Natural History of Sharks, Skates, and Rays

Phylogeny of Holocephali

MARE 380Dr. Turner

Chimaeroid FishesExclusively marine – inhabit all oceans except Arctic & Antarctic

Deep water dwelling – 500+m

Live on or near bottom

Local migrations for breeding

Males, females, juveniles form distinct groups

Chimaeroid EcologyPrey on benthic inverts & small fishes

Tooth plates used to crush crustaceans, mollusks, & echinoderms – some soft-bodied prey

Sharks major predators

Mature at 3-4 yrs

Chimaeroid ToothologyHolocephalans characterized by ever-growing, nonreplacable hypermineralized tooth plates

6 tooth plates in 3 pairs; 1 lower – 2 upper

Mandibular (lower) and vomerine (anterior upper) form beaklike bite

Tooth plates typically only fossil remains

Subclass HolocephaliDistinguished from other chondrichthyan fishes by morphological features:

Mode of fusion of lower jaw to cranium

Possession of non-replaceable, hypermineralized tooth plates

Extant Holocephali33 described species

Several new but undescribed; total probably < 45 species

All belong to Order Chimaeriformes3 Families

Order ChimaeriformesFamily Callorhichidae

1 Genus, 3 species

Family Rhinochimaeridae3 Genus, 8 species

Family Chimaeridae2 Genus, 22 species

Family CallorhichidaeProminent, plow-shaped snout, torpedo-like body, heterocercal tail, large anal fin

Enclosed lateral line canals underneath the skin

Plow-nose Chimaeras or elephantfish

Most primitive living Chimaera

Callorhinchus callorynchusPlownose chimaera

Family RhinochimaeridaeLong, tapering fleshy snout extending anterior to the head

Long-nose chimerians or spookfish

Large bodies, elongate spearlike snout, narrow tail with elongate filament

Inhabit deep waters; 1000-2000m

Harriotta raleighanaPacific longnose chimaera

Family ChimaeridaeConical fleshy snout bluntly pointed at tip

Short-nose chimerians or ratfish

Lateral line canals on the snout expanded with wide dilations

Compressed, elongate bodies tapering to whip-like tail

Hydrolagus collieiSpotted ratfish

Chimaeroid MorphologySlender fishes 60cm – robust fishes >1m

Skin scaleless in adults; embedded denticles in small juveniles

Single gill opening; adults lack a spiracle

2 dorsal fins, caudal, paired pect & pelvic

Chimaeroid DimorphismSexual dimorphism; males possess 2° sexual characteristics:

-front tenaculum, paired preprelvic tenacula, and paired pelvic claspers

Front tenaculum – small club-like structure on head anterior to eyes

unique to chimaeras; used to grasp pectoral fin of ♀ during copulation

Chimaeroid Dimorphism

Chimaeroid ReproductionEmbryonic development only described in 2 species

Internal fertilization; ♂ transfer sperm via pelvic claspers

All chimaroids are oviparous; 2 egg capsules simultaneously – one from each oviduct; several pairs per season

Chimaeroid Egg Capsules