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Onychophorans (Velvet Worms): Natural History and Conservation of a Vulnerable Invertebrate Taxon in the Caribbean Islands
Kenneth W. McCravy and Ivo de Sena Oliveira

Caribbean Naturalist, Special Issue No. 2 (2019):135–155

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Caribbean Naturalist 135 K.W. McCravy and I.S. Oliveira 2019 Special Issue No. 2 Onychophorans (Velvet Worms): Natural History and Conservation of a Vulnerable Invertebrate Taxon in the Caribbean Islands Kenneth W. McCravy1,* and Ivo de Sena Oliveira2,3 Abstract - Onychophorans, or velvet worms, are an enigmatic group of soft-bodied, terrestrial invertebrates. These organisms are of keen interest in investigations comprising a variety of topics, including animal evolution, biogeography, and conservation, given their close affinities with the arthropods and remarkable distribution pattern, as well as the pointendemism of almost all species. Onychophorans are found in moist habitats in tropical and subtropical forests, but given their nocturnal activity and cryptic behavior, relatively little is known about the biology and conservation status of the ~200 valid described species. Onychophorans are subdivided into 2 major subgroups: the Peripatidae (81 species) inhabiting the Neotropics (= Neopatida), equatorial Africa, and Southeast Asia, and the Peripatopsidae (120 species) occurring in the Australasian region, Chile, and southern Africa. The Caribbean islands house 22 described species of Peripatidae—over 25% of the diversity known for this subgroup. Only 3 species are of recognized conservation concern and included on the International Union for Conservation of Nature Red List: Macroperipatus insularis (endangered), Plicatoperipatus jamaicensis (lower risk/near threatened), and Speleoperipatus spelaeus (critically endangered). The restricted geographic ranges of onychophoran species, together with their occurrence in insular habitats subject to natural and/or anthropogenic disturbance, suggest that onychophorans might be at risk in the Caribbean islands. Herein, we present a short review of Onychophora, with particular attention to Caribbean species and discuss how these organisms, despite embodying the challenges and difficulties inherent in conservation of cryptic and poorly known invertebrates, may still be used as flagship species for habitat conservation. Introduction Onychophorans, also known as velvet worms (Phylum Onychophora; Fig. 1A–C) are enigmatic soft-bodied, predatory invertebrates considered the only animal phylum with marine ancestors that became entirely endemic to terrestrial environments (Piper 2007). Phylogenetically, onychophorans are, together with the tardigrades (water bears), the closest relatives of the arthropods—the world’s largest and most diverse animal group—even though the relationships among these 3 groups within the major clade Panarthropoda are still under debate (see Martin et al. 2017 for detailed review). Onychophorans are of considerable interest to 1Department of Biological Sciences, Western Illinois University, 1 University Circle, Macomb, IL 61455, USA. 2Department of Zoology, Institute of Biology, University of Kassel, Heinrich-Plett-Straße 40, D-34312 Kassel, Germany. 3Departamento de Zoologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, 31270-901 Belo Horizonte, Brazil. *Corresponding author - Manuscript Editor: Julian Monge Endangered and Threatened Species of the Caribbean Region 2019 CARIBBEAN NATURALIST Special Issue No. 2:135–155 Caribbean Naturalist K.W. McCravy and I.S. Oliveira 2019 Special Issue No. 2 136 evolutionary biologists investigating the early radiation of arthropods, and they have been important subjects of study in biogeography and conservation as well (Brinck 1957; Brues 1923; New 1995; Oliveira et al. 2015, 2016; Smith and Ortega- Hernández 2014). To date, the ~200 onychophoran species described are subdivided into 2 major subgroups, Peripatidae and Peripatopsidae, distributed in moist habitats in tropical and subtropical forests of the Neotropics, Chile, Southeast Asia, the Australasian region, and equatorial and southern Africa (Fig. 2A). Since nearly all onychophoran species are point-endemic and restricted to habitats susceptible to disturbance, they are considered potentially important flagship species for habitat conservation (New 1995, Oliveira et al. 2015). Indeed, onychophorans are among the few invertebrate groups with high impact in conservation and habitat preservation, as previously demonstrated in Brazilian savannah, Atlantic rainforest, and Tasmania (COPAM, 1988, Mesibov and Ruhberg 1991, Oliveira et al. 2015). Lack of data for most onychophoran species, however, still prevent their use for conservation purposes in different areas of the world (Oliveira et al. Figure 1. (A) Speleoperipatus spelaeus; photograph © of Jamaican Caves Organisation. (B) An undescribed species of onychophoran from Martinique Island; photograph © of Patrick Marechal. (C) An undescribed species of onychophoran from Puerto Rico; photograph © of Alejandro J. Sánchez and Johann D. Crespo Zapata. Caribbean Naturalist 137 K.W. McCravy and I.S. Oliveira 2019 Special Issue No. 2 2015). For example, the fauna of Neopatida, i.e., Neotropical Peripatidae, remains largely unexplored, and several undescribed species may have disappeared silently as their natural habitats were impacted by humans and/or natural disasters such as earthquakes, hurricanes, and volcanoes, although Epiperipatus biolleyi (Bouvier) Figure 2. Geographical distributions of onychophorans and their occurrence in the Caribbean islands. (A) World map showing the geographical distribution of the 2 major onychophoran subgroups. (B) Details of the Caribbean islands indicating the onychophoran species described from this region. Caribbean Naturalist K.W. McCravy and I.S. Oliveira 2019 Special Issue No. 2 138 demonstrated the resilience of onychophorans by surviving heavy volcanic ash on the hillsides of the Irazu volcano during eruptions of 1963 in Costa Rica (Barquero- González et al. 2016). Toledo-Matus et al. (2018) pointed out that only 2 species of onychophorans have been properly recorded from Mexico, where there may be at least 14 additional species (Monge-Nájera 2000) present. Their conservation status cannot be assessed due to our lack of knowledge of these species, especially because they have not yet been formally described. To date, over 70 species of Neopatida are formally known, with 22 of them being described from different Caribbean Islands (Oliveira et al. 2012a, Read 1988a). On one hand, peculiarities of insular habitats (e.g., long-term isolation, unique biota, and distinct climate) and their fragility suggest that these onychophoran species deserve special attention for conservation. On the other hand, only 3 of these species are officially included on the IUCN Red List (New 1996a, 1996b, 1996c). This paper, therefore, aims to present an overview of onychophoran natural history, followed by a discussion of onychophoran conservation issues, with particular attention to Caribbean species. Onychophoran Anatomy, Physiology, and Reproduction Onychophorans can be considered “living fossils”, with a highly conserved body plan that has changed little since the Carboniferous (Garwood et al. 2016, Haug et al. 2012, Thompson and Jones 1980). Like their panarthropod kin, onychophorans are metamerically segmented animals, but unlike arthropods, they show little tagmosis, or specialization of multiple segments into functional regions (Brusca and Brusca 2003). Onychophorans are cylindrical in cross section and vary from 5 mm to 220 mm in length (Morera-Brenes and Monge-Nájera 2010, Ruhberg 1985). The head of each onychophoran has 3 pairs of modified appendages, including a pair of sensory antennae, a pair of chewing/slicing mandibles, and a pair of slime papillae (Mayer et al. 2015a), and is posteriorly followed by 13 to 43 trunk segments bearing a pair of unjointed walking legs each (Ruhberg and Mayer 2013). The anal cone is a true, limbless segment (Mayer et al. 2015b). The onychophoran epidermis is covered with a thin chitinous cuticle, and the integument bears numerous dermal papillae formed by micro-scales, which give them their peculiar “velvety” appearance. This characteristic of the integument provides onychophorans with a repellent skin that prevents water, dirt, and even their own slime from sticking to it (Mayer and Ruhberg 2013). The integument is folded into transverse ridges, or plicae, and this characteristic gives onychophorans amazing abilities to squeeze and stretch their bodies substantially, to the extent that the worm can squeeze its body through an opening one-ninth the worm’s normal cross-sectional area (Manton 1977, Wright 2012)—an advantageous ability for creatures that live in environments with many tight crevices such as decaying logs. Tracheal openings allow gas exchange via a tracheal system similar to that of insects. Unlike many arthropods, however, onychophoran tracheal openings are distributed over the body surface rather than occurring as segmental pairs (Wright 2012) and lack a closing mechanism, thus explaining their confinement to moist habitats and rapid loss of moisture in dry environments (Weldon et al. 2013). Onychophorans lose moisture at a rate 40 times Caribbean Naturalist 139 K.W. McCravy and I.S. Oliveira 2019 Special Issue No. 2 faster than do caterpillars, which have a similar body form (Clusella-Trullas and Chown 2008, Manton 1949, Weldon et al. 2013). Moreover, they can lose >10% of their body mass per hour in dry, fast-flowing air (Meyer and Eisenbeis 1985). Internally, onychophorans possess circular, diagonal, and longitudinal musculature that works to lengthen, flatten, and contract the body during movement (Wright 2012). The circulatory system is primarily an open design with a fluid-filled hemocoel that serves as a hydrostatic skeleton, and a dorsal heart equipped with paired, segmental ostia that extend almost the entire length of the worm and pump the blood, or hemolymph. The hemolymph transports nutrients but has apparently little role in oxygen transport (Mendes and Sawaya 1958), although oxygen binding protein (hemocyanin) is present in the hemolymph (Kusche et al. 2002). The nervous system is mainly composed of a bipartite brain and a pair of ventral nerve cords interconnected by ring (dorsal) and median (ventral) commissures (Martin et al. 2017). Onychophorans have a complete digestive tract; most nutrient absorption takes place in the midgut region, with indigestible material passing through the hindgut within a peritrophic membrane, which is also excreted together with the feces (Brusca and Brusca 2003, Ruhberg and Mayer 2013). Onychophorans excrete nitrogenous wastes as uric acid together with their feces (Campiglia and Maddrell 1986, Manton and Heatley 1937). In addition, onychophorans possess segmental nephridia that are responsible for hemolymph filtration and excretion of urine (Manton and Heatley 1937). In contrast to their generally highly conserved morphology, onychophorans show an amazingly diverse array of reproductive strategies that include oviparous, lecithotrophic viviparous, matrotrophic viviparous, combined lecithotrophic/ matrotrophic viviparous, and placentotrophic viviparous forms (Mayer et al. 2015, Walker and Tait 2004). All Neopatida species are viviparous and show a placentalike structure, thus being classified as placentotrophic viviparous (Barquero- González et al. 2016, Mayer et al. 2015b, Ostrovsky et al. 2015). Onychophorans reproduce sexually with 1 exception: a parthenogenetic population of Epiperipatus imthurni (Sclater) reported from the island of Trinidad (Read 1988a). Many onychophoran species show sexual dimorphism (Reid 1996). Onychophoran Ecology Onychophorans generally inhabit tropical and subtropical forests, and are restricted to moist microhabitats such as leaf litter, decomposing logs, and soil galleries (Monge-Nájera 1995). Some species inhabit grasslands if there are sufficient refugia during the day, and there are also a few cave-dwelling species (e.g., Espinasa et al. 2015, Peck 1975). Ecologically, onychophorans occupy a soil/litter predatory niche somewhat similar to that of centipedes (Ruhberg and Mayer 2013), although their actual ecological relevance remains unknown. Onychophorans are nocturnal, a behavior that allows them to avoid the risk of desiccation associated with daytime activity, although a recent study suggests that onychophorans become most active during the driest and darkest nights of the year (Barquero-González et al. 2018). Exposure during daylight has been rarely observed in natural environments Caribbean Naturalist K.W. McCravy and I.S. Oliveira 2019 Special Issue No. 2 140 (e.g., Carvalho 1942). They feed on soil and epigean invertebrates such as crickets, woodlice, cockroaches, and small spiders (Read and Hughes 1987). Onychophorans have also been documented feeding on large ctenid or theraphosid spiders, although it was not clear whether the onychophorans had killed healthy spiders or were feeding on spiders that were already dead or weakened (Dias and Lo-Man- Hung 2009, González et al. 2018). Onychophorans are ambush predators, moving slowly and stealthily over the forest floor. They mainly use leg propulsion for locomotion, although alternate extension and contraction of the body via circular and longitudinal muscles working in tandem with the hydrostatic skeleton, similar to annelid worms, may be used as well (Hoyle and Williams 1980, Manton 1973). Larger prey are captured using a remarkable method. The onychophoran squirts a sticky slime from their pair of oral papillae (Baer et al. 2014). The 2 streams cross, forming a slime net that ensnares the prey (Morera-Brenes and Monge-Nájera 2010). Concha et al. (2015) have recently suggested that this oscillation of the onychophoran slime jet could be accomplished by passive elastohydrodynamic instability resulting from the interaction of the elastic oral papillae and the rapid but unsteady flow achieved during squirting. This slime is generally used at short range (1 cm or so), but distances of up to 45 cm have been recorded (Wright 2012). This slime net becomes sticky in a fraction of a second by mechanical stress, hardening due to a complex interplay between proteins and lipids (Baer et al. 2017, 2018), and the onychophoran then uses its mandibles to slice through the trapped prey’s integument, injecting saliva which contains enzymes that begin digesting the prey (Mayer et al. 2015a, Ruhberg and Mayer 2013). The liquefied prey is subsequently sucked in with the muscular pharynx (Wright 2012). The onychophoran often consumes the dried slime as well, presumably as an energy or nutrient conservation measure (Read and Hughes 1987). The protein composition of the onychophoran slime might be species-specific (Baer et al. 2014). The slime may also be used to deter potential predators, e.g., arthropods such as spiders and centipedes (Read 1985). Because onychophorans are well defended, they may even serve as models in Batesian mimicry systems. The first evidence for such mimicry has recently been uncovered by Zitani et al. (2018), who found a putative lepidopteran mimic of an arboreal onychophoran in an Ecuadorian cloud forest. Franco and Monge-Nájera (2016) describe cases of “role-reversal” in which Ctenus spp. (wolf spiders) were observed feeding on onychophorans. No slime could be detected, so apparently the spiders ambushed the onychophorans before defensive measures could be taken. These researchers noted that the effectiveness of the spider venom suggests that onychophoran muscles and nerves are similar to those of insects biochemically. Vertebrate predators of onychophorans include birds and reptiles. Turdus grayi Bonaparte (Clay-colored Thrush) have been observed feeding onychophorans to nestlings (Dyrcz 1982), and the South American coral snake Micrurus hemprichii (Jan) preys almost totally on onychophorans (Monge- Nájera et al. 1993, Roze 1982). Inactive onychophorans have been observed resting on leaves about 0.5 m above ground level in locations where this snake is found, Caribbean Naturalist 141 K.W. McCravy and I.S. Oliveira 2019 Special Issue No. 2 perhaps as a defensive measure to avoid this predator (Monge-Nájera et al. 1993). Recently, another case of a semifossorial snake, Trimetopon slevini Dunn, preying on an unidentified onychophoran was recorded in Costa Rica (Smokoska and Acosta-Chaves 2017). The reproductive behavior of onychophorans is largely understudied. It is known that the modes of sperm transfer may vary greatly, especially among peripatopsids. In representatives of Peripatopsis and Metaperipatus, sperm transfer is particularly unusual, with the male depositing spermatophores on the body surface of the female (Manton 1938, Mayer 2007). Leucocytes then break down the ectoderm and the cuticle and the spermatophores are ruptured, resulting in the release of the spermatozoa into the female’s hemacoel. The spermatozoa then migrate to the ovary (Manton 1938). Males of some Australian species use specialized, eversible head organs to transfer the spermatophore into the female (Tait and Norman 2001). On the other hand, direct transfer by pairing genital openings seems to be the rule among peripatids, including all Caribbean species (Oliveira et al. 2012b). Reproduction may either be seasonal or occur year-round depending on the species, and females seem to have postcopulatory influence over fertilization (Curach and Sunnucks 1999; Lavallard and Campiglia 1975; Oliveira et al. 2012b, 2015; Sunnucks et al. 2000). Onychophoran Diversity, Evolution, and Biogeography Onychophorans are an ancient group, known in the fossil record from at least the late Carboniferous period, ~300 million years ago (Haug et al. 2012, Wright 2012). Extant onychophorans, together with the tardigrades and arthropods, form a monophyletic group called Panarthropoda. Recent evidence suggests that onychophorans arose from lobopodians—a paraphyletic assemblage of marine Cambrian fossils from which all 3 major lineages of Panarthropoda derived (Smith and Ortega-Hernández 2014). Lobopodians were worm-like invertebrates with fleshy, unjointed legs; these animals survived until the late Carboniferous Period, although broader definitions of the Lobopodia include extant onychophorans, tardigrades, and arthropods (Budd 1998). Within Panarthropoda, onychophorans are usually described as the sister taxon of the “Tactopoda” (tardigrades + arthropods) or sister to Arthropoda (Martin et al. 2017). The 2 families of onychophorans, Peripatidae and Peripatopsidae, contain a total of 221 described species, but only 201 are valid species, with 20 representing nomina dubia (Oliveira et al. 2012a). Considering their cryptic habits, this number may only represent a small part of the onychophoran species diversity, and more species undoubtedly await discovery. A new “giant” species of onychophoran, Peripatus solorzanoi Morera-Brenes & Monge-Nájera, was recently discovered from Caribbean coastal forest of Costa Rica. This is the longest onychophoran ever recorded at 22 cm (Morera-Brenes and Monge-Nájera 2010). The smallest onychophoran (4–20 mm) is the peripatopsid Ooperipatellus nanus Ruhberg from New Zealand (Ruhberg 1985). More recently, a new onychophoran, Cerradopatus sucuriuensis Oliveira et al., was described from the Brazilian Cerrado, one of the world’s most threatened environments Caribbean Naturalist K.W. McCravy and I.S. Oliveira 2019 Special Issue No. 2 142 (Conservation International 2004, Oliveira et al. 2015). Undescribed species from additional threatened environments such as Martinique and Puerto Rico (Fig. 1B, C) await formal description. Onychophorans have a primarily tropical distribution (Fig. 2A). This distribution corresponds with the sequence of geographic isolation of the landmasses. One branch of the onychophoran evolutionary tree, the Peripatidae, has a more northerly distribution, with the Peripatopsidae present in more southern locations. Neotatida and equatorial African peripatid species show the closest affinities, with Indomalaysian species being more distantly related (Giribet et al. 2018, Murienne et al. 2014). Among the Peripatopsidae, Chilean and South African species diverged most recently, whereas Australasian species are more distantly related (Giribet et al. 2018, Murienne et al. 2014). However, the presence of a putative fossil onychophoran in Baltic amber suggests that these animals were present in northern Europe in the Eocene and that the geographic range of this phylum was once more extensive (Oliveira et al. 2016; see Giribet et al. 2018 for alternative view). Onychophorans were most likely distributed throughout the former Pangaean landmasses, and early diversification occurred before the break-up of Pangaea, with regionalization maintained even in landmasses that have remained contiguous (Murienne et al. 2014). It appears that the present-day Gondwanan distribution of extant onychophorans, rather than reflecting restricted invasion of land in the southern hemisphere, is a result of a more global terrestrial invasion followed by range contraction due to unsuitable environmental conditions (Poinar 1996, 2000; Tait et al. 1995). Analyses by Monge-Nájera (1994) demonstrated a correlation (though not necessarily causation) of present-day global onychophoran distribution with Pleistocene vegetation. Ecological barriers limiting onychophoran distributions appear to be taxon-specific (Monge-Nájera 1994). There are ~70 extant species of New World onychophorans based on the species type localities; 22 of these are reported from the Caribbean islands, although 2 of them have been regarded nomina dubia (Table 1, Fig. 2B; Oliveira et al. 2012a). In the New World, the Peripatidae ranges from Mexico through Central America, the northern half of South America, and the Caribbean. Representatives of the Peripatopsidae are found in Chile. Haiti and Jamaica contain the greatest Caribbean diversity based on these records. When considering the onychophoran fauna of the Caribbean islands, the question arises, how did they get there? There are 2 potential biogeographical explanations: (1) a vicariance model, in which the proto-Antilles, from their position joined to what is present-day Central America, carried their Mesozoic fauna with them as they moved eastward to their present position, and (2) a dispersal model, in which ancestors of the present Antilles fauna crossed ocean gaps to reach their new island homes (Peck 1999). Peck (1999) analyzed the historical biogeography of Jamaica, focusing on cave invertebrates. Under scenario #1, Jamaica was continuously habitable (emergent) during its movement eastward from Central America, and the cave fauna of Jamaica would be more distantly related to the local fauna. Under scenario #2, the cave fauna would be the result of a more recent adaptive radiation, Caribbean Naturalist 143 K.W. McCravy and I.S. Oliveira 2019 Special Issue No. 2 since the last island emergence, and there would be closer links with the local fauna. Geological evidence indicates that Jamaica has been continuously emergent only since the early Miocene, about 20 mya (Buskirk 1985). Peck’s (1999) analyses support the hypothesis that epigean ancestors of Jamaican cave invertebrates probably reached Jamaica in the Neogene, with the cave faunas being closely related to Jamaican forest faunas. The troglobitic onychophoran Speleoperipatus spelaeus Peck is believed to be most closely related to the genera Epiperipatus, Peripatus, and Macroperipatus on Jamaica (Peck 1975), but this hypothesis has not yet been tested based on molecular data. The divergence of Plicatoperipatus, also endemic to Jamaica, from other Jamaican onychophorans was previously assigned to the Table 1. Species and type localities of onychophorans found in the Caribbean Islands. *species considered nomen dubium (see Oliveira et al. 2012a for further details). Taxon Type locality Epiperipatus E. barbadensis (Froehlich) BARBADOS, Saint John, Coddrington College E. barbouri (Brues) GRENADA, Grand Etang, 548 m E. broadwayi (Clark) TOBAGO, probably Tobago Forest Reserve E. lewisi (Arnett) JAMAICA, Portland, John Crow Mountains, ~16 km SW of Priestman’s River E. trinidadensis (Sedgwick) TRINIDAD, Northern Range Macroperipatus M. clarki (Arnett) JAMAICA, Portland, John Crow Mountains, ~8 km SW of Priestman’s River, 457 m M. insularis Clark HAITI, between Jacmel and Tronin M. torquatus (von Kennel) TRINIDAD, Northern Range Peripatus *P. antiguensis Bouvier ANTIGUA ISLAND, Barlar, near Warburton P. basilensis Brues HAITI, Morne Basile, NW part of the island *P. bavaysi Bouvier GUADELOUPE ISLAND P. danicus Bouvier VIRGIN ISLANDS, Saint Thomas Island P. darlingtoni Brues HAITI, Massif de la Hotte, SW peninsula of Haiti, between Camp Perrion and Mafin, 914 m P. dominicae Pollard DOMINICA ISLAND, Laudat P. haitiensis Brues HAITI, Massif de la Selle, Furcy, possibly La Visite National Park, 1524–2134 m P. juanensis Bouvier PUERTO RICO, Utuado, Utuado P. juliformis Guilding SAINT VINCENT ISLAND, possibly Mount Bonum P. lachauxensis Brues HAITI, SE foothills of Massif de la Hotte, SE peninsula of Haiti, 305 m P. manni Brues HAITI, Massif de la Selle, possibly La Visite National Park, 1524–2134 m P. swainsonae Cockerell JAMAICA, Saint Thomas Parish, Bath, Beacon Hill Plicatoperipatus P. jamaicensis (Grabham & JAMAICA, Saint Thomas Parish, Bath, Beacon Hill Cockerell) Speleoperipatus S. spelaeus Peck JAMAICA, Clarendon, Pedro River, Pedro Great Cave, 518 m Caribbean Naturalist K.W. McCravy and I.S. Oliveira 2019 Special Issue No. 2 144 Pliocene (Hebert et al. 1991), but recently proved to be older than expected (Giribet et al. 2018). However, all Jamaican onychophorans seem to have evolved from a common ancestor and most likely diverged during the Miocene (Giribet et al. 2018), thus being in line with geological data and Peck’s previous assumption. Onychophorans would seem to be poorly suited for long-distance oceanic dispersal. Individuals of E. biolleyi, for instance, only survive for a few minutes when placed in sea water (Monge-Nájera 1995). However, rafts composed of soil, wood, and vegetation could provide a means of onychophoran dispersal to islands (Monge-Nájera 1995). This might have been the case for onychophorans recently described from Galapagos, which most likely dispersed overseas from Ecuador (Giribet et al. 2018). Bates (1863) observed that the Amazon River serves as a source of such flotsam rafts, and ocean currents generally flow from eastern South America to the Antilles. The Orinoco River is another possible source of dispersal rafts (Peck 1981). Morera-Brenes and Monge-Nájera (2010) observed that all Antillean species of Peripatus occur on continental islands, suggesting that this genus colonized current islands during times of relatively low sea levels, a variation of the vicariance explanation (model #1). To further complicate matters, recent molecular studies suggest that some Caribbean species from the islands of Jamaica, Trinidad, Tobago, and Dominican Republic are more closely related to each other than to species occurring in the continental plate (Giribet et al. 2018, Murienne et al. 2014). Therefore, despite the ongoing discussion (see Giribet et al. 2018), it is currently difficult to assess unambiguously the evolutionary history of onychophorans in the Caribbean islands. Onychophorans generally show high levels of endemism and low vagility. Because of the risk of desiccation, their dispersal is restricted by arid conditions, meaning populations are often isolated. Consequently, onychophoran species richness has probably been underestimated because many “widespread” species may actually be species complexes (Oliveira et al 2011). Because of their sensitivity to microhabitat changes, low vagility, cryptic behavior, and high levels of endemism, onychophorans are particularly susceptible to habitat disturbances (Lacorte et al. 2011; Monge-Nájera 1995, 1996; New 1995). Onychophoran Conservation Onychophorans are a part of the diverse world of invertebrates that has been described as “the little things that run the world” (Wilson 1987). Over 95% of all documented species of animals are invertebrates, and when estimated numbers of species are included, the proportion approaches 99% (Scheffers et al. 2012). However, invertebrate-focused conservation efforts are relatively rare compared to efforts directed at vertebrates, which are for the most part larger and more appealing to humans (Böhm et al. 2012). There are undoubtedly many reasons for the lack of emphasis on invertebrate conservation, including their small size and often cryptic behavior, and the “pest” status of a small proportion of invertebrates which gives the group as a whole a bad name. Educational efforts to make the public aware of the importance and fascinating ways of invertebrates are helpful in this Caribbean Naturalist 145 K.W. McCravy and I.S. Oliveira 2019 Special Issue No. 2 regard (Monge-Nájera 2017). But there are serious challenges to be faced from a more scientific standpoint as well, primarily stemming from the incredible diversity of invertebrates, our woefully incomplete knowledge of their biology, and the difficulty of obtaining reliable identifications at the species or in many cases even genus level. All these aspects concern onychophorans directly, thus hampering studies on the group and turning conservation attempts into frustrating experiences. New (1995:80) suggests that invertebrate groups suitable for conservation efforts should “(1) be taxonomically tractable and recognisable to non-specialists, (2) have some broader appeal on aesthetic or evolutionary grounds, to facilitate communication, (3) be ecologically informative, perhaps entering an array of community interactions, or as indicator species, (4) have known geographical distribution patterns, both on broad and fine scales, (5) be susceptible to environmental change, with threats and the means to counter these definable, and (6) co-occur with other taxa of conservation concern so that the ‘political weight’ of conservation efforts can be compounded.” Onychophorans fulfill many of these prerequisites that make them attractive subjects for prioritized conservation efforts. As New (1995) points out, onychophorans are charismatic animals that, as a group, are readily distinguishable from other animals, and so conservation-based generalizations at the phylum level may be possible. Compared to invertebrate groups like arthropods, mollusks, or nematodes (Zhang 2011, 2013), onychophoran species richness is not excessively high, perhaps making the group taxonomically tractable. But this point is complicated by the fact that, at the species level, many onychophorans are rare, poorly known, and difficult to distinguish (Read 1988a,b). The latter difficulty to a great extent stems from the highly conserved morphology of these animals. The lack of obvious taxonomic characters (Daniels et al. 2013, 2016; Oliveira et al. 2011) makes many species virtually indistinguishable using traditional morphological methods such as light microscopy (Oliveira et al. 2011). In the past, this situation has resulted in variations or subspecies being proposed, such as Macroperipatus insularis insularis Clark and M. insularis clarki Arnett in Hispaniola and Jamaica, respectively. Wide distributions have also been assigned to some species, such as Epiperipatus edwardsii (Blanchard), which is reported from Panama to Brazil, even though the species type-locality is most likely Cayenne in French Guiana (Costa et al. 2018, Oliveira et al. 2012a), or Oroperipatus eisenii (Wheeler), the distribution of which spans from Mexico to Brazil (see Peck 1975 for further examples). Use of molecular techniques together with a wealth of new characters revealed by using more modern morphological methods such as scanning electron microscopy have made it clear that most onychophoran species are point-endemic and confined to small geographic ranges (Costa et al. 2018; Oliveira et al. 2010, 2015). To date, wider distributions have only been demonstrated for a few Peripatopsis species from South Africa (Daniels et al. 2013, 2017; McDonald and Daniels 2012) Available data suggest that, at least in Brazil, most clades are at localities at least 10–30 km apart, so that if putative clades are located over 30 km apart, they are likely to be separate species (Lacorte et al. 2011; Oliveira et al. 2011, 2012a; Reid 1996). Thus, the point-endemism of most onychophoran species Caribbean Naturalist K.W. McCravy and I.S. Oliveira 2019 Special Issue No. 2 146 suggests that geographical information is useful to rule out conspecificity and may thus be used for conservation purposes (Oliveira et al. 2012a). Sosa-Bartuano et al. (2018) have proposed combining geographic information with a description of salient characteristics to create common names for undescribed onychophoran species for conservation purposes. This approach, however, may lead to ambiguity in that (1) morphological features like color are intraspecifically variable in representatives of Neopatida (Morera-Brenes and Monge-Nájera 2010, Oliveira et al. 2012b); (2) the actual geographic range of most onychophoran species is not known; and (3) the suggested names may be mistakenly interpreted as formal species descriptions, even though this approach does not fulfill the amendments of the International Code of Zoological Nomenclature. Therefore, this approach may lead to arbitrary conservation actions and should be considered with reservation. Onychophorans are the focus of broader interest among evolutionary biologists because of their key phylogenetic position and status as “living fossils” (New 1995). The similarities that onychophorans share with the putative lobopodian ancestors of panarthropods make them of interest to systematists attempting to reconstruct arthropod phylogeny, as well as important models to infer evolution of different traits among the highly diverse arthropods (Martin et al. 2017). The unique onychophoran prey-capture mechanism has also found expression among non-scientists in folklore and art, as described by Monge-Nájera and Morera- Brenes (2015). Ecologically, much remains to be learned about onychophoran natural history, community relationships, and coarse- and fine-scale distributions, and their generally cryptic habits may limit their usefulness as indicator species (New 1995). Biogeographically, onychophorans might represent one of the best extant taxa to test biogeographical hypotheses predating continental drift, given their ancient evolutionary history and their low dispersion capability (Allwood et al. 2010; Monge-Nájera 2005, 2006; Murienne et al. 2014; Oliveira and Mayer 2017). Nevertheless, onychophorans remain biogeographically challenging given the growing evidence that many species have quite restricted geographic ranges, the high levels of diversity of these cryptic species, and the limited numbers of studies being carried out on these animals (Oliveira et al. 2011). Based on the vulnerability of some of their most important habitats, such as humid forests and caves, and their apparently limited dispersal abilities, habitat destruction appears to be a serious threat to many onychophorans (New 1995, Oliveira et al. 2015). Protection of habitat would appear to be of substantial benefit. Industrialization, slash-and-burn agriculture, and forest fires have caused the disappearance of onychophorans in specific locations (Wells et al. 1983). As mentioned previously, onychophorans are highly susceptible to desiccation, so reduction of leaf litter or edge effects that alter moisture or humidity levels could adversely affect these animals in a short time scale. Mesibov and Ruhberg (1991) found Tasmanipatus individuals that had evidently taken refuge in rot pockets and moist downhill ends of logs in recently burned locations, suggesting that these onychophorans can survive occasional fire. However, they also found an absence of onychophorans in otherwise suitable habitat that had a history of frequent or Caribbean Naturalist 147 K.W. McCravy and I.S. Oliveira 2019 Special Issue No. 2 intense fire, which indicates that fires that are too hot or frequent can have an adverse effect. Despite their apparent fragility, some onychophorans can survive volcanic eruptions (Barquero-González et al. 2016) as mentioned previously, and at least 19 species have been reported from urban areas (Monge-Nájera 2018). The latter author hypothesizes that diet and lack of detectability favor these species. It should be noted that, in addition to habitat destruction, excessive collecting could also be a threat to onychophorans living in very restricted habitats, such as caves (Espinasa et al. 2015, New 1995). Currently, only 3 species of Caribbean onychophorans are included on the IUCN Red List: M. insularis (endangered; New 1996a), Plicatoperipatus jamaicensis (lower risk or near threatened; New 1996b), and S. spelaeus (critically endangered; New 1996c). The latter 2 are restricted to Jamaica. M. insularis is now considered to be 2 separate species: M. insularis, with type locality in Haiti; and M. clarki, with type locality in Jamaica (Oliveira et al. 2012a). Macroperipatus insularis (now M. clarki in Jamaica) and P. jamaicensis are evidently forest species, but little is known regarding details of their ecology and habitat requirements. Hebert et al. (1991) collected these species by searching debris, rotten logs, and tree-fern stumps in the John Crow Mountains of Jamaica. Of 4 onychophoran species known from these habitats, only these 2 were collected. Over 1000 P. jamaicensis individuals were collected, but only 4 M. clarki were found. Only 1 onychophoran was collected per 4 hours of searching in mature forest, whereas 5 onychophorans per hour were collected in banana plantations (Hebert et al. 1991). These numbers indicate that P. jamaicensis was by far the most abundant of the 2 species that were collected, and that P. jamaicensis may be tolerant (or even prefer) certain anthropogenically altered habitats. However, allozyme and mtDNA analyses indicated that P. jamaicensis includes at least 2 different species that diverged in the early Pleistocene (Hebert et al. 1991), complicating assessment of this species’ ecology and conservation status. It also appears that other species of onychophorans that were not found (not specified, but presumably E. lewisi and P. swainsonae) may be very rare in these habitats and in need of protection. It should also be noted that in the intervening few decades since Hebert et al.’s (1991) survey, the Jamaican landscape has been and continues to be altered. Broadleaf forest habitat types declined by 0.65% in Jamaica from 1989 to1998, while land devoted to bauxite extraction has more than quadrupled, with bauxite areas almost doubling in broadleaf forest habitats and a net degradation of forest cover occurring (Evelyn and Camirand 2003). More recently, loss of forest cover in Jamaica has been estimated at 3.9% for the period 2001–2012 (Mongabay 2013). While these rates of change are not as alarming as those of some other tropical countries, such landscape changes probably have adverse effects on onychophoran species endemic to particularly limited areas (Monge-Nájera 2018). Speleoperipatus spelaeus (Fig. 1A) is an eyeless and depigmented troglobitic onychophoran first described by Peck (1975), with the type locality of Pedro Great Cave in south-central Jamaica. Peck (1975) states that a subsequent visit to the cave produced no S. spelaeus, and visits to more than 50 other Jamaican caves Caribbean Naturalist K.W. McCravy and I.S. Oliveira 2019 Special Issue No. 2 148 likewise yielded none, although many of the other cave invertebrates collected at Pedro Great Cave were collected elsewhere. This finding suggests that S. spelaeus is not widespread and is present in small numbers, and thus future collecting should be limited (Peck 1975). In 2010, a single individual was photographed (Fig. 1A) in Swansea Cave in central Jamaica (Jamaican Caves Organisation 2010a). This cave, as well as Pedro Great Cave, has no official protection (Jamaican Caves Organisation 2010a, 2010b). Guidelines for protection of Jamaican caves were proposed (Haiduk et al. 2010), but no action was taken by the Jamaican government. Swansea Cave is well protected due to its location on a major sugar cane estate. The owners appreciate the importance of the caves on the estate, and they monitor and protect them. The location in the cave where the onychophoran was found in 2010 is relatively inaccessible, but Pedro Great Cave is less protected and is often visited by local people for guano extraction (R.S. Stewart and J. Pauel, Jamaican Caves Organisation, Ewarton, St. Catherine, Jamaica, pers. comm.). Peck (1975) notes the possibility that this species may not be a true troglobite and could be present in forest-litter habitats. Lack of eyes and pigmentation are traits found in some litter-evolved species, and some troglobites had litter-inhabiting ancestors (Barr 1968). However, no documented findings of S. spelaeus outside of caves have been reported, indicating that this species is troglobitic. Given the apparently limited range and numbers of this species, aggressive conservation measures should be taken, for example, by pressuring the government to establish strict control over cave access, ideally limiting it to authorized researchers, together with the legal protection of the surrounding areas. The remaining 19 onychophoran species reported from other Caribbean islands might very well also require special conservation attention. Much past research has focused on the Caribbean islands, and their various habitat types have been well sampled (Giribet et al. 2018; Read 1988a, b). Nevertheless, onychophorans historically described from these islands have not been repeatedly reported in the literature, suggesting that their numbers might not be as great as, for example, those of P. jamaicensis, but also that conservation actions are long overdue in these islands. On the other hand, substantial effort is required to generate sound data for these species, and decisions based on misplaced zeal may result in ineffective, arbitrary conservation actions (New 1995). Last but not least, it is worth mentioning that the onychophoran natural habitats in these islands have recently been substantially affected by severe natural disasters such as earthquakes, tsunamis, and hurricanes. It is unclear whether or not these events have been frequent in the past or are becoming more so with recent global climate changes. While there may be no conservation action effective against natural forces, it is critical that we investigate these species before they disappear together with their valuable biological, ecological, biogeographical, and evolutionary history. Conclusion The fascinating predatory behaviors and unique phylogenetic position of onychophorans make them a potentially attractive focus of wide support for Caribbean Naturalist 149 K.W. McCravy and I.S. Oliveira 2019 Special Issue No. 2 conservation efforts. As point-endemic flagship species, onychophorans could be effective in the promotion and establishment of relatively small, protected areas that would benefit other small organisms as well. Such a reserve has been established in Brazil—the 3.92 km2 Estacão Ecológica do Tripuí for the onychophoran Epiperipatus acacioi (Marcus and Marcus) (Oliveira et al. 2015). Based on detailed studies of the newly described species C. sucuriuensis, Oliveira et al. (2015) concluded that a reserve as small as 1.68 km2 might ensure the survival of this species. The Brazilian Cerrado is one of the most biologically diverse and threatened environments in the world (Conservation International 2004), so a reserve such as this would benefit other threatened species as well. More such studies are needed to clarify the diversity, habitat associations, and conservation needs of Caribbean onychophorans. It has been recommended that all members of Phylum Onychophora be assigned a listing of at least “vulnerable” (Wells et al. 1983). While this is a good beginning, greater knowledge of the biology of individual species is needed to effectively assess their vulnerability. Acknowledgments We thank Patrick Marechal, Alejandro J. Sánchez, Johann D. Crespo Zapata, and the Jamaican Caves Organisation for kindly granting permission to use photographs, and Stefan Stewart and Jan Pauel (Jamaican Caves Organisation) for helpful information on the status of Jamaican cave protection and conservation. This study was supported by grants from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq Brazil: 290029/2010-4) to I.S. Oliveira. Literature Cited Allwood, J., D. Gleeson, G. Mayer, S. Daniels, J.R. Beggs, and T.R. Buckley. 2010. Support for vicariant origins of the New Zealand Onychophora. Journal of Biogeography 37:669–681. Baer, A., I.S. Oliveira, M. Steinhagen, A.G. Beck-Sickinger, and G. Mayer. 2014. Slime protein profiling: A non-invasive tool for species identification in Onychophora (velvet worms). Journal of Zoological Systematics and Evolutionary Research 52:265–272. Baer A., S. Schmidt, S. Haensch, M. Eder, G. Mayer and M.J. Harrington. 2017. 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