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Crinoids are well known for their striking regenerative potential and can rapidly and completely regenerate arms lost following self-induced or traumatic amputation. Thus they provide a valuable experimental model for investigation of the regenerative process from the macroscopic to the molecular level. In these last years we have studied in detail the overall process of arm regeneration in the comatulid Antedon mediterranea. This phenomenon can be described on the whole as a typical blastemal regeneration in which new structures develop from migratory pluripotential, actively proliferating cells in the presence of presumptive regulatory factors. The overall process can be subdivided into three main phases: a repair phase, an early regenerative phase, and an advanced regenerative phase, whose crucial aspects are related to common fundamental mechanisms such as cell migration and proliferation, intervention of stem cells and/or dedifferentiated cells, contribution of putative growth factors, particularly in terms of specific neurally derived factors, and mechanisms of pattern formation. This article focuses on the main aspects of the phenomenon and gives a brief account of the most recent and relevant results. Our approach employs classical methods of light (LM) and electron (TEM and SEM) microscopy, immunocytochemistry, and histofluorescence on experimentally induced arm regenerations of standard or abnormal type obtained in significantly different experimental conditions, including extreme mutilations (explants) or exposure to pseudo-estrogenic environmental contamination.

Crinoids have remarkable regenerative capacities. After traumatic or self-induced amputation they can replace one or several arms through a complex sequence of morphogenetic events which lead quickly to the complete reconstruction of the lost part. These phenomena are well known in their general aspects and a comprehensive description of arm regeneration was previously provided (Candia Carnevali et al., Recent Trends in Regeneration Research. Plenum Press, New York, '89). However, there is a considerable gap in knowledge of the early regenerative phases which are particularly significant for the following development. The aim of the present work is to describe and interpret the different aspects of these early stages of arm regeneration in Antedon mediterranea. According to our results the regenerative development ofAntedon arm seems to consist of an epimorphic

All species of the Ophiuroidea have exceptional regenerative capabilities; in particular, they can replace arms lost following traumatic or self-induced amputation. In order to reconstruct this complex phenomenon, we studied arm regeneration in two diVerent ophiuroids, Ophioderma longicaudum (Retzius, 1805) and Amphiura Wliformis O. F. Müller, 1776, which are quite distantly related. These species present contrasting regeneration and diVerentiation rates and diVer in several ecological traits. The aim of this paper is to interpret the primary sequence of morphogenetic and histogenetic events leading to the complete reconstruction of a new arm, comparing the arm regenerative processes of these two ophiuroid species with those described in crinoids. Arm regeneration in ophiuroids is considered an epimorphic process in which new structures develop from a typical blastema formed from an accu-mulation of presumptive undiVerentiated cells. Our results showed that although very diVerent in some respects such as, for instance, the regeneration rate (0.17 mm/week for O. longicaudum and 0.99 mm/week for A. Wliformis), morphogenetic and histogenetic aspects are surprisingly similar in both species. The regenerative process presents similar characteristics and follows a developmental scheme which can be subdivided into four phases: a repair phase, an early regenerative phase, an intermediate regenerative phase and an advanced regenerative phase. In terms of histogenesis, the regenerative events involve the development of new structures from migratory pluripotent cells, which proliferate actively, in addition in both cases there is a signiWcant contribution from dediVerentiated cells, in particular ded-iVerentiating myocytes, although to varying extents. This evidence conWrms the plasticity of the regenerative phenomenon in echinoderms, which can apparently follow diVerent pathways in terms of growth and morphogenesis, but nevertheless involve both epimorphic and morphallactic contributions at the cellular level.

Collagen has become a key-molecule in cell culture studies and in the tissue engineering field. Industrially, the principal sources of collagen are calf skin and bones which, however, could be associated to risks of serious disease transmission. In fact, collagen derived from alternative and riskless sources is required, and marine organisms are among the safest and recently exploited ones. Sea urchins possess a circular area of soft tissue surrounding the mouth, the peristomial membrane (PM), mainly composed by mammalian-like collagen. The PM of the edible sea urchin Paracentrotus lividus therefore represents a potential unexploited collagen source, easily obtainable as a food industry waste product. Our results demonstrate that it is possible to extract native collagen fibrils from the PM and produce suitable substrates for in vitro system. The obtained matrices appear as a homogeneous fibrillar network (mean fibril diameter 30–400 nm and mesh < 2 μm) and display remarkable mechanical properties in term of stiffness (146 ± 48 MPa) and viscosity (60.98 ± 52.07 GPa·s). In vitro tests with horse pbMSC show a good biocompatibility in terms of overall cell growth. The obtained results indicate that the sea urchin P. lividus can be a valuable low-cost collagen source for mechanically resistant biomedical devices.