First report of the order Mysida (Crustacea) in Antarctic marine ice caves, with description of a new species of Pseudomma and investigations on the taxonomy, morphology and life habits of Mysidetes species

SCUBA diving explorations of three islands off Dumont d’Urville Station at the coast of Adélie Land, East Antarctica, enabled the observation of marine ice caves. Sampling in this unusual habitat yielded a total of three species of Mysidae, altogether previously poorly known or unknown to science. Pseudomma kryotroglodytumsp. nov. is described, based on the structure of the antennal scale, telson and on cornea-like lateral portions set off against the main body of eyeplates. Mysidetes illigi is re-established at species level after almost a century in synonymy. Re-descriptions are provided for M. illigi and M. hanseni, based on types and ice cave materials. Keys to the Southern Ocean species of Pseudomma and to the world-wide species of Mysidetes are given. Phylogenetic trees are provided for the genera Pseudomma and Mysidetes. 18S rDNA sequences of P. kryotroglodytum differ from GenBank sequences of other Pseudomma species. First sequence data are given for species of the genus Mysidetes: 18S differs between the two examined species and COI is quite diverse between and within species. We found previously unknown, probably sensorial structures in these ice cave species: in P. kryotroglodytum, the basal segment of the antennula shows a pit-like depression with striated pad on the bottom and a median cyst, connected with the bottom of the eyeplate cleft. M. illigi shows a female homologue of the appendix masculina bearing a field of modified setae. Subsequent investigations demonstrated these structures also in species from other habitats. The feeding apparatus and stomach contents of the three ice cave species point to brushing of small particles (detritus, microalgae) from available surfaces, such as sediment, rock and the ice surface. Differences in the feeding apparatus are very subtle between the two Mysidetes species. The high content of fat bodies in M. hanseni could help it to survive periods of starvation. The large storage volume of the foregut in P. kryotroglodytum points to the collection of food with low nutritional quality and could help to balance strongly fluctuating food availability. Summer specimens of M. hanseni showed a bimodal frequency of developmental stages in the marsupium and bimodal size-frequency distribution of free-living stages. The females with younger brood (embryos) were, on average, larger and carried more marsupial young than those with older brood (nauplioid larvae). All examined incubating and spent females showed (almost) empty foreguts and empty ovarian tubes, suggesting possible semelparity and death following the release of young. The absence of juveniles and immature females from summer samples suggests that growth and accumulation of fat and yolk occur outside ice caves, while such caves could be used by fattened adults as shelter for brooding. A provisional interpretation proposes a biannual life cycle for M. hanseni, superimposed with shifted breeding schedules, the latter characterised by early breeding and late breeding females, probably in response to harsh physical and trophic conditions along the continental coast of Antarctica.

Overcoming a 'forbidden phenotype': The parrot's head supports, propels, and powers tripedal locomotion

No vertebrate, living or extinct, is known to have possessed an odd number of limbs. Despite this ″forbidden phenotype″, gaits that utilize odd numbers of limbs (e.g., tripedalism or pentapedalism) have evolved in both avian and mammalian lineages. Tripedal locomotion is commonly employed by parrots during climbing, who utilize their beaks as an additional support. However, it is unclear whether the beak functions simply as a stabilizing hook, or as a propulsive limb. Here, we present data on kinetics of tripedal climbing in six rosy –faced lovebirds (Agapornis rosiecollis). Our findings demonstrate that parrots utilize cyclical tripedal gaits when climbing and the beak and hindlimbs generate comparable propulsive and tangential substrate reaction forces and power. Propulsive and tangential forces generated by the beak are of equal or greater magnitudes to those forces generated by the forelimbs of humans and non –human primates during vertical climbing. We conclude that the feeding apparatus and neck musculature of parrots has been co–opted to function biomechanically as a third limb during vertical climbing. We hypothesize that this exaptation required substantive alterations to the neuromuscular system including enhanced force–generating capabilities of the neck musculature and modifications to limb central pattern generators.

Three-dimensional reconstruction of the face and feeding apparatus of the predatory nematode Pristionchus pacificus

Pristionchus pacificus is a nematode model for the developmental genetics of morphological polyphenism, especially at the level of individual cells. The polyphenism of P. pacificus includes an evolutionary novelty, moveable teeth, which have enabled predatory feeding in this species and others in its family (Diplogastridae). From transmission electron micrographs of serial thin sections through an adult hermaphrodite of P. pacificus, we three-dimensionally reconstructed the 73 epithelial cells of its face, mouth, and pharynx. We found that the epithelia that produce the predatory morphology of P. pacificus are identical to Caenorhabditis elegans in the number of cell classes and nuclei. However, differences in cell form, connectivity, and nucleus position correlate with gross morphological differences from C. elegans and outgroups. Moreover, we identified fine-structural features, especially in the anteriormost pharyngeal muscles, that underlie the conspicuous, left-right asymmetry that characterizes the P. pacificus feeding apparatus. Our reconstruction provides an anatomical map for studying the genetics of polyphenism, feeding behaviour, and the development of novel form in a satellite model to C. elegans.

Exceptional multifunctionality in the feeding apparatus of a mid-Cambrian radiodont

Radiodonts (stem Euarthropoda) were ecologically diverse, but species generally displayed limited functional specialization of appendages along the body axis compared with crown group euarthropods. This is puzzling, because such functional specialization is considered to have been an important driver of euarthropod ecological diversification. One way to circumvent this constraint could have been the functional specialization of different parts of the frontal appendages, known to have been ecologically important in radiodonts. This hypothesis has yet to be tested explicitly. Here we redescribe the poorly known mid-Cambrian hurdiid radiodont Stanleycaris hirpex from the Burgess Shale (Stephen Formation) and quantitatively assess functional specialization of the frontal appendages of stem euarthropods. The appendages of Stanleycaris are composed of 14 podomeres, variously differentiated by their possession of pectinate endites, mono- to trifurcate medial gnathites, and outer spines. The oral cone is tetraradially organized and can be uniquely distinguished from those of other hurdiids by the presence of 28 rather than 32 smooth tridentate plates. Our phylogenetic analysis finds Stanleycaris in a grade of hurdiids retaining plesiomorphic raptorial appendicular functionality alongside derived adaptations for sweep feeding and large, bilaterally opposed gnathites. We conclude that the latter performed a masticatory function, convergent with gnathal structures like mandibles in various panarthropods. Taken together, Stanleycaris and similar hurdiids provide an extreme example of the evolution of division of labor within the appendage of a stem euarthropod and suggest that this innovation may have facilitated the functional transition, from raptorial to sweep feeding, at the origin of the hurdiid clade.

Ontogenetic Changes of the Aquatic Food Uptake Mode in the Danube Crested Newt (Triturus dobrogicus Kiritzescu 1903)

The study of the feeding mechanisms in vertebrates requires an integrative approach since the feeding event consists of a chain of behaviors. In the present study we investigated the food uptake behavior in different ontogenetic stages in the Danube crested newt (Triturus dobrogicus). We focused on the coordination in the kinematics of the elements of the locomotor and the feeding systems at the transition between the approach of the newt to the prey and the food uptake start. In the feeding strategy of the larvae of T. dobrogicus, the phase of food search is replaced by an initial “food detection phase.” In both larvae and adult specimens, the animals approached the food to a close distance by a precise positioning of the snout besides the food item. The larvae were able to reach food items offered at over 80° relative to the longitudinal midline of the head. When the food was offered at a large distance or laterally, the food uptake was either not successful or the coordination chain at the transition between food approach and food uptake was interrupted. In young larvae we detected an abrupt change in the activity of the locomotor system and the feeding system. The larvae approached the food by tail undulation and after reaching the final position of attack, no further activity of the locomotor apparatus was detectable. The larvae used a pure form of inertial suction to ingest food. In pre-metamorphic larvae and adults we registered an integrated activation of the locomotor apparatus (both limbs and tail) and the feeding apparatus during prey capture in the form of compensatory suction. The drastic change in the feeding mode of the pre-metamorphotic larvae and the adults compared to the younger larvae in T. dobrogicus may indicate the evolutionary development of a defined relation in the activity of the locomotor system and the control of the feeding apparatus. We propose that in newts, the interaction between the control execution in both systems switched from successive (body movement – feeding) into integrated (body movement – body movement and feeding) during the ontogeny. The main trigger for such a switch (at least in T. dobrogicus) is the formation of functional limbs during the late larval development.

Brachial supporting structure of Spiriferida (Brachiopoda)

The filter-feeding organ of some extinct brachiopods is supported by a skeletal apparatus called the brachidium. Although relatively well studied in Atrypida and Athyridida, the brachidial morphology is usually neglected in Spiriferida. To investigate the variations of brachidial morphology in Spiriferida, 65 species belonging to eight superfamilies were analyzed. Based on the presence/absence of the jugal processes and normal/modified primary lamellae of the spiralia, four types of brachidium are recognized. Type-I (with jugal processes) and Type-II (without jugal processes), both having normal primary lamellae, could give rise to each other by losing/re-evolving the jugal processes. Type-III, without jugal processes, originated from Type-II through evolution of the modified lateral-convex primary lamellae, and it subsequently gave rise to Type-IV by evolving the modified medial-convex primary lamellae. The evolution of brachidia within individual evolutionary lineages must be clarified because two or more types can be present within a single family. Type-III and Type-IV are closely associated with the prolongation of the crura, representing innovative modifications of the feeding apparatus in response to possible shift in the position of the mouth towards the anterior, allowing for more efficient feeding on particles entering the mantle cavity from the anterior gape. Meanwhile, the modified primary lamellae adjusted/regulated the feeding currents. The absence of spires in some taxa with Type-IV brachidium might suggest that they developed a similar lophophore to that in some extant brachiopods, which can extend out of the shell.