A collection of sea spiders (Pycnogonida: Pantopoda) in the National Museum, Prague (Czech Republic)

The arachnological collection of the National Museum, Prague contains material preserved in ethanol and a microscopic slide of recent sea spiders (Pycnogonida: Pantopoda). The collection is small, containing only twelve specimens. A revision of all of them revealed the presence of nine species from five families: Anoplodactylus lentus Wilson, 1878, Boreonymphon abyssorum (Norman, 1873), Callipallene sp., Endeis spinosa (Montagu, 1808), Nymphon grossipes (Fabricius, 1780), Nymphon hirtipes Bell, 1853, Nymphon stroemi Krøyer, 1844, Nymphon tenellum (Sars, 1888) and Pycnogonum litorale (Ström, 1762). The material preserved in ethanol was collected in the North Atlantic Ocean and adjacent seas, the pycnogonid mounted on the slide was collected in Mediterranean. Four of the sea spiders came from the Sars collection (Bergen, Norway) and four specimens came from the V. Frič collection (Prague, Czech Republic). From these two sources, six specimens were mounted for exhibition and educational purposes. Although the collection contains no types, it introduces an interesting group of marine animals.

Sea spiders (Pycnogonida) are strange looking, exclusively marine invertebrates feeding on sessile or slow-moving (or sometimes dead) animals.However, catching quick-moving prey was also reported (Lotz 1968).They are often considered the sister group of Euchelicerata, i.e. a class of the subphylum Chelicerata but alternative hypothesis also exist -see Dunlop et al. (2014) for a review.
Their body, termed the trunk, is extremely reduced and serves just as attachment for the legs.The first segment, the cephalosoma, contains four primordial segments that are telescoped into the first trunk segment -the first for an ocular tubercle with four eyes (may be absent) and a proboscis, and the next three giving rise to the appendage pairs of the chelifores, palps and ovigers.The fourth pair of appendages in the cephalosoma is the first pair of walking legs and belongs to the trunk (Winter 1980).Behind the cephalosoma, there are three trunk segments, each bearing a pair of nine-articled walking legs comprised from coxa 1, coxa 2, coxa 3, femur, tibia 1, tibia 2, tarsus, propodus and the main claw.There has been long-lasting controversy concerning which appendages are homologous among arthropods.According to Jager et al. (2006), Manuel et al. (2006) and Brenneis et al. (2008), the pycnogonid appendages are homologous to those of euchelicerates and mandibulates as follows: chelifores ~ chelicerae ~ antennae I (innervated from deutocerebrum), palps ~ pedipalps ~ antennae II (innervated from tritocerebrum), ovigers ~ legs I ~ mandibles, legs I ~ legs II ~ maxillae I, legs II ~ legs III ~ maxillae II.The last (fourth) trunk segment bears the abdomen which is reduced to a small protuberance.
The reduced body of sea spiders causes several organ systems, like the intestine and gonads, to protrude into the legs, such that the genital openings are often located on the ventral surface of coxa 2 (usually of legs III and IV).Eggs are stored in the femora of all legs of the female.The typical first lar-val form (feeding on cnidarians), the protonymphon, usually hatches from the eggs that are carried by the male in many families.The larval body possesses a proboscis, chelifores and two pairs of ambulatory legs that turn into palps and ovigers during ontogeny.Information about biology of sea spider can be found in Arnaud & Bamber (1987).
Catalogues of sea spiders were published by museums in Germany (Dunlop et al. 2007, Weis et al. 2011, Lehmann et al. 2014).The National Museum in Prague has already published catalogues of various non-type zoological material (e.g.Jiroušková et al. 2011, Mlíkovský et al. 2013, Dolejš & Vaňousová 2015) and this paper continues by providing information about the sea spider collection in Prague.

Material and methods
All eleven ethanol-preserved pycnogonid specimens are kept in 80 % ethanol.Eight of them had been identified, three (plus the specimen mounted on the slide) only to genus level.Therefore, all specimens were first revised based on the literature mentioned below each species.Of the formerly identified specimens, only two of them had been identified correctly.Thus, labels with appropriate species names were put on the jars.Second, specimens were cross-referenced with the accessory catalogues.However, data for only four specimens were found in the catalogues (N o s 1876/1902, 19/1960/3066 and  19/1960/3109); the remaining specimens thus have a "general" number for Pycnogonida: P6d-9/2003 (P6j-118/1988 for the specimen mounted on the slide).Conversely, one specimen was not found in the collection despite being mentioned in the accessory catalogue from the year 1902: Colossendeis proboscidea (Sabine, 1824) from Bjørnøya ("W von Bären Insel").This specimen had come to the National Museum in Prague as an exchange from the Museum für Naturkunde Berlin on 21 October 1902 (accessory N o 1875/1902), but was either lost or destroyed.The remaining specimens in Berlin are deposited under N o ZMB 19 (Dunlop et al. 2007).
The third step was the determination of sex and measuring body lengths using an Olympus SZX12 stereomicroscope equipped with an ocular micrometer.Males were recognized by the presence of cement gland openings and hairy swellings located distally on the fifth article of the ovigers helping the (nymphonid) males in carrying the eggs.Females were recognized according to the swollen femora of the legs (and sometimes eggs visible inside them) without cement glands and missing ovigers (except members of the families Callipallenidae and Nymphonide where ovigers are also present in females but the swellings are lacking) (Bamber 2010).The body length in sea spiders means the distance between the anterior margin of the cephalosoma (i.e.without the proboscis) and posterior margin of the last (fourth) segment including the lateral processes but not the abdomen ( Just 1972, Bamber 2010).
Current nomenclature and the Life Science Identifier numbers (lsid) were adopted from PycnoBase (Bamber et al. 2015).The species are arranged systematically according to Bamber (2010).Data for each specimen are arranged as follows: Material -number of specimens (with a note in the case they are mounted), their sex (body length), name of the collector, date of collection and locality.Identification -name on the original label and literature used for revision/redetermination/identification.Biology and ecology -any available data.Notes -if any.(Dunlop et al. 2007).It is probable that they were also erroneously identified and that they are in fact B. abyssorum like the specimen deposited in Prague.