Pycnogonida

T

he pyconogonids (Gr. pyknos = crowded, gony = knee) are strictly marine group of arthropods found in intertidal to abyssal depths up to 7000m from tropics to polar seas. The pycnogonids were first discovered from Antarctic waters by James Eight (Eight 1835), since then these organisms are often referred as a characteristic component of Antarctic habitat. They are commonly known as sea spiders as they resemble spiders and other arachnids with small bodies and relatively long, hinged legs. These organisms found as cryptive epibenthic community on other invertebrates, algae, corals etc.; occasionally observed as swimming in coastal surface and also spread in fouling communities on ship's hulls. Dispersion of pycnogonids is severely restricted due to absence of a planktonic larval phase and hence, they tend to contribute high endemism in a particular region. Pycnogonids are extremely important, comprise a primitive lineage of arthropods and hold potential to reveal insights into arthropod evolution. Recent phylogenetic analyses have supported their position as either basal chelicerates or as a separate, fifth major lineage of extant arthropods.

Morphology The body is variable in shape, discoid to elliptic, degree of separation. The body of the pycnogonid is always much reduced and only connector between each pair of legs; thus, the digestive and reproductive organs have migrated to the legs. However, some deep-sea species can have five or six body segments and ten or twelve legs respectively (polymerous forms). Most of them have four pairs of legs, although species with 5 or 6 pairs exist. No respiratory system in these animals while gaseous exchange took place by diffusion. They are usually white or colored; tan or brown or red to blend in perfectly with their backgrounds. They range in size from tiny midgets having leg spans of only 2mm to deep-sea giants with leg spans of up to 75 cm.

Feeding Pycnogonids are carnivorous and some species have parasitic associations with hydroids, molluscs and echinoderms. Generally they feed on sessile fauna such as coelenterates, cnidarians, bryozoans, ascidians, molluscs and polychaetes. A proboscis suck nutrients from soft bodied invertebrates, and their digestive tract has diverticula extending into the legs.

Reproduction and Development Sexes are separate in pycnogonids although hermaphrodism was also seen. In both males and females the reproductive openings are situated at the base of some or all of the legs. The specific legs and the number of legs possessing gonopores vary in different species and also in both sexes. Females possess a pair of ovaries, while males possess a pair of testes located dorsally in relation to the digestive tract. Reproduction involves external. The eggs are developed within the legs of female, extruded through the female gonopores, fertilized externally during extrusion, and then carried by the ovigers or on the legs of the male. In anormorphic development, eggs are hatched as protonymphon larvae.

Fossil History The oldest fossil record of pycnogonids is dating back to the Upper Cambrian from Hunsruck Shale of western Germany. The records from the Devonian are significant in that some taxa exhibit character states quite different from those of extant species. In 2007 remarkably well preserved 70 fossils from three distinct species in the 160 million year old Jurassic La Voulte Largestatte were found in fossil beds at La Voulte-sur-Rhone, south Lyon in south-eastern France by the researchers from University of Lyon.

Global and Indian Status A total of 1330 species of pygnogonid belonging to 4 orders, 15 families and 85 genera were recorded from the world oceans. Among them Pantapoda is the major order in which 12 families, 82 genera and 1327 species are recognized (Table 1). Antarctic and sub-Antarctic waters represent 20% of them. 264 pycnogonid species from the Southern Ocean, 192 species from Antarctic waters, 138 species from Sub-Antarctic waters, 122 species in Southwest Pacific have been recorded. The diversity of endemism was recorded 108 species from Antarctic waters, 62 species from sub-Antarctic, 10 genera from austral waters, 10 species are endemic to South America, 23 species from New Zealand, 7species from Australian waters, 36 species from New Caledonia. Knowledge on Indian pycnogonid at present is very meager as very few reports available at few localities. Indian pycnogonid fauna comprises of 34 species under 16 genera in 9 families. Nymphon andamanense Calman, 1923 is the only endemic species of India.

Habitat The pycnogonid species are found from shallow region to over 5600m depth. The majority of the mean depths of species (~ 72% of the species) are shallower than 500m. Mostly found on sandy bottom, seagrass, seaweeds, dead corals and crevices

Threats Physical alteration of habitat areas, alien species introductions, and changes in atmospheric composition are the major threats for pycnogonids. Due to global warming the southern Ocean and Antarctic are facing threats. Dredging, exploration of mineral reserves, oil and gas may also pose threats to pycnogonids as they are bottom dwellers. Other threats are occurring to the life of pycnogonid in the oceans are siltation, nutrient loading, pollution by toxic chemicals etc.

LESSER KNOWN MARINE ANIMAL Table 1: Global Diversity of Pygcnogonida Family Genus Species 1.Palaeoisopodidae 1 1 2.Palaeopantopodidae 1 1 3.Haliestidae 1 1 4.Austrodecidae 2 56 5.Colossendeidae 6 102 6.Ascorhynchidae 8 113 7.Ammotheidae 21 281 8.incertaesedis 9 16 9.Nymphonidae 6 268 10.Callipallenidae 14 139 2 11.Pallenopsidae 81 4 12.Phoxichilidiidae 154 4 13.Endeidae 21 3 14.Pycnogonidae 75 1 15.Rhynchothoracidae 19 2 16.Sub order incertaesedis 2

Total

85

Sea Spider

1330

Distribution in India Arabian Sea

Achelia boschi Stock, 1992 Nymphopsis acinacispinatus Williams, 1933 Ammothella omanensis Stock, 1992 Anoplodactylus digitatus (Böhm, 1879) Anoplodactylus sandromagni Krapp, 1966 Callipallene pectinata (Calman, 1923) Seguapallene echinata (Calman, 1938) Nymphon foxi Calman, 1927 Nymphon arabicumCalman, 1938 Colossendeis macerrima Wilson, 1881 Pycnogonum moolenbeeki Stock, 1992 Pycnogonum tesselatum Stock, 1968

Vishakapatinam

Ammothea sp. Anoplodactylus sp. Anoplodactylus cribellatus Calman, 1923

Lakshadweep

Bathypallenopsis annandalei Calman, 1923 Colossendeis macerrima Wilson, 1881 Vizhinjam

Anoplodactylus cribellatus Calman, 1923 Pallenopsis crosslandi Carpenter, 1910

Madras

Endeis flaccidus Calman, 1923 Endeis meridionalis (Bohm, 1879) Endeis mollis (Carpenter, 1904) Endeis ghaziei Rajagopal, 1963 Anoplodactylus digitatus (Böhm, 1879)

Andaman Sea

Gulf of Mannar

Endeis mollis (Carpenter, 1904) Ascorhynchus ramipes (Böhm, 1879) Anoplodactylus eroticus Stock, 1968 Nymphon longicadautum Carpenter, 1904 Bathypallenopsis safari (Stock, 1984) Pycnogonum indicum Sundara Raj, 1930

Anoplodactylus cribellatus Calman, 1923 Colossendeis colossea Wilson, 1881 Colossendeis macerrima Wilson, 1881 Endeis mollis (Carpenter, 1904) Eurycyde flagella Nakamura & Chullasorn, 2000 Nymphon andamanense Calman, 1923 Pallenopsis alcockiCalman, 1923 Pallenopsis ovalisLoman, 1908 Rhopalorhyncus kroeyeri Wood Mason, 1873

Released on the occasion of “National Workshop on Lesser Known Marine Animals of India” during11th to 13th June, 2015 held at ZSI, Port Blair

LEKMAI-2015 ZOOLOGICAL SURVEY OF INDIA Government of India Ministry of Environment and Forests and Climate Change Port Blair - 744102, Andaman and Nicobar Islands

Prepared by: K. Venkataraman, C. Raghunathan, Smitanjali Choudhury, Tamal Mondal and R. Raghuraman