Evolution of organ systems in the Crustacea: Mystacocarida and Cephalocrida in retrospect

The morphology of the internal organs of two representative species of the crustacean classes Mystacocarida, Derocheilocaris typica (Pennak & Zinn, 1943), and Cephalocarida, Hutchinsoniella macracantha (Sanders, 1955), has been studied ultrastructurally from 1990 onwards. A review of the subject offers a unique opportunity to compare and contrast the two taxa at a time when their key positions in discussions of crustacean relationships and evolution makes any new knowledge particularly valuable. The same internal organ or organ system can be constructed very differently in the two groups, but similarities also occur. Both the similarities and differences suggest functional interpretations and shed light on evolutionary pathways. The importance of including anatomy and functional morphology in phylogenetic discussions is emphasized

A Non-Ciliary Receptor in the Mandible of a Mystacocarid Crustacean, Derocheilocaris Typica

The mystacocarid crustacean Derocheilocaris typica Pennak and Zinn, 1943 lives in sand interstices and is less than one mm long. It is unique among Arthropoda. It has sensory cells in the mandible, which lack cilia. The function as mechano- and/or chemo-receptors has been replaced by dendrites, the sensory cell protrusions carrying cilia. The dendrites swell, flatten, and fill the endite- a medial outgrowth from the mandible, which is the main masticating appendage. The dendrites have many contacts with the inside of the cuticle, which insures close proximity to the food outside the body. Another feature specific to D. typica is the reduced cilia in the cuspidate setae of the food handling appendages: first and second maxillae, and maxilliped. The remaining approximate 50 setae on the body, not related to food handling, conform to those of all arthropods

The frontal eyes of crustaceans

Frontal eyes of crustaceans (previously Called nauplius eye and frontal organs) are usually simple eyes that send their axons to a medial brain Centre in the anterior margin of the protocerebrum. Investigations of a large number of recent species within all major groups of the Crustacea have disclosed four kinds of frontal eyes correlated with taxonomic groups and named after them as the malacostracan, ostracod-maxillopodan, anostracan, and phyllopodan frontal eyes. The different kinds of eyes have been established using the homology concept coined by Owen [Owen, R., 1843. Lectures on the Comparative anatomy and physiology of the invertebrate animals. Longman, Brown, Green, Longmans, London] and the criteria for homology recommended by Remane [Remane, A., 1956. Die Grundlagen des naturlichen Systems, der vergleichenden Anatomic und der Phylogenetik. 2nd ed. Akademische Verlaosgeselischaft, Geest und Portig, Leipzig]. Common descent is not used as a homology criterion. Frontal eyes bear no resemblance to compound eyes and in the absence of compound eyes, as in the ostracod-maxillopodan group, frontal eyes develop into complicated mirror, lens-mirror, and scanning eyes. Developmental studies demonstrate widely different ways to produce frontal eyes in phyllopods and malacostracans. As a result of the Studies of recent frontal eyes in crustaceans, it is concluded by extrapolation that in crustacean ancestors four non-homologous frontal eye types evolved that have remained functional in spite of concurrent compound eyes

The nauplius eye and frontal organs in decapoda (Crustacea)

The present investigation concerns the nauplius eye and frontal organs in decapod Crustaceans. Representatives from all groups of the Decapoda are included. Some of the more important results are abstracted.The nauplius eye in several families within the Eucyphidea is more complicated than generally believed. It consists of a nauplius eye s. s. with three cups and three sensory cells in each and the incorporated dorsal frontal organ, which functions as an eye. The sensory cells are everse.The dorsal frontal organ is thus intimately connected with the nauplius eye s. s. and must not be mixed up with the eye papilla and the sensory pore X organ.The dorsal frontal organ is subjected to a considerable degree of variation. As part of a nauplius eye s, 1. as mentioned above it is an eye. In many species all over the Decapoda the frontal organ is reduced. A line of transformation can be shown from eye appearance through intermediate stages to “globuli” cells situated in the ganglion layer of the brain.The ventral frontal organ is more common than formerly believed and its paired nature is stressed.The author acceds to Hanström's hypothesis (1926) concerning the phytogeny of the frontal organs

Brain and eyes of Zygentoma (Thysanura)

The brain, the compound eyes and the ocelli are described for some zygentomid species. Special interest has been focused on Tricholepidion gertschii, a newly discovered, primitive species. The brain morphology shows great similarities in the general shape and in details within the whole suborder. The compound eyes of Tricholepidion gertschii and Lepisma saccharina resemble each other closely. The present investigation has shown that the zygentomid and pterygote compound eyes are similar in that there are no corneagen cells. The view that the compound eyes of the Zygentoma should constitute a connecting link between crustacean and insect compound eyes can no longer be maintained. Tricholepidion gertschii possesses three ocelli. Their structure stresses the connection between thysanurans and pterygote insects. In this connexion the homology of reduced ocelli is discussed and their nerve contacts reinvestigated

The nauplius eye and frontal organs of the non-Malacostraca (Crustacea).

The present work is a continuation of the morphological studies of the nauplius eye and frontal organs of the Crustacea. The previous papers on this topic comprised the Decapoda (ELOFSSON, 1963) and the Malacostraca (ELOFSSON, 1965). Its has been found that the nauplius eye and frontal organs of the Crustacea are separated into four different types. These comprise the Phyl-lopoda, Anostraca, Maxillipoda-Ostracoda and Malacostraca. Frontal organs do not appear in the maxillopod-ostracod group, but are present as paired dorsal and ventral frontal organs in the Malacostraca, paired ventral frontal organ in the Anostraca, and paired distal and unpaired posterior medial frontal organ in the Phyllopoda. The frontal organs of the different groups are not homologous. Their nature as reduced frontal eyes is maintained. The nauplius eye (and frontal organs when present and developed as eyes) shows, for instance, the following dissimilarities. The sensory cells of the eyes of the Malacostraca are everse with rhabdomeres at their sides combining into rhabdoms. The remaining groups have inverse sensory cells and rhabdomeres around the distal tip of the cells. Each cup in the maxillopod-ostracod line has tapetal and lens cells which are not found in the other types. The phyllopod group has a unique arrangement of the eye and frontal organs, depending on the typical and special development of the organs. Due to the structural dissimilarities and lack of transitional forms the frontal eyes (= nauplius eye and frontal organs) of the four different groups are considered non-homologous, and this view is discussed with regard to morphological, phylogenetical and functional viewpoints

A peculiar kind of pigment cell in the compound eye of Lepisma saccharina L. (Thysanura)

The ultrastructure of the primary pigment cells of the compound eye of Lepisma saccharina is described. The cells are four in number. The pigment granules are contained in fingerlike protrusions from the pigment cells. These protrusions project into the enlarged basal lamina surrounding the ommatidial top. The large basal lamina could have given the impression of a cell (called corneagen) in the light microscope