Outer Flagellum Research Articles

Tanaidaceans (Crustacea: Peracarida: Apseudidae) from southern Portugal with description of the new species Apseudopsis formosus, report of five first records and a biogeographic overview: unexpected expansion or understudied hotspot?

This study describes Apseudopsis formosus sp. nov., a new apseudomorph tanaidacean species from the Ria Formosa lagoon (southern Portugal). Species description was based on 223 individuals (22 juveniles, 60 males and 141 females), comprising diverse developmental stages (juveniles II, males I and II, preparatory, copulatory and intermediate females). The total length of the studied population ranged from 2.2 to 3.0 mm in juveniles, 2.5 to 4.8 mm in males and 2.9 to 4.9 mm in females. Overall, Apseudopsis formosus sp. nov. differs from congeneric tanaidaceans from the Atlantic Ocean and Mediterranean Sea by the presence of combined different morphological characters such as short pointed rostrum, posterolateral pointed corners on pereonites 2–6, hyposphenium only on pereonite 6, antennular outer flagellum 7- to 10-segmented, inner flagellum 3-segmented and five spines on propodus of pereopod 1, and sexual dimorphism evidenced by a pronounced mid-dorsal triangular wing-shaped protuberance on male merus cheliped, unique in Apseudopsis genus. At each studied developmental stage, some individuals presented abnormalities in spination, having only four spines in one of the propodus of pereopod 1. Additionally, five first records of Apseudopsis from the Algarve coast (A. adami, A. bacescui, A. elisae, A. mediterraneus and A. uncidigitatus) are reported for Portuguese waters. A biogeographic overview of the genus Apseudopsis is presented through the compilation and mapping of all worldwide reported occurrences. Passive dispersion can explain the most recent species distribution, yet not disregarding that the study area is taxonomically understudied. This study contributes to improve the current knowledge on tanaidacean taxonomy and updates the geographical distribution range of the Apseudopsis–complex.

A new genus and species of Sphyrapodidae (Crustacea, Peracarida, Tanaidacea) from the southern coast of the South Korea.

Wandogarida canalicula gen. n et sp. n. (Tanaidacea, Sphyrapodidae) is described from the southern coast of Korea (NW Pacific). The genus is included in the subfamily Sphyrapodinae Guţu, 1980 by having a mandible lacking a palp. It has a close affinity with the genus Poligarida Bamber & Marshall, 2013 in the third pereonite having lateral pointed apophyses, the antennule of males with fringes of aesthetascs on articles 1 and 2 of the outer flagellum and the antenna with an elongate article 2. However, it is distinguished from Poligarida by having a maxillular palp. Wandogarida gen. n. can be differentiated from other genera within the subfamily Sphyrapodinae by the unique shape characterised by the male’s antennule article 1 with its rough denticles and a deep groove, pleonites each with a ventral hyposphenium, the maxillule with uniarticulate palp and the presence of prominent sexual dimorphism in the mouthparts. An identification key to the five genera of the subfamily Sphyrapodinae is presented.

Cryptapseudes leroyi, a New Species of Apseudomorphan Tanaidacean (Crustacea: Peracarida: Metapseudidae) from the Hawaiian Archipelago

Previously nine species belonging to the crustacean order Tanaidacea have been described from Hawaiian waters. Specimens of a new metapseudid tanaidacean, Cryptapseudes leroyi David & Heard, n. sp., from the western Main Hawaiian Islands were discovered in collections of the Bernice P. Bishop Museum. The new species, which represents the fourth member of the genus Cryptapseudes Bacescu, is distinguished from the other three members of the genus by a combination of characters including an antennule with the outer flagellum having three or four articles (no more than two reported for other known species) and article-3 of the mandibular palp with seven to eight finely pectinate setae. An artificial key is presented to distinguish the four species. Discovery of C. leroyi in Hawaiian waters extends the range for the genus from the western Indian Ocean over 14,000 km northeast to the tropical waters of the midnorthern Pacific Ocean.

Atopobathynella paraoperculata n. sp. (Syncarida, Bathynellacea, Parabathynellidae) from the River Krishna, southeastern India

To date, the genusAtopobathynellaSchminke, 1973, is known by 11 species in the world. Here,Atopobathynella paraoperculatan. sp., the second species of this genus from India, is described from the interstitial hyporheic zone of the River Krishna in Andhra Pradesh state. It has closest similarity with its Indian congener,AtopobathynellaoperculataRanga Reddy, Drewes & Schminke, 2008, as borne out by the fusion of the inner flagellum of the antennule with the first segment of the outer flagellum, the presence of a seta on the subdistal outer surface of the uropodal sympod; the antennal organ consists exclusively of two massive lobes; the antenna has three instead of four armature elements; the proximal segment of the maxillule has two instead of four distinct claws; the uropodal sympod has an inhomonomous row of spines; and the anal operculum is massive. However, the new species can be easily separated fromA. operculataby several other criteria such as the labrum without vs. with tubular pores; the second endopodal segment of Th I has two setae vs. one seta; the uropodal sympod has four vs. eight spines; the uropodal endopod has two weak setae vs. one normal seta; the pleotelson is unarmed vs. armed; and the anal operculum has a subacute vs. a rounded tip. Further, based on the novelties observed in the two Indian congeners, some of the principal generic characters and their states are briefly discussed, and also some ecological notes are added.

New species and records of Apseudomorpha (Crustacea: Tanaidacea) from Taiwan.

The present study reports the first record of Apseudomorpha from Taiwan and includes descriptions of three new species and one new species record. Paradoxapseudes pangcahi sp. nov. differs from the most similar congener, Paradoxapseudes littoralis, by having one segment less in the antennal flagellum and fewer segments in the uropod endopod. Pseudoapseudomorpha tagopilosus sp. nov. is distinguished from its most similar congener, Pseudoapseudomorpha ornata, by having one long lateral seta on pleonite 4, a four-segmented antennular outer flagellum, and a male with smaller and thinner 'small' cheliped than that of the female and with vestigial pleopods on pleonite 3. Indoapseudes multituberculata sp. nov. stands out from its congeners by having pleopods only on the last two pleonites in females, many small tubercles terminally on the pleotelson, and mandibular palp article 1 with noticeable distal teeth. The Synapseudes species recorded in the present study morphologically agrees with Synapseudes hansmuelleri that was originally described from the Tioman Archipelago, Malaysia, South China Sea. Morphological comparisons between each of the three newly described species and its congeners are tabulated.

A new stygobitic species of Stygocarididae (Crustacea: Anaspidacea) from South America.

The only South American Anaspidacean families are the Stygocarididae Noodt and the monotipic Patagonaspididae Grosso & Peralta. I describe a new Stygocarididae, Parastygocaris luisgrossoi n. sp. from the hyporheic zone of a stream in Sierra de San Luis, Argentina. The main characters of the new species include: antennula outer flagellum with 9-10 articles, sexual dimorphism in flagella; antenna with 4-segmented peduncle and 5-articulate flagellum; maxilla with row of 8 setae along inner margin of proximal endite; uropod: inner margin of protopod with 7-8 setae and distal segment of exopod lined by 7 setae; pereopod 6 female with 1 long plumose seta on basis. The morphology and chaetotaxy of the new taxon is compared with congeneric species. The long evolutionary history of the Gondwanan Anaspidacea and the accompanying fauna of the new species, suggest the probable existence of an ancient groundwater basin in western Argentina, south of 28ºS that would have harboured interstitial fauna of great and diverse antiquity.

A new species of the genus Atopobathynella Schminke, 1973 (Crustacea, Syncarida, Bathynellacea) from the hyporheic zone of the River Godavari, South India

Atopobathynella Schminke, 1973 is the third genus of Parabathynellidae to be discovered in India. A. operculata sp. n. shows three characters, which are unique within Parabathynellidae: fusion of the inner flagellum of the antennule with the first segment of the outer flagellum, presence of a single seta on the lateral surface of the uropodal sympod, and conspicuous tubes on the labrum. A. operculata sp. n. is also the first species of the genus with an inhomonomous spine row on the uropodal sympod and with an anal operculum almost reaching the end of the furca. Atopobathynella has a Gondwanan distribution, and is being reported for the first time from Asia.

Behavioral and Electrophysiological Experiments Suggest That the Antennular Outer Flagellum Is the Site of Pheromone Reception in the Male Helmet CrabTelmessus cheiragonus

Sexually competent females of Telmessus cheiragonus (helmet crab) release two pheromones that elicit grasping and copulation behaviors in males (Kamio et al., 2000, 2002, 2003). Our study aimed to use behavioral and electrophysiological techniques to identify the site of reception of these sex pheromones. In behavioral experiments, either the inner or the outer flagella of the antennules were ablated bilaterally from male crabs, and responses of male crabs to female odor were examined. When the inner flagella were surgically ablated, the sexual response (i.e., grasping and copulation behavior) of male crabs was not significantly changed relative to control animals that had their second antennae ablated. In contrast, the sexual response was significantly reduced when the outer flagella of the antennules were ablated, suggesting that the outer flagellum is the receptor organ that detects the sex pheromones. In electrophysiological experiments, urine, which in females contains the pheromone that elicits grasping behavior by males but does not contain the pheromone eliciting copulation, whose release site is not known, was tested. Female and male urine as well as shrimp extract evoked phasic responses of chemosensory afferents innervating aesthetasc sensilla on the outer flagellum of male crabs. The response of the afferents had significantly higher magnitude and lower threshold when female urine was applied. Thus, behavioral and electrophysiological observations suggest that in male helmet crabs, the outer flagellum of the antennule is the chemosensory organ that detects female sex pheromone.

First larvae ofLebbeus comanthiandThor amboinensis(Decapoda: Hippolytidae) hatched in the laboratory

The decapodid stage of Lebbeus comanthi Hayashi and Okuno and the first zoea of Thor amboinensis (De Man) are described based on laboratory‐hatched eggs from females collected from Japan. The decapodid stage of L. comanthi is readily distinguished from that of L. groenlandicus by the carapace without anteroventral denticle and tooth behind rostrum, the absence of the antennal spine, the four‐segmented outer flagellum of the antennule, the absence of the palp of the mandible, and the telson with posterior margin concaved medially and without dorsolateral spine. The carapace with anteroventral denticle and the third abdominal somite distinctly curved in lateral view distinguish the first zoea of T. amboinensis from that of T. dobkini Chace and T. floridanus Kingsley. Larval characters of the genus Thor are summarized.

Concurrent Signals and Behavioral Plasticity in Blue Crab (Callinectes sapidus Rathbun) Courtship.

Behavioral flexibility and behavioral regulation through courtship signals may both contribute to mating success. Blue crabs (Callinectes sapidus) form precopulatory pairs after courtship periods that are influenced by female and perhaps male urine-based chemical signals. In this study, male and female crabs were observed in 1.5-m circular outdoor pools for 45 min while the occurrence and sequence of courtship behaviors and pairing outcomes were recorded. These results were then compared with trials in which males or females were blindfolded; lateral antennule (outer flagellum) ablated; blindfolded and lateral antennule ablated; or had received nephropore blocks. The relative importance of visual and chemical sensory systems during blue crab courtship were then determined and urine and non-urine based chemical signals for both males and females were examined. Courtship behaviors varied considerably in occurrence and sequence; no measured behavior was necessary for pairing success. Male or female blindfolding had no effect on any measured behavior. Males and females required chemical information for normal courtship behaviors, yet blocking male or female urine release did not affect courtship behaviors. Males required chemical information to initiate pairing or to maintain stable pairs. Male urine release was necessary for stable pairing, suggesting that male urine signals may be involved in pair maintenance rather than pair formation. Females that could not receive chemical information paired faster and elicited fewer male agonistic behaviors. The results demonstrate a great variability and flexibility in blue crab courtship, with no evidence for stereotyped behavioral sequences. However, these behaviors appear regulated by urine- and nonurine-based redundant chemical signals emanating from both males and females. Although urine-based signals play roles in blue crab courtship, chemical signals from other sites appear to carry sufficient information to elicit a full range of behavioral responses in males and females.

Orthodromically and antidromically evoked local field potentials in the crayfish olfactory lobe

A local field potential, consistent in form and duration, can be recorded from the olfactory lobe of crayfish following electrical stimulation of the outer flagellum of the antennule. The field potential is reversibly blocked by perfusion of the brain with low-[Ca2+] saline or <IMG src="/images/symbols/gamma.gif" WIDTH="9" HEIGHT="12" ALIGN="BOTTOM" NATURALSIZEFLAG="3">-aminobutyric acid and, to a lesser extent, histamine. Paired shocks to the antennule and antidromic electrical stimulation of olfactory lobe output neurones also partially block the field potential. Comparing the field potential with simultaneously recorded intracellular responses of olfactory interneurones reveals a coincidence between excitatory and inhibitory effects in the interneurones and the appearance of identifiable components of the field potential. We interpret the field potential to reflect the response of neural elements in the olfactory lobe to orthodromic activity in the axons of the olfactory receptor neurones on the antennule. We conclude from the blocking experiments that the greater part of the field potential stems from neurones in the olfactory lobe that are postsynaptic to olfactory receptor neurones. As such, it provides a robust indication of olfactory neurone activity.

The callynophore, a eucaridan/peracaridan sensory organ prevalent among the Amphipoda (Crustacea)

The callynophore is a sensory organ located at the proximal end of the outer flagellum of the antennule. The organ is considered to be formed through fusion of the proximal flagellar articles and proliferation of transverse rows of aesthetases on the medial or ventral face of the fused articles. It is found in eucaridan and peracaridan groups. Among the eucaridans it is well developed in the Penaeoidea and the Caridea. Among the peracaridans it is best developed and most diverse in the Amphipoda, where it occurs in two suborders and 15 superfamily groups. One function of the callynophore, where it occurs in reproductively mature males, is considered to be detection of receptive females by chemoreception. Another function, where it occurs in males and females of the same species, is considered to be food detection, also by chemoreception. Other functions may include prey detection in predators and host detection in parasitoids. It is hypothesized that the callynophore appeared early in the evolution of the peracaridans as part of the swimming male reproductive strategy.

Fine structure of aesthetasc chemoreceptors in the crayfish Orconectes propinquus

The outer antennular flagella of decapod crustaceans bear chemoreceptive hairs called aesthetascs. In the crayfish Orconectes propinquus these sensilla are located ventrally on the 11–13 most distal segments of the outer flagella. Two clumps of 3–6 aesthetascs occur on each segment, giving a total of approximately 80 aesthetascs per outer flagellum. Aesthetascs are100–150 μm long and about 12 μm in diameter. Each has a single annulation 30 μm from the hair base. The sensilla arise from immovable sockets and are directed distally at a 45° angle to the main body of the antennule. Aesthetascs lack an apical pore. However, the distal portion of each sensillum has thin cuticular walls which are readily penetrated by dye; this is probably the site where chemical stimuli enter. In O. propinquus each aesthetasc is innervated by 40–110 sensory neurons. Each neuron gives rise to a dendrite that branches into two cilia (9 × 2 + 2 structure; 0.15–0.20 μm in diameter). No further branching of outer dendritic segments occurs and thus each aesthetasc contains 80–220 sensory endings. Within the antennule lumen the dendrites are surrounded by two sheath cell layers, an inner layer and an outer layer. The inner sheath cells ascend 50 μm into the aesthetasc lumen; the outer sheath cells terminate at the sensilla bases. The outer dendritic segments gradually taper in diameter and terminate 25 μm from the sensilla tips.

MORPHOLOGICAL AND BEHAVIORAL IDENTIFICATION OF THE SENSORY STRUCTURES MEDIATING PHEROMONE RECEPTION IN THE BLUE CRAB,CALLINECTES SAPIDUS

Scanning electron microscopy was used to survey the aesthetasc tuft on the outer flagellum of the antennule (1st antenna) in order to identify sensilla potentially involved in pheromone detection by the male blue crab. These studies showed that the tuft of each antennule is divided into a mesial and lateral half by a region of cuticle from which no sensilla arise. Two setal types were revealed: the aesthetascs and previously undescribed sensilla which originate exclusively on the mesial side of the tuft and project to the lateral half between the rows of aesthetascs. Experiments were performed in which the mesial half, lateral half, or entire aesthetasc tuft was bilaterally ablated from the antennules of test males. As revealed by behavioral tests, pheromone responses in "mesial half" and "lateral half" ablation groups were reduced 22% and 21%, respectively, relative to control (P > 0.10); whereas a highly significant (P < 0.005) response decrement (80% relative to control) occurred in the "entire tuft" ablated group. The data suggest that pheromone reception in the male blue crab is effected via the aesthetascs. The relationship of these findings to those for other decapod crustaceans is discussed.

The motor innervation and the musculature of the antennule of the Australian mud crab, Scylla serrata (Forskäl) (Portunoidea, Brachyura)

The motor innervation and musculature of the antennule of the Australian mud crab Scylla serrata (Forskäl) (Portunoidea, Brachyura) is described. The musculature of the medial and distal segments of the antennule can be divided into three muscle groups: 30, 31 and 32, which are innervated by 11 motor axons. Muscle group 30 serves to raise the distal segment and is composed of two slow muscles, M30V and M30D. These muscles are innervated by three motor axons, A30V, A30D and A30V–D, which form a specific antennular nerve (nerve 2). Muscle groups 31 and 32 are innervated by 8 motor axons, which also form a specific nerve (nerve 1) in the proximal portions of the medial segment of the antennule. Muscle group 31 serves to depress the distal segment and is composed of two slow muscles, M31S V and M31S m , and one fast muscle, M3IF. Both slow muscles are innervated by branches of two motor axons, A31S 1 and A31S 2 . The fast muscle M31F is innervated by two motor axons, A31F and A31–32F. Muscle group 32 serves to depress the outer flagellum and is composed of one slow muscle and one fast muscle. The slow muscle, M32S, is innervated by two motor axons, A32S 1 and A32S 2 , while the fast muscle, M32F, is innervated by two motor axons, A32F and A31–32F which also innervates M31F. A single motor axon, A32F–S, innervates both M32F and M32S. The anomuran and brachyuran antennules are compared in relation to the homology between specific muscles, the functional adaptations of the antennular muscles, and the total number of motor axons present. The results suggest that, in contrast to the situation in the leg and abdominal neuromuscular systems, the peripheral connections and/or the total number of antennular motoneurons show considerable phylo­genetic plasticity.

Movement dependent position changes of the antennular flagellum ofPalaemon xiphias (Risso)

The angular positions of the outer flagellum ofPalaemon xiphias were obtained by cinematographic measurements during different phases of locomotion. Contrary to the upright resting position the flagella are stretched forward into a distinct starting position preliminary to any forward movement, and then pushed down with acceleration of swimming speed. These phenomena are discussed in context with comparable behaviour in other decapods and in insects.

Central patterning and reflex control of antennular flicking in the hermit crab Pagurus alaskensis (Benedict).

1. The effects of altering sensory input on the motoneuronal activity underlying antennular flicking have been tested. 2. Removal of the short segments of the outer flagellum results in a reduction of the number of spikes/burst in the fast flexor motoneurones A31F and A32F. 3. During a flick the delay between the burst in motoneurone A31F and the burst in motoneurone A32F is insensitive to alteration of sensory input. 4. Sensory feedback from the flexion phase of a flick is necessary for the activation of either extensor motoneurone. Evidence is presented to suggest that this feedback is primarily from joint-movement receptors at the MS-DS and DS-OF joints. 5. The results are incorporated into a model in which the patterns of flexor activity result from some specified properties of three components: a trigger system, a follower system, and the spike initiating zone of the flexor motoneurones. The trigger system determines when a flick will occur. The follower system determines the number of flexor spikes during a flick. Properties of the spike initiating zone determine the spike frequency and the timing between bursts in the flexor motoneurones. Extensor activity in the model is reflexively elicited by feedback from phasic, unidirectional receptors sensitive to joint flexion. 6. The functional significance of reflex control of extensor activity is discussed in relation to the form and proposed function of antennular flicking. It is suggested that this form of control is adapted to the function of antennular flicking because flexion at the MS-DS joint is not always necessary for the fulfilment of the fuction of a flick.

Surface structures of the antennular flagella of the hermit crab Pagurus alaskensis (Benedict): A light and scanning electron microscopy study.

The surface structures of the antennular flagella of Pagurus alaskensis are described in detail. Attention is directed towards the surface morphology of two types of possible sensilla: (1) exoskeletal pores (1.0-3.0 μm in diameter); (2) setae of various kinds. In addition, small (0.1-0.2 μm) pits occur in the exoskeleton which are not considered to be sensory in function. The exoskeletal pores are found at fairly specific locations on both the inner and outer flagella, particularly on the short segments of the outer flagella. Neither the inner nor the outer flagella are bilaterally symmetrical with respect to their setal armature. On the outer flagellum six groups of setae may be distinguished: lateralmesial; dorsal; ventral; accessory; aesthetasc; setae of the distal segment. On the inner flagellum setae of the mesial and lateral rows form distinctive groups. The morphology, orientation and locations of all the flagellar setae are defined and where possible the numbers of the various morphological types within the specific setal groups are given. It is noteworthy that many setal types have obvious apical pores and yet no pores could be found in the chemoreceptive aesthetasc setae. The functions of the various setae are discussed in relation to their topographical position and to existing electrophysiological and behavioral data. Some suggestions are made about future experiments to demonstrate the central connections of specific sensilla or groups of sensilla and to show their significance in the whole animal.

Regeneration of the antennules in the Australian freshwater crayfish, Cherax destructor.

AbstractRemoval of one eye from the Australian freshwater crayfish, Cherax destructor, results in the growth of a heteromorph appendage which re‐ sembles the outer flagellum of the antennule. The heteromorph is con‐ sistently uniramous.Transplanting part of the animal's own antennule into the eye stalk after removal of the ipsilateral eye results in a significant number of biramous appendages being developed in the eye socket. Biramous appendages when they possess fully differentiated hairs, can be identified as being the external and internal flagella of the antennule. Triramous appendages were never observed.The specificity of the antennular sensilla was tested in relation to the cleaning behavior released by stimulating them electrically. Sensilla on the external flagellum of the antennule produce depression of the antennule and cleaning using the maxillipeds. This behavior is also produced when the heteromorph appendage is stimulated although in this case it is misdirected. Stimulation of the hairs in the eye socket releases cleaning of the eye socket with the 2nd and 3rd walking legs. Eye socket cleaning is not released by stimulation of the heteromorph indicating that the antennular sensilla retain their specificity in relation to the cleaning behavior released.Removal of the antennule results in the ipsilateral olfactory lobe becoming smaller than the contralateral lobe. No change was observed in the accessory lobes.

The Antennular Activities of the Hermit Crab, Pagurus Alaskensis (Benedict)

ABSTRACT The antennular activities of the hermit crab, Pagurus alaskensis, were studied with the aid of motion pictures taken at speeds of 50, 200 and 400 frames/sec. Most movements of the antennule represent one of four types of antennular activity: flicking, rotation, wiping and withdrawal. These activities are described in detail. Water resistance forces contribute to the timing and duration of some antennular movements. Flicking occurs non-rhythmically and flicks of the left and right antennules ail never synchronized. The factors which influence the mean frequency of flicking are discussed. The timing of joint movements during a flick, and the morphology of the outer flagellum and the aesthetasc hairs, appear to be adapted to facilitate splaying of the aesthetascs. It is proposed that this splaying might facilitate the chemoreceptive process by circulating water around the aesthetasc hairs. During antennular wiping the endopodites of the 3rd maxillipeds are used to remove debris caught amongst the aesthetasc hairs. Light mechanical stimulation of the aesthetascs is sufficient to elicit wiping. The antennules are reflexively withdrawn from certain stimuli either by extension or by slow or fast flexion. The functional significance of the withdrawal reflexes are discussed in relation to the stimuli involved and the form of the reflexes. Continued application of certain stimuli to the antennules, eyestalks, antennae or body results in tonic flexion withdrawal which involves postural modifications of the antennules, eyestalks and antennae.