Invertebrate with internal skeleton

[Moontanman]

Can you name an invertebrate with an internal skeleton?

[Dracontes]

Lessee... Animals with endoskeletons besides Chordates

 

Echinodermata: their skeleton, even the spines are covered in thin layer of epidermis.

 

Coleoidea: the shells of belemnites, squid and cuttlefish are internal so I guess it counts in a way.

 

Porifera: the siliceous/calcareous/spongin spicules are internal to the cells that produce them.

 

I heard something about some arthropods, like arachnids or crustaceans, having internal extensions of their exoskeleton or internal organic/mineralized plates to provide attachment sites for muscles. So after some sleuthing I found that spiders and relatives do have an internal skeleton: the endosternite (character 5 in the list) and that decapod crustaceans also share the distinction (page 36 of the *.pdf onward; lengthy download ~6 MB). Another link and an abstract:

 

Colette Bitsch & Jacques Bitsch. (2002). "The endoskeletal structures in arthropods: cytology, morphology and evolution". Arthropod Structure & Development Volume 30, Issue 3, Pages 159-177

 

The paper proposes an overview of the endoskeletal structures of the head and trunk in the different arthropod groups: Chelicerata, Crustacea, Myriapoda and Hexapoda (=Insecta s.l.). Two major endoskeletal systems are reported with their cytological characteristics: those made up of connective tissue derived from muscular tendons, and those consisting of cuticular rods or plates arising from integumentary ingrowths. The morphological value of the various endoskeletal structures, their possible homologies in different groups, and their presumed evolutionary changes are discussed. This survey may be considered as a first step to use morphological characteristics of the endoskeleton in future cladistic analyses to assess the phylogeny of arthropods.

 

I hope to have helped :)

[Moontanman]

Lessee... Animals with endoskeletons besides Chordates

 

Echinodermata: their skeleton, even the spines are covered in thin layer of epidermis.

 

Coleoidea: the shells of belemnites, squid and cuttlefish are internal so I guess it counts in a way.

 

Porifera: the siliceous/calcareous/spongin spicules are internal to the cells that produce them.

 

I heard something about some arthropods, like arachnids or crustaceans, having internal extensions of their exoskeleton or internal organic/mineralized plates to provide attachment sites for muscles. So after some sleuthing I found that spiders and relatives do have an internal skeleton: the endosternite (character 5 in the list) and that decapod crustaceans also share the distinction (page 36 of the *.pdf onward; lengthy download ~6 MB). Another link and an abstract:

 

Colette Bitsch & Jacques Bitsch. (2002). "The endoskeletal structures in arthropods: cytology, morphology and evolution". Arthropod Structure & Development Volume 30, Issue 3, Pages 159-177

 

 

 

I hope to have helped :)

 

 

Possibly I should have been more exact, sea urchins and their kin are the only invertabrate that has a complete interenal sckeleton, The others have extentions of their external sceletons that are internal. the good news is you got it right, i should have knwn not to ask such simple question to this group!

 

Michael