摘要:

Post‐Palaeozoic asteroids share a large number of derived characters of the ambulacral column and the mouth frame, and constitute the crown group of the monophyletic group Asteroidea. This crown group is here called the Neoasteroidea (new subclass). The stem species of the crown group lived in the Permian or early Triassic and so the evolution of the asteroids parallels that of the echinoids. Character distribution within the Neoasteroidea, especially morphology of the skeleton, digestive system, larvae and tube feet, allows subdivision into four orders (Paxillosida, Notomyotida, Valvatida, Forcipulatida). The latter three orders possess the synapomorphy of suckered tube feet and are united as the Surculifera (new superorder); the Paxillosida are their primitive sister group. Palaeozoic asteroids represent the stem group of the class, and may be divided into plesions according to the order of appearance of synapomorphies with the crown group. Classification of Palaeozoic asteroids requires much further study. The appearance of new characters within the crown group asteroids, such as suckered tube feet, implies that these were absent in the stem group. The range of life‐habits possible in Palaeozoic asteroids can thus be partly deduced from evidence provided by living asteroids. Palaeozoic asteroids are deduced to have lacked suckered tube feet and were presumably unable to evert the stomach; hence they were precluded from life on hard substrates and extraoral feeding on epifaunal organisms. It is suggested that they lived on soft substrates by deposit feeding, scavenging and predation on small bent

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1987.tb00652.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The Japanese Ayu,Plecoglossus altivelisTemminck&Schlegel is the sole representative of the salmoniform family Plecoglossidae. The Ayu is remarkable for its dentition which in adults comprises groups of diagonally arranged comb‐like teeth in the outer tissue of the jaws. In juveniles (below 63 mm SL) the teeth are attached normally to the jaws. The transition of tooth form is correlated with a switch from zooplanktivory to algal oraufwuchsgrazing. The present study follows the development of the teeth, jaws, oral cavity ethmoid and suspensorial elements in specimens ranging in size from 41–70 mm SL. The possible mode of function of the adult dentition is discussed. Comparisons are made with the jaws of other salmoniform fishes and a suite of supposed apomorphic characters are identified which are also shared with certain genera of the family Osmeridae, thus supporting the ideas of others that the Osmeridae is a paraphyletic assembl

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1987.tb00653.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Analysis is presented of the characteristics of spheres coating the chorion surface of the eggs from 41 species belonging to 15 families of spiders. Examples of eggs from the arachnid orders Opiliones, Amblypygi and Uropygi are illustrated for the first time. The spheres are unique, among arachnids, to the Araneae. Their form and size class distributions overlap considerably between families and the spheres are present in all 22 families of Araneae that have been examined; they represent a very conservative morphological feature in the evolution of the Araneae. Evidence of specialized regions of the egg surface (micropyllar areas and plastrons) was found only in an opilionid. As spiders' eggs are laid in silk egg sacs, mostly in clutches, the possible effects of these characteristics are discussed from evidence in the literature and from a functional theoretic stance.

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1987.tb00654.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY