Circulatory organs of Diplura (Hexapoda): the basic design in Hexapoda?

The circulatory systems of Campodea augens and Catajapyx aquilonaris (Hexapoda: Diplura) have been examined by means of light and electron microscopy. Hemolymph flow has also been investigated in vivo. Both species share features that deviate conspicuously from the common textbook design of the insect circulatory system: (i) antennal vessels connected to the anterior end of the dorsal vessel; (ii) presence of a circumoesophageal vessel ring in the head; (iii) a bidirectional flow within the dorsal vessel, made possible by intracardiac valves; (iv) posterior end of the dorsal vessel tube opens into a caudal chamber connected to cercal vessels (in Campodea) or to cercal channels (in Catajapyx); (v) dorsal diaphragm barely realized, ventral diaphragm absent altogether, and (vi) legs without specific organs serving hemolymph circulation. Comparative analysis has revealed that these characters in Diplura represent the most plesiomorphic condition in the circulatory organs of all extant Hexapoda. In the basic evolutionary lineages of insects, some organ components have been lost and the peripheral vessels decoupled from the dorsal vessel; as a result, autonomous accessory pulsatile organs have evolved to supply hemolymph to long body appendages and a unidirectional hemolymph flow mode prevailed within the dorsal vessel.     

The insect abdomen--a heartbeat manager in insects?

Different possibilities of coordination between circulation, respiration and abdominal movements were found in pupae of Pieris brassicae, Tenebrio molitor, Galleria mellonella and Leptinotarsa decemlineata. Coordination principles depend on metabolic rate: the need to support circulation with abdominal movements appears only at higher metabolic rates. Integration between different abdominal movements and circulation depends on species, on physiological state and, supposedly, on internal morphology. At low metabolic rates, there is no need for a very intensive hemolymph flow, and the dorsal vessel is capable of initiating and/or maintaining necessary hemolymph flow. Starting from a certain metabolic level, it is possible that the abdomen is used to accelerate hemolymph flow in the case of a large amount of hemolymph. When the necessary flow speed has been reached, relatively weak pulsation of the dorsal vessel with accessory pulsatile organs and diaphragms can easily maintain the necessary flow intensity. Heart activity may sometimes be initiated by abdominal movements via cardiac reflex or mechanical excitation. Sometimes, when heart function is weakened by histolysis, the abdomen may temporarily take over the main circulatory function or occasionally contribute to acceleration of low-speed hemolymph flow. In this case the functions are simultaneous and may be triggered by some mediator(s). In active adult insects the whole body is moving, and hence hemolymph circulates and the tracheal system is effectively ventilated by a whole body ensemble consisting of the dorsal vessel, moving organs, body appendages and accessory pulsatile organs. The mechanism of autocirculation (analogous to autoventilation in gas exchange) is a probable mechanism in circulation in adult insects.     

An evolutionary treatment of the morphology and physiology of circulatory organs in insects

An overview from an evolutionary perspective is presented on the research of the past 2 decades on insect circulatory organs. Based on various functional morphology it is clear that the flow mode of the dorsal vessel ('heart') has changed during the evolution of hexapods. In all apterygotes and mayflies the flow is bidirectional. In most pterygote insects, however, it is unidirectional. In some endopterygote insects, the direction of the flow alternates. This is achieved by heartbeat reversal, which may have various physiological functions and is a derived condition that probably occurred several times during the course of insect evolution. Special attention is given to the hemolymph flow in body appendages. In ancestral hexapods, they are supplied by arteries, whereas circulation in appendages of higher insects is accomplished by accessory pulsatile organs. These auxiliary hearts are autonomous pumps and exhibit a great diversity in their functional morphology. They represent evolutionary innovations which evolved by recruitment of building blocks from various organ systems and were assembled into new functional units. Almost all pulsatile circulatory organs in insects investigated exhibit a myogenic automatism with a superimposed neuronal control. The neuroanatomy of insect circulatory organs has been investigated only in a small number of species but in considerable detail. Numerous potential peptidergic and a few aminergic mediators could be demonstrated by immunocytochemical and biochemical methods. The cardiotropic effectiveness of these mediators may vary among species and it can be stated that there is no uniform picture of the control of the various circulatory organs in insects. A possible explanation for the differences may lie in the different evolutionary origins of the muscular components. Furthermore, insect circulatory organs may represent important neurohemal releasing sites.     

Antennal circulatory organs in Onychophora,Myriapoda and Hexapoda: Functional morphology and evolutionary implications

Summary A comparative investigation of the antennal circulatory organs in representatives of the Onychophora, all subtaxa of the Myriapoda and numerous taxa of the Hexapoda (comprising a total of 54 species) revealed an unexpected diversity in structure and function.In the Onychophora, antennal vessels exist which are connected to the enlarged anterior end of the aorta dorsal to the brain.In the Chilopoda, Diplopoda and Symphyla, antennal vessels exist which originate from the dorsal vessel caudal to the brain. They extend under the optic lobes, lateral to the circumoesophageal connectives, into the antennae.In the Hexapoda, the investigations include representatives of all higher taxa, apart from the Paraneoptera and the Holometabola. Generally, antennal vessels exist. In the Diplura, they originate from the anterior end of the aorta in front of the brain. In all other insects the antennal vessels are separate from the dorsal vessel. Their proximal ends form ampullary enlargements which are attached to the frontal cuticle near the antenna bases. They communicate via valved ostia with the haemolymph sinus in front of the brain. In the Archaeognatha, Zygentoma, Odonata, certain Plecoptera and the Notoptera, no muscles are connected to these organs. In all other groups the ampullae are pulsatile as a result of associated muscles (antennal hearts). These muscles diverge widely in their attachments and act either as compressors (Dermaptera) or dilators of the ampullae (Embioptera, Blattopteroidea, Orthopteroidea, and some Plecoptera).In the Collembola and Ephemeroptera, special antennal circulatory organs are lacking. In some forms the anatomical arrangement of the inner organs, in conjunction with short diaphragms at the antenna bases, apparently leads to a channelling of haemolymph flow. This condition may be explained by the very short antennae of these insects and is considered as a convergent and apomorphic state in these taxa.The antennal vessels are supposed to be homologous within the Tracheata and to represent the lateral arteries of the antenna segment. An origin from the dorsal vessel is considered an ancestral state, which was lost in the stem lineage of the Ectognatha. Specific space constraints within the cephalic capsule are discussed as the possible reason for this loss. The evolution of pulsatile antennal circulatory organs in the Neoptera is the result of the association of muscles with the proximal ampullary ends of the antennal vessels. The attachments and innervation of these muscles indicate a derivation from precerebral pharyngeal dilators.Abbreviations Amp ampulla - Ant antenna - ant anterior - AN antennal nerve - Ao aorta - AV antennal vessel - Br brain - BrSi brain sinus - CC corpora cardiaca - CoeC circumoesophageal connectives - CM compressor muscle of ampulla - CT connective tissue - Dia diagphragm - do dorsal - DM dilator muscle of ampulla - DM1 ampullo-ampullary dilator muscle - DM2 ampullo-pharyngeal dilator muscle - DM3 ampullo-frontal dilator muscle - DM Acc accessory dilator muscle of ampulla - DV dorsal vessel - EB elastic band - FbDM fronto-buccal pharynx dilator muscle - FG frontal ganglion - FSa frontal sac - FSe frontal septum - FSi frontal sinus - Lb labium - LV lateral vessel of aorta - MA mouth-angle - Nr nervus recurrens - Oc ocellus - Oe oesophagus - OeSi oesophageal sinus - Ost ostium - Ph pharynx - Pl labial palpus - RM retractor muscle of mouth-angle - RMl lateral retractor of mouth-angle - RMm medial retractor of mouth-angle - SceSi supracerebral sinus - SD salivary duct - T tentorium     

The copulatory complex of Hemianax ephippiger (Burmeister) (Aeshnidae: Anisoptera)

Like other Anisoptera Hemianax ephippiger (Burmeister) bears two sets of copulatory apparatuses. The first set which is primary in nature is located on the ventral surface of the ninth abdominal segment and consists of the vestigial penis, the gonocoxites, the supra-anal appendages, the infra-anal appendage. The supra-anal appendages are well developed, lanceolate with serrate margin and spinous apices. They are dorso-ventrally flattened and furnished with long hairs and black teeth-like tubercles (T). The secondary copulatory complex is lodged inside the membranous fossa located on the ventral surface of second and third abdominal segments. It consists of anterior lamina, the posterior lamina, the supporting framework, the hamules, the penis sheath, the penis vesicle and the penis. The anterior lamina is deeply cleft at the posterior margin to accommodate the ovipositor of the female during copulation. Both the portions of the supporting framework are well developed. The anterior portion is somewhat rectangular while the posterior portion is nearly U-shaped. The anterior hamules are well developed with truncated and hooked portions, while the posterior hamules are very much reduced. The penis sheath is forcepate with well developed rectangular flap which hangs over the penis. The penis is stout, clearly demarcated into three segments, and bears a prominent groove on the mid-ventral line.     

The circulatory system in Phreatoicidea: implications for the isopod ground pattern and peracarid phylogeny

The circulatory systems of four species of Phreatoicidea and two species of Oniscidea were studied on the basis of serial semi-thin sections and a corrosion cast method. A 3D computer reconstruction was used to visualize the circulatory organs in the head of the Phreatoicidea. In the Phreatoicidea, the circulatory system consists of a longitudinal dorsal heart extending from the third thoracic to the border between the fourth and fifth pleonal segments. It is equipped with two pairs of asymmetrically arranged ostia, while five pairs of lateral cardiac arteries and an unpaired anterior aorta extend from the heart. Entering the head, the aorta is accompanied by the two first lateral arteries, which supply the muscles of the mandibles. Four pairs of arteries branch off the aorta to supply both pairs of antennae, the eyes, and sinuses in the head. In addition, several minute capillaries extend from the aorta to supply the brain. The two oniscidean species were re-investigated with regard to some characters which have been controversially discussed. In these species, the heart extends from the border between the fifth and sixth thoracic segments to the fifth pleonal segment. Five pairs of lateral cardiac arteries and the unpaired anterior aorta lead off the heart. A ventral vessel was not observed. The ground pattern of the circulatory system in isopods is reconstructed with greater reliability through optimisation of its characters based on proposed phylogenetic relationships. The results do not support a phylogenetic position of the Isopoda as basal Peracarida or even basal Eumalacostraca.     

Allatotropin Modulates Myostimulatory and Cardioacceleratory Activities in Rhodnius prolixus (Stal).

Haematophagous insects can ingest large quantities of blood in a single meal and eliminate high volumes of urine in the next few hours. This rise in diuresis is possible because the excretory activity of the Malpighian tubules is facilitated by an increase in haemolymph circulation as a result of intensification of aorta contractions combined with an increase of the anterior midgut peristaltic waves. It has been previously described that haemolymph circulation during post-prandial diuresis is stimulated by the synergistic activity of allatotropin (AT) and serotonin in the kissing bug Triatoma infestans; resulting in an increase in aorta contractions. In the same species, AT stimulates anterior midgut and rectum muscle contractions to mix urine and feces and facilitate the voiding of the rectum. Furthermore, levels of AT in midgut and Malpighian tubules increased in the afternoon when insects are getting ready for nocturnal feeding. In the present study we describe the synergistic effect of AT and serotonin increasing the frequency of contractions of the aorta in Rhodnius prolixus. The basal frequency of contractions of the aorta in the afternoon is higher that the observed during the morning, suggesting the existence of a daily rhythmic activity. The AT receptor is expressed in the rectum, midgut and dorsal vessel, three critical organs involved in post-prandial diuresis. All together these findings provide evidence that AT plays a role as a myoregulatory and cardioacceleratory peptide in R. prolixus.     

小地老虎成虫循环系统形态的初步研究

本文对小地老虎Agrotis ypsilon 成虫循环系统的形态作了初步研究,表明背血管由6个心室的心脏和倒V形的胸部大血管及头部分支的大血管组成.中胸辅搏动器很发达,与大血管的腔直接相连,具有一个小盾片腔前半部的肌肉搏动膜.后胸辅搏动器很小,与背血管无直接通道,具有一个没有肌肉的搏动膜.腹膈显著,具有翼肌.还描述了心脏和辅搏动器的搏动情形.     

Comparative analysis of the circulatory system in Amphipoda (Malacostraca, Crustacea)

We present data on the haemolymph vascular system (HVS) in four representatives of the major amphipod lineages Gammaridea, Hyperiidea and Caprellidea based on corrosion casting and three‐dimensional reconstructions of histological semi‐thin sections. In all these species the HVS comprises a dorsal pulsatile heart, which is continued in the body axis by the anterior and posterior aortae. The heart is equipped with three pairs of incurrent ostia. The number of cardiac arteries that lead off the heart varies among species: in the studied Gammaridea four pairs occur, in Hyperia galba only the three posterior pairs of cardiac arteries occur, while in Caprella mutica cardiac arteries are absent. In all the studied species the posterior aorta leads as a simple tube into the pleon attached to the dorsal diaphragm. The anterior aorta runs from its origin in the anterior part of the second thoracic segment into the cephalothorax. Both pairs of antennae have an arterial supply off the anterior aorta. An overview of previously studied species including our present findings shows the amphipod HVS to be relatively uniform and the gammarid form is discussed as being closest to the ground pattern of Amphipoda.     

绿盲蝽腹神经节的解剖结构

【目的】揭示绿盲蝽Apolygus lucorum腹神经节的组成结构。【方法】采用免疫组织化学染色方法,利用突触蛋白抗体对绿盲蝽成虫的腹神经节进行免疫标记,激光共聚焦扫描显微镜扫描照相获得原始数据,用图像分析软件进行标记,构建三维结构模型。【结果】绿盲蝽成虫腹神经节位于腹神经索的末端,与其前方的后胸神经节和中胸神经节紧密融合,形成后部神经节。与脑和胸神经节类似,腹神经节由周围的细胞体和内部的神经髓构成。腹神经节的神经纤维束主要包括位于腹侧的两条纵向神经连索和向两侧发出的9束神经纤维。9束神经纤维连接着9个神经原节,即富含突触联系的神经髓。这些神经原节紧密融合,无明显的边界,最后两节形成膨大的末端腹神经节。两侧的神经原节由横向的神经连锁连接起来。腹神经节外周的细胞体数量较多,排列紧密,大小一致,仅在前端背侧中间和后端腹侧中间位置分别有2个和5个体积较大的细胞体。【结论】本研究结果明确了绿盲蝽腹神经节的结构,为进一步研究昆虫的行为调控及神经系统发育和演化奠定一定的形态学基础。     

Homeotic genes autonomously specify the anteroposterior subdivision of the Drosophila dorsal vessel into aorta and heart

The embryonic dorsal vessel in Drosophila possesses anteroposterior polarity and is subdivided into two chamber-like portions, the aorta in the anterior and the heart in the posterior. The heart portion features a wider bore as compared with the aorta and develops inflow valves (ostia) that allow the pumping of hemolymph from posterior toward the anterior. Here, we demonstrate that homeotic selector genes provide positional information that determines the anteroposterior subdivision of the dorsal vessel. Antennapedia (Antp), Ultrabithorax (Ubx), abdominal-A (abd-A), and Abdominal-B (Abd-B) are expressed in distinct domains along the anteroposterior axis within the dorsal vessel, and, in particular, the domain of abd-A expression in cardioblasts and pericardial cells coincides with the heart portion. We provide evidence that loss of abd-A function causes a transformation of the heart into aorta, whereas ectopic expression of abd-A in more anterior cardioblasts causes the aorta to assume heart-like features. These observations suggest that the spatially restricted expression and activity of abd-A determine heart identities in cells of the posterior portion of the dorsal vessel. We also show that Abd-B, which at earlier stages is expressed posteriorly to the cardiogenic mesoderm, represses cardiogenesis. In light of the developmental and morphological similarities between the Drosophila dorsal vessel and the primitive heart tube in early vertebrate embryos, these data suggest that Hox genes may also provide important anteroposterior cues during chamber specification in the developing vertebrate heart.     

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.     

Morphological organization of abdominal colour patterns in pyrrhocorid bugs (Hemiptera-Heteroptera: Pentatomomorpha)

Postembryonic development of abdominal colour patterns, both epidermal pigmentation and cuticular melanization, of two model species, Pynhocoris apterus and Dysdercus cingulatus (Heteroptera: Pyrrhocoridae) is analysed with the aim of revealing morphological regularities involved in colour-pattern organization. This analysis is supplemented with a comparative study of diversity of colour patterns among 90 species of the Pyrrhocoridae. Comparison of both these approaches suggests that epidermal and cuticular patterns are ontogenetically independent of each other; that the ventral cuticular melanization is paired and respects boundaries delineated by epidermal pigmentation; that the dorsal cuticular melanization is unpaired and does not respect epidermal-colour boundaries; that the adult cuticular melanization develops almost independently of the larval one; and that the anterior and posterior regions of different segments are developmentally (and also evolutionarily) more tightly correlated than anterior and posterior parts of the same segment. These regularities are then compared with data concerning intrasegmental patterning of Drosophila and other insects.     

Extracardiac versus cardiac haemocoelic pulsations in pupae of the mealworm (Tenebrio molitor L.)

Pulsations in mechanical pressure of the pupal haemocoele were investigated by means of simultaneous recording from multiple sensors. It has been determined that cardiac and extracardiac haemocoelic pulsations are each regulated by substantially different and quite independent physiological mechanisms. At the beginning and in the middle of the pupal interecdysial period the anterograde heartbeat and extracardiac pulsations occur in similar, but not identical periods. During the advanced pharate adult stage, there appear almost uninterrupted pulsations from different sources: cardiac, extracardiac, intestinal, and the ventral diaphragm.Extracardiac pulsations are associated with pressure peaks of 200-500 Pa, occurring at frequencies of 0.3-0.5 Hz. The effect of heartbeat on haemocoelic pressure is very small, 100- to 500-fold smaller, comprising only some 1 or 2 Pa during the vigorous anterograde systolic contractions. Accordingly, extracardiac pulsations are associated with relatively large abdominal movements from 30-90 μm whereas heartbeat produces movements of only 100-500 nm. This shows that extracardiac pulsations can be easily confused with the anterograde heartbeat. It does not seem realistic to assume that the relatively weak insect heart, and not the 100- to 500-fold more powerful extracardiac system of abdominal pump, could be at all responsible for selective accumulation of haemolymph in anterior parts of the body, for inflation of wings or enhancement of tracheal ventilation.It has been established that thermography from the pericardial region is not specific for the heartbeat. It records subepidermal movement of haemolymph resulting from the actions of both dorsal vessel and extracardiac pressure pulses as well. Shortly before adult eclosion the cardiac and extracardiac pulsations occasionally strike in concert, which profoundly increases the flow of haemolymph through pericardial and perineural sinuses. The relatively strong extracardiac pulsations cause passive movements of various visceral organs, tissue membranes, or tissue folds, giving thus a false impression of an authentic pulsation of tissues. In addition, extracardiac pulsations cause rhythmical movements of haemolymph between various organs, thus preventing haemolymph occlusion at the sites where the heart does not reach. It has been emphasized, finally, that the function of the autonomic nervous system (coelopulse), which integrates extracardiac pulsations, depends on homeostatic moderation of excessive or deficient conditions in insect respiration and haemolymph circulation.     

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.     

The circulatory system in Mysidacea--implications for the phylogenetic position of Lophogastrida and Mysida (Malacostraca, Crustacea)

The morphology of the circulatory organs in Mysida and Lophogastrida (traditionally combined as Mysidacea) is revisited investigating species so far unstudied. In addition to classical morphological methods, a newly developed combination of corrosion casting with micro computer tomography (MicroCT) and computer aided 3D reconstructions is used. Lophogastrida and Mysida show a highly developed arterial system. The tubular heart extends through the greater part of the thorax and is connected with the ventral vessel via an unpaired descending artery. It is suggested that a distinct ostia pattern supports the monophyly of Mysidacea. The cardiac artery system is more complex in Lophogastrida than in Mysida, consisting of up to 10 pairs of arteries that supply the viscera. In both taxa, an anterior and posterior aorta leads off the heart. In the anterior part of the cephalothorax the anterior aorta forms dilations into which muscles are internalized; these structures are called myoarterial formations. One of these myoarterial formations can also be found in all the other peracarid taxa but not in other Malacostraca.     

Tonganoxichnus a new insect trace from the Upper Carboniferous of eastern Kansas

Upper Carboniferous tidal rhythmites of the Tonganoxie Sandstone Member (Stranger Formation) at Buildex Quarry, eastern Kansas, USA, host a relatively diverse arthropod-dominated ichnofauna. Bilaterally symmetrical traces displaying unique anterior and posterior sets of morphological features are well represented within the assemblage. A new ichnogenus, Tonganoxichnus, is proposed for these traces. T. buildexensis, the type ichnospecies, has an anterior region characterized by the presence of a frontal pair of maxillary palp impressions, followed by a head impression and three pairs of conspicuous thoracic appendage imprints symmetrically opposite along a median axis. The posterior region commonly exhibits numerous delicate chevron-like markings, recording the abdominal appendages, and a thin, straight, terminal extension. T. buildexensis is interpreted as a resting trace. A second ichnospecies, T. ottawensis, is characterized by a fan-like arrangement of mostly bifid scratch marks at the anterior area that records the head- and thoracic-appendage backstrokes against the substrate. The posterior area shows chevron-like markings or small subcircular impressions that record the abdominal appendages of the animal, also ending in a thin, straight, terminal extension. Specimens display lateral repetition, and are commonly grouped into twos or threes with a fix point at the posteriormost tail-like structure. T. ottawensis is interpreted as a jumping structure, probably in connection with feeding purposes. The two ichnospecies occur in close association, and share sufficient morphologic features to support the same type of arthropod producer. T. buildexensis closely mimics the ventral anatomy of the tracemaker, whereas T. ottawensis records the jumping abilities of the animal providing significant ethologic and paleoecologic information. The presence of well-differentiated cephalic, thoracic, and abdominal features, particularly in T. buildexensis, resembles the diagnostic tagmosis and segmentation of insects. Detailed analysis of trace morphology and comparison with described Paleozoic insect fossils and extant related forms suggest a monuran as the most likely tracemaker.     

Morphology of the haemolymph vascular system in Tanaidacea and Cumacea: - implications for the relationships of "core group" Peracarida (Malacostraca; Crustacea)

Tanaidacea and Cumacea are crucial for understanding the phylogenetic relationships of "core group" peracarids. Here, the haemolymph vascular system in three tanaidacean and four cumacean species was studied on the basis of histological sections and 3D reconstruction. The circulatory organs in Tanaidacea include a tubular heart which extends through most of the thorax. It is extended into the cephalothorax by an anterior aorta. Haemolymph enters the heart through one to two pairs of incurrent ostia. Up to five pairs of cardiac arteries emanate from the heart to supply viscera in the body cavity. In the anterior cephalothorax, the aorta forms a pericerebral ring from which the arteries for the brain and the antennae branch off. In Cumacea, the heart is shorter but more voluminous. In all cumaceans studied, five pairs of cardiac arteries supply the thoracopods and the pleon. The single pair of ostia is situated in the centre of the heart. The anterior aorta runs into the anterior cephalothorax where it supplies the brain and antennae. This paper provides a general comparative discussion of all available data from the literature and the data provided herein. In certain details, the haemolymph vascular system of the Tanaidacea resembles that of Amphipoda, and some correspondences between Cumacea and Isopoda are pointed out. These findings might support a closer relationship between the latter two taxa while they show no support for an amphipod/isopod clade.