Gymnophiona: the Caecilians

Caecilians dates back to

190 mil years ago

Caecilian limbs

no limbs or no limb girdles

Caecilian lifestyle

burrowing mode of life in moist soil (some aquatic

Caecilian Retractable tentacle

unique sensory organ, one of each side of head; present in all and only caecilians; transmits senses (chemoreception like smell and tactile like touch); located at the foramen (behind naris and before eye orbit); closer to eye is ancestral condition

Caecilian skull

compact and very solid; fused block like; adaptation because they use their head to dig

• Stegokraphic skull on left 

  • More stiff, more subterranean lifestyle

• zygokrotaphic on the right in the picture

  • A little bit more mobile

  • Lives a  little closer the the surface

Caecilian jaw

• completely novel jaw-closing apparatus

• Two systems:

  • normal adductor mandibulae (ancestral condition seen in most vertebrates)

  • interhyoideus muscle + retro articular process

    • Muscles is behind the skull instead of on the side (where body is narrower) → widens the neck but not the head

    • It allows them to close and open their jaw in a burrow 

    • Pulls the jaw up and back

    • Adaptation to a burrowing lifestyle 

Caecilian eyes

• Eyes small to vestigial - no lids

  • Underground so they don't need to see

  • The more and more derived: more absent eyes or eyes completely covered under tissue 

Caecilian lungs

•  Left lung usually rudimentary (reduced)

  • Rely on the right lung

  • like snakes (but this is unrelated)

caecilian body and skin

• Body is ringed with primary folds (annuli)

  • Primary fold is associated with one backbone segment (one vertebrae)

• Tiny dermal scales in folds 

  • Durability

caecilian ears

• No external ear openings (but can hear low frequency sounds transmitted through skull to inner ear).

• Adaptation to a burrowing lifestyle (ears would just get filled with dirt)

caecilian distribution

worldwide in tropics (except madagascar and australia)

caecilian reproductive organs

• Phallodeum copulatory organ, part of / extension of cloaca – supports internal fertilization (with a copulatory organ!!! Only order of the 3 lissamphibia)

  • Males insert into the female cloaca - internal fertilization!!!

• Male Mullerian glands - enhance fluid transport of sperm

caecilian reproductive mode

• ~70% oviparous (lay eggs)

  • 45% lay terrestrial eggs (direct development) , 25% aquatic 

  • Some young feed on the mother’s skin or skin secretions

    • Skin is fatty (helps keep water in)

• ~30% viviparous – young scrape oviductal epithelium with fetal dentition, stimulating secretion of “uterine” milk

caecilian feeding

larvae, juveniles, adults all carnivorous

Family Rhinatrematidae

• Genera = 3 Species = 14

• Oviparous with aquatic eggs

  • brood eggs and have aquatic larvae

• Eye well developed for a caecilian (ancestral trait)

• Has true short tail and a terminal mouth (ancestral)

  • There are backbones/vertebrae past the cloaca

• Kinetic skull - not as well adapted to fossorial existence

  • Moveable skull (more ancestral condition)

• Many have bright yellow stripes on sides

  • Maybe flash predators?

• Tentacle close to eye (ancestral)

• South America distribution

Family Ichthyophiidae

• Genera = 2 Species = 58

• Southern Asia

• Oviparious, lays eggs near water.

• Maternal nest care; metamorphosis in 1 year.

• Terminal or sub-terminal mouth

• True tails present

• Tentacles move forward toward nostril

Family Typhlonectidae

• Genera = 5 Species = 14

• Tail absent

• No secondary folds — no scales

• Posterior of body often laterally compressed with fins

  • Highly aquatic group

• Anal region of males modified as sucker or clasper, apparently for adhering to female during mating

• Viviparous (live birth) – fetuses feed intrauterinely (scrapes inside of oviducts)

• South America

Family Typhlonectidae

• Lacks “true lungs” – tracheal “lungs” instead

• Obligately or highly aquatic species.

• Atretochoana eiselti is largest known lungless tetrapod (nearly 1 m)

Family Caeciliidae

• Genera = 2 Species = 51

• Recently split into new families, unstable.

• Lacks a true tail.

• Wide diversity of reproductive modes.

• Direct development common.

• Viviparity also somewhat common.

• Central and South America

Family Siphonopidae

• Genera = 6 Species = 28

• Dermatophagy!!! Siphonops annulatus

  • Juveniles are feeding on the skin tissues of the mother