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Characteristics of brachiopods - Bryozoan Devonian Foraminifera Ordovician Permian Silurian Fossil Reef

May 1, 2017 · However, the ecological characteristics of brachiopod faunas immediately after

Brachiopods and molluscs are lophotrochozoans with hard external shells which are often believed to have evolved convergently. While palaeontological data indicate that both groups are descended from biomineralising Cambrian ancestors, the closest relatives of brachiopods, phoronids and bryozoans, are mineralised to a much lower …Simply put, a lophophorate is any organism that bears a lophophore. This is a pair of spiral feeding structures that form a crown on the head superficially similar to the feeding tentacles of feather-duster worms. Traditionally the lophophorates include the brachiopods or lampshells, the bryozoans or moss-animals, and the phoronids as well as ...Brachiopods, or lampshells, are a phylum of small marine animals with a two-valved shell that, at first glance, resemble bivalved mollusks such as clams.Three of the main characteristics of bivalves are: 1. Two equally sized shells that close together for protection using muscles. ... Brachiopods are similar to bivalves but with a few deviations ... Blank 3: Ectoprocta. Select all the phyla that belong to Clade Brachiozoa. Nemertea. Brachiopoda. Phoronida. Within the Lophotrochozoa, Annelida and Mollusca are all members of Clade ______. Trochozoa. Members of the clade Trochozoa are named because they have a modified ______. trochophore larvae. Characteristics of Brachiopoda: Body has more than two cell layers, tissues and organs. Body cavity a true coelom. Body possesses a U-shaped gut with or without an anus. Body enclosed in a pair of shells, one dorsal and the other ventral.General characteristics They are triblastic and coelomed They are protostomados Longevity Behavior Feeding Morphology Valves Loptophore Internal anatomy Circulatory system Digestive system Excretory system Nervous system Habitat Reproduction Fertilization and embryonic development Articulated Unarticulated Classification Articulata ClassThe two classes of brachiopods are distinguished by the way the two shells fit together and the mechanism for opening and closing them. Articulated brachiopods ...Terms in this set (20) Archaeocyathids were characterized by a strong single-walled structure. False. Fossil forms of crinoids occupied deep marine habitats. False. The shell morphology of brachiopods can tell us about their general environment. True. All Cnidarians have radial symmetry and stinging cells. True. the Brachiopoda, the Bryozoa, and the Phoronida. The lophophore can most easily be described as a ring of tentacles, but it is often horseshoe-shaped or coiled. Phoronids have their lophophores in plain view, as shown above, but brachiopods like the one below must be opened wide in order to get a good view of their lophophore. This result demonstrates that the occurrence of these peculiar rhynchonellide brachiopods in South China, regardless of the depositional environments, is within the Lower Famennian instead of the previously suggested Upper Famennian. ... Conodonts from the rest part of the section are characteristics of the Upper rhomboidea Zone with …Brachiopod Fossils. The most common seashells at the beach today are bivalves: clams, oysters, scallops, and mussels. However, from the Cambrian to the Permian (542 to 252 million years ago), another group of organisms called brachiopods dominated the world's oceans. Over 12,000 fossil species of these hinge-valved organisms have been described ...Chapter contents: 1.Brachiopoda –– 1.1 Brachiopod Classification–– 1.2 Brachiopods vs. Bivalves←–– 1.3 Brachiopod Paleoecology –– 1.4 Brachiopod Preservation Above image: Left, Brachiopod Paraspirifer brownockeri on exhibit in the Houston Museum of Natural Science, Houston, Texas. Image by "Daderot" (Wikimedia Commons; Creative Commons CC0 1.0 Universal Public Domain ... the Brachiopoda, the Bryozoa, and the Phoronida. The lophophore can most easily be described as a ring of tentacles, but it is often horseshoe-shaped or coiled. Phoronids have their lophophores in plain view, as shown above, but brachiopods like the one below must be opened wide in order to get a good view of their lophophore.Conservation Biology 24m. Brachiopoda is a phylum within the Lophotrochozoa. Even though they are not closely related to bivalve mollusks (such as clams or mussels), brachiopods look and act like bivalve mollusks. Specifically, brachiopods suspension feed, secrete calcium carbonate shells with two valves that hinge together in some species, …Jan 12, 2021 ... 1.1: Shells of brachiopods showing external morphology: a) dorsal view; and b) side view. Fig. 1.2: Dorsal view of a brachiopod shell ...Brachiopod fossils have been useful indicators of climate changes during the Paleozoic era. They do look rather like bivalves, but their internal organisation is quite different. Their mostly calcium carbonate shells or "valves" have upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear …Bryozoan Devonian Foraminifera Ordovician Permian Silurian Fossil Reef Terrane Add to Mendeley About this page Volume 3 Jun Chen, Shuzhong Shen, in Encyclopedia of Geology (Second Edition), 2021 Brachiopods Brachiopods are one of the major fossil groups involved in the discussion of the end-Guadalupian mass extinction.At least 3,500 living species and 15,000 fossil species are known. Bryozoans are small animals (just large enough to be seen with the naked eye) that live exclusively in colonies. In fact, the Phylum Bryozoa is the only animal phylum in which all known species form colonies. The name comes from two Greek words, bryon (moss) and zoon (animal ...Study with Quizlet and memorize flashcards containing terms like What is a trochophore? Draw and label a diagram of a trochophore including important morphology. Finally list and discuss the taxa that have a trochophore and taxa that have something that resembles a trochophore., Briefly describe characteristics of the hypothetical ancestral mollusk, and tell how each class of molluscs differs ... The key characteristics of each subphylum are outlined in Table 1. In addition, each possesses a double row of tentacles throughout their ontogeny, which was previously considered to be an apomorphic feature of linguliform brachiopods (Holmer et al. 1995; Williams et al. 1997). Emig (in Zhang et al.In that time, the first undoubted fossil annelids, arthropods, brachiopods, echinoderms, molluscs, onychophorans, poriferans, and priapulids show up in rocks all over the world. Stratigraphic boundaries are generally determined by the occurences of fossils. For instance, the trace fossil Treptichnus pedum marks the base of the Cambrian. This …Brachiopoda: [plural noun] a phylum of invertebrates that has persisted with reduced numbers from the Lower Cambrian to the present and that consists of sedentary unsegmented marine animals with well-developed coelom and hemocoel, a lophophore, and often a fleshy stalk extending into the substrate, the body being enclosed in a bivalve ...the Brachiopoda, the Bryozoa, and the Phoronida. The lophophore can most easily be described as a ring of tentacles, but it is often horseshoe-shaped or coiled. Phoronids have their lophophores in plain view, as shown above, but brachiopods like the one below must be opened wide in order to get a good view of their lophophore.Examination of compositional heterogeneity revealed that Polyzoa, Brachiopoda |$+$| Phoronida, and Kryptrochozoa (Giribet et al. 2009; a hypothesized grouping of Brachiopoda, Phoronida, and Nemertea) were supported by characters with apparently deviant amino acid compositions, whereas there was no indication for …A Modern Day Brachiopod. Brachiopods are an ancient group of organisms, at least 600 million years old. They might just look like clams, but they are not even closely related. Instead of being horizontally symmetrical along their hinge, like clams and other bivalves, they are vertically symmetrical, cut down the middle of their shell. Brachiopod fossils are often well-preserved, as well as being abundant and exhibiting diverse shell morphology (i.e., a variety of shell shapes) over time. Because of these characteristics and their long presence in the geologic record, they are perhaps the best index fossil for correlation and relative time dating.Description. Members of the Branchiopoda are unified by the presence of gills on many of the animals' appendages, including some of the mouthparts.This is also responsible for the name of the group (from the Ancient Greek: βράγχια, gills, akin to βρόγχος, windpipe; Greek: πούς, foot). They generally possess compound eyes and a carapace, which may be a …Apr 10, 2021 · The main characteristic of brachiopods is that they are made up of two valves, placed in such a way that one goes up and the other goes down. Its size is variable, there are from 5mm to more than 80mm. Even fossils have been found that measure 38 cm. The valves or shells are secreted by the mantle. Dictyoclostus, genus of extinct brachiopods, or lamp shells, that were common invertebrate forms in the shallow seas of North America from the Carboniferous to the Permian periods (between 359 million and 251 million years ago). Dictyoclostus often grew to large size. Its distinctive shell is concavo-convex and is frequently highly ornamented …Lab #3: Brachiopods and Bryozoans. Identify a fossil as an articulate brachiopod, inarticulate brachiopod, or bryozoan. Be able to determine the order of an articulate brachiopod using the chart below. Know the skeletal structure and material of each of these animals. Know the ecological characteristics of each of these animals.Brachiopoda: Subphylum: Rhynchonelliformea: Class: Rhynchonellata: Orders See text The Rhynchonellata is a class of Lower Cambrian to Recent articulate brachiopods that combines orders from within the Rhynchonelliformea (Articulata revised) with well developed pedicle attachment. Shell forms vary from those with wide hinge lines to beaked forms …For example, a previously classified group of animals called lophophorates, which included brachiopods and bryozoans, were long-thought to be primitive deuterostomes. Extensive molecular analysis using rRNA data found these animals are actually protostomes, more closely related to annelids and mollusks.SN#101022736 Brachiopoda and Bivalvia ERTH2312A Earth Sciences, Carleton University Page 1 Abstract The Brachiopoda phylum is compared to the Bivalvia class. An attempt is made at explaining what could have influenced their morphology as well as to explore what similarities and differences these two groups exhibit.Phylum: Brachiopoda ("ArmFoot") Habitat: deep ocean and caves Age: Early Cambrian 545 million years ago to present Size: 0.5 to 4 inches (1.25 to 10 centimenters) Number of Living Species: about 300 Characteristics: filter-feeder, uses lophophore to catch prey, covered by two shells. Stumper. Brachiopods spend most of their time: buried deep in ...The Independent Financial Portal Financial Web reports that though all contracts have certain basic elements, insurance contracts usually have certain characteristics that are not usually found in other kinds of contractual agreements. Some...The Cambrian Explosion by nature is a three-phased explosion of animal body plans alongside episodic biomineralization, pulsed change of generic diversity, body size variation, and progressive increase of ecosystem complexity. The Cambrian was a time of crown groups nested by numbers of stem groups with a high-rank taxonomy of …lophophorate, any of three phyla of aquatic invertebrate animals that possess a lophophore, a fan of ciliated tentacles around the mouth. Movements of the cilia create currents of water that carry food particles toward the mouth. The lophophorates include the moss animals (phylum Bryozoa), lamp shells (phylum Brachiopoda), and phoronid …Distinguishing features of a branchiopod include a small body (0.25 mm - 10 cm long), paired compound eyes, single simple eye, simple mouth parts, leaflike or phyllopodous appendages, …Traditional classification: inarticulates vs. articulates Inarticulates: shells lack defined hinges and are made of calcium phosphate (phosphatic). Example: Order Lingulida. Articlulates: shells with articulated hinges (with teeth and sockets) and made of calcium carbonate. Examples: all brachiopods other than Lingulida.Brachiopod fossils show great diversity in the morphology of the shells and lophophore, while the modern genera show less diversity but provide soft-bodied characteristics. Both fossils and extant species have limitations that make it difficult to produce a comprehensive classification of brachiopods based on morphology.Characteristics of Microorganisms. Microorganisms are the smallest organisms on Earth. In fact, the term microorganism literally means "microscopic organism." Microorganisms may be composed of prokaryotic or eukaryotic cells, and they may be single-celled or multicellular. Examples of microorganisms include algae, fungi, …True or false: All members of the phylum Nematoda are parasites on plants or animals. Hookworms, most of the genus Necator, suck blood through the _______ wall of humans, causing anemia. Which of the following are disease-causing nematodes in humans? McGraw Hill Connect Learn with flashcards, games, and more — for free.Brachiopods are marine animals that, upon first glance, look like clams. They are actually quite different from clams in their anatomy, and they are not closely related to the molluscs. They are lophophorates, and so are related to the Bryozoa and Phoronida. Although they seem rare in today's seas, they are actually fairly common. Introduction. Lophotrochozoa is a monophyletic group of animals that includes annelids, molluscs, bryozoans, brachiopods, platyhelminthes, and other animals that descended from the common ancestor of these organisms. Lophotrochozoa is one of the three major clades that comprise bilateral animals, or Bilateria.a–d, Proposed relationships of the five major clades of lophotrochozoans.a, Kryptrochozoa hypothesis (monophyly of Nemertea, Phoronida and Brachiopoda).b, Nemertea as a sister group to other ...Brachiopods are solitary creatures that inhabit the seafloor across a variety of habitats. Because they are sessile (unmoving), they filter food particles and nutrients out of the water. Like many marine invertebrates, brachiopods have …Branchiopoda. By Judy Follo and Daphne G. Fautin. Ap­prox­i­mately 800 species of bran­chiopods are found world­wide in fresh­wa­ter ponds, lakes, and in­land saline wa­ters such as the Great Salt Lake in Utah. Their fos­sil record in­cludes the ex­tinct order Li­pos­traca and dates back to the De­von­ian pe­riod (ap­prox­i ...Characteristics of Sustainable Living Communities - Sustainable living communities aim to minimize waste, reduce consumption and preserve open space. See what sustainable living communities are like. Advertisement Sustainable communities ge...Morphology. The Branchiopoda are separated as a distinct class of Crustacea based primarily on the form of the larvae, which eclose as a nauplius or metanauplius. The larvae have reduced, undifferentiated first antennae, the second antennae are elongated and used for swimming, and the mandible is uniramous.GENERAL CHARACTERISTICS. -Brachiopods are bilaterally symmetrical animals that have been marine creaturs through out their history. -They are filter feeding animals. -Most lived in marine conditions, but some were tolerable of brackish waters. They preferred tropical to sub-tropical climates. -They often lived attached to the sea floor or they ... Lamp shells and relatives (brachiopods) are marine animals that are one of the world's oldest forms of multicellular organisms. Although no longer numerous ...Characteristic Features of Brachiopods: 1. Exclusively marine and are found in all seas from the intertidal zone to the deep sea (about 5000 meters). 2.True or false: All members of the phylum Nematoda are parasites on plants or animals. Hookworms, most of the genus Necator, suck blood through the _______ wall of humans, causing anemia. Which of the following are disease-causing nematodes in humans? McGraw Hill Connect Learn with flashcards, games, and more — for free.Lamp shells and relatives (brachiopods) are marine animals that are one of the world's oldest forms of multicellular organisms. Although no longer numerous ...Diversity. Phylum Bryozoa (or Bryozoa), commonly known as “moss animals”, includes over 5,000 currently recognized species (with over 5,000 additional, extinct forms known) of sessile, almost exclusively colonial (only one solitary species, Monobryozoon ambulans, is known), coelomate organisms that superficially resemble soft coral polyps.Based on newly collected material from the lower Famennian Aramazdospirifer orbelianus brachiopod zone (coeval to the Palmatolepis crepida conodont zone) of Armenia, we here introduce two new cyrtospiriferid genera and fully document their type species, including their intraspecific variability.Brachiopod fossils are commonly preserved in three main ways: Unaltered remains, internal molds, or external molds (learn more about fossil preservation here). Unaltered remains preserve the original shell as if you picked it up off the ocean floor. Internal molds preserve the inside of the shell including internal supports, hinge characteristics, and …Brachiopods (ToL: Brachiopoda<Lophotrochozoa<Bilateria<Metazoa<Eukaryota) Brachiopods. Brachiopods were an important part of the marine fauna for the last time during the Permian, bordering on extinction ever since. Multiple specimens of three species represent brachiopods in …The key characteristics of each subphylum are outlined in Table 1. In addition, each possesses a double row of tentacles throughout their ontogeny, which was previously considered to be an apomorphic feature of linguliform brachiopods (Holmer et al. 1995; Williams et al. 1997). Emig (in Zhang et al.Brachiopods still exist today, but are much less common than clams (bivalves) and very rarely found as seashells on the beach. In the Paleozoic Era, however, brachiopods were abundant and far outnumbered the shells of clams and snails living in the sea. Brachiopods are common fossils in Ordovician, Silurian, Devonian, Mississippian, …Feb 1, 2019 ... Details of shell microstructural features, such as thickness of the primary layer, density and size of endopunctae and morphology of the basic ...Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) [6] are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about 0.5 millimetres ( 1⁄64 in) long, they have a special feeding structure called a lophophore, a "crown" of tentacles used for filter feeding.Ladogia sp., a rhynchonellid brachiopod from the Devonian of western Russia (side view). The taxonomic order Rhynchonellida is one of the two main groups of living articulate brachiopods, the other being the order Terebratulida. They are recognized by their strongly ribbed wedge-shaped or nut-like shells, and the very short hinge line.Moreover, understanding the ecological and evolutionary characteristics of this genus may hold valuable lessons relevant to identifying potential survivors of ...photo A Modern Day Brachiopod Brachiopods are an ancient group of organisms, at least 600 million years old. They might just look like clams, but they are not even closely related. Instead of being horizontally symmetrical along their hinge, like clams and other bivalves, they are vertically symmetrical, cut down the middle of their shell.Brachiopods range in size from 1 mm to 9 cm in length, and all known species are solitary, benthic, marine animals with a two part shell (valve); the valves of Inarticulataspecies are attached only by muscles, while the valves of Articulataspecies have a tooth-and-socket hinge.In this article, we’ll explore the key characteristics of brachiopods and bivalves, and compare and contrast the two. Let’s define our terms. Brachiopods and bivalves are both types of mollusks, but they belong to different classes. Brachiopods are members of the class Brachiopoda, while bivalves belong to the class Bivalvia. Highlights. •. Morphospace occupation of lingulid brachiopods through the Phanerozoic. •. Maximum morphospace occupation was achieved by the Early Ordovician. •. End Ordovician and Permian mass extinctions impacted morphological diversity. •. The shift to infaunal forms likely reflects historical contingency events.This result demonstrates that the occurrence of these peculiar rhynchonellide brachiopods in South China, regardless of the depositional environments, is within the Lower Famennian instead of the previously suggested Upper Famennian. ... Conodonts from the rest part of the section are characteristics of the Upper rhomboidea Zone with …In brachiopods, this ancestral type of lophophore changed due to the appearance of a double row of tentacles ... According to Table 1, at least nine characteristics (1a,3,6,7b,10,11,14,15,17) are similar in craniiforms and rhynchonelliforms, whereas only six features (1b,5,8,9,13,18) are shared by craniiforms and linguliforms. …The brachiopod shell is a multilayered complex of both organic and inorganic material that has proven to be of fundamental importance in the classification of the phylum. The shells of most rhynchonelliformean brachiopods consist of three layers (Figure 4). The outer layer (periostracum) is organic, whereas underneath are the mineralized ...Brachiopods, or lamp-shells, are a highly characteristic group of benthic, marine organisms. The two valves, usually called dorsal and ventral (but see discussion below) make both living and extinct brachiopods immediately recognizable. Nearly 400 living and over 12 000 fossil species have been recognized, with the fossil record going back to ...Lophotrochozoa, Diversification of. K.M. Halanych, in Encyclopedia of Evolutionary Biology, 2016 Introduction. Lophotrochozoa is a monophyletic group of animals that includes annelids, molluscs, bryozoans, brachiopods, platyhelminthes, and other animals that descended from the common ancestor of these organisms. Lophotrochozoa is one …Brachiopods are bivalved, sessile, occasionally infaunal or interstitial, generally epifaunal or epibenthic protostomes. They were among the earliest mineralised fossils in the Lower Cambrian and have an excellent, continuous fossil record. ... and would be worse if the Zhanatellidae, which share some characteristics with discinids and …Inferred crown group brachiopod and mollusc species (n = 76) do not appear until the Fortunian, ~537 Ma, radiate in the early Cambrian Stage 3 (~522 Ma), and with minimal loss of diversity at the ...Lophotrochozoa, Diversification of. K.M. Halanych, in Encyclopedia of Evolutionary Biology, 2016 Introduction. Lophotrochozoa is a monophyletic group of animals that includes annelids, molluscs, bryozoans, brachiopods, platyhelminthes, and other animals that descended from the common ancestor of these organisms.For example, a previously classified group of animals called lophophorates, which included brachiopods and bryozoans, were long-thought to be primitive deuterostomes. Extensive molecular analysis using rRNA data found these animals are actually protostomes, more closely related to annelids and mollusks.Study with Quizlet and memorize flashcards containing terms like Archaeocyathids were characterized by a strong single-walled structure., Fossil forms of crinoids occupied deep marine habitats., The shell morphology of brachiopods can tell us about their general environment. and more.Articulate brachiopods have toothed hinges and simple, vertically oriented opening and closing muscles. Conversely, inarticulate brachiopods have weak, untoothed hinges and a more complex system of vertical and oblique (diagonal) muscles used to keep the two valves aligned.Apr 26, 2021 ... The filter-feeding organ of some extinct brachiopods is supported by a skeletal apparatus called the brachidium.As a result, fossil brachiopods are frequently found with both sides together. This is different from the bivalves introduced in the next section. Brachiopod shells vary greatly in shape and …The brachiopod is a type of shellfish that is related to the clam. It is also known as the lampshell. The Brachiopoda, or arm and foot, is a major invertebrate phylum (from Latin bracchium, arm and new Latin -pods, foot). sessile marine animals with bivalve-like external morphology, both of which have two shells.Jun 27, 2017 · The key characteristics of each subphylum are outlined in Table 1. In addition, each possesses a double row of tentacles throughout their ontogeny, which was previously considered to be an apomorphic feature of linguliform brachiopods (Holmer et al. 1995; Williams et al. 1997). Emig (in Zhang et al. Highlights. •. Morphospace occupation of lingulid brachiopods through the Phanerozoic. •. Maximum morphospace occupation was achieved by the Early Ordovician. •. End Ordovician and Permian mass extinctions impacted morphological diversity. •. The shift to infaunal forms likely reflects historical contingency events.Branchiopods are generally regarded as primitiveChapter contents: 1.Brachiopoda –– 1.1 Brachiopod Classification–– 1.2 Brachiopods vs. Bivalves←–– 1.3 Brachiopod Paleoecology –– 1.4 Brachiopod Preservation Above image: Left, Brachiopod Paraspirifer brownockeri on exhibit in the Houston Museum of Natural Science, Houston, Texas. Image by "Daderot" (Wikimedia Commons; Creative Commons CC0 1.0 Universal Public Domain ... Apr 10, 2020 ... Brachiopod is a group of lophotrochozan animals that have shells both on the upper and lower surfaces. Brachiopods range from 0.039 to 3.937 ...Articulata (Articulate lampshells) Phylum Brachiopoda. Class Articulata. Number of families 20. Thumbnail description Brachiopods that live within a rounded, hinged, and mostly calcareous shell composed of two bilaterally symmetrical but dissimilar valves, and that generally attach themselves to hard substrates with a pedicle (foot-like structure) supported by connective tissue Three of the main characteristics of bivalves are: 1. Two equally sized shells that close together for protection using muscles. ... Brachiopods are similar to bivalves but with a few deviations ... Key words: brachiopod, Cambrian, Ordovician, phylogeny, diversity. OUR current understanding of the Cambrian origin and early history of the brachiopods is far from complete; nonetheless the Brachiopoda provides a rich source of data for addressing major research questions relevant to their evolution and that of other invertebrate phyla.Brachiopods possess a primitive heart with an open circulatory system. They have blood channels to supply necessary parts of the body with nutrients. The blood system is responsible for the circulation of digested food, while oxygen transport is the reponsibility of the coelomic fluid. Some Interesting Facts: Brachiopods feed by means of a …Brachiopoda (lampshells) A phylum of solitary, benthic, marine, bivalved, coeloma, Characteristic Features of Brachiopods: 1. Exclusiv, Brachiopod Fossils. The most common seashells at the beach today are bivalves: cl, May 21, 2019 · Archaea: Structure, Characteristics & Domain. Archaea , Brachiopod fossils have been useful indicators of climate changes during the Paleozoic era. They do look , Brachiopods have one of the longest fossil records of any multicellular animal. Brachiopod, Brachiopoda [edit | edit source] Brachiopod Isocrania costata., ical characteristics enable organisms to obtain a new leve, "CHARACTERISTICS OF BRACHIOPODS" Brachiopods are ex, a–d, Proposed relationships of the five major clades of lop, 8 days ago ... Articulate brachiopods have toothed hinges , However, the ecological characteristics of brachiopo, Brachiopoda is a phylum within the Lophotrochozoa. Even though th, Givetian through middle Famennian brachiopods of Hunan are used to , Analogous Structures Examples. A bird’s wing and an insect’s wing ar, As with brachiopods and phoronids, bryozoans possess a peculi, Clams and other bivalves share some characteristics with brachiopo, Inarticulated brachiopods two adductor muscles, each divided dor.