Ray Gibson

Observations on the feeding mechanism, structure of the gut, and digestive physiology of the european lobster Homarus gammarus (L.) (Decapoda: Nephropidae)

Abstract Investigations have been made on the feeding mechanism, structure of the gut, and digestive physiology of the European lobster Homarus gammarus (L.). Cine-photography has shown that the mandibles do not possess a masticatory function, merely serving to grip food morsels during the tearing process effected by the pulling action of the third maxillipeds. The remaining maxillipeds, together with the maxillae, then direct food fragments to the mouth for ingestion. Ingestion is facilitated by mucoid secretions discharged from the oesophageal tegumental glands; the glands do not appear to produce any enzymes which directly contribute to the digestive processes. The hepatopancreas is the principal organ concerned with digestion. It possesses a complex tubular organization in which sequential cellular differentiation culminates in the discharge of enzymes from the B-cells for extracellular digestion in the cardiac stomach. The enzymes are synthesized within vacuoles contained in the B-cell precursors (F-cells) and are secreted in three bursts of activity at 0–15 min, 1–2 h, and 3.5–5 h after a meal. The initial secretory phase is holocrine. Extracellular digestion involves esterases, arylamidases, and lipases; endopeptidases have not been positively identified by histochemical means despite the fact that Homarus is a carnivore. There is an intracellular digestive phase, not previously described in decapod crustaceans, at the 7–9 h post-ingestive stage in the hepatopancreatic R-cells which is effected by arylamidases and lipases. Various phosphatase enzymes have been identified in the hepatopancreatic cells. Acid and alkaline phosphatases are apparently concerned with several stages in the digestive cycle, including enzyme synthesis and secretion, and the absorption of digestive products. Adenosine triphosphatase activity is primarily associated with granules located in the distal R-cell cytoplasm; the possible significance of these granules in the elimination of metabolic wastes is discussed. Acid phosphatases and esterases are present in the midgut epithelium. The possibility of a passive uptake of material from the midgut lumen is considered. Faecal material in the hindgut is bound by mucoid secretions derived from the tegumental glands of this alimentary region; the mucus may also assist in defaecation. A complete digestive cycle in Homarus occupies ≈ 12 h. Food reserves in the gut consist principally of fat deposits in the R-cells, but minute amounts of glycogen can also be detected. No evidence of calcium, copper or ferric iron deposition in any part of the alimentary tract was found.

Nemertean genera and species of the world: an annotated checklist of original names and description citations, synonyms, current taxonomic status, habitats and recorded zoogeographic distribution

Names used for nemertean genera and species of the world are listed alpha-betically, with their original description citations, synonymy and current taxonomic status. Though many remain inadequately described, 250 genera and 1149 species are recognized as valid; these comprise Archinemertea (3 genera, 28 species), Palaeonemertea (11, 70), Heteronemertea (79, 401), monostiliferous Hoplonemertea (91, 500), reptantic polystiliferous Hoplonemertea (22, 45), pelagic polystiliferous Hoplonemertea (40, 97), Bdellonemertea (1, 5) and three monotypic genera whose higher taxonomic affinities are uncertain. In addition, three monotypic genera of fossil Nemertea are also listed. The higher systematic position and typical ecological habits of its species are shown for each valid genus, type-species are indicated, and brief details of species known habitats and distribution are noted.

THE EVOLUTION AND COMPARATIVE PHYSIOLOGY OF TERRESTRIAL AND FRESHWATER NEMERTEANS

(1) Parallel evolution from separate marine ancestors has given rise to two groups of genera of terrestrial nemerteans, representative of at least two different family stocks. They have colonized land by the direct route, moving up the shore on widely separated oceanic islands. The relationships between the known terrestrial and semi‐terrestrial nemerteans, comprising seven genera and 15 species, are defined and their geographic distribution is discussed.

The Geonemertes problem (Nemertea)

A new genus of monostiliferous hoplonemerteans, Pantinonemertes gen. nov., provides evidence for the separate evolution of terrestrial nemerteans. The genus is established for two new species found in Australia, P. enalios sp. nov., an intertidal form, and P. winsori sp. nov., which lives in fallen timber in the supralittoral brackish water regions of mangrove swamps. One only of the known species of land nemerteans, Geonemertes agricola from Bermuda, closely resembles these two species morphologically and is transferred to the new genus as Pantinonemertes agricola. A re‐examination of all the known species of Geonemertes has shown that two major groups can be distinguished on the basis of morphological characters. In one group the rhynchocoel musculature is in two distinct layers, a frontal organ is present, the mid‐dorsal blood vessel has a single vascular plug, and the flame cells are binucleate and reinforced with cuticular support bars. It comprises the genus Pantinonemertes gen, nov, and the Pelaensis or Indopacific group of terrestrial nemerteans, for which the generic name Geonemertes is retained. In the second major group the rhynchocoel musculature is composed of interwoven longitudinal and circular fibres, there is no frontal organ, the mid‐dorsal blood vessel bears two vascular plugs, and the flame cells are mononucleate and lack support bars. Five genera, three of which are new, are distinguished in this group. Australian species are united in the genus Argonemertes gen. nov., and New Zealand forms comprise the genus Antiponemertes gen. nov., while Acteonemertes bathamae from New Zealand and the Auckland and Ocean Islands remains in a separate genus. Geonemertes nightingaleensis is transferred to a new genus, Katechonemertes gen. nov., and for Geonemertes chalicophora a previously used generic name, Leptonemertes, is adopted. A key to the terrestrial, brackish‐water and marine nemertean species described in the present paper is provided.

The developmental stages of larval turbot, Scophthalmus maximus (L.)

Abstract The development of turbot ( Scophthalmus maximus (L.)) larvae from hatching to the completion of metamorphosis is described and illustrated. Five major developmental stages, each divisible into sub-stages, are recognized and defined on the basis of morphological characters. The formation, distribution and ultimate resorption of spines on the head, which exhibit a complex but highly characteristic pattern in larval turbot, are described and a nomenclature applicable to the various spines is suggested.

Evolutionary relationships between mono- and polystiliferous hoplonemerteans: Nipponnemertes (Cratenemertidae), a “missing link” genus?

Histological studies on several species of the monostiliferous hoplonemertean genus Nipponnemertes show that they share certain significant features with reptantic Polystilifera. A brief survey of these features provides a basis for an analysis of possible evolutionary relationships between mono- and polystiliferous Hoplonemertea. It is suggested that ancestral enoplans possessed a rhynchocoel wall containing two muscle layers and a simple “protopolystiliferous” type of proboscis armature, and that this ancestral pool gave rise to two distinct evolutionary lineages, one leading to cratenemertid, group 2 terrestrial and freshwater, and polystiliferous hoplonemerteans, the other to the typical modern monostiliferous forms. A reclassification of the Enopla is proposed.

Enzyme electrophoresis, genetic identity and description of a new genus and species of heteronemertean (Nemertea, Anopla) from northwestern Spain and North Wales

The anoplan order Heteronemertea, particularly the genera Cerebratulus, Lineus and Micrura, contains a very large number of nominate species, many of which are inadequately described. As a consequence, systematic difficulties are encountered with the identification of many taxa in this group, especially those originally established primarily on the basis of their external features. The present paper concerns heteronemerteans collected from two locations, the Foz Estuary (north-western Spain) and Llandudno (North Wales). The Spanish collection included specimens identified as Lineus longissimus (Gunnerus), whilst samples from Llandudno contained large numbers of Lineus viridis (Muller); samples of a third similar but apparently undescribed species were found at both locations. Starch gel electrophoresis showed that samples of the apparent third species were genetically almost identical from each of the two locations, but were clearly different from the two described Lineus species. Histological studies of the unknown specimens revealed anatomical characters, including the unique feature of a proboscis epithelium ciliated throughout its length, which exclude it from any known heteronemertean taxon; it is accordingly placed in a new genus and species, for which the name Riseriellus occultus is proposed.

A new genus and species of monostiliferous hoplonemerteans, ectohabitant on lobsters

Abstract A new genus and species of monostiliferous hoplonemerteans, Pseudocarcinonemertes homari , is described and illustrated. The nemerteans live as ectohabitants on the lobster Homarus americanus Milne Edw. 1837. Adult worms of both sexes, together with cocoons containing eggs, are found on the egg masses of lobsters, whilst immature nemerteans occur on the gills. The gills of immature male lobsters can be experimentally infected with the nemerteans, but natural infections have only been obtained from female hosts. After the lobster eggs are shed, the nemerteans move anteriorly, congregate between the pereiopods and eventually move into the branchial chamber to settle between the gill filaments. Host egg laying and larval development appear to be affected by an infection with the nemerteans. The eggs of the nemertean take about two months to hatch at 4–5°C. Development is direct, with immature worms emerging from the egg cocoons. It appears that the nemerteans can release eggs at any time whilst the host is berried, but that they are unable to lay eggs on non-berried lobsters except under experimental conditions after a certain stage of maturation.

The production of tetrodotoxin-like substances by nemertean worms in conjunction with bacteria

Abstract Evidence is presented which strongly indicates a relationship between the presence of Vibrio bacteria, probably Vibrio alginolyticus , and the synthesis of tetrodotoxin (TTX)-like chemicals in seven species of British nemerteans. The occurrence of these substances and associated Vibrio bacteria in these species was investigated by bacteriological, chromatographic, spectroscopic and ultraviolet spectrometric techniques. It is suggested that these toxins are utilised by the nemerteans as a chemical defence against potential predators.

Marine relatives of terrestrial nemerteans: The genus Prosadenoporus Bürger, 1890 (Hoplonemertea)

A diagnosis of the monostiliferous hoplonemertean genus Prosadenoporus is provided and the type-species, P. arenarius, is redescribed and illustrated from Malaysian material; this identification is related to Bürgers (1890) original description. The remaining four species can on present evidence neither be accepted as valid taxa nor regarded with certainty as synonymous with P. arenarius; they are accordingly designated as nomina dubia. A comparison between Prosadenoporus, Prosorhochmus and the group I genera of terrestrial nemerteans (Geonemertes, Pantinomemertes) indicates that they belong in the same family, Prosorhochmidae, and a definition of this family is given.