In memoriam: Leendert P. van Ofwegen (1953–2021), octocoral taxonomist

Abstract none

part of Leen's first co-authored publication (Krans et al. 1982). Apparently, he did not consider this work relevant to his career because he always left it out of his CV (e.g., van Ofwegen 2007). For the second research project, Leen became an intern at the Rijksmuseum van Natuurlijke Historie (RMNH, presently Naturalis Biodiversity Center), which at that time was a centre of systematic research on Cnidaria. He worked under supervision of Koos den Hartog (curator of "Coelenterata"), who proposed that Leen could work on the taxonomy of octocorals from the Saba Bank, which were collected during an expedition to the former Netherlands Antilles, currently the Dutch Caribbean (van der Land 1972;Hoeksema et al. 2017). The work was not published but the specimens were identified and are present in the RMNH.Coel collection in Leiden, where they are available for future research (Hoeksema et al. 2011). Leen's internship at the RMNH was the start of his interest and expertise in octocoral taxonomy.
Following his MSc, as no jobs were available in octocoral taxonomy, Leen did freelance work as a computer programmer but continued his research in his spare time, under the supervision of Koos den Hartog, while he also exchanged ideas with Hydrozoa specialist Prof. Willem Vervoort (Figure 2e). During this period, Leen started to work on a collection of gorgonians collected by the International Indian Ocean Expedition of R/V Anton Bruun (1963 and1964). That collection belonged to the Invertebrate Zoology department of the Smithsonian Institution in Washington, D.C. (USNM), and was on loan to the RMNH to make it available for research by octocoral expert Dr. Jacob Verseveldt. Verseveldt, however, was mostly interested in studies of fleshy octocorals (den Hartog 1987) rather than gorgonians, which may explain why this collection remained untouched for several years. Someone had to do the job and Leen made himself available. After the study (van Ofwegen 1990), the collection was returned to Washington.
Following the suggestion of Koos den Hartog, Leen decided to follow Jacob Verseveldt in his work on the taxonomy of soft corals, for which the same methodology was used as in the taxonomy of gorgonians. This methodology consisted of morphological examination of the coral colonies and in particular analyses of their sclerites, being microscopic calcite skeletal elements embodied in the soft tissue of the animals. At first, Leen made hand drawings with a light microscope and a camera lucida but later he made extensive use of high-resolution scanning electronic microscopy (SEM). At a later stage, he also became involved in molecular analyses applied to the taxonomy of octocorals, as shown by co-authored publications with colleagues in Leiden and from abroad (e.g., McFadden et al. 2006;van Ofwegen and Groenenberg 2007;. In 1992, Leen got a position as manager of the editorial office of the RMNH museum journals, Zoologische Mededelingen and Zoologische Verhandelingen, and continued publishing papers on octocorals in his spare time. Owing to Leen's growing publication record, his reputation as world-renowned octocoral taxonomist began to attract attention and he was approached by several young scientists who wanted to be trained in his field of research. Leen's first student was Dr. Jayasree Vennam from the National Institute of Oceanography (NIO) at Dona Paula, Goa, India (Figure 2e), who stayed six months in Leiden as a visiting scientist during 1989-1990(den Hartog and Vennam 1993. One reason for this interest in octocorals was their major role as producers of novel chemicals for the design of medicinal compounds. This pharmacological application of octocoral taxonomy resulted in Leen's co-authorships of various publications on marine natural products derived from species that he undertook to identify (Appendix 2). In these projects, he mainly collaborated with Dr. R. Andersen (Canada), Dr. M. Jaspars (United Kingdom), Dr. Wenhan Lin (China), and Prof. Dr. P. Proksch (Germany).
In 2001, Leen became employed as curator of coelenterates at the Leiden museum, succeeding Koos den Hartog, who passed away in 2000 (van der Land 2003). Leen's main research was focused on (1) a taxonomic revision of the soft-coral genera Litophyton, Nephthea, and Stereonephthya (family Nephtheidae), which resulted in the establishment of Chromonephthea and many new species in that genus (Figure 5c;van Ofwegen 2005), and (2) on collections made in the Indo-West Pacific centre of maximum octocoral biodiversity. For this research he made use of the octocoral collection in the Leiden museum, but also those in Berlin and Washington, DC, which he visited in the company of stony-coral specialist and co-worker Bert Hoeksema. Various colleagues from abroad regularly came to Leiden to work with Leen on the octocoral collections, such as Dr. Yehuda Benayahu (Israel), Dr. Tatiana Dautova (Russia), Dr. Asako K. Matsumoto (Japan; Figure 2f ), and Dr. Cathy McFadden (USA). These visits resulted in several co-authored publications (Appendix 2), covering a large variety of biogeographic regions. Undoubtedly, Leen has become a world authority on octocoral taxonomy and was approached by numerous colleagues for his expertise. His name is mentioned in many field guides, acknowledging his help in the identification of species illustrated in photographs.
Octocoral material in museum collections is either stored in ethanol or dried, both of which cause specimens to lose their original shape and often their colour. In order to learn about the natural habitus of soft corals, Leen decided that he had to learn diving with the use of SCUBA. This enabled him to participate in fieldwork sampling during surveys and large-scale expeditions in the company of his colleagues of the Naturalis marine research team ("Naturalis Zeeteam"), even before he got a position as a curator (Figures 1, 3 Most of these expeditions were in Indonesia and in this way Leen established a close collaboration with two octocoral scientists from the Research Centre for Oceanography, Indonesian Institute of Sciences, Jakarta: M.I.Y.T. Hermanlimianto (Yosephine Tuti), specialised in gorgonians, and Anna E.W. Manuputty, specialised in soft corals. Both of them also visited Leen and his collection; Yosephine did so several times ( Figure 2c). All in all, Leen spent much time on collection work for which he collaborated with collection managers Chiel Slierings (who retired in October 2007) and Koos van Egmond until Leen's own retirement on 31 December 2016.
In order to strengthen his international contacts, Leen attended several international conferences and workshops to meet with other octocoral workers ( Figure 5),    (2010); and the 8 th International Conference on Coelenterate Biology, Eilat, Israel (2013). He acted as an instructor with other colleagues during two octocoral taxonomy workshops: in Trivandrum, Kerala, India (2005) and in Phuket, Thailand (2007).  Figure 2d) and Bastian T. Reijnen (Reijnen 2016), both at Leiden University under supervision of Edi Gittenberger. Leen also supervised two MSc students from Leiden University, Frank R. Stokvis and Yee Wah Lau. In 2001, Leen also succeeded Koos den Hartog in his capacity of editor-in-chief of the two zoological museum journals until these ceased publication. In 2004, Zoologische Verhandelingen became incorporated in Zoologische Mededelingen, which stopped publication in 2014. In 2008, Leen became an associate editor for ZooKeys (with a focus on octocorals and other anthozoans). In the same year he also became editor of Octocorallia for the World Register of Marine Species, now also accessible through the World List of Octocorallia , with which he first collaborated with Dr. Gary Williams, who oversaw the sea pen data (Pennatulacea). After his retirement, Leen stopped his editorial tasks, but he continued publishing papers until his death. His dedication and expertise in octocoral taxonomy is demonstrated by an impressive series of publications and a large collection of specimens. In honour of Leen's octocoral expertise one species was named after him, Fasciclia ofwegeni Janes, 2008, based on type material collected by Leen in the Seychelles (Janes 2008).
Leen described many new taxa himself or with co-authors, including seven families, 25 genera, and 214 species, ranging in publication years from 1987 until the present (Appendix 1). Various new species were named after Naturalis colleagues (Chromonephthea egmondi, C. franseni, C. goudi, C. hoeksemai, C. slieringsi, Dendronephthya vervoorti, Lignella hartogi, Sinularia vanderlandi), and several others were named after octocoral specialists (Chromonephthea aldersladei, C. bayeri, C. benayahui, C. cairnsi, C. grasshoffi, C. tentoriae, C. williamsi, Sinularia verseveldti, Wrightella stiasnyi). Having known Leen for more than 35 years, it is beyond doubt that he will be missed by his colleagues and students, who will remember him not only for his life-time dedication to octocoral taxonomy and his vast knowledge on that topic, but also for his characteristic smile (Figures 1-5), unique sense of humour, and heartfelt friendship. van