Peripatopsis Alba
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''Peripatopsis alba'', the white cave velvet worm, is a
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of
velvet worm Onychophora (from , , "claws"; and , , "to carry"), commonly known as velvet worms (for their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, '' Peripatus''), is a phylum of e ...
in the
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
Peripatopsidae Peripatopsidae or the Southern Velvet Worms are one of two extant families of velvet worm. This family includes more than 140 described species distributed among 41 genera, but some authorities deem only 131 of these species to be valid. The Fre ...
. This species is notable as one of only two species of velvet worm known to be
troglobitic A troglobite (or, formally, troglobiont) is an animal species, or population of a species, strictly bound to underground habitats, such as caves. These are separate from species that mainly live in above-ground habitats but are also able to live u ...
; the only other velvet worm known to be a
troglobiont Troglofauna are small cave-dwelling animals that have adapted to their dark surroundings. Troglofauna and stygofauna are the two types of subterranean fauna (based on life-history). Both are associated with subterranean environments – troglofaun ...
is ''
Speleoperipatus spelaeus ''Speleoperipatus'' is a monospecific genus of velvet worm in the Peripatidae family, containing the single species ''Speleoperipatus spelaeus''. This species is a pale greenish yellow, almost white, with 22 or 23 pairs of legs and no eyes. Spec ...
''. The white cave velvet worm is rare and limited to one cave system on
Table Mountain Table Mountain (; ) is a flat-topped mountain forming a prominent landmark overlooking the city of Cape Town in South Africa. It is a significant tourist attraction, with many visitors using the Table Mountain Aerial Cableway, cableway or hik ...
in
South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...
.


Discovery

This species was first described by the South African
zoologist Zoology ( , ) is the scientific study of animals. Its studies include the structure, embryology, classification, habits, and distribution of all animals, both living and extinct, and how they interact with their ecosystems. Zoology is one ...
Reginald F. Lawrence in 1931 based on four specimens, including two
type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * ...
specimens, an adult male and a
subadult A juvenile is an individual organism (especially an animal) that has not yet reached its adult form, sexual maturity or size. Juveniles can look very different from the adult form, particularly in colour, and may not fill the same niche as t ...
female. The male measures 48 mm in length, whereas the female is smaller, only 32 mm long. Lawrence collected these specimens from Wynberg Cave near the top of Table Mountain, including some from the main gallery, about 100 feet (30 m) below the surface. These velvet worms were found under stones or climbing up the wet walls of the cave.


Description

This species has no eyes and lacks pigmentation. The body of this species is a striking white, with a thin opaque stripe running from the head down the back but fading near the posterior end of the body. This species has 18 pairs of clawed legs, with the last pair reduced. In the male, the penultimate pair is also smaller than the preceding pair. The soles of the feet feature three pads with the middle pad two or three times as broad as the proximal pad. The claws are a dirty white tipped with brown. LIke other velvet worms in the
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
''
Peripatopsis ''Peripatopsis'' is a genus of velvet worms in the Peripatopsidae family. These velvet worms are found in the KwaZulu-Natal, Western Cape, and Eastern Cape provinces of South Africa. This genus was proposed by the British zoologist Reginald I. ...
'', this species has three distal papillae on each foot, two anterior and one posterior. The feet are elongated, and the legs are notably longer and more slender than in other species of ''Peripatopsis''. In the larger male type specimen, for example, the legs in the middle of the body measure 2.1 to 2.6 mm in length, and the feet are 0.8 to 0.9 mm long. Long legs reflect an adaptation to life in the dark, where the velvet worm can use these legs to explore its surroundings, much as a blind person might use a cane. This species also features longer antennae, another characteristic common among troglobitic species. The other troglobitic species of velvet worm, ''S. spelaeus'', for example, also lacks pigment, has no eyes, and features legs and antennae that are unusually long.


Phylogeny

As noted by Lawrence, this species resembles its close relative '' P. balfouri'', both in terms of the number of legs and the conical papillae on the
integument In biology, an integument is the tissue surrounding an organism's body or an organ within, such as skin, a husk, Exoskeleton, shell, germ or Peel (fruit), rind. Etymology The term is derived from ''integumentum'', which is Latin for "a coverin ...
. He describes ''P. alba'' as an eyeless version of ''P. balfouri'', but with longer legs and lacking pigment. The species ''P. balfouri'' is also close in terms of geography, living just outside the cave where ''P. alba'' was discovered.
Phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...
analysis using molecular data confirms that ''P. alba'' is part of the ''P. balfouri''
species complex In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...
but maintains ''P. alba'' as a separate species. An analysis of the molecular evidence places ''P. alba'' in its own
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
on a branch of a
phylogenetic tree A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA. In ...
with a
sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...
formed by two other clades, one belonging to ''P. balfouri'' and the other comprising '' P. bolandi'' and '' P. purpureus''.


Distribution and habitat

''Peripatopsis alba'' is known only from two caves, Wynberg Cave and Bats' Cave, both part of a cave system about 750 m above sea level on Table Mountain in South Africa. This cave system is the third largest sandstone cave system in the world, and Wynberg and Bats' caves are the most frequently visited of the Table Mountain caves. Wynberg Cave measures 300 m in length and reaches a maximum depth of 50 m, whereas Bats' Cave is shorter (only 60 m long) but deeper. The walls of Wynberg Cave is an extensive labyrinth of horizontal galleries with surfaces kept damp by water seeping in through fissures in the rock. The only vegetation in this cave is a greyish lichen. Bats' Cave is similarly humid with a perennial pool in a small deep zone chamber. Like other deep caves with small entrances, these caves maintain a fairly constant temperature and humidity over the course of the day and through the year. The white cave velvet worm preys on cave crickets, but prey is not plentiful, so the population density is low. This velvet worm is found only in the deep zone of the caves under stones or on damp walls where moisture is plentiful. This species is so sensitive to its environment that all attempts to keep them alive outside the cave system have failed. Lawrence collected two live specimens and kept them under conditions that would have sustained other ''Peripatopsis'' species, but both died 24 hours later.


Conservation

This species is listed as Vulnerable on the
IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological ...
in light of its restricted distribution, small population, and the threat of collection by humans and disruption by cavers.Hamer, M. 2003.
Peripatopsis alba

2006 IUCN Red List of Threatened Species.
Downloaded on 5 August 2007.
This species is so scarce that a survey conducted from 1995 to 1996 found ''P. alba'' to be the rarest of all the Table Mountain troglobites. Furthermore, this species is so stenotopic and the ecosystem of this cave system is so fragile that even small changes in the environment could be disastrous and cause the extinction of this species.


References

{{Taxonbar, from=Q3600865 Animals described in 1931 Blind onychophorans Endemic fauna of South Africa IUCN-assessed onychophorans Onychophorans of temperate Africa Onychophoran species Troglobitic onychophorans