Embryonic development of Carabus insulicola (Insecta,Coleoptera, Carabidae) with special reference to external morphology and tangible evidence for the subcoxal theory

The egg morphology and successive changes in the developing embryos of the carabid ground beetle Carabus insulicola (Carabidae) are described based on light and scanning electron microscopy observations. Newly laid eggs of this species are ellipsoid and measure approximately 6.1 × 2.9 mm, before increasing to 6.6 × 3.4 mm at hatching. The egg period is about 11 days at 23°C. The egg shell is characterized by a thin fragile chorion covering a hard serosal cuticle. The embryo forms on the ventral egg surface, where it develops for the duration of the egg period. During the process of thoracic leg formation, two subcoxal rings, subcoxae‐1 and 2, are clearly discernible at the basalmost region of the leg rudiments, and these subcoxae participate in the formation of the larval pleura and sterna. The result thus provides tangible evidence for the subcoxal theory, that is, that thoracic pleura and sterna are derived from subcoxal regions. Despite the complete absence of abdominal appendages in the larvae of this species, two pairs of appendage‐like swellings, the medial and lateral ones, temporarily arise in the first eight abdominal segments during the middle of embryonic development. The medial swellings are assumed to be serially homologous with the coxal part of the thoracic leg, and they later flatten out and participate in the formation of the larval pleura (hypopleurites). In the light of the serially homologous relationships among gnathal appendages, thoracic legs, and abdominal appendage‐like swellings, we identified the subcoxal regions in both the gnathal and abdominal segments. Although, the lateral swellings soon degenerate and disappear, it is considered that the swellings originate in the abdominal subcoxae‐2 and may be homologous to the tracheal gills of larvae of Gyrinidae. Based on the embryological results, new interpretations for the constituent of gnathal appendages are proposed. J. Morphol. 274:1323–1352, 2013. © 2013 Wiley Periodicals, Inc.     

条背萤幼虫水生适应性形态与游泳行为研究

研究了条背萤Luciolasubstriata幼虫的形态特征及其对游泳行为的适应。形态及扫描电镜观察发现,条背萤幼虫存在二态现象。1～2龄幼虫虫体扁平,多毛。有7对呼吸鳃,分别位于腹部第1～7节。3～6龄幼虫虫体扁平呈船形,无呼吸鳃,靠气管呼吸。二者均具有扁平桨状的足、燕尾状尾节及位于尾节末端的圆柱形粘附器官。条背萤幼虫游动时身体腹面朝上,呈仰泳姿态,足向后划水。3～6龄幼虫仰泳时足共有8种摆动姿势。幼虫仰泳时足摆动1个周期所需时间为(0.611±0.16)s。腹部末端可上下左右摆动,当幼虫向前游动时,尾部上下摆动1个周期所需时间为(1.795±0.44)s。幼虫的游泳速度为(0.85±0.16)mh。仰泳中的幼虫改变方向时,头部和尾部同时向身体的一侧弯曲,当头部与尾部呈近90°时,幼虫用力将尾部伸直,此时水产生一个反作用力继续推动幼虫转向,幼虫转向的范围为0～90°。条背萤2种类型幼虫呼吸系统的不同决定着幼虫外部形态的差异及游泳行为的不同,而导致这种呼吸系统、形态及运动行为不同的原因很可能是条背萤对环境的适应性进化。     

Are abdominal prolegs serially homologous with the thoracic legs in panorpidae (Insecta: Mecoptera)? embryological evidence

It is a long standing question whether the abdominal prolegs of holometabolous insect larvae are serially homologous with their thoracic legs. The histology and ultrastructure of proleg embryonic development in the scorpionfly Panorpa magna were studied using light and scanning electron microscopy. During the early embryonic development, paired primary abdominal appendages appeared laterally in line with the thoracic legs. Several hours later, a pair of proleg primordia arose along the midventral line on each of the first eight abdominal segments mesial to the primary abdominal appendages, which then ceased to grow and eventually degenerated into flat vestiges. Histological observation showed that the thoracic legs were obviously connected with lateral thoracic muscle cells, whereas the abdominal prolegs resembled secondary outgrowths. No apparent contact was observed between the lumen of abdominal prolegs and the hemocoel. After dorsal closure, each thoracic segment bore a pair of well‐developed five‐jointed legs, whereas the prolegs were unjointed, fleshy structure. The remnants of the primary abdominal appendages could still be clearly seen in the mature embryo. On the basis of the histological and morphological observation of the embryonic development, we confirm that the abdominal prolegs of Panorpidae lack the characters of the primary appendages; hence they are not serially homologous with the thoracic legs. The reasons why the primary abdominal legs are reduced in scorpionflies are briefly discussed. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

雷氏黄萤幼虫呼吸系统和呼吸行为

研究雷氏黄萤Luciola leii Fu and Ballantyne幼虫的呼吸系统及其呼吸行为。结果表明:雷氏黄萤幼虫的呼吸系统中只有气管无气囊。前胸、中胸和后胸均分布有气门,无气管鳃,腹部1~8节分布有气门和气管鳃,气门腔基部和气管鳃基部相连,呈"√"状,气管鳃内气管与气门气管相连通。雷氏黄萤幼虫的呼吸行为分为3种:利用胸部气门呼吸、腹部气门呼吸和气管鳃呼吸,其中以腹部气门呼吸为主。     

Cloning of a<Emphasis Type="Italic"> decapentaplegic</Emphasis> orthologue from the sawfly,<Emphasis Type="Italic"> Athalia rosae</Emphasis> (Hymenoptera), and its expression in the embryonic appendages

The cDNA of a decapentaplegic (dpp) orthologue from the sawfly, Athalia rosae (Hymenoptera), was cloned and characterized. The clone (Ar dpp) was 2,566 bp long and encoded 395 amino acids in a single open reading frame. Genomic Southern blotting showed that Ar dpp is a single copy gene. The deduced amino acid sequence can be aligned along its entire length with known insect DPPs. It shared common characteristics such as a signal sequence, a pro-domain region, and a ligand domain with seven cysteines at conserved locations. Ar dpp was expressed as a single 5.0-kb mRNA in embryos, larvae, pupae and adults. In situ hybridization showed that Ar dpp was expressed in the dorsal region proper in early embryonic stages and in the embryonic appendages of cephalic segments (labrum, antenna, mandible, maxilla, and labium), thoracic segments (thoracic legs), and all abdominal segments except the tenth segment (pleuropodia and proleg primordia). The present results indicate that Ar dpp expression reflects the primary determination of embryonic appendages.Edited by D. TautzThe sequence reported in this paper has been deposited in the DDBJ/EMBL/GenBank database with the accession number AB121072     

Sensory neurons and peripheral pathways in Drosophila embryos

Summary The thoracic and abdominal segments of the Drosophila embryo contain 373 neurons innervating external sensory structures and 162 neurons innervating chordotonal organs. These neurons are arranged in ventral, lateral and dorsal clusters within each segment, in a highly invariant pattern. Two fascicles are formed in each segment as the sensory axons grow ventrally towards the CNS and meet motor axons growing dorsally from the CNS. In all but the last segment, the anterior fascicle is contributed by the dorsal and lateral neurons, while the posterior one is formed by the ventral neurons. Five distinct segmental patterns are described, corresponding to (1) the prothorax, (2) the other two thoracic segments, (3) the first seven abdominal segments, (4) the eighth and (5) the ninth (and possibly the tenth) abdominal segments.The publisher regrets that two companion papers unfortunately were published out of sequence. The present paper should have preceded the paper entitled The sense organs in the Drosophila larva and their relation to the embryonic pattern of sensory neurons, which appeared in Volume 195, Number 4 of the journal (pp 222–228)     

Some aspects of segment formation and post-placental development in Peripatus acacioi marcus and marcus (Onychophora)

The surface morphology of the anterior-to-posterior sequence of segment formation in embryos of a viviparous neotropical onychophoran and aspects of post-placental development seen using scanning electron microscopy are described. When all the segments have formed and the walking legs have completed their elongation, the body surface becomes covered with an embryonic cuticle that does not exhibit the hydrofuge properties seen in the adult cuticle. As soon as the walking legs have reached their full length, barbed projections are formed at their distal extremities. These projections are extensions of single cells and are covered by the embryonic cuticle. Transmission electron microscopy reveals that the cells at the distal ends of the legs and their projections have many pinocytotic vesicles at their surfaces. The cytoplasm of these cells and their projections is rich in mitochondria, rough endoplasmic reticulum, glycogen, and granules of storage material. There are minor differences in the surface morphology of the projections found at the ends of the walking legs in embryos of Peripatus acacioi and those of Peripatus biolleyi. The projections and the embryonic cuticle persist thoughout postplacental development. The role of the projections in the uptake of material by the embryo from the uterus is discussed and the possible phylogenetic significance of these projections is suggested.     

普通齿蛉幼虫的呼吸系统及呼吸行为

研究了普通齿蛉Neoneuromus ignobilis Navás幼虫的呼吸系统及其呼吸行为。结果表明:普通齿蛉幼虫为全气门式(10对气门)呼吸系统,前中胸、中后胸之间、腹部8节各有1对气门,腹部8节各有气管鳃1对,前6对细短,管状,有较短绒毛,后2对气管鳃较粗长,呈羽毛状。腹部1～7节各有1对毛簇,第8腹节无毛簇。侧纵干气管较粗,4束,自前胸前缘部分成左右2组,每组两根侧纵干气管,向胸腹部延伸,二级气管分别伸达各个气门和毛簇,腹部每节由毛簇处的二级气管分支而来的三级气管相连或延伸至消化道等处。气管鳃中无气管。有毛簇呼吸、气门呼吸和体壁呼吸3种呼吸方式,在水中以毛簇呼吸为主,在陆上进行气门呼吸和体壁呼吸。     

Expression of a surface epitope on cells that link branches in the tracheal network of Manduca sexta.

A monoclonal antibody (MAb 2F5) to a cell surface epitope labels a small subpopulation of tracheal epithelial cells in each thoracic and abdominal segment of Manduca. These cells (nodes) represent the sites within the tracheal network at which invaginating tracheal tubes join during embryonic establishment of the tracheal network. Tracheal nodes are also the sites at which tracheal cuticle fractures during each molt. Since tracheal cuticle is shed through each spiracle, a tracheal node lies between each pair of contralateral spiracles within a segment (commissural node) and between each pair of adjacent, ipsilateral spiracles (lateral longitudinal node). MAb 2F5 first labels presumptive nodal cells of tracheal epithelium immediately prior to the linking of epithelial tubes from successive and opposite spiracles. One cell at the tip of each invaginating tracheal branch labels with MAb 2F5. The highly localized expression of the cell surface epitope recognized by MAb 2F5 may be instrumental in the orderly coupling of tracheal branches during embryonic development. On the basis of immunolabeling of Western blots and tissues, MAb 2F5 is believed to recognize Manduca fasciclin II, a member of a class of molecules involved in cell adhesion/recognition.     

The probable significance of tracheal tufts in the 8th abdominal segment of Heliothis virescens (F.) on the development of its parasitoid, Toxoneuron nigriceps (Viereck)

The 8th abdominal segment of Heliothis virescens (Fabricius) larvae contains aerating trachea and tracheole tufts that end in the hemocoel of the 8th segment, unlike the tracheae that invade tissues in other segments. These tracheal tufts from the 8th abdominal segment extend to the tokus region, which along with the telson cavity is known to act as a “lung” for hemocytes in Calpodes ethlius and a few other lepidopteran larvae. The goal of this research was to study the effects of these tracheal tufts in the 8th abdominal segment on parasitoid development inside the host larvae, H. virescens. The first objective was to determine if the eggs of the parasitoid, Toxoneuron nigriceps, are predominantly located among the tracheal tufts of the 8th abdominal segment compared to other body cavity regions irrespective of their oviposition site or the position of the host larvae. The results showed that several hours after oviposition most of the eggs are found in the 8th abdominal segment irrespective of the oviposition site or the position of the host larvae. The second objective was to study the effect of varying oxygen concentrations in vitro on various developmental stages of the egg. The results showed that decreasing oxygen concentrations adversely affects the parasitoid egg development in vitro. A third objective was to determine the oxygen concentration in 8th abdominal segment of the host larvae and compare it to other regions of the body using an oxygen sensor placed in vivo. The results suggested relatively high concentration of oxygen in the 8th abdominal segment compared to other regions of the host, thus supporting our hypothesis that the increased oxygen level in the 8th abdominal segment is important to the development of the parasitoid eggs.     

东亚飞蝗胚胎体节的形成过程

体节形成是昆虫胚胎发育过程中的关键问题.东亚飞蝗Locusta migratoria manilensis(Meyen)是一种重要的农业害虫,其体节形成的时序过程尚无详细报道.本研究采用免疫组化和品红染色方法研究了室内人工饲养东亚飞蝗的体节形成过程.结果表明:完成受精后,细胞核开始分裂并向卵表面迁移.细胞核到达卵表面的...     

The larval morphology of the spongefly Sisyra nigra (Retzius, 1783) (Neuroptera: Sisyridae)

The morphology of mature larvae of Sisyra nigra was studied and documented with a broad spectrum of techniques. Special emphasis is on the cephalic anatomy and on the digestive tract. Cephalic structures are highly modified, with numerous autapomorphic conditions, including a globular head capsule, an extended area with large cornea lenses, a massive tentorium, a strongly developed prepharyngeal pumping apparatus with a horizontal arrangement of dilators, a sharp bend between the prepharynx and pharynx, and an unusual filter apparatus at the entrance of the large crop. The thoracic and abdominal muscle sets, and the legs are largely unmodified. Postcephalic apomorphies are conspicuous tergal setiferous tubercles, trifid setiferous pleural projections, single pretarsal claws, zigzag-shaped abdominal tracheal gills, and a dense vestiture of setae on the terminal abdominal segments. Mandibulo-maxillary stylets curved outwards are an unusual apomorphy also found in the semiaquatic larvae of Osmylidae. Semiaquatic or aquatic habits and secondarily multisegmented antennae are potential synapomorphies of these two groups and Nevrorthidae (Osmyloidea). A sistergroup relationship between Sisyridae and Nevrorthidae suggests that fully aquatic habits of larvae may be a synapomorphy of both families. A specialized terminal antennal seta is a potential groundplan apomorphy of Neuroptera, with secondary loss in Nevrorthidae and Ithonidae + Myrmeleontiformia, respectively. A trumpet-shaped empodium is likely an apomorphy of Neuroptera excluding Coniopterygidae and Osmyloidea, and the secondary loss an apomorphy of Ithonidae on one hand, and Myrmeleontiformia excl. Psychopsidae on the other.     

Comparative embryogenesis of Mecoptera and Lepidoptera with special reference to the abdominal prolegs

The eruciform larvae of holometabolous insects are primarily characterized by bearing a varying number of abdominal prolegs in addition to three pairs of thoracic legs. However, whether the prolegs are evolutionarily homologous among different insect orders is still a disputable issue. We examined the embryonic features and histological structure of the prolegs of the scorpionfly Panorpa byersi Hua and Huang (Mecoptera: Panorpidae) and the Oriental armyworm Mythimna separata (Walker) (Lepidoptera: Noctuidae) to investigate whether the prolegs are homologous between these two holometabolous insect orders. In the scorpionfly, paired lateral process primordia arise on abdominal segments I–VIII (A1–A8) in line with the thoracic legs in early embryonic stages, but degenerate into triangular protuberances in later stages, and paired medial processes appear along the midventral line before dorsal closure and eventually develop into unjointed, cone‐shaped prolegs. Histological observation showed that the lumina of the prolegs are not continuous with the hemocoel, differing distinctly from that of the basic appendicular plan of thoracic legs. These results suggest that the prolegs are likely secondary outgrowths in Mecoptera. In the armyworm, lateral process primordia appear on A1–A10 in alignment with the thoracic legs in the early embryonic stages, although only the rudiments on A3–A6 and A10 develop into segmented prolegs with the lumina continuous with the hemocoel and others degenerate eventually, suggesting that the prolegs are true segmental appendages serially homologous with the thoracic legs in Lepidoptera. Therefore, we conclude that the larval prolegs are likely not evolutionarily homologous between Mecoptera and Lepidoptera. J. Morphol. 277:585–593, 2016. © 2016 Wiley Periodicals, Inc.     

The controversial origin of the abdominal appendage‐like processes in immature insects: Are they true segmental appendages or secondary outgrowths? (Arthropoda hexapoda)

In this article, I review the major characteristics of different types of appendage‐like processes that develop at the abdominal segments of many immature insects, and I discuss their controversial morphological value. The main question is whether the abdominal processes are derived from segmental appendages serially homologous to thoracic legs, or whether they are “secondary” outgrowths not homologous with true appendages. Morphological and embryological data, in particular, a comparison with the structure and development of the abdominal appendages in primitive apterygote hexapods, and data from developmental genetics, support the hypothesis of appendicular origin of many of the abdominal processes present in the juvenile stages of various pterygote orders. For example, the lateral processes, such as the tracheal gills in aquatic nymphs of exopterygote insects, are regarded as derived from lateral portions of appendage primordia, homologous with the abdominal styli of apterygotan insects; these processes correspond either to rudimentary telopodites or to coxal exites. The ventrolateral processes, such as the prolegs of different endopterygote insect larvae, appear to be derived from medial portions of the appendicular primordia; they correspond to coxal endites. These views lead to the rejection of Hinton's hypothesis (Hinton [1955] Trans R Entomol Soc Lond 106:455–545) according to which all the abdominal processes of insect larvae are secondary outgrowths not derived from true appendage anlagen. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

Embryonic development of Galloisiana yuasai Asahina, with special reference to external morphology (insecta: Grylloblattodea)

The embryogenesis of Grylloblattodea, one of the most primitive of the polyneopteran orders, is described using Galloisiana yuasai with special reference to external morphology. The egg membranes are characterized by an endochorion crossed by numerous vertical aeropyles and a fairly thin vitelline membrane, features shared by Mantophasmatodea. The inner layer formation is of the fault type. Serosal elements in the amnioserosal fold differentiate into hydropylar cells, to function in water absorption together with specialized amniotic structures, i.e., an amniotic strand and a thickened amnion. The germ band is of the short germ type. The germ band immerses deep into the yolk after its full elongation along the egg surface, and in this respect blastokinesis closely resembles that of Mantophasmatodea. The embryological features, i.e., those on egg membranes and blastokinesis, may suggest a closer affinity of Grylloblattodea and Mantophasmatodea. Appendages, ectodermal invaginations, and sternal and pleural sclerites are discussed in the light of serial homology, to provide a new basis for elucidating the insect body plan. Appendages are divided into the proximal coxopodite and distal telopodite, the former being divided further into the subcoxa and coxa. Subcoxal and coxal elements are identified in the mandible as well as in the abdominal appendages. The subcoxa is divided into the epimeron and episternum by the pleural suture in thoracic segments. Likewise, in the abdominal segments the subcoxa is divided into two, although the homologs of the epimeron and episternum are not sclerotized, and in the labial segment the subcoxal derivative or the postmentum is divided into the submentum and mentum. Two coxal endites bulge out from the medial side of the gnathal appendages. The mandibular molar and incisor, maxillary lacinia and galea, and labial glossa and paraglossa are serially homologous with each other. In the thoracic segments the original embryonic sternum or "protosternum" is largely replaced by subcoxal elements, and merely remains as a small anterior presternum and a posterior spinasternum. A major part of the venter is represented by the derivatives of the episternum such as an extensive basisternum, katepisternum, and trochantin and the medial element of the epimeron. The pleuron is derived from the episternal elements or the anepisternum and preepisternum, which bears a spiracle in the mesothorax and metathorax, and the lateral element of the epimeron. The homolog of the preepisternum in the prothorax is the cervical sclerite, but with no spiracle developed. A median ventral invagination arises in the thoracic segments as a spina, and the homolog of the spina develops into the eversible sac in the first abdominal segment.     

Embryogenesis of Heliconius erato (Lepidoptera,Nymphalidae): A contribution to the anatomical development of an evo‐devo model organism

This study reports on the embryogenesis of Heliconius erato phyllis between blastoderm formation and the prehatching larval stage. Syncytial blastoderm formation occurred approximately 2 h after egg laying (AEL) and at about 4 h, the cellular blastoderm was formed. The germ band arose from the entire length of the blastoderm, and rapidly became compacted occupying approximately two‐thirds of the egg length. At about 7 h AEL, protocephalon and protocorm differentiation occurred. Continued proliferation of the germ band was followed by penetration into the yolk mass, forming a C‐shaped embryo at about 10 h. Approximately 12 h AEL, the gnathal, thoracic and abdominal segments became visible. The primordium of the mouthparts and thoracic legs formed as paired evaginations, while the prolegs formed as paired lobes. At about 30 h, the embryo reversed dorsoventrally. Approximately 32 h AEL, the protocephalon and gnathal segments fused, shifting the relative position of the rudimentary appendages in this region. At about 52 h, the embryo was U‐shaped in lateral view and at approximately 56 h, the bristles began evagination from the larval cuticle. Larvae hatched at about 72 h. We found that H. erato phyllis followed an embryonic pattern consistent with long‐germ embryogenesis. Thus, we believe that H. erato phyllis should be classified as a long‐germ lepidopteran. The study of H. erato phyllis embryogenesis provided a structural glimpse into the morphogenetic events that occur in the Heliconius egg period. This study could help future molecular approaches to understanding the evolution of Heliconius development.     

Scanning electron microscopy of Drosophila melanogaster embryogenesis: III. Formation of the head and caudal segments

The formation of both the anterior most and posterior most segments in higher dipteran embryos involves complex movements of primordia which can be best visualized with the scanning electron microscope. During head formation, the gnathocephalic segments partially involute through the stomodeum. The labial segment forms the floor of the mouth, and the fused maxillary and mandibular segments form the lateral sides of the mouth. The involuted clypeolabrum forms the roof of the mouth. Invaginations of cells for segmentally derived sense organs can be found prior to involution on all the gnathocephalic and thoracic segments as well as on the labrum. The antennal sense organ derives from the lateral surface of the procephalic lobe. Following involution of the mouth parts, the dorsal ridge, which arises just anterior to the first thoracic segment, is drawn over the dorsal procephalic lobe producing the deep dorsal sac. The optic lobes of the brain invaginate anterior to the dorsal ridge just prior to the covering over of the head. The formation of the anal segment is similarly complex. Two rudimentary segments are found posterior to the eighth abdominal segment. During shortening of the germ band, the posterior most segment is drawn around the posterior tip of the embryo to lie ventrally. Two large anal pads form lateral to the anus from this segment. The next segment, following dorsal closure, produces a pair of anal sense organs and a central tuft of setae. Finally, the eighth abdominal segment gives rise to the posterior spiracles. Following dorsal closure these three segments fuse to produce the terminal (anal) segment of the larva.     

洪泽湖鱼类寄生甲壳动物区系调查及一新种的记述

1979年秋对江苏省洪泽湖鱼类寄生甲壳动物的调查研究结果,共得18种寄生甲壳动物,其中包括一个新种。分析了该湖寄生甲壳动物的区系组成、繁殖季节及种类分布的情况,同时还根据虫体感染率和感染强度,提出了对鱼类危害性较大的中华鳋和多态锚头鳋,在洪泽湖中不可能出现严重感染的见解。       

hunchback, a gene required for segmentation of an anterior and posterior region of the Drosophila embryo

The locus hunchback (hb) is a member of the gap class of segmentation genes of Drosophila. A number of X-ray-induced deletions locate the hb locus at the chromosomal site 85A3-B1, to the right of the pink locus, which maps in the same interval. A total of 14 EMS and 3 X-ray-induced hb alleles have been studied. Homozygous mutant embryos show deletions of segments in two separate regions. In the six strong alleles, the labium and all three thoracic segments are deleted anteriorly while posteriorly the 8th abdominal segment and adjacent parts of the 7th abdominal segment are lacking. The eight weak alleles show smaller deletions both in the thoracic and posterior abdominal region. In the weakest allele only part of the mesothorax is deleted. Three hb alleles produce a homoeotic transformation: superimposed on a strong or weak deletion phenotype, head or thoracic segments are transformed into abdominal segments, respectively. This suggests that hb might also be involved in the regulation of genes in the Bithorax complex (BX-C). Fate mapping of the normal-appearing segments in strong mutant embryos using the UV-laser beam ablation technique (Lohs-Schardin et al., 1979) shows that these segments arise from the normal blastoderm regions. The mutant phenotype can be recognized soon after the onset of gastrulation in a failure to fully extend the germ band. In 6-hr-old mutant embryos, two clusters of dead cells are observed in the thoracic and posterior abdominal region. These observations indicate region specific requirement of hb gene function. The analysis of germ line chimeras by transplantation of homozygous mutant pole cells shows that hb is already expressed during oogenesis. Homozygous mutant embryos derived from a homozygous mutant germ line have a novel phenotype. The anterior affected region is enlarged, including all three gnathal segments and the anterior three abdominal segments. In addition three abdominal segments with reversed polarity are formed between the remaining head structures and the posterior abdomen. Heterozygous mutant embryos derived from a homozygous mutant germ line develop normally, indicating that maternal gene expression is not required for normal development.     

Two new species of Mediomastus (Annelida,Capitellidae) from Tokyo Bay,Japan

Two undescribed species of polychaetes in Mediomastus (Annelida: Capitellidae) were collected from intertidal to shallow habitats in Tokyo Bay, Japan. These are M. duobalteus sp. n. and M. hanedaensis sp. n. Mediomastus duobalteus sp. n. is distinguishable from all congeners by the following characters: 1) segments 3, 4, 8–11 stainable with methyl green, 2) thoracic capillary chaetae unilimbate, 3) abdominal capillary chaetae absent, 4) paddle-like chaetae in the thorax absent, and 5) abdominal hooded hooks not flared. Mediomastus hanedaensis sp. n. is similar to M. warrenae Green, 2002, but differs from the latter in the shapes of the thoracic capillary chaetae and the abdominal hooded hooks, and the staining pattern with methyl green. In addition, a key to all Mediomastus species is provided.