Chondrichthyes: Chimaeriformes

Taxa on This Page

1. Chimaeriformes
2. Chimaeroidei
3. Iniopterygii X
4. Myriacanthoidei X

Chimaeroidei

"Its ground tone is silver, but at every movement it reflects metallic hues -- brass, copper, and gold. Its snout is translucent, its optic cup is luminous, refracting pale greenish-blue, its iris brassy, and on head and trunk are tinges of rose, cobalt, pale-green and madder. ... Its back region is dark umber, through which pass, as the fish changes position, shades of olive and rose-madder. Its ventral region and fin bases are white, the fins themselves translucent and even transparent. In the adult, the paired fins show little pigment; they stand out from the body prominently, their anterior rims white, and their constant movement adds greatly to the fish's beauty. It may be added that the dorsal spine shows brightly in the water, forming a conspicuous anterior rime to the dorsal fin, whose remaining margin, in reality of a dark umber, now appears jet-black."

Dean (1906: 12-13), describing Chimaera colliei.

Image: Chimaera phantasma from Catalogue of Fishes of Kochi Prefecture.

Descriptions

Myriacanthoidei: probably Myriacanthus > Chimaera.  Acanthorhina, Chimaeropsis, Delphyodontos, Myriacanthus.

Range: Late Triassic (Rhaetian) to Late Jurassic Tithonian) of Europe (a belt from Britain to Italy)  [DD93]; but also Delphyodontos, Early Carboniferous of North America.

Phylogeny: Chimaeriformes: Chimaeroidei + *.

Characters: head not flattened [P65]; long snout [D06]; snout somewhat expanded distally and bent at right angle [D06]; mouth ventroterminal [L80]; rostrum studded distally with plates and dermal denticles [D06]; 1+ tuberculated dermal plates on head [P65]; various dermal plates, some with sharp spinous processes, particularly a mandibular spine [D06]; some may have extensive dermal armor [L80]; spine-like frontal clasper [D06]; frontal clasper in both sexes? [P65]; symphysial tooth plate present, small, but sharp and very deep, extending well below jaw line [D06]; "descending laminae" indicating shark-like dentition [D+94]; at least two (2-3) upper and 1 lower pairs of tooth plates [DD93]; tooth plates with diffuse distribution of tritors, rather than tritoral pads as in chimaeroids [DD93] [P65]; some myriacanthoid genera (Halanodon) have more chimaeroid-like tritoral areas [DD93]; lower main plates with diagonal ridges running posteriorly or posterolaterally from the mesial end and labial margin [DD93]; vomerine plates have three rows of large tritors [D06]; may be an even smaller third anterior vomerine pair [D06]; folded areas on palatine and mandibular plates have many tritoral points [D06]; notochord with calcified rings in notochordal sheath [P65]; usual synarcual present [P65]; dorsal fin located more posterior than in Recent chimaeroids [D06]; anterior dorsal fin spine with lateral faces tuberculated [P65] and/or striated [W06]; prepelvic tenaculum consisting of enlarged scales without skeletal support [P65]; squamation placoid & not reduced [P65]; sensory line crescentic scales fused into short cylinders [P65].

Links: Dossier sur les elamobranches

References: Dean (1906) [D06]; Didier et al. (1994) [D+94]; Duffin & Delsate 1993) [DD93]; Lund (1980) [L80]; Patterson (1965) [P65]; Woodward 1906) [W06]. ATW020906.

Chimaeroidei: last common ancestor of all living chimaeras (various extinct taxa between Chimaeriformes & Chimaeroidei have been omitted). Callorhinchus, Chimaera, Harriotta, Hydrolagus, Rhinochimaera.

Range: from the Middle Jurassic (Patterson, 1965) or Late Carboniferous (Carroll, 1988), based on Similihariotta

Phylogeny: Chimaeriformes: Myriacanthoidei + *.

Characters: 50-200 cm [D06]; body usually laterally compressed [P65]; mouth very small but flexible [D06]; external nares ventrally placed and on margin of mouth [J96]; internal "choanae", but these are connected with external nares by slit [J96]; 3 well-developed rostral cartilages, with median cartilage dorsal to laterals [P65]; frontal "claspers" [C88]; frontal claspers small & present only on males [P65]; frontal clasper with enlarged scales supported by "calcified fibro-cartilage" [P65]; no dermal plates on head [P65]; principle jaw adductors (m. preorbitalis) originate on lateral face of ethmoid [L90]; palatoquadrate very short [C88]; palatoquadrate fused to braincase [L95]; maxillary branch of Vth nerve has some motor fibers [J96]; ethmoidal canal present [P65]; dorsal interorbital septum present [P65]; most of tooth plates histologically trabecular dentine with tritoral pads of more strongly mineralized "tubular dentine" or pleromin" [D+94]; crushing plate dentition, but also sharp, cutting surfaces [L95]; tritoral pads on all tooth plates [P65]; dentition reduced to 2 pairs of tooth plates in upper jaw and 1 pair in lower [C88] [P65]; tooth plates with continuously growing "descending lamina" on basal or aboral surface [D+94]; pulp cavities and growth areas of plates located distally and medially, so that tooth material moves mesially anteriorly) and laterally during life [D+94]; gills below posterior braincase [C88]; spiracle closes early in development and is absent in adult [P65]; 1st gill arch behind palatoquadrate has pharyngohyal and is not differentiated from other gill arches [1] [C88]; operculum present [L95]; body long, with whip-like tail [L95]; notochord unrestricted but with polyspondylous calcifications in notochordal sheath [C88] [P65]; anterior synarcual with attached anterior dorsal fin spine [C88]; anterior dorsal fin with single basal (+ synarcual) [P65]; anterior dorsal fin and spine may be housed in a median slit along the back [J96]; anterior dorsal spine erectile and articulates with plate of synarcual [J96]; anterior dorsal fin spine smooth [P65]; posterior dorsal without spine [P65]; posterior dorsal with parallel, rod-like radials [P65]; pectoral girdle fused on midline [C88]; pectoral fin dibasal, with large metapterygium and small propterygium [P65]; pectoral fin with fused anterior radials [P65]; pelvic girdles separate and do not contact [C88]; male prepelvic tenacula with enlarged scales articulating with pelvic girdle [P65]; male anterior tenacula with independent cartilaginous endoskeleton [P65]; male clasping organs supported by calcified cartilage rods articulating with pectoral basipterygium [P65] [L95]; sensory lines in open grooves, with crescentic scales [C88]; scales few, hook-shaped & placoid [J96] [P65]; internal fertilization (as all chondrichthyes) [L95]; males usually smaller & more gracile [D06]; significant sexual dimorphism (males generally with sharper snout, pronounced peak in mandibular dental plate, fins shorter & wider)  [D06]; may occur in schools, and females often numerically dominant by a wide margin [D06]; respiratory water through nares, probably powered by operculum [D06]; swim with "fluttering" of pectoral fins plus slow movements of tail [L95]; dorsoventral movement of pectorals coupled with waves in fin radials along margin of fin from posterior to anterior which "suggest the movement of the keys of a piano when a finger is drawn across the keyboard" [D06]; generally benthic, but some species often found at or near surface [D06]; prefer rocky bottoms with small rock fragments [D06]; feed on crustaceans, mollusks (including squid) and sometimes small fishes [D06].

Notes: [1] the implication being that the hyoid arch never supported the palatoquadrate in the ancestors of chimaeroids. This has been used as an argument for a placoderm ancestry. Perhaps more likely, this is an example of an illusory relationship based on shared primitive characters. In any case, yet a third school asserts that the pharyngohyal has been misidentified and that the chimaeroid first branchial arch is fully equivalent to the hyoid of sharks [C88]. In this regard, we may note that -- whatever chimaeroids may be -- all chimaeriforms show a remarkable amount of novelty and creativity in the development of labial or "premandibular" cartilages. Thus, we would do well to develop a dark suspicion of anything odd observed in the branchial cartilages of these eldritch fishes.

Links: Dossier sur les elamobranches; Chimaeroid.

References: Carroll (1988) [C88]; Dean (1906) [D06]; Didier et al. (1994) [D+94]; Janvier 1996) [J96]; Long (1995) [L95]; Lund (1990) [L90] Patterson 1965) [P65]. ATW020906.