On the Microanatomy of the Supraoesophageal Ganglion of Some Amphinomids (Polychaeta Errantia), with Further Discussion of the Innervation and Homologues of the Polychaete Palps

Earlier papers dealing with the anatomy of the amphinomid brain were studied. Discrepancies in the studied works prompted a re-investigation of the central nervous system of these animals. In this paper the brain commissures, the clusters of ganglion cells and the innervation of the antennae, the palps and the nuchal organs of Eurythoe complanata, Amphinome rostrata, Pherecardia striata, and Notopygos variabilis are described in some detail. The brain of Hermodice carunculata is studied more cursorily. The results, summarized in schematic diagrams, are compared with corresponding observations of the brains of ‘spiomorphic’ and ‘serpulimorphic’ polychaetes and to information given by earlier authors about structures in the Nereidiformia and Aphroditiformia. Using the major Remanian criteria for identifying homologies, equivalents in the amphinomid brain and the central nervous systems of some ‘sedentary’ and ‘errant’ families are proposed. As a consequence, some earlier opinions about the morphological value of the cephalic appendages of the amphinomids are strengthened while others are rejected. The necessity of further investigations of the polycheaete nervous system is emphasized.     

On the anatomy of the central nervous system and the morphological value of the anterior end appendages of Ampharetidae, Pectinariidae and Terebellidae (Polychaeta)

Earlier papers dealing with the anatomy of the central nervous system of ampharetids, pectinariids and terebellids were studied. On this basis a re‐investigation appeared necessary: statements in the literature about the structure of the brain and the innervation of the appendages of the anterior end were incomplete and contradictory. In the present paper, the brain, the circum‐oesophageal connectives and the innervation of, inter alia, the tentacular membrane (including the dorsal ridge), the buccal tentacles, the alimentary canal, the nuchal organs and the branchiae (when present) of Amphicteis gunneri, Anobothrus gracilis, Melinna cf. cristata, Pectinaria auricoma, P. belgica, P. koreni, Petta pusilla, Pista cristata, Eupolymnia nebulosa, Thelepus cincinnatus and Polycirrus medusa are described. The results are summarized in schematic diagrams and compared with each other and with the central nervous system of other polychaetes. It is concluded that the ampharetids, the pectinariids and the terebellids bear no antennae and no palps and that their buccal tentacles belong to the alimentary canal. It is emphasized that all attempts to range their cephalic nervous system into previously proposed common and general schemes of ‘the polychaete nervous system’ seem totally fruitless.     

On the Innervation and Homologues of the Anterior End Appendages of the Eunicea (Polychaeta), with a Tentative Outline of the Fundamental Constitution of the Cephalic Nervous System of the Polychaetes

Earlier papers dealing with the architecture of the cephalic nervous system of the Eunicea were studied. Thereby, a re-investigation appeared necessary: the existing literature proved insufficient for detailed comparisons with other polychaete families and many earlier statements and conclusions turned out to be quite contradictory, especially as concerns the homologues of the anterior end appendages. In the present paper, the microanatomy of the brain and the innervation of, inter alia, the antennae, the nuchal organs and the alimentary canal of Hyalinoecia tubicola, Nothria conchylega, Eunice norvegica and E. pennata are described. The results are summarized in schematic diagrams and tables and compared with corresponding observations in other polychaete families. Thereby, some earlier opinions about the morphological value of the cephalic appendages of the Eunicea are strengthened while others are rejected. On the basis of the present observations and earlier results arrived at by the present author, and as an object for future discussion and criticism, a diagram of the fundamental constitution of the cephalic nervous system of the Polychaeta is tentatively outlined.     

On the Microanatomy of the Cephalic Nervous System of Nereidae (Polychaeta), with a Preliminary Discussion of Some Earlier Theories on the Segmentation of the Polychaete Brain

Abstract Earlier papers dealing with the microanatomy of the nereid brain have been studied. On this basis a re-investigation of the cephalic nervous system and of the innervation and homologues of the anterior end appendages of these animals appeared necessary: the existing literature proved insufficient for detailed comparisons with other polychaete families and many earlier statements were quite contradictory. In the present paper, the brain commissures and the innervation of, inter alia, the antennae and the palps of Neanthes virens and Nereis pelagica are described. Special attention was paid to the roots of the circum-oesophageal connectives and the ganglia in this part of the nervous system. The results, summarized in schematic diagrams and tables, are compared with corresponding observations in 14 other polychaete families. In a discussion of the architecture of the polychaete nervous system as a phylogenetic instrument, the supposed segmentation of the polychaete brain is questioned and the idea that the configuration of the polychaete nervous system offers support to the cyclomer theory is rejected. Other conclusions concerning the relationships within the Polychaeta are pointed out.     

On the Anatomy of the Central Nervous System of Phyllodocidae (Polychaeta) and the Phylogeny of Phyllodocid Genera: a New Alternative

A reinvestigation of the central nervous system of the Phyllodocidae appeared necessary as the existing literature proved insufficient for detailed comparisons with other polychaete families. Many earlier opinions turned out to be quite contradictory, especially as concerns the morphological value of the anterior end appendages. In the present paper the microanatomy of the brain and the anterior ventral cord, as well as the innervation of, inter alia, the cephalic appendages, the nuchal organs and the alimentary canal of Eulalia viridis (main object of study), Eumida sanguinea, Pterocirrus macroceros, Sige fusigera, Eteone picta, E. foliosa, Phyllodoce groenlandica, P. longipes, P. mucosa, Paranaitis wahlbergi, Notophyllum foliosum and Nereiphylla lutea are described. The results are summarized in schematic diagrams and compared with corresponding observations on other polychaete families. Thereby, some earlier opinions about the nature of the cephalic appendages of the Phyllodocidae are strengthened while others are rejected. Most significantly, it is concluded that the so-called ventrolateral antennae of phyllodocids are homologous with the palps of other polychaetes and the median antenna found in certain genera is homologous with the nuchal papilla found in most other genera of the family. These partly new or revised characters and character states formed the basis for a reconsideration of earlier ideas about the phylogeny of the Phyllodocidae: a new alternative.     

Central nervous system and sense organs, with special reference to photoreceptor-like sensory elements, in Polygordius appendiculatus (Annelida), an interstitial polychaete with uncertain phylogenetic affinities

Abstract. The phylogenetic position of Polygordius is still pending; relationships with either Opheliidae or with Saccocirrus are the most favored hypotheses. The present study of Polygordius appendiculatus was designed to look for morphological characters supporting either of these two hypotheses. The homology of the anterior appendages, and the structure of the central nervous system and nuchal organ all required clarification; we also examined whether photoreceptor‐like sense organs exist in adults. From their innervation pattern, it is likely that the anterior appendages represent palps. They lack structures typical of palps in Canalipalpata, such as musculature and coelomic cavities, which would be expected in the case of a saccocirrid relationship. Thirteen photoreceptor‐like sense organs were found in front of the brain, the only structures resembling photoreceptors in adults of P. appendiculatus. These multicellular sense organs comprise a supportive cell and several sensory cells enclosing an extracellular cavity. There are three different types of sensory cells: one rhabdomeric and two ciliary. These sensory cells are combined differently into three forms of sense organ: the most frequent uses all three types of sensory cells, the second possesses one rhabdomeric and one ciliary cell type, and the third has two types of ciliary sensory cells. Whereas similar sensory cells are frequently found in various polychaetes, their combination in one sensory organ is unique to Polygordius and is considered to represent an autapomorphy. The nuchal organs exhibit features typical of polychaetes; there are no specific features in common with Saccocirrus. Instead, the covering structures show obvious similarities to Opheliidae, as can also be found in the central nervous system. Altogether, the current observations do not contradict a relationship with opheliids but provide no evidence of a relationship with Saccocirrus as has been found in certain molecular analyses, and thus currently leave the phylogenetic position of Polygordius unresolved.     

Structure of the prostomial appendages and the central nervous system in the Protodrilida (Polychaeta)

Summary The prostomial appendages and the central nervous system have been investigated by electron microscopy in Protodriloides chaetifer, P. symbioticus, Protodrilus haurakiensis, P. oculifer, P. ciliatus, P. helgolandicus, P. adhaerens, Saccocirrus krusadensis and S. papillocereus. The tentacles are highly developed, mobile sensory structures and consist of cuticle, epidermis, a different number of intraepithelial nerves, a small blind-ending blood vessel and a bundle of longitudinal muscle fibres. An internal canal is only present in Protodrilus and Saccocirrus species. On the tentacles seven types of sensory cells have been found including different multiciliated and uniciliated sensory cells with cilia penetrating the cuticle, sensory cells with non-penetrative cilia, phaosomes and basal ciliated sensory cells. The latter are described for the first time in polychaetes. From the specific pattern of innervation by up to five nerves originating close to the brain from the dorsal and ventral roots of the circumoesophageal connectives it is evident that the prostomial appendages represent palps. In the palps the nerve fibres form neuroneuronal, myoneuronal and epithelioneuronal synapses. The brain also gives rise to the stomatogastric nerves and various dorsal nerves. The palp canals are separated from the surrounding tissue by a prominent extracellular matrix. The wall is formed by muscle cells. The centre is usually completely filled with the cell bodies of these muscle fibres and large coelenchyme-like cells. These cells move freely in the canals and they are very likely the structural basis for the hydroskeletal function of the canals. The canals are completely separated from other body cavities and fluid is probably driven into the canals from the blood vascular system via podocytes located in a specific zone in the prostomium. In particular, the structure of the central nervous system with its nerves, the pattern of innervation of the palps and the palp canal system are compared with those of other polychaetes with special emphasis to the Spionida, the taxon presumed to include the sister group of the Protodrilida.     

On the Microanatomy of the Brain and the Innervation and Homologues of the Cephalic Appendages of Hesionidae and Syllidae (Polychaeta)

Abstract Earlier papers dealing with the anatomy of the hesionids and syllids were studied. Thereby it was found that information about the structure of the central nervous system was meagre. As a result, the anterior end appendages, especially the large, laterloventral ones of the Syllidae, have been differently interpreted. This prompted a re-investigation. The circum-oesophageal connectives, the brain commissures and the innervation of the alimentary canal and the cephalic appendages of a number of hesionid and syllid species were studied. The results, summarized in schematic diagrams, were compared with corresponding observations in other polychaete families. Among other things, it was concluded that not only the latero-ventral cephalic appendages of the hesionids but also those of the syllids are homologous with the palps of the nereids and of many other “errant” and “sedentary” families.     

The female postabdomen and genitalia of the basal moth family Heterobathmiidae (Insecta: Lepidoptera): Structure and phylogenetic significance

Female Heterobathmia have the segments behind VIII forming a compact ‘terminal unit’ with a large saddle-shaped dorsal plate and a membranous ventroposterior surface bearing the separate gonopore and anus. While females of most of the nine known species are overall similar, Heterobathmia valvifer is unique amongst lepidopterans in possessing paired ventral appendages (‘ovipositor valves’) arising from the intersegmental groove following segment VIII; evidence from musculature contradicts an interpretation of these appendages structures as ‘true’ ovipositor valves. The ventroposterior wall of the terminal unit in H. valvifer bears paired sclerites, possible homologues of the ‘ventral rods’ in basal Lepidoptera-Glossata. In Heterobathmia megadecella sclerites on paired longitudinal elevations in comparable positions probably are/include homologues of these sclerites. Their similarity with paired sclerotizations in the corresponding region of hydrobiosid caddisflies is noted. A prominent frame-like sclerotization in the genital chamber, located in front of the spermathecal duct origin, is present only in H. megadecella.Putative heterobathmiid autapomorphies include an enlarged ‘subgenital plate’ on venter VIII, absence of apophyses on segment VIII, shortened apophyses on the terminal unit, multilobed accessory glands (but their ‘type 1’ secretory epithelium is plesiomorphic at this level), a conspicuous papilla in the chamber cuticle bearing the opening of the ductus bursae on its apex, and inwards-pointing spines in the ductus bursae. A variably developed thickening of the anterior genital chamber intima is another putative family autapomorphy, while an extreme thickening of the posterior intima seen in Heterobathmia pseuderiocrania is not of general occurrence in heterobathmiids. A sistergroup relationship between Heterobathmiidae and Glossata is supported by their fully developed ‘2-compartment section’ of the spermathecal duct and losses of some likely lepidopteran groundplan muscles.     

The development of the nervous system in Laevicaudata (Crustacea, Branchiopoda): insights into the evolution and homologies of branchiopod limbs and ‘frontal organs’

We investigated the development of the external morphology and of the nervous system in Lynceus biformis and Lynceus brachyurus (Laevicaudata, Branchiopoda), by using immunohistochemical methods in combination with a confocal laser scanning analysis. In both Lynceus species, a free-swimming nauplius larva, equipped with three appendages, hatches from resting eggs. Despite their close phylogenetic relationship to each other, considerable differences are present in their external morphology. Hatching L. brachyurus larvae are equipped with a large and flattened labrum, where in contrast, the L. biformis larvae possess a smaller labrum with four conspicuous posteriorly directed spines at its margin. Despite these differences, the development of the nervous system is quite similar in both species. The hatching larvae are equipped with a naupliar nervous system, and only in the more advanced stages, the development of the ventral nerve cord starts. Furthermore, our investigation into the nervous system provided insights into architecture and evolution of protocerebral sensory organs, the dorsal setae field and the dorsal frontal organ, only present in Laevicaudata. The identification of frontal filaments with an associated frontal filament organ in Lynceus revealed—after a comprehensive comparison with other branchiopods—that these organs exist throughout Branchiopoda and are comparable to those in other crustaceans. Additionally, our results of the peripheral nervous system analysis showed that the innervation pattern of the naupliar appendages (antenna and mandible) and the trunk appendages could be serially homologized, despite much difference in gross morphology of these. Based on the innervation pattern of limbs, we suggest that the larval uniramous mandibular palp, found in the larvae of all ‘large’ branchiopods, is largely exopodal of nature (contrary to most earlier statements) and that the endopodite of the trunk limbs consists of only one distal endite-like segment (confirming some earlier statements) and not of three as proposed by others.     

The morphology and anatomy of the vestimentiferan worm <Emphasis Type="Italic">Oasisia alvinae</Emphasis> Jones, 1985 (Annelida: Siboglinidae). II. Integument,nervous system and musculature

The histological structure of the epidermis, nervous system, and musculature of the vestimentiferan worm Oasisia alvinae is examined. The differentiation of the integument of different regions of the body and the histological structure of the pyriform glands and papillae with cuticular plaques are described. All the main elements of the nervous system lie in the thickness of the epidermis. The brain structure is examined and an attempt is made to homologize parts of the vestimentiferan brain with the polychaete brain. Part of the vestimentiferan brain above the intrabrain channel corresponds to the supraesophageal ganglion of polychaetes, while part of the vestimentiferan brain under the channel corresponds to the subesophageal ganglion. Two commissures are located in the brain region that corresponds to the supraesophageal ganglion. These commissures could be related to the ventral and dorsal roots of the circumesophageal connectives of sedentary polychaetes. Bundles of fiber occur, which presumably correspond to the circumesophageal connectives and the transverse commissure inside the subesophageal ganglion. The musculature differentiation in the trunk region is a characteristic feature of O. alvinae, i.e., feather-like muscles that occur only in the anterior part of the trunk.     

A large new leanchoiliid from the Burgess Shale and the influence of inapplicable states on stem arthropod phylogeny

Characterized by atypical frontalmost appendages, leanchoiliids are early arthropods whose phylogenetic placement has been much debated. Morphological interpretations have differed, some of which concern critical characters such as the number of eyes and head appendages, but methodological approaches also have diverged. Here, we describe a new leanchoiliid, Yawunik kootenayi gen. et sp. nov., based on 42 specimens from the newly discovered Marble Canyon locality of the Burgess Shale (Kootenay National Park, British Columbia; middle Cambrian). This new morphotype demonstrates the presence of a four‐segmented head in leanchoiliids, along with two small antero‐median eyes in addition to lateral eyes. Yawunik is characterized by a 12‐segmented trunk and a carinate, lanceolate telson adorned with minute spines. The ‘great appendages’ of the animal bear teeth on their two distal rami, which would have enhanced their ability to grasp prey. Attitudes of specimens, resulting from burial at multiple aspects of bedding, suggest the ‘great appendages’ were flexible and capable of antero‐posterior rotation. We also discuss the nature of intersegmental tissues and filaments present within the ‘great appendages’. Our phylogenetic analyses extend the monophyly of leanchoiliids to include Haikoucaris and Yohoia in a new clade, the Cheiromorpha nom. nov. (within Heptopodomera nom. nov.). Other nodes are poorly resolved unless implied weights are used, and in this case, the topology is critically sensitive to the coding prerogative of inapplicable states (NAs). Both the traditional ‘Arachnomorpha’ hypothesis (NAs as additional states) and the more recently favoured ‘Artiopoda + Crustacea’ (NAs as uncertainties) were obtained using the same data set and outgroup. This result stresses, first, the historical importance of polarization over data content in scenarios of early arthropod evolution, and second, a pressing need to investigate the impacts of coding inapplicables, especially given the inflating effect of implied weights.     

A HEXAPOD FROM THE EARLY DEVONIAN WINDYFIELD CHERT, RHYNIE, SCOTLAND

Abstract: New diagnostic morphological features discovered following a re‐examination and further preparation of the holotype of Leverhulmia mariae Anderson and Trewin from the Early Devonian (Pragian) Windyfield chert are described and discussed here. The discovery of anterior (thoracic?) leg appendages with attached pretarsal elements comprising a fixed median unguis, a pair of articulated lateral ungues and possible unguitractor plate has allowed us to reclassify this enigmatic fossil as Hexapoda incertae sedis. We interpret the holotype as part of an abdomen bearing at least five pairs of segmented leglets. The condition of the ungues on the anterior appendages is strongly reminiscent of Archaeognatha and Zygentoma (= Thysanura s.s.), and the segmented leglets on the abdomen show similarities with certain fossil ‘apterygotes’ known from the Carboniferous. Leverhulmia is the third hexapod species found in the cherts at Rhynie, the other forms being the collembolan Rhyniella praecursor Hirst and Maulik, and the pterygote insect Rhyniognatha hirsti Tillyard. Showing closer affinities with Archaeognatha and Zygentoma, Leverhulmia may well represent the earliest fossil apterous insect known to date.     

Trends and patterns in the evolution of vascular plants: macroevolutionary implications of a multilevel taxonomic analysis

Cascales‐Miñana, B., Muñoz‐Bertomeu, J., Ros, R., Segura, J. 2010: Trends and patterns in the evolution of vascular plants: macroevolutionary implications of a multilevel taxonomic analysis. Lethaia, 10.1111/j.1502‐3931.2009.00212.x Studying the macroevolutionary patterns of vascular plants from the Silurian to the present‐day provides a global record of plant life history. Evolutionary rates (origination, extinction and diversification) for families, orders, classes and divisions were analysed, as was abundance and richness for 21 time intervals. An accumulative analysis, based on the total plant fossil record, the accumulated extinctions and relative diversity, was also carried out. The diversification rate shows a uniquely constant and progressive reduction from the end of the Carboniferous to the Permian when the lowest values are registered. Very small peaks seem to reflect Cretaceous extinction for families. At family level, only two time intervals present higher extinctions, than originations. Richness and accumulative analyses reveal that only 32% of the families analysed became extinct, and that approximately 90% of them disappeared at the end of the Palaeozoic. Our results indicate that plants did not undergo mass extinction events in the ‘big five’ sense, but rather, mass ecological reorganization the absence of important extinction events or evolutionary innovations producing diversification patterns without abrupt changes. □Diversification, evolutionary, extinction, fossil record, innovations, radiation, vascular plants.     

On the hoplonemertean Sagaminemertes nagaiensis (Iwata, 1957), with consideration of its systematics

Summary The polystiliferous hoplonemertean Sagaminemertes nagaiensis (Iwata, 1957) has been redescribed.A distinct pre-cerebral region is wanting. The rhynchocoel opens directly at the tip of the head, whilst the mouth opens seperately below the ventral commissure of the brain which is situated at the anterior end of the head. The dorsal ganglia are well developed and extend posteriorly far behind the ventral ganglia. The cerebral sense organs are situated behind the brain and possess posterior ciliated canals. Cephalic glands are poorly represented, but ocelli are well developed. The sickle-shaped basis of the proboscis bears about 20 central stylets. The caecal appendages of the rhynchocoel are arranged pseudometamerically throughout the body. The foregut is straight, consisting of mouth, oesophagus, stomach and pylorus. Intestinal caeca and lateral diverticula are present. The cephalic lacunae have no anterior anastomosis. A cerebral lacuna is present, there is a rhynchocoel vessel, but transverse vessels are absent. The protonephridia extend throughout the foregut region. Mature spermatogonia are well developed.A systematic discussion of Sagaminemertes nagaiensis suggests that it is taxonomically close to Siboganemertes weberi in the archireptantic family Siboganemertidae.     

Convergent camouflage and the non‐monophyly of ‘seadragons’ (Syngnathidae: Teleostei): suggestions for a revised taxonomy of syngnathids

Wilson, N. G. & Rouse, G. W. (2010). Convergent camouflage and the non‐monophyly of ‘seadragons’ (Syngnathidae: Teleostei): suggestions for a revised taxonomy of syngnathids. —Zoologica Scripta, 39, 551–558. The phylogeny and classification of the charismatic Syngnathidae (e.g. pipefish, seahorses) has not been comprehensively examined to date. In particular, we assessed morphological hypotheses that previously suggested the three ‘seadragon’ genera (Phycodurus, Phyllopteryx, Haliichthys) do not form a monophyletic group. We used three mitochondrial markers to investigate evolutionary relationships within Syngnathidae, and demonstrated that Phycodurus + Phyllopteryx formed a clade that excluded Haliichthys, indicating the elaborate appendages used for camouflage have evolved independently. A time‐calibrated tree revealed the divergence of true seadragons as coincident with other kelp‐associated fauna. We found evidence for the resurrection of neglected subfamily names, and recovered Doryrhampinae, Nerophinae, Soleganthinae, Phyllopteryginae, Sygnathoidinae and Haliichthyinae as clades. Even after removing these groups from what is currently recognized as Syngnathinae, we showed that the remaining members of Syngnathinae are not monophyletic. In the light of this information, some conclusions about the diversity of reproductive strategies found within ‘Syngnathinae’ need to be re‐examined and further revision of syngnathid classification is needed.     

Synaptic and Synaptoid Vesicles Constitute a Single Category of Inclusions: New Evidence From Invertebrate Nervous Systems

Parallel observations on synaptic and neurohaemal terminals in the polychaete annelids Nereis diversicolor and Harmothoe imbricata have revealed a remarkable identity of ultrastructure. Even features peculiar to the synaptic vesicles of polychaetes are mirrored by those of synaptoid inclusions. A wide range of terminal types show a clear duality of secretory inclusions, featuring both ‘storage granules’ and synaptic/synaptoid vesicles. The inclusions exhibit a marked zonation. Vesicles form tight clusters with interstitial dense material in many terminals and these make contact with release sites. Terminals containing larger, typically peptidergic granules often have mainly dense-cored synaptic/synaptoid vesicles, although some such inclusions are present in other endings also. A variety of synaptic associations are present, and ‘serial synaptoids’ are formed by neurohaemal terminals. The results are interpreted to suggest that synaptic and synaptoid vesicles have a common functional significance.     

The GAIF-Positive Population of Neurons in the Evolution of the Temnocephalida

The nervous system of three species of the Temnocephalida has been studied using the GAIF method (which in small flatworms mostly reveals sensory catecholaminergic neurons). These species represent the evolution from the primitive “turbellarian-like” temnocephalids to the most specialised ones with tentacles and a sucker. The numbers and positions of GAIF-positive neurons are invariant within each species and do not change from hatching to full maturity. A characteristic unpaired neuron contributing to the innervation of the anterior margin of the body is present in all species: such a cell has previously been found only in marine Thalassovortex tyrrhenicus (Dalyellidae) which confirms close relationships between these taxa. Our series of species shows (i) a reduction in number of GAIF-positive perikarya associated with the lateral cords and reduction of GAIF-positive innervation on the ventral side of the body, which is probably related to the loss of ciliary locomotion (the shift to passive hunting and looping locomotion) and (ii) reinforcement of the GAIF-positive innervation of the anterior end of the body which begins to play an important role in capturing the prey. The retention of the medial unpaired neuron and nearly identical sets of GAIF-positive neurons in Diceratocephala boschmai and Craspedella pedum (rather different in morphology) give the first indication (in the Plathelminthes) of persistence of homologous neurons through significant evolutionary transformations of the organs they innervate.     

Divergence of 3′ ends as a driver of short interspersed nuclear element (SINE) evolution in the Salicaceae

Short interspersed nuclear elements (SINEs) are small, non‐autonomous and heterogeneous retrotransposons that are widespread in plants. To explore the amplification dynamics and evolutionary history of SINE populations in representative deciduous tree species, we analyzed the genomes of the six following Salicaceae species: Populus deltoides, Populus euphratica, Populus tremula, Populus tremuloides, Populus trichocarpa, and Salix purpurea. We identified 11 Salicaceae SINE families (SaliS‐I to SaliS‐XI), comprising 27 077 full‐length copies. Most of these families harbor segmental similarities, providing evidence for SINE emergence by reshuffling or heterodimerization. We observed two SINE groups, differing in phylogenetic distribution pattern, similarity and 3′ end structure. These groups probably emerged during the ‘salicoid duplication’ (~65 million years ago) in the Salix–Populus progenitor and during the separation of the genus Salix (45–65 million years ago), respectively. In contrast to conserved 5′ start motifs across species and SINE families, the 3′ ends are highly variable in sequence and length. This extraordinary 3′‐end variability results from mutations in the poly(A) tail, which were fixed by subsequent amplificational bursts. We show that the dissemination of newly evolved 3′ ends is accomplished by a displacement of older motifs, leading to various 3′‐end subpopulations within the SaliS families.