The ability to discard body parts at a preferential locus of weakness is widespread across the Metazoans' Tree of Life and has received attention from ecological and behavioral perspectives. Still, in many cases, a clear understanding of its genetic, morphological, and anatomical pathways is lacking. Distinct terms (autotomy, autotilly, autospasy) have been used in the literature to describe the process of limb detachment, usually carrying in their meaning information regarding the mechanics involved in it, and appendotomy is the most general word to encompass all of them. Appendotomy is found early in the evolution of the Arthropoda lineage and varies among taxa. Spiders, for example, have four distinct pre-determined fracture lines on their exoskeleton, and little is known about the co-occurrence of these lines within spider species. In this study, we examine the appendotomy at the trochanter of spiders using light and scanning electron microscopy to reconstruct the evolution of this character across the spider's tree of life. We describe trochanter structures and correct previous misunderstandings on how the appendotomy at the trochanter occurs in spiders. Our data show a clear, preferred breakage plane on the spider trochanter and although we focused on this appendotomy, we investigated its concomitant occurrence with other fracture areas of the leg. We show that the proximal rim of the trochanter breaks during appendotomy, leaving fragments on the distal end of the coxal arthrodial membrane. We also present several new records of appendotomy among 127 spider families examined and reconstruct the ancestral state of this character. Due to these discoveries, we conclude that the term "coxa-trochanter" appendotomy is misleading, and we propose replacement by the term "trochanter appendotomy".
So far, a full exocrine system survey exists for the major ant subfamilies but not yet for Pseudomyrmecinae. This study provides a morphological survey of the exocrine system in workers of Tetraponera ants using the large Tetraponera rufonigra and the smaller T. allaborans, T. penzigi and T. tessmanni. We found 20 glands of which the antennal bulb gland is a new exocrine structure in ants. The cardo base gland is well-developed in all species which is striking as this gland so far was mainly found in the subfamily Formicinae. Gland size is linked with worker size, in which larger workers clearly have more cells rather than bigger cells. A study of the exocrine system in other ant subfamilies often revealed differences that are relevant for species’ lifestyle and communication system. In spite of the numerous glands described in the present paper, almost nothing is known about their function in Tetraponera as surprisingly poor literature data exist on the communication system in this genus. Our study hopefully inspires researchers to perform bioassay experiments using gland extracts to fill this gap in the social biology of these ants.
Pycnogonids are a fascinating clade of marine epibenthic chelicerates that generally undergo indirect development, unlike all other chelicerates, where direct development prevails. Here we describe the first instar, known as the "protonymphon", of a species within the Phoxichilidiidae, namely Phoxichilidium quadradentatum Hilton, 1942a, using scanning electron microscopy (SEM). To date, the protonymphons of only four other species in this family have been described. Our morphological analysis places P. quadradentatum within the type 4 mode of development, hatching as a small larva that lacks attachment spines on the chelifores and has distal extension of the larval limbs. Based on this classification, P. quadradentatum most likely lives as an endoparasite of hydrozoans during its post-embryonic development, similar to Phoxichilidium femoratum.
Sea spiders (Pycnogonida) are benthic, marine chelicerates of shallow to deep water environments. They are mostly dioecious and engage in copulation that leads to external insemination, followed by brooding of large embryo masses by the male. In this study, we perform the first ultrastructural and elemental characterization of brooded embryos in pycnogonids. Scanning (SEM) and transmission electron microscopy (TEM) reveals the embryo masses to be covered by a contiguous extracellular matrix that consists of electron-dense fibers embedded in an electron-lucent medium. The matrix appears to be derived from the vitelline envelopes of individual embryos, thereby confirming recent hypotheses that the matrix is not a product of the male femoral glands. Elemental analysis using SEM-energy dispersive X-ray spectroscopy (EDS) reveals the vitelline envelope to contain high levels of C, O, and N with lesser amounts of Fe, Si, and Ni. The underlying embryos possess a separate fertilization membrane, which is devoid of ornamentation and has a relatively homogeneous, electron-opaque ultrastructure without distinct zonation or inclusions. The fertilization membrane contained C, O, and N as well as trace elements including Fe, Al, Au, Ca and P. The encapsulated embryo consists of numerous electron-dense yolk granules among other organelles. EDS of the embryos reveals high levels of C, O, and N, with trace amounts of Si, Au, Ni, P, and Zn. These results add new data for pycnogonid embryos, and with further investigations of additional species, may provide a wealth of information relevant for understanding more about the ecology, evolution, and systematics of this extraordinary marine taxon.
