Subdivision Batoidea rays Hypotremata Superorder Batidoidimorpha of Nelson 1984 Order Rajiformes of Nelson 1994

Gill openings ventral; anterior edge of the greatly enlarged pectoral fin attached to side of head, anterior to the gill openings; anal fin absent; eyes and spiracles on dorsal surface; anterior vertebrae fused to form a synarcual; suprascapulae of pectoral girdles joined dorsally over vertebral column and articulating with column or synarcual or fused with synarcual; nictitating membrane absent, cornea attached directly to skin around the eyes; body generally strongly depressed; jaws protrusible in most; teeth pavementlike; in most, water for breathing taken in chiefly through the spiracle rather than the mouth (except for those living off the bottom); most rays give birth to live young (however, the skates are oviparous, i.e., egg layers, and have eggs encased in a horny capsule); the snout may function as an electroreceptive organ (as in all elasmobranchs). McEachran and Aschliman (2004) comment on the diversity of claspers in batoids and suggest that they offer potential in resolving interrelationships. Two basic shapes are apparent in external form: Rajiformes have claspers that are long, slender, and depressed distally while the other batoids, as far as studied, have claspers that are short, stout, and cylindrical to moderately depressed.

Monophyly of the batoids seems well established, but their internal interrelationships remain very uncertain. Although McEachran and Aschliman (2004) regard their classification as a working hypothesis, it is an advance over the largely phenetic classification presented in Compagno (1999) and that of earlier authors. McEachran and Aschliman (2004) examined more morphological characters in more representatives of genera than previously done. They also used basal taxa as out-groups as a result of other recent studies. While batoids are regarded as monophyletic, there is much controversy as to whether modern sharks are monophyletic without the inclusion of rays (i.e., whether rays are an offshoot of a branch of sharks or whether both modern sharks and rays are sister taxa). This disagreement is discussed above under the infraclass Euselachii, and reasons are given there for accepting the hypothesis that modern sharks and rays are separate groups.

Many different views have been proposed on batoid interrelationships, with various taxa seen as the basal group (these ideas are briefly reviewed in McEachran and Aschliman, 2004). The higher classification given here is based on McEachran and Aschliman (2004), while the number of species given in each genus follows Compagno (1999, 2005), unless otherwise noted.

Although most batoids have a strongly depressed body, some are relatively shark-like. The phylogenetic study of McEachran and Aschliman (2004) showed that the depressed, disclike body characteristic of most higher rays was probably independently achieved in two lineages. The depressed body of rajids was probably derived from a more robust-bodied rhinobatidlike ancestor, while the depressed body of higher myliobatiforms was probably derived from a robust-bodied platyrhinidlike ancestor.

The table on the following page compares the classifications of Nelson's (1994) order Rajiformes, Compagno's (1999) unranked group of rays or batoids, McEachran and Aschliman's (2004) cohort Batoidea, and the one employed here as the subdivision Batoidea, closely reflecting that of McEachran and Aschliman (2004). Compagno (2005), with all rays or batoids placed in his order Rajiformes, closely followed Compagno (1999) in the sequence of family level taxa; however, Compagno (2005) recognized the Rhynchobatidae and the orders of Compagno (1999) are ranked as suborders with additional suborders given. Indentations of taxa reflect differing ranks.

The common names skate and ray are sometimes used to refer to mutually exclusive groups (where skates would be a monophyletic group but rays would be a paraphyletic group). However, I prefer to use the term ray as a collective name for all members of the following four orders of batoids. Thus, skates, in the strictest sense, are members of one particular family of rays, the Rajidae. In this usage, both names refer to monophyletic groups, but skates are a subset of the rays, just as are sawfishes and stingrays. Skates (Rajiformes) differ from the other rays in many features in morphology and biology.

Fossil batoids are known as far back as the Jurassic in Europe and Argentina and include taxa such as Asterodermus, Belemnobatis, and Spathobatis (Cappetta, 1987; Cione, 1999); the latter two genera may be sister taxa and were found by Brito and Seret (1996) to be basal batoids, supporting an earlier view of J. G. Maisey. The following poorly known fossil batoids from the Cretaceous are described in Cappetta (1987): i) Cyclobatidae—Upper Cretaceous rays from Lebanon, and ii) Sclerorhynchidae—Lower to Upper Cretaceous rays resembling pristiophorids and pristids including Ankistrorhynchus, Ganopristis, Ischyrhiza, and Sclerorhynchus. The study of Kriwet (2004a) provided insight into possible relationships of this group with other batoids. He concluded from his

Nelson (1994)

Compagno (1999)

McEachran and Aschliman (2004)

Herein

Pristoidei

Pristiformes

Torpediniformes

Torpediniformes

Pristidae

Pristidae

Torpedinidae

Torpedinidae

Torpedinoidei

Rhiniformes

Narcinidae

Narcinidae

Torpedinidae

Rhinidae

Pristiformes

Pristiformes

Narcinidae

Rhinobatiformes

Pristidae

Pristidae

Rajoidei

Rhinobatidae

Rajiformes

Rajiformes

Rhinidae

Platyrhinidae

Rhinobatidae

Rhinidae

Rhinobatidae

Zanobatidae

Rajidae

Rhynchobatidae

Rajidae

Torpediniformes

Myliobatiformes

Rhinobatidae

Myliobatoidei

Narcinidae

Platyrhinoidei

Rajidae

Plesiobatidae

Narkidae

Platyrhinidae

Myliobatiformes

Hexatrygonidae

Hypnidae

Zanobatoidei

Platyrhinoidei

Dasyatidae

Torpedinidae

Zanobatidae

Platyrhinidae

Urolophidae

Rajiformes

Myliobatoidei

Zanobatoidei

Gymnuridae

Arhynchobatidae

Hexatrygonidae

Zanobatidae

Myliobatidae

Rajidae

Urolophidae

Myliobatoidei

Anacanthobatidae

Urytrygonidae

Hexatrygonidae

Myliobatiformes

Dasyatidae

Plesiobatidae

Plesiobatidae

Potamotrygonidae Urolophidae

Hexatrygonidae

Gymnuridae

Urytrygonidae

Urolophidae

Myliobatidae

Dasyatidae

Potamotrygonidae

Potamotrygonidae

Dasyatidae

Gymnuridae

Gymnuridae

Myliobatidae

Myliobatidae

Rhinopteridae

Mobulidae

analysis that the Pristiorajea (of de Carvalho, 1996, the Pristiophoriformes + batoids in the hypnosqualean hypothesis—see above under "infraclass Euselachii") is a monophyletic clade, with Sclerorhynchidae being the sister group to pristiforms and all remaining pristiorajeans. These results require further study to verify monophyly and to resolve the conflict they present with the classification adopted herein. Brito and Seret (1996) discuss the possible relations and implications to our views on batoid classification of the Lower Cretaceous fossil Iansan, from Brazil, with the rhinobatids and other taxa.

Four orders, 17 families, 72 genera, and at least 534 species.

Order TORPEDINIFORMES (13)—electric rays. Powerful electric organs, derived from branchial muscles in head region (strongest discharges in the Torpedinidae); skin soft and loose; eyes small to obsolete; caudal fin well developed; dorsal fins 0-2. Electrical production is largely for feeding and defense.

Torpedininforms are regarded as the basal batoid group and sister to the remaining members of this order (McEachran and Aschliman, 2004). Several species are blind.

Two families, 11 genera with about 59 species. McEachran and Aschliman (2004) recognized the monophyly of these taxa as shown.

Family TORPEDINIDAE (42)—torpedo electric rays. Marine, continental and insular shelves and slopes; Atlantic (including Mediterranean Sea), Indian, and Pacific.

Disc truncate or emarginate anteriorly; jaws extremely slender; no labial cartilages; rostrum reduced. Two genera with 22 species.

Subfamily Torpedininae (torpedo electric rays) . Tail and dorsal and caudal fins well developed. This taxon is ranked as a separate family by some workers (e.g., Compagno, 2005).

One genus, Torpedo (including Tetronarce), with about 21 species (plus two doubtfully valid ones and several undescribed species) (Compagno, 1999, 2005; de Carvalho et al., 2002).

Subfamily Hypninae (coffin rays). Tail and dorsal and caudal fins very small. Continental shelf and uppermost slope, off Australia. This taxon is ranked as a separate family by some workers (e.g., Compagno, 2005). One species, Hypnos monopterygius (Compagno, 1999, 2005).

Family NARCINIDAE (43)—numbfishes. Marine, tropical to warm temperate, continental and insular shelves and uppermost slopes; Atlantic, Indian, and Pacific.

Disc rounded anteriorly; jaws stout; strong labial cartilages; rostrum present.

Nine genera with at least 37 species. Several undescribed species are known to exist.

Subfamily Narcininae (numbfishes). Deep groove around mouth and lips; jaws long and strongly protractile; rostrum broad; usually two dorsal fins. This taxon is ranked as a separate family by some workers (e.g., Compagno, 2005).

Four genera, Benthobatis (4), Diplobatis (4), Discopyge (1), and Narcine (17), with 26 species and many undescribed species (de Carvalho, 1999; de Carvalho et al., 2002, 2003; de Carvalho and Randall, 2003; Compagno, 1999, 2005). Four species of Diplobatis are recognized based on McEachran and de

Carvalho's (2003:518-20) recognition of two subspecies of Diplobatis pictus (Compagno, 2005) as species.

Subfamily Narkinae (sleeper rays). Shallow groove around mouth; jaws short and weakly protractile; rostrum narrow; usually a single dorsal fin. IndoWest Pacific. This taxon is ranked as a separate family by some workers (e.g., Compagno, 2005).

Five genera (validity of Crassinarke and its species is questionable), Crassinarke (1), Heteronarce (4), Narke (3), Temera (1), and Typhlonarke (2), with 11 species (Compagno, 1999, 2005).

Was this article helpful?

0 0

Post a comment