The First Organ-Based Ontology for Arthropods (Ontology of Arthropod Circulatory Systems - OArCS) and its Integration into a Novel Formalization Scheme for Morphological Descriptions.

Morphology, the oldest discipline in the biosciences, is currently experiencing a renaissance in the field of comparative phenomics. However, morphological/phenotypic research still suffers on various levels from a lack of standards. This shortcoming, first highlighted as the "linguistic problem of morphology", concerns the usage of terminology and also the need for formalization of morphological descriptions themselves, something of paramount importance not only to the field of morphology but also when it comes to the use of phenotypic data in systematics and evolutionary biology. We therefore argue, that for morphological descriptions, the basis of all systematic and evolutionary interpretations, ontologies need to be utilized which are based exclusively on structural qualities/properties and which in no case include statements about homology and/or function. Statements about homology and function constitute interpretations on a different or higher level. Based on these "anatomy ontologies", further ontological dimensions (e.g., referring to functional properties or homology) may be exerted for a broad use in evolutionary phenomics. To this end we present the first organ-based ontology for the most species-rich animal group, the Arthropoda. Our Ontology of Arthropod Circulatory Systems (OArCS) contains a comprehensive collection of 383 terms (i.e., labels) tied to 296 concepts (i.e., definitions) collected from the literature on phenotypic aspects of circulatory organ features in arthropods. All of the concepts used in OArCS are based exclusively on structural features, and in the context of the ontology are independent of homology and functional assumptions. We cannot rule out that in some cases, terms are used which in traditional usage and previous accounts might have implied homology and/or function (e.g. heart, sternal artery). Concepts are composed of descriptive elements that are used to classify observed instances into the organizational framework of the ontology. That is, descriptions in ontologies are only descriptions of individuals if they are necessary/and or sufficient representations of attributes (independently) observed and recorded for an individual. In addition, we here present for the first time an entirely new approach to formalizing phenotypic research, a semantic model for the description of a complex organ system in a highly disparate taxon, the arthropods. We demonstrate this with a formalized morphological description of the hemolymph vascular system in one specimen of the European garden spider Araneus diadematus. Our description targets five categories of descriptive statement: "position", "spatial relationships", "shape", "constituents", and "connections", as the corresponding formalizations constitute exemplary patterns useful not only when talking about the circulatory system, but also in descriptions in general. The downstream applications of computer-parsable morphological descriptions are widespread, with their core utility being the fact that they make it possible to compare collective description sets in computational time, that is, very quickly. Among other things, this facilitates the identification of phenotypic plasticity and variation when single individuals are compared, the identification of those traits which correlate between and within taxa, and the identification of links between morphological traits and genetic (using GO, Gene Ontology) or environmental (using ENVO, Environmental Ontology) factors. [Arthropoda; concept; function; hemolymph vascular system; homology; terminology.].

Evolutionary morphology of the hemolymph vascular system of basal araneomorph spiders (Araneae: Araneomorphae).

The superfamily Austrochiloidea (Austrochilidae and Gradungulidae) take a pivotal position in araneomorph spider phylogeny. In this discussion crevice weaver spiders (Filistatidae) are of equal interest. Especially data from these phylogenetically uncertain yet basal off branching groups can enlighten our understanding on the evolution of organ systems. In the course of a survey on the evolutionary morphology of the circulatory system in spiders we therefore investigated the hemolymph vascular system in two austrochiloid and one filistatid species. Additionally some data on a hypochilid and a gradungulid species are included. Using up-to-date morphological methods, the vascular systems in these spiders are visualized three dimensionally. Ground pattern features of the circulatory systems in austrochiloid spiders are presented and the data discussed along recent lines of phylogenetic hypotheses. Special topics highlighted are the intraspecific variability of the origins of some prosomal arteries and the evolutionary correlation of respiratory and circulatory systems in spiders.

Comparative morphology of the hemolymph vascular system in krill (Euphausiacea; Crustacea).

The phylogenetic position of Euphausiacea within Malacostraca is still under debate. Either they are seen as sister group to a taxon comprising Pancarida and Peracarida or closer related to Decapoda. Both hypotheses can be supported by characters of the circulatory system. Therefore, a comparative re-evaluation of the circulatory system seems to be feasible. Here we present the first three-dimensional data of the circulatory system of three euphausiacean species based on semi-thin sections and micro computer tomography in combination with corrosion casting. We were also able to study for the first time representatives of Bentheuphausia amblyops, the suggested sister taxon to all other euphausiaceans. The main pumping structure in the open circulatory system of Euphausiacea is the globular heart in the rear thoracic segments. From the anterior and posterior end of the heart two unpaired and four pairs of arteries emanate. The unpaired anterior aorta runs below the carapace from the anterior part of the heart into the anterior cephalothorax, where it supplies the first antennae, the brain and the eyes. The paired posterior aortae run into the pleon supplying the pleopods, uropods and the telson. The four pairs of cardiac arteries supply appendages in the cephalic region and viscera in the trunk. The unpaired descending artery connects to the subneural vessel supplying the thoracopods. A myoarterial formation of the anterior aorta is described in Bentheuphausia amblyops. The observed pattern of a globular heart situated in the posterior cephalothorax and comprising a meshwork of muscular strands (also running through its lumen) is highly likely to be homologous in Euphausiacea and Decapoda. The data are compared with the scarce literature present to date.