Muscle and Nerve Terminal Fine Structure of a Primitive Crustacean, the Cephalocarid Hutchinsoniella macracantha.

Abdominal muscles of the cephalocarid Hutchinsoniella macracantha resemble the striated muscle fibers of other crustaceans, having regularly aligned sarcomeres that average 5 µm in length; thick, wavy Z-lines; and orbits of eight thin filaments surrounding a thick filament. However, unlike most crustacean muscle fibers, the cephalocarid muscle fibers are not subdivided into myofibrils by elaboration of the longitudinally oriented sarcoplasmic reticulum. Consequently, elements of the transverse tubule and sarcoplasmic reticulum in the form of triads occur scattered over the entire fiber. Motor innervation is by means of scattered nerve terminals, populated with round synaptic vesicles, indicative of excitatory axons. By lacking myofibrils, the cephalocarid and ostracod muscle represents a much simpler condition than the myofibril-rich muscles of the other crustacean classes and signifies a primitive condition in its resemblance to the onycophoran muscle.

Colonization and succession in deep-sea ecosystems.

Experimental studies reveal generally slow but variable colonization rates in deep-sea soft bottoms. Species successions following biological disturbance appear to be complex and unpredictable, potentially playing a role in structuring these diverse communities. In contrast, physical processes probably play a prominent role in the rapid species turnovers observed at hydrothermal vents. Better information concerning disturbance regimes, recruitment processes and resource utilization is required to elaborate successional mechanisms in both soft-bottom and vent environments.

Respiration of Benthopelagic Fishes: In situ Measurements at 1230 Meters.

The respiration rate in situ of two common benthopelagic fishes, Coryphaenoides acrolepis and Eptatretus deani, was monitored at 1230 meters in the San Diego Trough. The respiration rate of C. acrolepis was two orders of magnitude lower and that of E. deani was significantly lower (P < .05) than rates in comparable shallow-water species.

Giant amphipod from the abyssal pacific ocean.

A baited camera has recorded a lysianassid amphipod that is twice as large as the largest amphipod previously recorded. The locality for this mobile omnivore is the sterile bottom of the eastern North Pacific Ocean, at a depth of 5304 meters.

Reproductive system of Hutchinsoniella macracantha.

The cephalocarid crustacean Hutchinsoniella macracantha is a hermaphroditic species. Ova and sperm develop simultaneously. Ovaries and testes are separate, but the oviducts and vasa deferentia join and exit through a pair of common genital ducts.