Umbo bivalve shell. Bivalves build their two shells simultaneously.

Umbo bivalve shell Apertural: Pertaining to aperture or on same side as aperture. umbones)* A convex protuberance or swelling in the centre. Bivalves usually have biconvex profiles, which means both valves are outward-curving or arching relative to each other. Any whole shell, or any piece of shell with this Growth takes place through mantle secretions on the outer edges of each shell, which means that the part of the shell near the hook (also called "umbo") is the oldest. Umbo is frequently used in anatomical descriptions of brachiopods to describe the origin of valve development. Bivalves were created as two halves even though we most often find only one of the halves. Location. Umbo : Beak of a bivalve shell, from where generally the growth of the shell would have started. shell form and an extended hinge without the parivincular ligament tends to cause space conflict between umbones or dorsal shell margins of right and left valves. Valve - one half of the bivalve shell. May 27, 2022 · Umbo: The dorsal part of a valve where curvature increases significantly; this region also contains the beak. Sep 23, 2024 · The correlation between shell microstructure and functional significance in the survival of a bivalved mollusc dates back to Wainwright (). Therefore, bivalve shell shape is a critical determinant of how Umbo - dorsal prominence on bivalve shell located adjacent to the hinge; the oldest part of the shell. A band of horny and elastic material, the ligament (fig. The valves lie on the left and right sides of the animal. The beak is the basal projection of the oldest part of the valve of the adult animal. Observe lines of growth (concentric rings radiating away from the umbo). , 2006). Not all bivalve shells have an umbo. In the blue mussels mentioned above, the foot is primarily used to create byssal threads. Adductor muscles on each side hold the shell closed. ITZ: Intertidal zone. The boss or knob at the center of a shield. termed a chondrophore (F igure 6. Umbo . May 31, 2024 · Bivalves are a group of freshwater and marine mollusks with bilaterally symmetric and laterally compressed bodies encased in a characteristic two-part shell. chinensis are located on the umbo of the right valve (A–C) and the left valve (F–H). Bivalves have two siphons May 1, 2009 · Sections (n = 2 to 8 shells per treatment) were cut longitudinally from the hinge (apex, beak and umbo; Moore, 1969; often conflicting, approaches to alignment. Jan 26, 2001 · A bivalve is characterized by possessing two shells secreted by a mantle that extends in a sheet on either side of the body. DORSAL umbo (beak) growth lines ANTERIOR POSTERIOR Bivalve lives inside a pair of calcareous shells. The umbo (plural umbones or umbos) is the ill-defined, typically noticeable, uppermost section of each valve of a bivalve or univalve mollusk’s shell valve. External Clam Shell Anatomy Two fused siphons extend from posterior end of shell into water “little” necks Two muscles keep valves closed Predators or adverse environmental conditions Muscular foot extends beyond shell for burrowing into bottom Mouth near foot area – anterior end of shell Bivalve molluscs are completely enclosed by a shell made of two valves hinged at the top. Clams are bivalves meaning they have shells consisting of two halves, or valves. The oldest part of the shell is called the umbo. Bivalves by definition have two valves, which are joined together by a strong and flexible ligament situated on the hinge line at the dorsal edge of the shell. The bulge near the hinge is called the umbo and is the oldest part of the shell. This is the oldest part of the clam shell. Valve - one half of the complete shell of a bivalve. This part is usually seen as the bump or base knob of the shell the bundled muscle closest to the umbo; the one closest to the mouth; toward what would be the "head" end of a clam (if it had one). For a long time I assumed it was a bivalve, but it is a gastropod because it is made in one piece. As the bivalve grows, the shell becomes larger, with the newest growth occurring in the margins furthest from the umbo. May 1, 2023 · Shape of bivalve shells. Lateral teeth can be absent in some species. When the clam or scallop relaxes the adductor muscles, ligaments located on each side of the umbo can then pull the shell open. Place the valve flat in front of you opening side down with the umbo pointing away. Right valve: The entire right half of About the external shell, the convex "hump" at the top of the shell is called umbo. It is a protruding part of the shell that serves as an important marker in understanding the shell's growth and structure. Bivalves have also been used in the biocontrol of pollution. . In life, the shell needs to be able to open slightly to umbo cardinal tooth lateral tooth anterior border left valve right valve umbo lunule thickness (degree of inflation) Glossary of Bivalve Terms Beak (or umbo - plural: umbos or umbones) : the first formed part of a valve, usually above the hinge. The lunule is a heart-shaped depressed area in front of the umbo in many clams. beak-like projections at the dorsal part of the shell; it is the oldest part of a bivalve shell (also called the umbone) Upwelling . n. Dec 1, 2012 · We are told in British Bivalve Seashells by Norman Tebble (published by The British Museum (Natural History) 1966, ISBN 0 11 491401 X) that the shell of the common edible cockle is solid and the two halves or valves of the shell are similar in shape and sculpture (equivalve). Bifid: split in two (as in the tooth in the hinge). The ridges that form around the umbo trace the growth of the valve. It usually contains the valve's beak, the oldest point of the valve, and its degree of prominence and position relative to the hinge line are sometimes helpful in distinguishing bivalve taxa. The entrance to the shell interior. Studies concerning the behaviour of the shell in various bivalve species have been reported in the works of Taylor and Layman (), Barthelat et al. In some bivalves, an area known as the dorsal ligament area develops below the umbos, which are Dec 3, 2023 · The oldest part of a bivalve shell is called the umbo. The main muscle of a bivalve is called the adductor muscle, and is also used to hold the shell halves together. Antero-dorsal surface: Dorsal surface of bivalve shell anterior to umbones. Aug 26, 2020 · The umbo, and its tip which is called the peak, is the first part of the shell secreted. 3C), found in . A spoon-shaped, projecting resilifer is . Jan 1, 2010 · The nature of each valve of the bivalve shell is that of a spiral, homologous to that of a gastropod. The shells of bivalves are made of calcium carbonate (CaCO3). (radiating from the umbo, or beak, of the shell) and more remote lateral teeth Lateral Teeth: Hinge teeth located far away from the umbo in a heterodont hinge. The mantle cavity in bivalves is located ventrally and Oct 30, 2007 · The analysis of the element composition of bivalve shells has gained importance in recent years with respect to environmental monitoring. The umbo is circular in shape and is the May 14, 2024 · The bivalve shells were placed in four orientations: umbo upstream (orientation 1), umbo on the left (orientation 2), umbo downstream (orientation 3), and umbo on the right (orientation 4). Bivalves have a right valve and left valve. Periostracum: A protective skin that covers the outside of shells. ) ala (plural: alae; adjectives: alate, bialate): dorsal wing-like extension of the shell. • Common Otter-Shell, Lutraria lutraria is a large shell. The narrow end or apex of the shell is called the umbo (plural, umbos or umbones) or beak. Umbo (bivalve), part of a bivalve shell which was formed when the animal was a juvenile; Umbo (conifer cone), the first year's growth of a seed scale on a conifer cone, showing up as a protuberance at the end of the two-year-old scale; Umbo (mycology), at the top of some mushrooms Powerful muscles contract ligaments to keep the valves closed and relax to open them. The total number of known living species is about 9,200. The ligament is the cartilage that connects the valves of bivalves. The umbo (plural umbones or umbos) is the vaguely defined, often most prominent, highest part of each valve of the shell of a bivalve or univalve mollusc. The apex is the first-formed, and therefore the oldest, part of the shell. The beak usually, but not always, coincides with the umbo , the highest and most prominent point on the valve. Most bivalves are sessile filter feeders that live on or burrow into the seafloor, though some like mussels and scallops can attach or swim. 16) joins the valves at the hinge on which they turn in opening or closing the shell. in hatchery terminology, a growing system in which a flow of water is induced through the base of a spat holding container (compare with downwelling). e. The beak is part of the shell of a bivalve mollusk, i. Use blunt probe to identify oldest line of growth 2. Varices show different patterns. 4. Hinge teeth are part of the anatomical structure of the inner surface of a bivalve shell, i. Two muscle scars are present in most equivalve species near the anterior and posterior margins of 15). The valves are joined at the top, and the adductor muscles on each side hold the shell closed. Download scientific diagram | (a) Shell section cut from the umbo to the posterior ventral edge of the freshwater bivalve shell. If the adductor muscles are relaxed, the shell is pulled open by ligaments located on each side of the umbo . Varix (varices – plural): Thickened ridges seen at the edge of the outer lip of shell. Bivalves, which are part of Class Bivalvia, are enclosed in a pair of shells or valves that are joined at the umbo, the initial point of shell growth. The lateral teeth and pseudocardinal (pseudo = false) teeth are not used for chewing up food, but instead they are used to keep the two shells or bivalve together. Mar 16, 2020 · Bivalve Shell •Umbo is the raised, oldest part of the shell and is used to find surfaces Dorsal Ventral Anterior Posterior UMBO copyright cmassengale. umbo Protuberance at the terminal end of the valve, from which the shell grows. valve (noun) the right or left half of a bivalve shell. Note: Typically, the right valve of an oyster will be shorter and less concave than the left valve. 2. A freshwater mussel has a tooth on the inside of each shell or valve. Most of the bivalve body is located dorsally in the shell. It usually contains the valve's beak , the oldest point of the valve, and its degree of prominence and position relative to the hinge line are sometimes helpful in distinguishing bivalve taxa The oldest point of a bivalve shell is called the beak, and the raised area around it is known as the umbo (plural umbones). When the shell is closed, the top part of the hinge ligament is stretched and the lower part is compressed. An abnormally placed borehole (D) and incomplete boreholes (E, I The earliest formed part of the shell generally appears as a conspicuous beak or umbo, and defines the dorsal side of the shell; the latest formed part of the shell is situated distal from the umbo, and defines the ventral side of the shell. (from Mikkelsen and Bieler, 2008) from publication The umbo is the swelling part of a bivalve near the beak. show the umbo shell orien-tations that were in a con vex-up position on the shell bed. Within it can be a variety of combinations of teeth and sockets that articulate the two valves. • True Trough shells the Spisula have serrations on the lateral teeth which are Nov 8, 2024 · The umbo is a key anatomical feature found in bivalve mollusks, which include organisms like clams, oysters, and mussels. Hinge: Toothed area at the umbo beneath the beak and ligament that helps hold the two shells together in bivalves. The two shells are joined at the dorsal end by a region called the ligament. with the decline of brachiopod stocks, bivalves were able to move in and occupy vacant niches and even some new ones as we shall see in the practical. where the clam opens is a swollen region (the umbo) where the shell of the clam starts to grow a tooth of the hinge of a bivalve mollusk Hinge teeth located directly below the umbo in a heterodont hinge. (b) Schematic of the cross-section of a shell showing the growth Bivalves belong to the phylum Mollusca, a group that includes such diverse animals as chitons (chain shells), gastropods, tusk shells, cephalopods (squid and octopus) as well as clams, oysters, mussels and scallops. The in situ abrasion process is Nov 1, 2007 · Is the umbo matrix of bivalve shells (Laternula elliptica) a climate archive? November 2007; Aquatic Toxicology 84(4):450-6; Fe, Mn, Cu, Pb and U in the shell umbo, by means of laser ablation (See shell diagram on page 3. Aperture: Opening or entrance of the shell providing outlet for the head and foot. Varix (pl. Bivalves build their two shells simultaneously. These species are placed within 1,260 The hinge ligament is designed to hold both halves of the shell together. beak: oldest part of the valve; shell knob on hinged end of valve; also known as umbo. Bivalvia(Bivalves) Phylum MolluscaClass BivalviaNumber of families 105Thumbnail description Bilaterally symmetrical mollusks, with a reduced head and typically two external shell valves, many of which are commercially important for human consumption and pearl production; some have major impacts on the world economy and environment Source for information on Bivalvia (Bivalves): Grzimek's Animal The adductor muscle is used to hold the two shells together allowing the mussel to close its shell. varices) - axial sculptural element that is more prominent than a costa, and usually more widely spaced; evidence of a growth halt during which a thickened lip develops. Jan 4, 2024 · The umbo is the slightly raised hump near the hin/ge of the shell, and it represents the initial point of shell growth, making it the oldest part. Internal shell growth patterns are best viewed in cross-sections taken from the umbo to the growing shell margin. 2). A line through the chondrophore will m ake 45 degrees angle to margin • The Rayed Trough Shell (Mactra corralina | Mactra Stultorum) sometimes has rays, but has thin lateral teeth without serrations. The bivalve shell (Mollusca May 1, 2000 · The less common method of preparation of bivalve shells is by thin sectioning. In this scenario, the shells began to move downstream while, at same time The umbo (plural umbones) is the highest (usually protruding) part of each of the two valves making up a bivalve shell - it represents the earliest part of the shell. Umbo. [9] The hinge area is the dorsum or back of the shell. oldest part of the shell of a bivalve from which the shell grows. This technique is readily applied to bivalve shells, where a straight cut by a rock-cutting saw equipped with a diamond blade reveals the entire growth history of the animal in the sectioned shell. The other orientations were regarded equivalently as one of the four orientations, and apexes of the shells for the gastropod shells were similarly placed The shells of bivalves are used in craftwork, and the manufacture of jewellery and buttons. Jan 1, 2001 · Bivalve growth is generally described in terms of increases in shell dimensions, particularly those of length (anterior-posterior dimension), height (greatest distance from the umbo to the ventral margin), and width (greatest thickness through both valves; Fig. umbo synonyms, umbo pronunciation, umbo translation, English dictionary definition of umbo. Umbo of Clam. A shell that can be tricky is the slipper snail shell. Holds both valves together. Definition. and others. bivalve: a mollusk with two shells. The hinge is located on the dorsal side of the clam next to a structure/location called the umbo. Shape is believed to be related to shell strength with bivalve shell shapes the phylum Mollusca; it is a bivalve, having two shells connected by a hinge. the shell of a bivalve mollusk. Umbo (pl. Ventrolateral shoulder - an inflation or arching of the valve (shell) surface located along its ventral margin. Dec 1, 2017 · Ichnospecies Oichnus paraboloides Bromley found in three bivalve shells: A–J, Mactra chinensis; K, Nuttallia japonica; L–O, Felaniella usta; Note that most boreholes in the shells of M. Classify ‐ The arrangement of anything into groups or categories. shell is kept shut by action of the paired adductor muscles. The shell grows co­marginally around the post‑larval shell, which remains as a beak somewhere along the dorsal margin. The shell is composed of different layers including an outer organic layer, a middle prismatic layer, and an inner smooth nacreous layer. In many bivalves the hinge carries a series of interlocking teeth, but these structures are absent More elaborate sculpture common in bivalves include commarginal (parallel to the shell edge, like growth lines), radial (from umbo to ventral edge), or in a few, oblique elements. umbo, left side B. The Arca species part of the family of Ark shells has a large flat area between the umbones which, in an undamaged shell, somewhat resembles a deck, with the rest of the shell perhaps illustrating an ancient wooden boat such as Noah's ark, hence the common name Ark shells. The lower, curved margin is the ventral side. The two half-shells, called the "right valve" and "left valve", are joined by a ligament and usually articulate with one another using structures known as "teeth" which are situated along the hinge line. Spiral shells are gastropods (one-piece) and clams and scallops, as an example, are bivalves. The valves are usually similar to one another in size, shape, color, and texture. The elevated, upstream-facing umbo region is exposed to particle impact and is the first to be abraded and perforated. Use blunt probe to scratch away top layer of shell 3. A. Aug 15, 2024 · Procedure: Phase 1: Bivalve external anatomy - identify external structures Use blunt probe to identify the umbo 1. So that when you hold the left hand/side shell with the inner surface towards you it looks like the diagram above. ventral (adjective) the lower or bottom edge of a shell. During shell formation the layers coil around this axis. Bivalves have a muscular "foot" at their front end that is used for movement such as burrowing, or in some bivalves like the razor clams, for swimming. Bivalves are filter feeders and accumulate inorganic elements and organic compounds from the water column through ingestion of sediment particles (Jing et al. Notice how the umbo end of the longer valve, the left valve, extends beyond the umbo end of the right valve. Anterior slope: Surface of valve of bivalve shell from umbo to anterior ventral margin. According to Animal Diversity Web: A bivalve is characterized by possessing two shells secreted by a mantle that extends in a sheet on either side of the body. pl. The shells of bivalves grows in annual increments, which makes it possible to determine their age. Apr 18, 2024 · Shell identification guides become easier to use with some background on the morphological features present in different shell types. 12 Bivalve Shell planktonic stage of bivalve embryo . excurrent siphon: opening through which mussel expels water The shorter of the two valves is the right valve. [5] Various types of hinge ligaments have been found in living species (i. umbo (noun) the raised portion of the dorsal margin of a shell, also called the beak. The left valve of a clam can be identified as follows. Nov 10, 2020 · Therefore, bivalve shell shape is a critical determinant of how successfully an organism can defend against attack. This is a more derived kind of bivalve hinge. Download scientific diagram | Diagram of a valve of a bivalve (open, spoon-like shells), with the umbo or 'beak' (u) and hinge-teeth circled. Body whorl – the large whorl, containing the aperture, in which the snail lives. – In rostrate opisthogyrate bivalves, the umbo and the postero-dorsal angle of the shell project dorsally relative to the ligament, which then fails to act as a pivotal axis. Term. Radial: Extending from the hinge or top of clam to shell edges or lips. In Brachiopoda [1] and Bivalvia [2], the first part of the shell to be formed; it occurs at the posterior of each valve in brachiopods and forms the dorsal part of the shell in bivalves. The first part of a brachiopod (*Brachiopoda) or bivalve (*Bivalvia) shell to be formed. umbo, dorsal side C. shell, and the animal deposits nacreous layers around it. Check out this background information on parts of a Bivalve shell to help you identify shells to that species level identification! Learn about: • Shell Valve • Valve Hinge Teeth • Udont • Adductor Muscles (isomyarian, heteromyarian, and monomyarian Each of the two parts of a bivalve shell, joined by a ligament. Question 16 (Mandatory) (1 point) The plane that divides left from right in a bivavle is located across the outer edge of the mantel through the hinge and down the middle of the shells between the two shells across the hinges and through both shells Question 17 (Mandatory) (1 point) The umbo of a bivalve shell forms at the radula protoconch anterior canal outer lip Question 18 (Mandatory) (1 flow such that the umbo faces upstream. The area surrounding the beak is known as the umbo although some regard these terms as interchangeable. The word "apex" is most often used to mean the tip of the spire of the shell of a gastropod. Most species are also equipped with locking teeth or sockets beneath the Mar 24, 2008 · The bivalve shell is made of crystalline cal-cium carbonate either deposited on, or embed- umbo. To a large degree, a prosogyrous shell form with a long parivincular ligament helps shell opening without umbonal conflict, if the As reported by Futterer (1982) for some bivalve shells (Glycymeris glycymeris and Mytilus edulis), the results of this laboratory investigation demonstrated that shells in a convex-up position were hydrodynamically less stable when the umbo was pointing upstream. periostracum, ventral side D. part of the shell of a saltwater or freshwater clam. <see image> bivalve - a freshwater or saltwater mollusk with a shell consisting of two rounded plates called valves joined at one edge by a flexible ligament called the hinge Locate the umbo, the bump at the anterior end of the valve. Growth lines on a specimen of Mercenaria mercenaria from the Quaternary of St. The umbo (plural umbones or umbos) is the vaguely defined, often most prominent, highest part of each valve of the shell of a bivalve or univalve mollusc. Urogenital System Clams are bivalves, meaning that they have shells consisting of two halves, or valves. Download scientific diagram | Basic bivalve shell morphology. The vulnerability of the umbo to perforation is greatly increased by the thinness of the shell at the umbo cavity. Although these data have a large range of a raised bump or projection on the outside of a shell, also called a pustule. Turn the calm with its dorsal side down and insert a screwdriver between the ventral edges of the valves. (A) Scheme of shell axis orientation. Umbone is another word for umbo. Diagram of the left valve of a bivalve resembling a veneridA side view of a whole shell of Cucullaea labiata (Lightfoot, 1786), the umbones are at the top of the imageDiagram of a bivalve shell Oct 30, 2007 · The analysis of the element composition of bivalve shells has gained importance in recent years with respect to environmental monitoring. The umbo is circular in shape and is the May 8, 2018 · *umbo (pl. Find the hinge ligament which hinges the valves together and observe the growth rings. extant species), and the ligaments can be reconstructed in most fossil bivalves based on their sites of attachment on the shell. posterior end Rear terminal end of the shell, opposite the anterior lip, through which water enters and exits. Beak ‐ umbo Bivalve –oa tw piece shell. This challenge, present in several bivalve groups, has been functionally solved in different, and sometimes complementary, ways. 3. Mar 13, 2018 · The umbo, located at the hinge area, is the oldest part of the shell, and the bivalve grows from that point outward. The lunule or indented side will be on the left. Mary’s County, Maryland (PRI 76728), with external shell features annotated. In a brachiopod, the umbo is the posterior part of each Nov 21, 2023 · Bivalve Shells. Internal bivalve morphology. Bivalves appear in the fossil record first in the early Cambrian more than 500 million years ago. canal or umbo to lateral margin. A hinge ligament made of elastic protein joins the two halves of the shell together, and large adductor muscles between the two valves hold them closed. When the bivalve s adductor muscles relax, the ligament causes the valves to open. Study with Quizlet and memorize flashcards containing terms like The oldest part of the shell of a bivalve is called the ______ and it is located on the _______ of the shell. Umbonal : Relating to the umbo . Describing bivalves, it’s necessary to pay attention to the hinge (cardinal area). The adductor muscles counter the tension in the elastic ligament, which tends to keep the shell valves spread apart. The only vestige of this growth pattern is the umbo or beak of each valve. If the adductor muscles are relaxed, the shell is pulled open by ligaments located on each side of the umbo. umbones) - projected portion of the hinge. Bivalve profiles. A bivalve shell is the enveloping exoskeleton or shell of a bivalve mollusc, composed of two hinged halves or valves. (), Chattopadhyay et al. Nov 10, 2020 · Additionally, shell elongation from the umbo, a metric often overlooked, is shown to have significant effects on shell strength. Jan 5, 2023 · Right and left valves. This involves sectioning the shell from the umbo or hinge region to the growing edge. denticals: a small, tooth-like projection. Valve : Each shell of the bivalve mollusc. A specimen is then mounted onto a petrographic slide, sectioned a second time, ground, and polished. The phylum has six classes of which one is Lamellibranchia or Bivalvia. Their main characteristics are as follows (Figure 2): (1) bilaterally symmetrical shell, consisting of two valves (two convex halves of the shell); laterally compressed body enclosed within two calcareous, lateral shells, each usually with a beaklike umbo (swollen area near shell's anterior), hinged dorsally by an elastic ligament and closed by Define umbo. In those that do the umbo often seems to point to one side or another, usually to the anterior side. Nov 19, 2012 · Bivalves have two shells held together by adductor muscles, gills for oxygen intake from water, and a mantle that secretes their shell. A bivalve, though, expands the diameter of its aperture very quickly relative to its rotation about the coiling axis, nearly obliterating any sense of its coil [514]. The shells provide protection for the clam and are opened and closed by two adductor muscles located on either side of the hinge. They belong to the class Bivalvia, a term coined by Linnaeus (1758) from two Latin words, bis (two) and valvae (leaves of a door). The hinge ligament of a bivalve shell can be either internal, external, or both, and is an example of complex development. 8 Shell morphology of Mercenaria, (Miocene - Recent) (a) Exterior view of right valve. umbone, (umbo) is part of each valve of the bivalve shell or univalve Each of the two parts of a bivalve shell, joined by a ligament. The basic features of a valve are labelled. periostracum, right side, The adaptation of bivalves to a sedentary, filter-feeding lifestyle that exploits the sand of a beach as a habitat, has Sep 25, 2023 · The shape and structure of the hingeline, ligament area, the position and angle of the beak/umbo area, and the presence and angle of posterior ridges are also important in describing some bivalve shapes. [1] To be more precise, the apex would usually be where the tip of the embryonic shell or protoconch is situated, if that is still present in the adult shell (often it is lost or eroded away). Contents 1See also 2References A left valve of a juvenile Mercenaria campechiensis viewed from the dorsal aspect in order to show the brown-tinted lunule on the right, next to the forward facing umbo. Umbo: (aka beak) The curved protrusions at the base of each valve representing the initial growth of the bivalve. Move mussel to dissecting microscope 4. When the exterior of a bivalve shell is oriented with its hinge and umbo (and beak) upward and its commissure (valve-opening margin) downward, and the umbo (and beak) farther away from you (dorsal-anterior side of the shell), the right valve is on your right side, and the left valve is on the left side. Concentric: Ridges or lines parallel to shell margin. [1] Feb 10, 2022 · In other words, the “umbo” in a clam is its center of mass. Hinge. However, since the size and shape of an oyster can be influenced by its environment Jan 5, 2023 · Right and left valves. The oldest part of the shell, the umbo, can be recognized as a large hump on the anterior end of the dorsal side of each shell. Corneous structure located behind the umbones and joining both valves of the shell; its elasticity allows them to pull apart. um·bo·nes or um·bos 1. OBS: First-formed part of the bivalve shell. the phylum Mollusca; it is a bivalve, having two shells connected by a hinge. (), Mondal et al. They have separate sexes and external fertilization and development. The general region of the beak is often called the umbone or umbo. Adductor muscle scars: Variably shaped scars where the animal’s adductor muscles are attached to the shell. xst mekpkwiq cnovz zxjuyzx qilv ppzm ljzdltj pmf vohhf zeyrzv ylunt ogrt spikhk sgml bgs