Note on Lepidosiren annectens,Owen.

Refeering to Prof. Owen's paper on Lepidosiren in the 18th volume of the Society's “Transactions,” the author states that the conclusion at which that gentleman has arrived, that the animal in question is a Pish, although controverted by some of our best naturalists, appears to him to receive confirmation from one or two points in its structure on which no great stress has hitherto been laid. The first of these relates to the mode in which the gill is covered, having only a single small external opening, in which respect Lepidosiren makes a very near approach to Muræna. Secondly, the two peculiar anterior teeth in the upper jaw 80 closely resemble those of some Fishes, that the vignette representing these teeth in Echiodon Drummondii, given in Mr. Yarrell's “History of British Fishes,” might serve as well for the front teeth of Lepidosiren. Thirdly, the continuous dorsal, caudal and anal fin, and the absence of pectorals and ventrals, are common characters among Murænidæ. And fourthly, the true Fish-scales, together with the lateral line extending from the gill to the extremity of the tail, are characters peculiar to Fishes, and not to be found among Amphibian Beptiles. Assuming then that Lepidosiren is unquestionably a Fish, and not either a Reptile or an osculant between Fishes and Reptiles, Mr. Newman regards it as completely obliterating the boundary set up by Cuvier between the two great subclasses of Fishes, the Osseous and the Cartilaginous. In support of this opinion he quotes several passages from Prof. Owen's paper, and concludes by stating his conviction that it is “equally impossible to place it in either the Cartilaginous or Osseous series; and we are compelled either to establish an intermediate series, consisting of but three species or perhaps genera, or to break up those great divisions, which have received the almost universal approbation of naturalists. The first course seems most undesirable in an age in which we are exerting ourselves to find associates and allies for every abnormal form, however apparently isolated. The alternative, the mingling of cartilaginous and osseous fishes, seems inevitable.”     

Very low pressures drive ventilatory flow in chimaeroid fishes

Chimaera (Holocephali) are cartilaginous fishes with flexible operculi rather than external gill slits, suggesting ventilation occurs in a manner different from other fishes. We examined holocephalan ventilation morphology, behavior, and performance by anatomical investigations, high‐speed video, and in vivo pressure measurements from the buccal and parabranchial cranial cavities in Hydrolagus colliei and Callorhinchus callorynchus. Ventilatory modes ranged from quiet resting breathing to rapid “active” breathing, yet external cranial movements—excepting the passive movement of the opercular flap—were always extremely subtle, and pressures generated were one to two orders of magnitude lower than those of other fishes. To explain ventilation with such minimal pressure generation and cranial motion, we propose an “accordion” model, whereby rostrocaudal movement of the visceral arches drives pressure differentials, albeit with little lateral or ventral movement. Chimaeroids have comparatively large oropharyngeal cavities, which can move fluid with a smaller linear dimension change than the comparatively smaller cavities of other fishes. Orobranchial pressures are often less than parabranchial pressures, suggesting flow in the “wrong” direction; however, the long gill curtains of chimaeroids may passively restrict backflow. We suggest that constraints on holocephalan jaw and hyoid movements were compensated for evolutionarily by novel visceral arch mechanics and kinematics. J. Morphol., 2012. © 2011 Wiley Periodicals, Inc.     

An updated classification for the hyper-diverse genus Corydalis (Papaveraceae: Fumarioideae) based on phylogenomic and morphological evidence

The genus Corydalis, with ca. 530 species, has long been considered taxonomically challenging because of its great variability. Previous molecular analyses, based on a few molecular markers and incomplete taxonomic sampling, were clearly inadequate to delimit sections and subgenera. We have performed phylogenetic analyses of Corydalis and related taxa, using 65 shared protein-coding plastid genes from 313 accessions (including 280 samples of ca. 226 species of Corydalis) and 152 universal low-copy nuclear genes from 296 accessions (including 271 samples of Corydalis) covering all 42 previously recognized sections and five independent “series”. Phylogenetic trees were inferred using Bayesian Inference and Maximum Likelihood. Eight selected morphological characters were estimated using ancestral state reconstructions. Results include: (i) of the three subgenera of Corydalis, two are fully supported by both the plastid and nuclear data; the third, subg. Cremnocapnos, is weakly supported by plastid DNA only, whereas in the nuclear data the two included sections form successive outgroups to the rest of the genus; (ii) among all 42 sections and five “series”, 25 sections and one “series” are resolved as monophyletic in both data sets; (iii) the common ancestor of Corydalis is likely to be a perennial plant with a taproot, yellow flowers with a short saccate spur, linear fruits with recurved fruiting pedicels, and seeds with elaiosomes; (iv) we provide a new classification of Corydalis with four subgenera (of which subg. Bipapillatae is here newly described), 39 sections, 16 of which are consistent with the previous classification, 16 sections have been recircumscribed, one section has been reinstated and six new sections are established. Characters associated with lifespan, underground structures, floral spur, fruit and elaiosomes are important for the recognition of subgenera and sections. These new phylogenetic analyses combined with ancestral character reconstructions uncovered previously unrecognized relationships, and greatly improved our understanding of the evolution of the genus.     

Towards a cohesive strategy for the conservation of the United States’ diverse and highly endemic crayfish fauna

The fossil record of cichlids is sparse, and every new discovery can provide new insights into the evolutionary history of this speciose freshwater fish family. In this article, we describe †Rebekkachromis gen. nov. from the middle-to-late Miocene (c. 11 MYA) of the Central Kenya Rift within the East African Rift system. †Rebekkachromis is represented by two species that differ from all other fossil and extant African cichlids, except Etia, in possessing the unique character combination of two supraneural bones and a set of robust tricuspid oral teeth in the outer row of the dentition. Furthermore, †Rebekkachromis exhibits the only proposed morphological synapomorphy of the Haplotilapiini, namely the presence of tricuspid teeth in the inner row of the oral dentition. We show that †Rebekkachromis constitutes the oldest reliably identified fossil record of a haplotilapiine. The evolution of cichlid fishes possessing tricuspid teeth in the rivers and lakes of the Central Kenya Rift during the middle-to-late Miocene could have been facilitated by volcanic activity, as repeated ash falls may well have fostered the growth of algae and in particular diatoms. These fishes could thus have had a major advantage, because they could exploit the newly available, rich food resources.

     

Linking cranial morphology to prey capture kinematics in three cleaner wrasses: Labroides dimidiatus,Larabicus quadrilineatus,and Thalassoma lutescens

Cleaner fishes are well known for removing and consuming ectoparasites off other taxa. Observers have noted that cleaners continuously “pick” ectoparasites from the bodies of their respective client organisms, but little is known about the kinematics of cleaning. While a recent study described the jaw morphology of cleaners as having small jaw‐closing muscles and weak bite forces, it is unknown how these traits translate into jaw movements during feeding to capture and remove ectoparasites embedded in their clients. Here, we describe cranial morphology and kinematic patterns of feeding for three species of cleaner wrasses. Through high‐speed videography of cleaner fishes feeding in two experimental treatments, we document prey capture kinematic profiles for Labroides dimidiatus, Larabicus quadrilineatus, and Thalassoma lutescens. Our results indicate that cleaning in labrids may be associated with the ability to perform low‐displacement, fast jaw movements that allow for rapid and multiple gape cycles on individually targeted items. Finally, while the feeding kinematics of cleaners show notable similarities to those of “picker” cyprinodontiforms, we find key differences in the timing of events. In fact, cleaners generally seem to be able to capture prey twice as fast as cyprinodontiforms. We thus suggest that the kinematic patterns exhibited by cleaners are indicative of picking behavior, but that “pickers” may be more kinematically diverse than previously thought. J. Morphol. 276:1377–1391, 2015. © 2015 Wiley Periodicals, Inc.     

Gastric teeth of some thoracotreme crabs and their contribution to the brachyuran phylogeny

The gastric teeth of three ocypodoid species were investigated using scanning electron microscopy, and the morphological results were discussed with respect to the known food preferences. The species were chosen in particular because of contrasting ideas about their relationships within the Thoracotremata. For the genera Heloecius, Dotilla, Mictyris, and “Uca” (s. str.), we find a specific correlation of the gastric teeth with the suspension feeding. The lateral gastric teeth of Uca have no prominent lateral teeth cusps, and most of their teeth surface consists of transverse comb‐like lamellae. However, this possible food adaptation does not exclude the usability of specific teeth characters to distinguish species of suspension feeders. The closer relationship of the Dotillidae to grapsoid lines of gecarcinid or sesarmid crabs suggested by molecular data is not supported by the gastric teeth. For the genus Ucides, we found several characters that distinguish Ucides from the remaining ocypodoid genera Heloecius, Dotilla, Mictyris, and “Uca.” In particular, the structures of the lateral and the dorsomedian teeth show some similarities to genera of the Gecarcinidae and Sesarmidae. Our results suggest that foregut characters can be used for phylogenetic analyses. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

CHLOROPLAST DNA SYSTEMATICS OF LILIOID MONOCOTS: RESOURCES,FEASIBILITY, AND AN EXAMPLE FROM THE ORCHIDACEAE

Although chloroplast DNA (cpDNA) analysis has been widely and successfully applied to systematic and evolutionary problems in a wide variety of dicots, its use in monocots has thus far been limited to the Poaceae. The cpDNAs of grasses are significantly altered in arrangement relative to the genomes of most vascular plants, and thus the available clone banks of grasses are not particularly useful in studying variation in the cpDNA of other monocots. In this report, we present mapping studies demonstrating that cpDNAs of four lilioid monocots (Allium cepa, Alliaceae; Asparagus sprengeri, Asparagaceae; Narcissus × hybridus, Amaryllidaceae; and Oncidium excavatum, Orchidaceae), which, while varying in size over as much as 18 kilobase pairs, conform to the genome arrangement typical of most vascular plants. A nearly complete (99.2%) clone bank was constructed from restriction fragments of the chloroplast genome of Oncidium excavatum; this bank should be useful in cpDNA analysis among the monocots and is available upon request. As an example of the utility of filter hybridization using this clone bank to detect systematically useful variation, we present a Wagner parsimony analysis of restriction site data from the controversial genus Trichocentrum and several sections of Oncidium, popularly known as the “mule ear” and “rat tail oncidiums.” Because of their vastly different floral morphology, the species of Trichocentrum have never been placed in Oncidium, although several authors have recently suggested a close relationship to this vegetatively modified group. The analysis of cpDNA presented here supports this affinity; in fact, it places Trichocentrum as a derivative of the mule ear oncidiums.     

Bony labyrinth morphology in early neopterygian fishes (Actinopterygii: Neopterygii)

Endocasts of the osseous labyrinth have the potential to yield information about both phylogenetic relationships and ecology. Although bony labyrinth morphology is well documented in many groups of fossil vertebrates, little is known for early Neopterygii, the major fish radiation containing living teleosts, gars and the bowfin. Here, we reconstruct endocasts of the bony labyrinth and associated structures for a sample of Mesozoic neopterygian fishes using high‐resolution computed tomography. Our sample includes taxa unambiguously assigned to either the teleost (Dorsetichthys, “Pholidophorus,” Elopoides) and holostean (“Aspidorynchus,” “Caturus,” Heterolepidotus) total‐groups, as well as examples of less certain phylogenetic position (an unnamed parasemionotid and Dapedium). Our models provide a test of anatomical interpretations for forms where bony labyrinths were reconstructed based on destructive tomography (“Caturus”) or inspection of the lateral wall of the cranial chamber (Dorsetichthys), and deliver the first detailed insights on inner ear morphology in the remaining taxa. With respect to relationships, traits apparent in the bony labyrinth and associated structures broadly support past phylogenetic hypotheses concerning taxa agreed to have reasonably secure systematic placements. Inner ear morphology supports placement of Dapedium with holosteans rather than teleosts, while preserved structure in the unnamed parasemionotid is generalized to the degree that it provides no evidence of close affinity with either of the crown neopterygian lineages. This study provides proof‐of‐concept for the systematic utility of the inner ear in neopterygians that, in combination with similar findings for earlier‐diverging actinopterygian lineages, points to the substantial potential of this anatomical system for addressing the longstanding questions in the relationships of fossil ray‐finned fishes to one another and living groups. J. Morphol. 279:426–440, 2018. © 2016 Wiley Periodicals, Inc.     

Cranial morphology of the Stellate Sturgeon,Acipenser stellatus Pallas 1771 (Acipenseriformes,Acipenseridae), with notes on the skulls of other sturgeons

Extant members of Acipenseridae are generally classified in four genera: Scaphirhynchus, Pseudoscaphirhynchus, Huso and “Acipenser,” which is widely recognized to be paraphyletic. Advances have been made in understanding the systematic relationships among sturgeons based on both morphological and molecular data. Analysis of mitochondrial DNA data suggested that Pseudoscaphirhynchus should be regarded as nested within “Acipenser,” specifically as sister group to the Stellate Sturgeon, A. stellatus. Recent morphological analyses also recovered this relationship, supported by a number of osteological synapomorphies, although these results were based on few and relatively small individuals. Here we describe the anatomy of the skull of A. stellatus based on newly prepared specimens of adult individuals, as well as examination of a large number of preserved individuals representing a broad range of ontogenetic stages. We present new anatomical data from all regions of the skull (dermatocranium, neurocranium, viscerocranium) and offer interpretations of these and other characters. In particular, we describe the allometry in the snout of A. stellatus, which undergoes substantial elongation relative to other sturgeons. Aspects of the skull of A. stellatus are compared to other members of the family, specifically the course of the occipital sensory canal and the morphology and distribution of cranial spines.     

Atavisms and the homology of hyobranchial elements in lower vertebrates

The homology of branchial arch segments in salamanders has been a matter of controversy since the last century. Many investigators term the most medial paired elements of salamander branchial arches “ceratobranchials” and the next distal paired elements “epibranchials.” This suggests that the first two segmental elements of the salamander branchial arch are not homologous with elements occupying the same position in ray-finned fishes, Latimeria, “rhipidistians,” and lungfishes, in which these bones are called hypobranchials and ceratobranchials, respectively. Three lines of evidence suggest that it is more parsimonious to interpret urodele branchial arch segments as being homologous with those of other vertebrate clades?(1) comparative osteology, (2) comparative myology, and (3) the discovery of cartilaginous structures forming a third segmental unit that we interpret as atavistic epibranchials of the branchial arch in one population of the salamander Notophthalmus viridescens. These structures possess all the defining attributes of atavisms, and illustrate the special role that atavistic features play in resolving questions of homology recognition.     

Evolution of electrosensory ampullary organs: conservation of Eya4 expression during lateral line development in jawed vertebrates

The lateral line system of fishes and amphibians comprises two ancient sensory systems: mechanoreception and electroreception. Electroreception is found in all major vertebrate groups (i.e. jawless fishes, cartilaginous fishes, and bony fishes); however, it was lost in several groups including anuran amphibians (frogs) and amniotes (reptiles, birds, and mammals), as well as in the lineage leading to the neopterygian clade of bony fishes (bowfins, gars, and teleosts). Electroreception is mediated by modified “hair cells,” which are collected in ampullary organs that flank lines of mechanosensory hair cell containing neuromasts. In the axolotl (a urodele amphibian), grafting and ablation studies have shown a lateral line placode origin for both mechanosensory neuromasts and electrosensory ampullary organs (and the neurons that innervate them). However, little is known at the molecular level about the development of the amphibian lateral line system in general and electrosensory ampullary organs in particular. Previously, we identified Eya4 as a marker for lateral line (and otic) placodes, neuromasts, and ampullary organs in a shark (a cartilaginous fish) and a paddlefish (a basal ray‐finned fish). Here, we show that Eya4 is similarly expressed during otic and lateral line placode development in the axolotl (a representative of the lobe‐finned fish clade). Furthermore, Eya4 expression is specifically restricted to hair cells in both neuromasts and ampullary organs, as identified by coexpression with the calcium‐buffering protein Parvalbumin3. As well as identifying new molecular markers for amphibian mechanosensory and electrosensory hair cells, these data demonstrate that Eya4 is a conserved marker for lateral line placodes and their derivatives in all jawed vertebrates.     

SPORELING COALESCENCE IN CHONDRUS CRISPUS (RHODOPHYCEAE)1

Coalescence of developing sporelings of Chondrus crispus Stackhouse was observed. Juvenile tetra-sporophytes showed a higher proportion of coalescence than developing gametophytes. Stages of complete coalescence between different sporelings are illustrated. Coalesced sporelings exhibit vertical and horizontal alignment of cells, as well as “cuticular” continuity and secondary pit connections between adjacent, coalesced sporelings. Ultimately the cells in the center of the coalesced sporelings produce upright, multiaxial fronds that grow more rapidly than fronds of non-coalesced sporelings. Other red algae, such as Gracilaria verrucosa (Hudson) Papenfuss and Gigartina stellata (Stackhouse) Batters also show a similar sequence of sporeling coalescence and enhanced growth. The ecological significance of sporeling coalescence is discussed.     

Morphological and functional bases of durophagy in the queen triggerfish,Balistes vetula (Pisces,tetraodontiformes)

Tetraodontiform fishes are characterized by jaws specialized for powerful biting and a diet dominated by hard-shelled prey. Strong biting by the oral jaws is an unusual feature among teleosts. We present a functional morphological analysis of the feeding mechanism of a representative tetraodontiform, Balistes vetula. As is typical for the order, long, sharp, strong teeth are mounted on the short, robust jaw bones of B. vetula. The neurocranium and suspensorium are enlarged and strengthened to serve as sites of attachment for the greatly hypertrophied adductor mandibulae muscles. Electromyographic recordings made from 11 cranial muscles during feeding revealed four distinct behaviors in the feeding repertoire of B. vetula. Suction is used effectively to capture soft prey and is associated with a motor pattern similar to that reported for many other teleosts. However, when feeding on hard prey, B. vetula directly bit the prey, exhibiting a motor pattern very different from that of suction feeding. During buccal manipulation, repeated cycles of jaw opening and closing (biting) were coupled with rapid movement of the prey in and out of the mouth. Muscle activity during buccal manipulation was similar to that seen during bite-captures. A blowing behavior was periodically employed during prey handling, as prey were forcefully “spit out” from the mouth, either to reposition them or to separate unwanted material from flesh. The motor pattern used during blowing was distinct from similar behaviors described for other fishes, indicating that this behaviors may be unique to tetraodontiforms. Thus B. vetula combines primitive behaviors and motor patterns (suction feeding and buccal manipulation) with specialized morphology (strong teeth, robust jaws, and hypertrophied adductor muscles) and a novel behavior (blowing) to exploit armored prey such as sea urchins molluscs, and crabs. © 1993 Wiley-Liss, Inc.     

Quantitative proteomic analysis of hepatic tissue in allotetraploid hybridized from red crucian carp and common carp identified crucial proteins and pathways associated with metabolism and growth rate

Allotetraploid is a new species produced by distant hybridization between red crucian carp (Carassius auratus red var., abbreviated as RCC) and common carp (Cyprinus carpio L., abbreviated as CC). There is a significant difference in growth rate between allotetraploid and its parents. However, the underlying molecular mechanism is largely unknown. In this study, to find direct evidence associated with metabolism and growth rate in protein level, we performed quantitative proteomics analysis on liver tissues between allotetraploid and its parents. A total of 2502 unique proteins were identified and quantified by SWATH-MS in our proteomics profiling. Subsequently, comprehensive bioinformatics analyses including gene ontology enrichment analysis, pathway and network analysis, and protein–protein interaction analysis (PPI) were conducted based on differentially expressed proteins (DEPs) between allotetraploid and its parents. The results revealed several significant DEPs involved in metabolism pathways in liver. More specifically, the integrative analysis highlighted that the DEPs ACSBG1, OAT, and LDHBA play vital roles in metabolism pathways including “pentose phosphate pathway,” “TCA cycle,” and “glycolysis and gluconeogenesis.” These could directly affect the growth rate in fresh water fishes by regulating the metabolism, utilization, and exchange of substance and energy. Since the liver is the central place for metabolism activity in animals, we firstly established the comprehensive and quantitative proteomics knowledge base for liver tissue from freshwater fishes, our study may serve as an irreplaceable reference for further studies regarding fishes’ culture and growth.     

Corallite wall and septal microstructure in scleractinian reef corals: Comparison of molecular clades within the family Faviidae

Recent molecular phylogenies conflict with traditional scleractinian classification at ranks ranging from suborder to genus, challenging morphologists to discover new characters that better agree with molecular data. Such characters are essential for including fossils in analyses and tracing evolutionary patterns through geologic time. We examine the skeletal morphology of 36 species belonging to the traditional families Faviidae, Merulinidae, Pectiniidae, and Trachyphylliidae (3 Atlantic, 14 Indo‐Pacific, 2 cosmopolitan genera) at the macromorphological, micromorphological, and microstructural levels. Molecular analyses indicate that the families are not monophyletic groups, but consist of six family‐level clades, four of which are examined [clade XV = Diploastrea heliopora; clade XVI = Montastraea cavernosa; clade XVII (“Pacific faviids”) = Pacific faviids (part) + merulinids (part) + pectiniids (part) + M. annularis complex; clade XXI (“Atlantic faviids”) = Atlantic faviids (part) + Atlantic mussids]. Comparisons among molecular clades indicate that micromorphological and microstructural characters (singly and in combination) are clade diagnostic, but with two exceptions, macromorphologic characters are not. The septal teeth of “Atlantic faviids” are paddle‐shaped (strong secondary calcification axes) or blocky, whereas the septal teeth of “Pacific faviids” are spine‐shaped or multidirectional. Corallite walls in “Atlantic faviids” are usually septothecal, with occasional trabeculothecal elements; whereas corallite walls in “Pacific faviids” are usually trabeculothecal or parathecal or they contain abortive septa. Exceptions include subclades of “Pacific faviids” consisting of a) Caulastraea and Oulophyllia (strong secondary axes) and b) Cyphastrea (septothecal walls). Diploastrea has a diagnostic synapticulothecal wall and thick triangular teeth; Montastraea cavernosa is also distinct, possessing both “Pacific faviid” (abortive septa) and “Atlantic faviid” (paddle‐shaped teeth) attributes. The development of secondary axes is similar in traditional Atlantic faviids and mussids, supporting molecular results placing them in the same clade. Subclades of “Pacific faviids” reveal differences in wall structure and the arrangement and distinctiveness of centers of rapid accretion. J. Morphol. 272:66–88, 2011. © 2010 Wiley‐Liss, Inc.     

Chondrichthyan teeth from the Early Triassic Paris Biota (Bear Lake County,Idaho, USA)

A new, diverse and complex Early Triassic assemblage was recently discovered west of the town of Paris, Idaho (Bear Lake County), USA. This assemblage has been coined the Paris Biota. Dated earliest Spathian (i.e., early late Olenekian), the Paris Biota provides further evidence that the biotic recovery from the end-Permian mass extinction was well underway ca. 1.3 million years after the event. This assemblage includes mainly invertebrates, but also vertebrate remains such as ichthyoliths (isolated skeletal remains of fishes). Here we describe first fossils of Chondrichthyes (cartilaginous fishes) from the Paris Biota. The material is composed of isolated teeth (mostly grinding teeth) preserved on two slabs and representing two distinct taxa. Due to incomplete preservation and morphological differences to known taxa, the chondrichthyans from the Paris Biota are provisionally kept in open nomenclature, as Hybodontiformes gen. et sp. indet. A and Hybodontiformes gen. et sp. indet. B, respectively. The present study adds a new occurrence to the chondrichthyan fossil record of the marine Early Triassic western USA Basin, from where other isolated teeth (Omanoselache, other Hybodontiformes) as well as fin spines of Nemacanthus (Neoselachii) and Pyknotylacanthus (Ctenachanthoidea) and denticles have been described previously.     

Deconstructing the long-standing a priori assumption that serial homology generally involves ancestral similarity followed by anatomical divergence

It has long been assumed that serial homologues are ancestrally similar—polysomerism resulting from a “duplication” or “repetition” of forms—and then often diverge—anisomerism, for example, as they become adapted to perform different tasks as is the case with the forelimb and hind limbs of humans. However, such an assumption, with crucial implications for comparative, evolutionary, and developmental biology, and for evolutionary developmental biology, has in general not really been tested by a broad analysis of the available empirical data. Perhaps not surprisingly, more recent anatomical comparisons, as well as molecular knowledge of how, for example, serial appendicular structures are patterned along with different anteroposterior regions of the body axis of bilateral animals, and how “homologous” patterning domains do not necessarily mark “homologous” morphological domains, are putting in question this paradigm. In fact, apart from showing that many so-called “serial homologues” might not be similar at all, recent works have shown that in at least some cases some “serial” structures are indeed more similar to each other in derived taxa than in phylogenetically more ancestral ones, as pointed out by authors such as Owen. In this article, we are taking a step back to question whether such assumptions are actually correct at all, in the first place. In particular, we review other cases of so-called “serial homologues” such as insect wings, arthropod walking appendages, Dipteran thoracic bristles, and the vertebrae, ribs, teeth, myomeres, feathers, and hairs of chordate animals. We show that: (a) there are almost never cases of true ancestral similarity; (b) in evolution, such structures—for example, vertebra—and/or their subparts—for example, “transverse processes”—many times display trends toward less similarity while in many others display trends toward more similarity, that is, one cannot say that there is a clear, overall trend to anisomerism.