新疆下寒武统玉尔吐斯组软舌螺口盖和口盖状化石

文中系统描述了新疆乌什－阿克苏地区下寒武统玉尔吐斯组软舌螺口盖和口盖状化石５属７种,其中包括２新属３新种。Ｘｙｓｔｒｉｔｈｅｃａ的口盖具有复杂的锁骨构造,Ｐａｃｈｙｔｈｅｃａ的口盖有明显的背腹扇面之分,它们与具口唇的软舌螺Ｍｉｃｒｏｃｏｒｎｕｓ共生。这些演化上较高级的软舌螺与原牙形类Ｊｉａｎｇｓｈａｎｏｄｕｓ,Ｇａｐｐａｒｏｄｕｓ,Ａｍｐｈｉｇｅｉｓｉｎａ;假牙形类Ｒｈｏｍｂｏｃｏｒｎｉｃｕｌｕｍ     

Operculum ultrastructure in leech cocoons

Clitellate annelids (i.e., oligochaetes including leeches) secrete cocoons as part of their normal reproductive cycle. Typically, the cocoon sheath is passed over the head of the leech and sealed at both ends by opercula (i.e., glue‐like material secreted by the clitellum). Both the fibrous cocoon wall (CW) and opercula are chemically‐related biomaterials that share unusual physiochemical properties, including thermal and chemical resiliency. To explore the underlying morphology of the operculum, we examined cocoons from four leech species (i.e., Myzobdella lugubris, Theromyzon tessulatum, Erpobdella obscura, and Erpobdella punctata) by transmission (TEM) and scanning electron microscopy (SEM). Transmission electron micrographs of all opercula revealed a common, ultrastructural pattern comprising an electron‐dense mosaic of ordered polygons that surrounded interspersed cavities. The long axes of cavities were often oriented directionally, suggesting that operculum material is pliable prior to solidification and distorted as a consequence of cocoon deposition. Concomitantly, the operculum permeates jagged edges of the cocoon sheath sealing the cocoon, which provides a mechanically strong CW/operculum boundary. SEM of leech opercula revealed globular nanoparticles comparable to that observed in bioadhesives from disparate animal phyla (e.g., mussel, barnacle, sea star), suggesting a convergent mechanism of bioadhesion among animals. J. Morphol. 274:940–946, 2013. © 2013 Wiley Periodicals, Inc.     

Surface topology and structural integrity of the Theromyzon tessulatum (Annelida: Hirudinea: Glossiphoniidae) cocoon

Cocoons secreted by the aquatic leech Theromyzon tessulatum comprise a tubular, membranous ovoid, sealed at each end by a glue‐like substance, called an operculum. Scanning electron microscopy showed surface features of the T. tessulatum cocoon that included a circuitous bulge, cups that conformed to the shape of embryos, relief folds that radiated from opercula, and asymmetric distributions of protuberances on the upper aspect of the cocoon surface. The structural integrity of the T. tessulatum cocoon was assessed after exposure to a variety of denaturing conditions (e.g., extreme heat, detergents, acids). Although both the fibrous cocoon membrane and opercula were strikingly resilient, the membrane/operculum boundary appeared to be the weakest structural component of the cocoon, consistent with its functional role as an escape hatch for juvenile leeches. The operculum itself was more sensitive to denaturation than the cocoon membrane, and thus was probably the source of a major protein component isolated from the T. tessulatum cocoon (i.e., Tcp; Theromyzon cocoon protein). J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

Terrestrial locomotion in the climbing perch, Anabas testudineus (Bloch) (Anabantidea, Pisces)

Climbing perches use the tail for forward propulsion when on land. The spiny gill covers are used to obtain purchase on the substratum. Unusually amongst teleosts, the opercular and subopercular bone are not bound strongly together into a single operculum. Instead they are joined only by a thin, flexible membrane, so that the fish has two sections of the gill cover hinged separately; the opercular on the suspensorium and the subopercular on the rearmost part of the lower jaw. The gill covers open very widely and the subopercular rotates ventrally as well as laterally. Two modes of locomotion are employed. Usually Anabus adopts a near-upright posture and alternately drives the left and right spiny suboperculars into the substratum, using the tail to vault over the subopercular (which acts in the manner of a short vaulting pole). During vigorous movement the fish may leave the substratum altogether during the vault. Fatigued fish, or fish which have fallen during climbing, move on their sides, using the tail for propulsion and a single spiny opercular which is repeatedly driven into the substratum. Maximum speeds observed on land corresponded to 1.8 body lengths S^?1. No evidence of involvement of the pelvic fins in locomotion was obtained; the pectorals seemed only to help in tilting the head from side to side and did not contribute significantly to forward propulsion. On mud and tree bark the fish were laterally unstable, often resting on their sides. Grassy substrata provided support and permitted a more upright posture. Slope climbing ability was restricted to 25° when climbing tree bark and 30° when climbing grass. Coupled with lateral instability these observations disqualify the species from any tree-climbing capacity. Anabas can climb vertical obstacles of at least half body length in height by pushing the head against the obstacle, using the spiny gill covers for purchase until one or other subopercular hooks over the top of the barrier. The subopercular is then used as a fulcrum for an upwards vault to clear the obstacle.     

Sound reasons for silence: why do molluscs not communicate acoustically?

Many adaptively beneficial states of form, behaviour and physiology are absent in large parts of the evolutionary tree of life. Although the causes of these absences can never be fully known, insights into the possibilities and limitations of adaptive evolution can be gained by examining the conditions that would be necessary for the forbidden phenotypes to evolve. Here, the case of acoustic communication in molluscs is considered. The production of sound as a warning to predators or as a means to attract mates is widespread among arthropods and vertebrates, both on land and in water, but is unknown among molluscs, even though many derived clades of gastropods and cephalopods are characterized by internal fertilization and by the evolution of long‐distance visual and chemical signalling. Many molluscs possess suitable hard parts – shell, operculum and jaws – for producing sound, but most shell‐bearing molluscs lack the agility or aggression necessary to cope with high‐activity enemies attracted to an acoustic beacon. Their evolutionary background, arising from the generally passive adaptations of molluscs and other animals with low metabolic rates, prevents selection favouring communication by sound, and indeed favours silence. Several clades of shell‐bearing gastropods and cephalopods were identified in which sound production has the greatest potential to arise or to be discovered. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 485–493.