyngeal groove The space between the posterior extremity of endostilo and the posterior edge of the esophageal opening.
Plate 1, fig. F; Plate 2, fig. B; Plate 4, figs. G, H; Plate 5, fig. F Rows of stigmata Transverse rows of stigmata in the brachial sac.
S
Sensorial vesicle Sensory organ of the larva that contains a light sensitive eyespot and a gravity-sensitive otolith. It is also called cerebral vesicle.
Side organ Circular structure or elongated shape that appears in the mantle laterally. Present in Didemnidae.
Plate 3, figs. A, D-F; Plate 6, fig. G Simple ascidian Consisting of a single individual, do not presents assexual reproduction.
Siphonal lining  Part of tunic inside the siphons; it finishes above the line of oral tentacles.
Siphonal scales  Projections flattened with rounded edges that are present in the siphons of Pyuridae and some Styelidae.
Siphonal spines Small spines that appear on the inside wall of the siphon of Pyuridae and some Styelidae.
Plate 1, figs. G, H; Plate 2, fig. G Siphons Tubular structures, that permits the flux of water to inside or to outside to the ascidian. It presents variable lenght.
Plate 3, figs. A, D-F; Plate 6, fig. G Solitary ascidian Consisting of a single individual, do not presents assexual reproduction.
Spermiduct Duct that leaves the testis and continues to the atrial opening. Presents the sperm.
Stalk Projection in the tunic to elevate the animal from the substrate. In colonial ascidians, contains the abdomen of the zooids.
Plate 2, fig. H; Plate 6, fig. D Statocyte Balance organ. Found in larvae.
Plate 4, fig. I Stigmata Perforations in the branchial sac, with ciliated margin.
Stolonic vessel Linear expansion in the tunic to connect many zooids in the base of them. It is present in Phlebobranchia and Stolidobranchia.
Plate 1, fig. B; Plate 5, fig. F Stomach  Digestive organ.
Storage cells Set of excretory cells, on the digestive tube of Ascidiidae. They increase in number when older the animal, masking the gonad.
System Set of zooids arranged around the same cavity or cloacal canal.
T
Plate 2, figs. H, I; Plate 6, figs. A-E Tadpole Free-swimming life stage.
Plate 2, figs. H, I; Plate 6, figs. A-E Tail Thin region which contains the notocord and the dorsal cord.
Terminal ampullae The extremity of the blood vessels in the tunic.
Plate 2, figs. H, I; Plate 3, fig. A; Plate 5, fig. A; Plate 6, fig. C-F Test  Tissue with different concentrations of tunicine fibers (similar to cellulose), blood cells and connective cells surrounding the animal. 
Plate 2, figs. H, I; Plate 3, fig. A; Plate 5, fig. A; Plate 6, fig. C-F Test vessels Blood vessels in the tunic.
Testis (pl. Testes) Male gonad.
Plate 2, fig. G Thorax  Anterior region of the zooid, presents the branchial sac and the siphons.
Plate1, fig. F; Plate 4, figs. G-I; Plate 5, fig. G Transverse vessels  Blood vessels present in the inner wall of the branchial sac, arranged transversally.
Plate 3, fig. H Transverse muscles Muscle bundles in the mantle, in the side of the thorax, between the endostyle and the dorsal lamin.
Plate 2, figs. H, I; Plate 3, fig. A; Plate 5, fig. A; Plate 6, fig. C-F Tunic The same as test.
V
Vanadocytes Blood cells that store vanadium.
Vas deferens The same as spermiduct.
Vascular stolon Linear expansion in the tunic to connect many zooids in the base of them. It is present in Phlebobranchia and Stolidobranchia.
Velum  Membrane which line the inner wall of the siphons.
Z
Plate 2, fig. G; Plate 5, figs. A, B, F, G Zooid Each individual in a colony.

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