Synspermiata is a

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 ...

of araneomorph

spider Spiders (order (biology), order Araneae) are air-breathing arthropods that have eight limbs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude spider silk, silk. They are the largest order of arachnids and ran ...

s, comprising most of the former " haplogynes". They are united by having simpler genitalia than other araneomorph spiders, lacking a

cribellum Cribellum literally means "little sieve", and in biology the term generally applies to anatomical structures in the form of tiny perforated plates. In certain groups of diatoms it refers to microscopically punctured regions of the frustule, or ...

, and sharing an evolutionary history of synspermia – a particular way in which

spermatozoa A spermatozoon (; also spelled spermatozoön; : spermatozoa; ) is a motile sperm cell (biology), cell produced by male animals relying on internal fertilization. A spermatozoon is a moving form of the ploidy, haploid cell (biology), cell that is ...

are grouped together when transferred to the female.

Synspermia

Spermatozoa A spermatozoon (; also spelled spermatozoön; : spermatozoa; ) is a motile sperm cell (biology), cell produced by male animals relying on internal fertilization. A spermatozoon is a moving form of the ploidy, haploid cell (biology), cell that is ...

are produced in a multi-step process. A primary spermatocyte with the full diploid number of

chromosome A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...

s divides to form two secondary spermatocytes which are haploid, i.e., each has half the diploid number of chromosomes. Each secondary spermatocyte then divides to produce two spermatids which undergo further development to form spermatozoa. In synspermia, two or more spermatids from the same spermatocyte fuse together and are enclosed in an envelope, forming a "capsule". This contrasts with cleistospermia, where the capsules enclose individual spermatozoa. After transfer to the female in either form, decapsulation and activation are necessary before the resulting spermatozoa can fertilize eggs.

Phylogeny

In 2014, Peter Michalik and Martín Ramírez published a study of the morphology of the reproductive system of male spiders, including their spermatozoa. They found a

within haplogyne spiders, Synspermatia, characterized by the absence of a

and the

synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel Phenotypic trait, character or character state that has evolution, evolved from its ancestral form (or Plesiomorphy and symplesiomorphy, plesiomorphy). A synapomorphy is an apomorphy sh ...

(shared derived character) of synspermia. Not all members of the clade exhibit synspermia, since it has evolved into cleistospermia multiple times and Telemidae have individually encapsulated sperm cells arranged in densely packed stacks. A much larger

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

study published in 2016 also found Synspermatia to be a clade, grouping with the families Hypochilidae and Filistatidae at the base of

Araneomorphae The Araneomorphae (also called the Labidognatha or "true spiders") are an infraorder of spiders. They are distinguishable by chelicerae (fangs) that point diagonally forward and cross in a pinching action, in contrast to the Mygalomorphae (taran ...

Families

Families placed in Synspermiata are: * Caponiidae * Diguetidae * Drymusidae * Dysderidae * Ochyroceratidae *

Oonopidae Oonopidae, also known as goblin spiders, is a family (biology), family of spiders consisting of over 1,600 described species in about 113 genus, genera worldwide, with total species diversity estimated at 2000 to 2500 species. The type genus of th ...

* Orsolobidae * Pacullidae * Periegopidae * Pholcidae * Plectreuridae * Scytodidae * Segestriidae * Sicariidae * Telemidae * Tetrablemmidae * Trogloraptoridae

Extinct families

† Eopsilodercidae (Telemidae was not included in the analysis by Wheeler et al., but is placed in Synspermiata in other studies.

References

{{Araneae