Table 2 in Fig. 5 in Acanthonyx petiverii " H. Milne Edwards 1834

Anomuran and Brachyuran Symbiotic Crabs in Coastal Areas between the Southern Ryukyu arc and the Coral Triangle Parinya Limviriyakul1,2, Li-Chun Tseng1, Jiang-Shiou Hwang1,3, and Tung-Wei Shih4,* 1Institute of Marine Biology, College of Life Sciences, National Taiwan Ocean University, Keelung 20224, Taiwan. E-mail: [email protected]; [email protected] 2Department of Marine Science, Faculty of Fisheries, Kasetsart University, Bangkok 10900, Thailand 3Department of Biomedical Science and Environmental Biology, Kaohsiung Medical University, Kaohsiung 80708, Taiwan 4National Museum of Marine Science and Technology, Keelung 20248, Taiwan (Received April 13, 2015; Accepted October 13, 2015) Parinya Limviriyakul, Li-Chun Tseng, Jiang-Shiou Hwang, and Tung-Wei Shih (2016) Symbiotic anomuran and brachyuran crabs were identified after extensive surveys of reef zones, especially from sponges, scleractinian corals, crinoids, and sea urchins, in the coastal areas of the southern East China Sea. Twenty-nine species belonging to 17 genera, 9 families, and 2 infraorders were identified (3 were identified to the generic level). More crabs belonged to the infraorder Brachyura (82.8%) than to Anomura (17.2%). Two anomuran symbionts (Allogalathea elegans and Petrolisthes virgatus) and 5 brachyuran symbionts (Tetralia glaberrima, Tetralia rubridactyla, Trapezia cymodoce, Trapezia septata, and Cymo melanodactylus) are common in this area. Two species of Anomura (Lauriea simulata, Petrolisthes virgatus) and 3 of Brachyura (Gonatonotus nasutus, Tetralia aurantistellata and Tetralia nigrolineata) were identified for the first time from waters adjacent to Taiwan. These records represent the northernmost recorded of L. simulata and T. aurantistellata. The occurrence of P. virgatus is the second in the western Pacific Ocean. This study revealed the geospatial distribution of symbiotic crabs, which connects the region from the southern Ryukyu arc to the Coral Triangle, and provides the supporting taxonomic account of symbiotic anomuran and brachyuran crab fauna inhabiting the reef zone in northern Taiwan. Key words: Symbiosis, Anomura, Branchyura, Reef, Southern East China Sea. *Correspondence: E-mail: [email protected].tw; [email protected] BACKGROUND Symbiotic associations are widespread across taxa and are generally found in all oceans around the world. The term symbiosis refers to members of different species living in close association (Castro and Huber 2003). Symbiotic crustaceans are common in most marine ecosystems, especially in tropical shallow waters (Bruce 1976; Castro 1988; Stella et al. 2011b). They associate with a variety of macro-invertebrate hosts such as sponges, cnidarians, polychaetes, mollusks, and echinoderms (Bruce 1972, 1976; Fautin et al. 1995; Guo et al. 1996; Marin et al. 2004; Thiel et al. 2003; Wei et al. 2005) The prevalence of such associations make coral reef communities the most complex and biodiverse marine ecosystems in coastal areas (Paulay 1997; Veron 2000). Stella et al. (2011b) described at least 860 invertebrate species as coral associates, 310 of which are decapod crustaceans. Among these symbiotic decapods, crabs play a crucial role in increasing the survival rate of their hosts. They defend host corals against predators (Glynn 1980; Pratchett 2001; Pratchett et al. 2000) and help moving sediments away from their coral hosts (Stewart et al. 2006; Stier et al. 2012). Some coral species are reliant on these services and are Zoological Studies 55: 7 (2016) doi:10.6620/ZS.2016.55-07 1 unable to survive without their symbionts (Glynn 1983; Stella et al. 2011b; Stewart et al. 2006). Cymo melanodactylus Dana, 1852 has been reported to eat both the mucus and living polyps of its host, Acropora (Patton 1994) Taiwan is located in the western North Pacific Ocean, with its northern part connected to the southern Ryukyu arc through the southern East China Sea, and the southern side connected to the Philippines, the South China Sea and the Coral Triangle through Luzon Strait. The biodiversity of anomuran and brachyuran crabs in Taiwan has been comprehensively studied since 1902, and more than 600 species from 64 families of brachyuran crabs have been recorded (Chan et al. 2009). Nearly one-tenth of all known crab species have been recorded in Taiwan. A substantial proportion of these records pertain to deep-water taxa (Ng et al. 2001). Studies on symbiotic crabs have been conducted in the reef and coastal waters of Taiwan (Chang et al. 1987; Galil 1983; Ho et al. 2000; Jeng 1994; Ng and Jeng 1999; Wei et al. 2013; Wei et al. 2005). Most of these studies collected specimens from southern Taiwan. The diversity and species composition of symbiotic crabs have not yet been explored in the southern East China Sea off the coast of northern Taiwan. The present study collected specimens in the reef zone of Fan-Zai-Aou Bay to evaluate the diversity of symbiotic anomuran and brachyuran crab fauna in order to provide baseline taxonomic information in the coastal areas of the southern East China Sea. MATERIALS AND METHODS Field sampling and sample treatment Specimens were collected weekly between April and August 2014 from western Fan-ZaiAou Bay, southern East China Sea, off the coast of Keelung City in northern Taiwan (Fig. 1). The seabed in the sampling area was characterized by rock, coral, and fine sediments. Anomuran and brachyuran crab specimens were collected by scuba diving in the zone above 24 m. Potential host animals (sponges, hydroids, sea anemones, scleractinian corals, soft corals, crinoids, and sea urchins) were investigated. Each host, along with its symbionts, was stored separately in a plastic zip-lock bag or box and taken to the Chaojing Ocean Center (National Museum of Marine Science and Technology) for identification. The associated decapods were carefully removed from their hosts by using flexible plastic rods. Some hosts were immersed in seawater containing a 5-ppt clove oil-ethanol solution for 3 min and vigorously shaken to extract their symbionts. The decapod specimens were photographed, preserved in 70% ethyl alcohol, and deposited at the Chaojing Ocean Center collection. After identification, all host animals were returned to their place of origin. Crab identification In the laboratory, the associated crabs were identified under a dissecting microscope (Olympus SZX16). Anomuran crabs were identified using keys by Baba et al. (2009), Osawa et al. (2010), and Macpherson and Robainas-Barcia (2013), and brachyuran crabs were identified using keys by Serène (1984), Kropp (1990), Dai and Yang (1991), Chia et al. (1999), Chia and Ng (2000), Castro et al. (2004), and Trautwein (2007). Fig. 1. Map of the sampling area (a) and locations (b) in northern Taiwan during the sampling period (April to August 2014). (a) (b) page 2 of 14Zoological Studies 55: 7 (2016) RESULTS Prevalence and host The prevalence of symbiotic crabs varied among the host specimens; from a total of 29 species, 6.9% were found in sponges (N = 11), 79.3% in scleractinian corals (N = 106; Acropora 76, Stylophora 20, Pocillopora 10), 6.9% in crinoids (N = 50), and 10.3% in sea urchins (N = 63; Diadema 20, Echinothrix 10, Echinometra 30, Prionocidaris 3) (Table 1). A comparison of the host composition revealed that most symbiotic crabs were associated with branching corals (23 species, 79.3%) (Fig. 2). Five species of Anomura (Fig. 3) and 24 species of Brachyura (Fig. 4) were identified. Twenty-nine species belonging to 17 genera, 9 families, and 2 infraorders were identified (3 were identified to generic level). More crabs belonged Table 1. Taxonomic list, occurrence rate (%), depth of collection (m), symbiotic host, and historical reports of anomuran and brachyuran crabs collected from northern Taiwan Scientific name Occurrence and depth Symbiotic host Historical records Infraorder Anomura MacLeay, 1838 Family Galatheidae Samouelle, 1819 Allogalathea elegans (Adams and White, 1848) ++++, 4-24 m Crinoid: Mariametroidea East China Sea (Miyake and Keiji 1967), Japan (Baba 1969), Red Sea, east coast of Africa (Baba 1988), Philippine (Baba 1988), Australia and Tasman Sea (Ahyong 2007), Taiwan (Baba et al. 2009), Thailand (Thamrongnawasawat et al. 2009) Galathea tanegashimae Baba, 1969 ++, 2-6 m Coral: Acropora hyacinthus, Sponge: unidentified Japan (Baba 1969), Tasman Sea (Ahyong 2007), Taiwan (Baba et al. 2009), South-West Indian Ocean (Macpherson and Cleva 2010) Lauriea simulata Macpherson and Robainas-Barcia, 2013* +, 4 m Coral: Pocillopora damicornis Philippines, Vanuatu and New Caledonia (Macpherson and Robainas-Barcia 2013), South China Sea (Dong and Li 2013) Family Porcellanidae Haworth, 1825 Petrolisthes virgatus Paul’son, 1875* +++, 0-3 m Sea urchin: Echinometra mathaei Red Sea (Ramadan 1936), Mozambique (Kalk 1958), Japan (Nakasone and Miyake 1972; Nomura et al. 1996), Somalia (Lewinsohn 1979), Oman (Hogarth 1988), Yemen (Simões et al. 2001) Petrolisthes sp. +, 4 m Coral: Pocillopora damicornis Infraorder Brachyura Linnaeus, 1758 Family Leucosiidae Samouelle, 1819 Nucia sp. +, 3 m Coral: Acropora hyacinthus Family Pilumnidae Samouelle, 1819 Echinoecus pentagonus (A. MilneEdwards, 1879) ++, 6-20 m Sea urchin: Diadema setosum, Echinothrix sp. Japan (Miyake 1939), Hawaii (Castro 1969), China Seas (Dai and Yang 1991), Red Sea, East Africa, Indo-West Pacific and French Polynesia (Chia et al. 1999), Taiwan (Ng and Jeng 1999), Thailand (Thamrongnawasawat et al. 2009), Southern Korea (Lee et al. 2011) Fig. 2. Number (a) and proportion (b) of symbiont identified in the investigation area. page 3 of 14Zoological Studies 55: 7 (2016) Table 1. (continued) Scientific name Occurrence and depth Symbiotic host Historical records Gonatonotus nasutus D. G. B. Chia and Ng, 2000* +, 12 m Sea urchin: Prionocidaris sp. Western and eastern Australia, New Caledonia, Vanuatu, Philippines and Japan (Chia and Ng 2000) Permanotus purpureus (Gordon, 1934) ++, 6-24 m Crinoid: Mariametroidea South-west Pacific, central Pacific, Japan (Chia and Ng 1998), Taiwan (Ng and Jeng 1999), Thailand (Thamrongnawasawat et al. 2009) Pilumnus sp. +, 17 m Sponge: Xestospongia sp. Family Domeciidae Ortmann, 1893 Domecia glabra Alcock, 1899 ++, 2-7 m Coral: Acropora hyacinthus, Acropora digitifera, Acropora sp. Japan (Nomura et al. 1996), China Seas (Dai and Yang 1991), Australia (Patton 1994), Taiwan (Ng et al. 2001) Domecia hispida Eydoux and Souleyet, 1842 +, 3 m Coral: Pocillopora damicornis China Seas (Dai and Yang 1991), Japan (Nomura et al. 1996), French Polynesia (Peyrot-Clausade 1989; Poupin 1996), Taiwan (Ng et al. 2001) Family Tetraliidae Castro, Ng and Ahyong, 2004 Tetralia aurantistellata Trautwein, 2007* +, 4 m Coral: Acropora hyacinthus New Caledonia and Fiji (Trautwein 2007), Philippines (Castro 2009) Tetralia cinctipes Paul’son, 1875 ++, 2-7 m Coral: Acropora hyacinthus, Acropora digitifera East Africa, Red sea, Japan, Taiwan, Indonesia (Galil and Clark 1988), Australia (Patton 1994), French Polynesia (Poupin 1996), Indonesia (Castro 1999), Guam (Castro 2003), Philippines (Castro 2009) Tetralia glaberrima (Herbst, 1790) +++, 2-12 m Coral: Acropora hyacinthus, Acropora digitifera, Acropora spp. Seychelles (Garth 1984), French Polynesia (PeyrotClausade 1989; Poupin 1996), China Seas (Dai and Yang 1991), Japan (Tsuchiya et al. 1993), Australia (Patton 1994), Indonesia (Castro 1999), Taiwan (Ng et al. 2001), Thailand (Castro 2002), Guam (Castro 2003), Philippines (Castro 2009), Andaman and Nicobar Is. (Kumaralingam et al. 2012), Galapagos (Tirado-Sanchez et al. 2014) Tetralia nigrolineata Serène and Pham, 1957* ++, 2-10 m Coral: Acropora hyacinthus, Acropora digitifera Thailand, Indonesia and Japan (Galil 1988), Singapore (Goh et al. 1990), Australia (Patton 1994), New Caledonia (Castro 1997b), Western Indian Ocean (Castro 1997b), Guam (Castro 2003), Philippines (Castro 2009) Tetralia rubridactyla Garth, 1971 +++, 2-12 m Coral: Acropora hyacinthus, Acropora digitifera, Acropora spp. East Africa (Galil and Clark 1988), Taiwan (Galil 1988), Japan (Tsuchiya et al. 1993), Australia (Patton 1994), Indian Ocean (Castro 1997a), French Polynesia (Castro 1997a), Indonesia (Castro 1999), Guam (Castro 2003), Philippines (Castro 2009) Tetraloides heterodactylus (Heller, 1861) +, 2-4 m Coral: Acropora hyacinthus, Acropora digitifera, East Africa (Galil and Clark 1988), French Polynesia (Castro 1997a), Indonesia (Castro 1999), Guam (Castro 2003), Philippines (Castro 2009), Japan (Komatsu 2011), Taiwan (Fisheries Research Institute 2014) Tetraloides nigrifrons (Dana, 1852) ++, 2-7 m Coral: Acropora hyacinthus, Acropora sp. East Africa (Galil and Clark 1988), Australia (Patton 1994), French Polynesia (Poupin 1996), Guam (Castro 2003), Philippines (Castro 2009), Taiwan (Fisheries Research Institute 2014) page 4 of 14Zoological Studies 55: 7 (2016) Table 1. (continued) Scientific name Occurrence and depth Symbiotic host Historical records Family Trapeziidae Miers, 1886 Trapezia cymodoce (Herbst, 1801) +++, 2-7 m Coral: Stylophora pistillata Seychelles (Garth 1984), Singapore (Goh et al. 1990), China Seas (Dai and Yang 1991), Oman (Hogarth 1994), Taiwan (Jeng 1994), French Polynesia (Poupin 1996), Japan (Nomura et al. 1996) , Indonesia (Castro 1999),Thailand (Castro 2002; Thamrongnawasawat et al. 2009), Guam (Castro 2003), Philippines (Castro 2009), Andaman and Nicobar Is. (Kumaralingam et al. 2012) Trapezia digitalis Latreille, 1828 +, 2 m Coral: Pocillopora damicornis Red Sea (Ramadan 1936), Taiwan (Chang et al. 1987), Japan (Nomura et al. 1996), Hawaii, Eastern Pacific (Castro 1996, 1997b), Australia (Castro 1997b), French Polynesia (Castro 1997a), Indonesia (Castro 1999), Philippines (Castro 2009), Andaman and Nicobar Is. (Kumaralingam et al. 2012) Trapezia lutea Castro, 1997 ++, 2-7 m Coral: Stylophora pistillata French Polynesia (Castro 1997a), Indonesia (Castro 1999), Taiwan (Ng et al. 2001), Guam (Castro 2003), Thailand (Naiyanetr 2007), Philippines(Castro 2009) Trapezia septata Dana, 1852 +++, 2-7 m Coral: Pocillopora damicornis, Stylophora pistillata, Acropora hyacinthus Japan, Taiwan, Sri Lanka, Australia, Hawaii, Samoa Is. (Jeng 1994), French Polynesia (Poupin 1996), New Caledonia (Castro 1997b), Indonesia (Castro 1999), Thailand (Castro 2002), Guam (Castro 2003), Philippines (Castro 2009), Andaman and Nicobar Is. (Kumaralingam et al. 2012) Trapezia serenei Odinetz, 1984 ++, 2-5 m Coral: Pocillopora damicornis French Polynesia (Poupin 1996), Indonesia (Castro 1999), Taiwan (Ng et al. 2001), Guam (Castro 2003) Family Xanthidae MacLeay, 1838 Chlorodiella laevissima (Dana, 1852) ++, 2-4 m Coral: Acropora hyacinthus, Acropora digitifera Seychelles (Garth 1984), French Polynesia (PeyrotClausade 1989; Poupin 1996), China Seas (Dai and Yang 1991), Japan (Nomura et al. 1996), Taiwan (Ng et al. 2001) Chlorodiella nigra (Forskål, 1775) ++, 2-7 m Coral: Acropora hyacinthus, Acropora digitifera, Stylophora pistillata Seychelles (Garth 1984), China Seas (Dai and Yang 1991), French Polynesia (Poupin 1996), Japan (Nomura et al. 1996), Taiwan (Ng et al. 2001), Thailand (Thamrongnawasawat et al. 2009) Cymo melanodactylus Dana, 1852 +++, 2-10 m Coral: Acropora hyacinthus, Acropora digitifera, Acropora spp. Seychelles (Garth 1984), Singapore (Goh et al. 1990), China Seas (Dai and Yang 1991), Australia (Patton 1994), Oman (Hogarth 1994), French Polynesia (Poupin 1996), Taiwan (Ho et al. 2000), Thailand (Thamrongnawasawat et al. 2009), Japan (Yamano et al. 2012), Red Sea (Broesing et al. 2014) Family Cryptochiridae Paul'son, 1875 Hapalocarcinus marsupialis Stimpson, 1859 ++, 2-6 m Coral: Stylophora pistillata Pacific Ocean and Andaman sea (Kropp 1990), China Seas (Dai and Yang 1991), Japan (Nomura et al. 1996), Taiwan (Wei et al. 2005) Utinomiella dimorpha (Henderson, 1906) +, 3 m Coral: Pocillopora damicornis Pacific Ocean (Kropp 1990), Taiwan (Wei et al. 2005) Occurrence: ++++ = 100%, +++ = >60%, ++ = 20% - 60%, + = <20%. * indicates first record of the species in waters adjacent to Taiwan. page 5 of 14Zoological Studies 55: 7 (2016) to Brachyura (82.8%) than to Anomura (17.2%). Among the specimens of Tetraliidae (Brachyura), totaling 7 species were dominant. Tetralia rubridactyla Garth, 1971 was the most abundant followed by Tetralia glaberrima (Herbst, 1790) and Tetralia nigrolineata Serène and Pham, 1957. Tetralia crabs were found inhabiting all colonies of Acropora corals, each coral head contained at least one adult Tetralia crab. Seven species shown high frequency of occurrence (more than 60%): Allogalathea elegans (Adams and White, 1848), Petrolisthes virgatus Paul’son, 1875, T. glaberrima, T. rubridactyla, Trapezia cymodoce (Herbst, 1801), Trapezia septata Dana, 1852 and Cymo melanodactylus Dana, 1852. Furthermore, 5 species, Lauriea simulata Macpherson and Robainas-Barcia, 2013, P. virgatus, Gonatonotus nasutus D. G. B. Chia and Ng, 2000, Tetralia aurantistellata Trautwein, 2007, and T. nigrolineata are recorded for the first time in waters adjacent to northern Taiwan. Most coral symbiotic crabs can be found in several host coral species. Species of tetraliids were recorded from more than 2 species of Acropora corals. DISCUSSION Distribution of dominant species Seven species of symbiotic crabs had a high occurrence in the investigated area. These species have varied distribution records worldwide. The galatheid crab Allogalathea elegans (Fig. 3a) occurred in all of the feather star specimens, each feather star containing at least 1 individual of A. elegans. A few feather star specimens contained both A. elegans and the brachyuran crab Permanotus purpureus (Gordon, 1934) (Fig. 4d). Allogalathea elegans usually lives on the aboral side, near the cirri of the feather star, whereas P. purpureus can be found on both the aboral and oral sides, near the crown. The occurrence of A. elegans has been recorded in the Red Sea and the east coast of Africa (Baba 1988), Thailand (Thamrongnawasawat et al. 2009), East China Sea (Miyake and Keiji 1967), Japan (Baba 1969), Taiwan (Baba et al. 2009), the Philippines (Baba 1988), and Australia and the Tasman Sea (Ahyong 2007). Its distribution ranges widely from the intertidal zone to 146 m (Baba 1988). It is usually found in several crinoid species: Anneissia bennetti (Müller, 1841), Capillaster multiradiatus (Linnaeus, 1758), Comanthus parvicirrus (Müller, 1841), Comaster schlegelii (Carpenter, 1881), Heterometra savignii (Müller, 1841), Himerometra robustipinna (Carpenter, 1881), Lamprometra palmata (Müller, 1841), Stephanometra indica (Smith, 1876) and Tropiometra carinata (Lamarck, 1816) (Baba et al. 2009). The occurrence frequency of P. virgatus (Fig. 3d) was 80%-90%, and most sea urchin specimens contained only 1 crab individual. This anomuran crab, characterized as cryptic with echinoderms, was found beneath the rock-boring sea urchin Fig. 3. Anomuran crabs recorded from the western Fan-Zai-Aou Bay in northern Taiwan. (a) Allogalathea elegans ( ♂ , ♀), (b) Galathea tanegashimae ( ♂ , ♀), (c) Lauriea simulata (♀), (d) Petrolisthes virgatus ( ♂ , ♀), (e) Petrolisthes sp. (♀). Scale bar represents 5 mm. (a) (d) (b) (e) (c) page 6 of 14Zoological Studies 55: 7 (2016) Fig. 4. Brachyuran crabs recorded from the western Fan-Zai-Aou Bay in northern Taiwan. (a) Nucia sp. ( ♂ ), (b) Echinoecus pentagonus ( ♂ , ♀), (c) Gonatonotus nasutus ( ♂ ), (d) Permanotus purpureus ( ♂ , ♀), (e) Pilumnus sp. (♀), (f) Domecia glabra ( ♂ ,♀), (g) Domecia hispida ( ♂ , ♀), (h) Tetralia aurantistellata ( ♂ ), (i) Tetralia cinctipes ( ♂ , ♀), (j) Tetralia glaberrima ( ♂ , ♀), (k) Tetralia nigrolineata ( ♂ , ♀), (l) Tetralia rubridactyla ( ♂ , ♀), (m) Tetraloides heterodactylus ( ♂ , ♀), (n) Tetraloides nigrifrons ( ♂ ), (o) Tetraloides nigrifrons with darker color on carapace ( ♂ , ♀), (p) Trapezia cymodoce ( ♂ , ♀), (q) Trapezia digitalis ( ♂ ), (r) Trapezia lutea ( ♂ , ♀), (s) Trapezia septata ( ♂ , ♀), (t) Trapezia serenei ( ♂ , ♀), (u) Chlorodiella laevissima ( ♂ ), (v) Chlorodiella nigra ( ♂ , ♀), (w) Cymo melanodactylus ( ♂ , ♀), (x) Hapalocarcinus marsupialis (♀), (y) Utinomiella dimorpha ( ♂ , ♀). Scale bar represents 5 mm. page 7 of 14Zoological Studies 55: 7 (2016) (a) (b) (c) (d) (e) (i) (m) (q) (u) (y) (f) (j) (n) (r) (v) (g) (k) (o) (s) (w) (h) (l) (p) (t) (x) Echinometra mathaei (Blainville, 1825). Its habitat is the intertidal zone (Nakasone and Miyake 1972), which is consistent with our record of P. virgatus in the 0-3 m zone. In addition, P. virgatus is usually observed with the symbiotic snapping shrimp, Arete indicus Coutière, 1903 in tunnels and holes made by sea urchins. Tetralia glaberrima (Fig. 4j) and T. rubridactyla (Fig. 4l) are small, brightly colored crabs with an obligatory symbiosis with various species of Acropora corals. Both species have been recorded across the Indo-West Pacific region (Castro 1997a, 2003; Galil 1988; Galil and Clark 1988). Tetralia glaberrima is found from the intertidal zone to 54 m (Castro 1997b), whereas T. rubridactyla has been found to a maximum depth of 27 m (Castro 1997a). T. glaberrima is easily distinguishable from T. rubridactyla by its color pattern, crestless cheliped merus, and the shape of the endopod of the first maxillipeds (Castro et al. 2004; Galil 1988). These two species have been found sympatrically with other species of tetraliids, Cymo crabs, Coralliocaris and Jocaste shrimps, and gobies (Gobiodon). Tetralia glaberrima has the highest occurrence frequency in the Great Barrier Reef and New Caledonia, followed by T. nigrolineata and T. rubridactyla (Castro 1997b; Patton 1994; Sin 1999). Species of Tetralia are dominant in the reef zone in our study area. The brachyuran crabs T. cymodoce (Fig. 4p) and T. septata (Fig. 4s) are common throughout the Indo-West Pacific region (Castro 1997a, b); T. cymodoce is more prevalent (Castro 1997a) and is more widely distributed. Both T. cymodoce and T. septata have been recorded off the southern coast of Taiwan and off the Peng-hu Islands, Hsiao Liuchiu Island, Kenting National Park, and Orchid Island (Chang et al. 1987; Jeng 1994) associated with the branching corals Seriatopora hystrix Dana, 1846, Stylophora pistillata Esper, 1797, Pocillopora damicornis (Linnaeus, 1758), and Pocillopora verrucosa (Ellis & Solander, 1786) in southern Taiwan. We recorded T. septata in 2 species of corals S. pistillata and P. damicornis, and T. cymodoce in S. pistillata. Trapezia cymodoce and T. septata has been reported from depths of 1-55 m (Castro 1997b) and 0.5-45 m (Castro 2009), respectively. Several studies have reported a positive correlation between the size and number of Trapezia crabs and the colony size of their host corals (Abele and Patton 1976; Austin et al. 1980; Castro 1978; Garth 1984; Tsuchiya et al. 1993). Despite the sampling a large number of small colonies of P. damicornis (diameter < 10 cm) in northeast Taiwan, we did not find T. cymodoce in any of them, suggesting that the corals were too small for the crabs. The mean carapace width of adult T. cymodoce individuals associated with P. damicornis is approximately 7.9 ± 2.0 to 9.7 ± 1.4 mm (mean ± SE) in southern Taiwan (Chang et al. 1987). Trapezia species have been reported as an obligate symbiont of pocilloporid corals worldwide (Castro 2002, 2003; Chang et al. 1987; Knudsen 1967; Stella et al. 2011a). This coevolution of trapeziid crabs and corals appears to have been established in the Eocene (Schweitzer 2005). Symbiotic coral crabs living with atypical hosts is a rare phenomenon, in T. cymodoce (Patton 1994; Tsuchiya and Nojima 2002), T. glaberrima (Garth 1984; Knudsen 1967) and T. rubridactyla (Chang et al. 1987). We nevertheless found T. septata living with the atypical host Acropora hyacinthus (Fig. 5). Cymo melanodactylus (Fig. 4w), a known obligatory symbiont, mainly inhabits acroporid corals (Garth 1984, Serène 1984). In this study, the occurrence frequency of C. melanodactylus was found to be higher than 60%, with low abundance (mostly 1 or 2 individuals per colony) and a small size (carapace width less than 6 mm). This species has been reported to be widespread in the IndoWest Pacific region (Goh et al. 1990; Dai and Yang 1991; Patton 1994; Poupin 1996; Ho et al. 2000; Thamrongnawasawat et al. 2009; Yamano et al. 2012) and in the western Indian Ocean (Garth 1984; Hogarth 1994; Broesing et al. 2014). These slow-moving crabs are known to feed on the tissues of their host, but do not appear to be harmful to their hosts when presented in a low number (less than 3 indivicuals per colony) (Patton Fig. 5. Brachyuran crab Trapezia septata living with the host coral Acropora hyacinthus. page 8 of 14Zoological Studies 55: 7 (2016) 1994). However, recent studies have revealed that overabundance of C. melanodactylus (up to 47 individuals per colony) may cause mortality in Acropora cytherea (Dana, 1846) (Pratchett et al. 2010, 2013). The host corals were not healthy, with partial mortality of the colonies, indicating that C. melanodactylus may forage on the dead tissues of the corals. New record of 5 species in Taiwan The present study recorded 5 species for the first time in Taiwan waters: L. simulata, P. virgatus, G. nasutus, T. aurantistellata, and T. nigrolineata. The anomuran L. simulata (Fig. 3c) was identified in the scleractinian coral P. damicornis. This is only the third record of this species after specimens collected from gorgonians from the Philippines (Macpherson and Robainas-Barcia 2013) and living corals from Hainan, South China Sea (Dong and Li 2013). In addition, this is the northernmost record of L. simulata. The species has been recorded from the intertidal zone to 120 m (Macpherson and Robainas-Barcia 2013) and from 1-3 m to 21-54 m (Dong and Li 2013). The present study recorded L. simulata at 6 m. A new host coral of L. simulata, namely P. damicornis, was identified. The anomuran crab P. virgatus (Fig. 3d) is abundant, with a high frequency rate (> 80%) in northeastern Taiwan. Its distribution record is unusual because the species has been found in Mozambique (Kalk 1958), Somalia (Lewinsohn 1979), Yemen (Simões et al. 2001), Oman (Hogarth 1988), the Red Sea (Ramadan 1936), and Japan (Nakasone and Miyake 1972; Nomura et al. 1996). Most reports are from the western Indian Ocean, and the only report from the western Pacific Ocean is from the Ogasawara and Ryukyu Islands, Japan. The identification of P. virgatus reported herein represents the second record of this species in the western Pacific Ocean, confirming its distribution in the Kuroshio-influenced regions. Our results suggest that the Kuroshio plays a crucial role in the distribution of the species, linking its habitats in the western Pacific Ocean. In the present study, the brachyuran G. nasutus (Fig. 4c) was collected from the sea urchin Prionocidaris sp. at 12-m depth. Its distribution depth ranges widely from shallow water to 210 m (Chia and Ng 2000; Sakai 1976). This species has been recorded in western and eastern Australia, New Caledonia, Vanuatu, the Philippines, and Japan (Chia and Ng 2000). Studies have reported it living with the branching coral S. pistillata (Sakai 1976) and sea urchins Phyllacanthus imperialis (Lamarck, 1816) and Phyllacanthus parvispinus Tension Woods, 1878 (Chia and Ng 2000). Our study is the first record of G. nasutus living with Prionocidaris sea urchins. Tetralia aurantistellata (Fig. 4h) and T. nigrolineata (Fig. 4k) are coral-dwelling crabs. The present study reports the northernmost distribution record of T. aurantistellata. The distribution depths of T. aurantistellata and T. nigrolineata are similar: 1-52 m (Castro 2009; Trautwein 2007) and shallow water to 52 m (Castro 1997b, 2009), respectively. Previous studies have revealed that T. nigrolineata associates solely with scleractinian corals of the genus Acropora (Castro 2003, 2009; Patton 1994). Surprisingly, a T. nigrolineata pre-adult individual was collected from a sea fan (Melithaeidae), suggesting that the megalopa of T. nigrolineata may be an opportunistic symbiont capable of living with diverse hosts (Castro 2009). Diversity of coral-symbiotic crabs The number of symbiotic crab species worldwide varies among studies according to collection frequency, sampling methods, location, and study period (Castro 2009). In southern Taiwan, Jeng (1994) and Chang et al. (1987) identified 8 and 20 species of symbiotic crabs in coral reefs, respectively. We identified 29 species from northeastern Taiwan because specimens were collected from diverse hosts such as sponges, corals, crinoids, and sea urchins. Shao (1998) estimated that the marine species around Taiwan represent 10% of those worldwide. The present study provides information on 5 species recorded for the first time in Taiwan, thus contributing to the baseline of symbiotic crustaceans in southern East China Sea. Although several groups have studied anomuran and brachyuran crabs, most have focused on brachyuran crabs (Table 2). A few reports have elaborated on crab families (or taxon) and their hosts. However, most have not explored the relationship between symbiotic crabs and their hosts. Thus, assigning the crabs to symbiotic groups is difficult. Recent review reports have characterized certain crabs among specific families and genera as obligate symbionts. For example, crabs belonging to Tetraliidae, Trapeziidae, and Cryptochiridae families and those belonging to Domecia and Cymo genera are known obligate symbionts of scleractinian corals and most colonial anthozoan cnidarians (Castro et al. 2004; Patton page 9 of 14Zoological Studies 55: 7 (2016)