Pinnotheres pisum is a small crab with a carapace between about 2−1 and 18 mm. wide. The females are commonly found parasitic in the mussel, Mytilus edulis, though they have been recorded from other bivalves. The males are free-swimming and are comparatively rarely found in mussels. These small crabs are never abundant, and not more than one female has ever been found in a mussel.
(Text-figs. 1-23)The lophophore of Platidia, as illustrated in most memoirs and text-books, bears little resemblance to its appearance in life, no doubt because such illustrations and the accompanying descriptions were based on dried specimens. The lophophore of Platidia has been considered to be of a peculiar sigmoid type, differing from that of any other known lophophore. The dredging by RV. 'Sarsia' of three species of the genus in recent years has afforded the opportunity of figuring the lophophore in its natural state, and the working out of its growth stages in P. davidsoni and P. anomioides: these were previously unknown for any species of Platidia. The third species, a new one, is described separately (Atkins, 1959).Although P. anomioides (Philippi) is the type species of the genus, P. davidsoni (Eudes Deslongchamps) is considered first as it was the first to be dredged by RV. 'Sarsia' and work on it was ready for publication when P. anomioides was obtained in May 1958.All figures have been drawn with the aid of a camera lucida. PLATIDIA DAVIDSONI (EUDES DESLONGCHAMPS)A species of Platidia dredged by R V. 'Sarsia' from off Penmarch and the north coast of Spain is evidently P. davidsoni (E. Deslongchamps) as it agrees with the description of that species by Eudes Deslongchamps (1855) in having 'small spinous asperities' on the outer surface of the ventral valve, although these are often confined to a submarginal zone, and in some individuals apparently worn and indistinguishable. Fischer (1872, 1873) noted of this species that 'elle porte quelquefois des asperites assez nombreuses'. The brachial support agrees with the figures accompanying E. Deslongchamps's paper, but not with his description. There appears to be some confusion over its actual state. In his description of his new species, Morrisia ( = Platidia) davidsoni, E. Deslongchamps (1855) described the' apophysary system consisting of two lamellae originating at the base of the sockets, and
Specimens of Crania anomala (Miiller) were dredged on several cruises by R.V. 'Sarsia' from La Chapelle Bank. Some of the work was done on specimens kindly sent by Dr G. Owen from near Garbh Reisa, off Craignish Point, Argyllshire.Crania is one of the few living brachiopods that are attached to the substratum by cementation. In C. anomala the whole ventral valve is cemented to the surface of a rock, stone or shell, and the dorsal valve assumes a limpetlike form above it. Rowell (1960) has described the character of a typical locality for the species: rocky current-swept bottoms in moderately shallow water are the usual habitat. THE ADULT LOPHOPHORE The ciliation of the filamentsCrania anomala was the first, and remained for many years the only, brachiopod species in which the ciliary feeding mechanism had been investigated. Orton (1914) showed that the row of long slender filaments on the lophophore constitutes a filter-feeding device, with lateral cilia drawing water through the narrow gaps between the filaments, and frontal cilia carrying particles to the base of the filaments for subsequent transport to the mouth.
SummaryA marine fungus, Plectospira dubia n.sp., has been found infecting crustacean eggs and small Crustacea in the Plymouth Laboratory. It has the following characteristics: mycelium mostly intra-matrical, coarse, hyphae 50–100µ in diameter. Sporangia irregularly inflated, emptying by efferent hyphae of variable length and frequently of irregular diameter; sometimes proliferous; wall persistent. Zoospores dicystic and dimorphic, but the first swimming stage largely suppressed, the first zoospores mostly encysting within the sporangium after a short period of feeble activity, then swimming in the second stage. The first zoospores pyriform and flagellate (probably biflagellate): in the second motile stage laterally grooved with two laterally inserted flagella. First zoospores about 1oµ long, when encysted 7–8µ in diameter; in the second motile stage 11–12µ long, when encysted 6–7µ. in diameter. Gemmae numerous, spherical, up to 1OOµ. in diameter. Sexual organs so far unknown.
(Text-figs. 1-7)The cyphonautes larva found in certain ectoproct Polyzoa is considered to be most probably a primitive larval form, which has been lost in viviparous species, the larvae of which are degenerate in varying degree and settle within a short time. The cyphonautes is truly planktonic and has a free swimming life of some length-of 2 months according to Marcus (1940, p. 334)-and unlike the other known larvae of the group, has a functional alimentary canal. It obtains its food by maintaining a continuous current of water through the mantle cavity or vestibule, its ciliary mechanism being organized on a plan somewhat resembling that of bivalve molluscs, with an inhalant and an exhalant chamber with interposed ciliary ridges bearing current-producing and food-conveying cilia. As in lamellibranchs the organ creating the water and food currents is separated by a considerable interval from the mouth. In lamellibranchs this interval is bridged by the palps and the oral grooves; in the cyphonautes by the ciliated tract of the funnel. The cyphonautes being a larval form of probably archaic character its method of feeding is of particular interest.For the study of the ciliary feeding mechanism the larva of Membranipora membranacea (L.) (= Nichtina telacea (Lamarck)) was mostly used, rather than that of Electra pilosa L., because of its greater size and transparency. The former larva attains a basal width of 840 p" while the latter reaches only 440 p, (see Atkins, 1955). For the indication of currents Chlorellastigmatophora, Peridinium trochoideumand Phaeodactylumtricornutum Bohlin were used. They were most kindly supplied by Dr M. Parke.Larvae for sectioningwere narcotized with magnesium chloride,a few drops of 7 %in tap water being added at intervals to a watch-glass of sea water. The narcotized larvae were first dropped into 10 % formalin for about a minute, and then transferred to a modification of Bouin's fixative (saturated picric acid in 90% alcohol, 2 parts; saturated corrosive sublimate (water), 3 parts; 4°% formalin, I part; glacial acetic acid, 2 parts). In this way larvae were fixed extended. If dropped directly into the second fixative they were found to contract strongly even after being well narcotized. Sections were cut 4, 6 and 8 fL in thickness.
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