Invertebrate Biology, Volume 122, No. 2

Contents and Abstracts
© 2003 American Microscopical Society, Inc.

HEADER ILLUSTRATION: Polyps of a colony of the soft coral Thrombophyton trachydermum n. g.n., n. sp., from the cold-temperate waters of the NE Pacific. McFadden & Hochberg summarize current knowledge of the geographic distribution, ecology, and reproductive biology of 4 species of encrusting alcyoniids and add descriptions of 2 new genera and 2 new species. (Photo by Ralph Buchsbaum.)


Abstracts for all articles in this issue are presented below.
Individual abstracts can also be accessed directly by clicking on the highlighted titles here:

Biology and taxonomy of encrusting alcyoniid soft corals in the northeastern Pacific Ocean with descriptions of two new genera (Cnidaria, Anthozoa, Octocorallia)
Catherine S. McFadden and F.G. Hochberg. pp 93-113

Phylogeny of the Cocculinoidea (Mollusca, Gastropoda)
Ellen E. Strong, M.G. Harasewych, and Gerhard Haszprunar. pp 114-125

Apoptotic-like morphology associated with annual synchronized death in kleptoplastic sea slugs (Elysia chlorotica)
William L. Mondy and Sidney K. Pierce. pp 126-137

Effects of biofilms on zebra mussel postveliger attachment to artificial surfaces
Jerry H. Kavouras and James S. Maki. pp 138-151

Gametogenesis and reproduction in Hormogaster elisae (Oligochaeta, Hormogastridae)
Marta H. Garvín, Dolores Trigo, Patricia Hernández, and Darío J. Díaz Cosín. pp 152-157

Description of intracerebral ocelli in two species of North American crayfish: Orconectes limosus (Cambaridae) and Pacifastacus leniusculus (Astacidae)
Marina Bobkova, Pierre Grève, Victor B. Meyer-Rochow, and Gilbert Martin. pp 158-165

Effects of variable water motion on regeneration of Hemipholis elongata (Echinodermata, Ophiuroidea)
Justin S. McAlister and Stephen E. Stancyk. pp 166-176

Peptidergic and serotonergic immunoreactivity in the metamorphosing ophiopluteus of Ophiactis resiliens (Echinodermata, Ophiuroidea)
Paula A. Cisternas and Maria Byrne. pp 177-185


Invertebrate Biology 122(2):93-113
© 2003 American Microscopical Society, Inc.

Biology and taxonomy of encrusting alcyoniid soft corals in the northeastern Pacific Ocean with descriptions of two new genera (Cnidaria, Anthozoa, Octocorallia) Abstract. In this paper we summarize current knowledge of the distribution, ecology, and reproductive biology of 4 encrusting species in the soft coral family Alcyoniidae, with descriptions of 2 new genera and 2 new species. The new genus Discophyton is erected for Alcyonium rudyi, a species common in the lower intertidal of exposed rocky headlands from Vancouver Island, British Columbia, Canada south to Point Lobos, California, USA. Discophyton rudyi n. gen. & n. comb. propagates extensively by clonal fission, giving rise to characteristic aggregations of small, regularly spaced, disc-shaped colonies. We describe 2 new species and place them in a new genus, Thrombophyton. Thrombophyton coronatum n. gen. & n. sp. forms irregularly shaped, membranous colonies on rock surfaces; it occurs subtidally along the southern California coast from the Palos Verdes Peninsula to San Diego and on the California Islands. Thrombophyton trachydermum n. gen. & n. sp. has a similar, membranous growth form; it occurs both intertidally and subtidally on Vancouver Island, British Columbia, Canada, and in the San Juan Archipelago, Washington, and intertidally in central California, USA. Alcyonium pacificum, reported for the first time from North American waters, occurs in subtidal kelp beds around the Aleutian islands of Attu and Adak; its mushroom-shaped colonies are raised above the substrate on a short stalk. D. rudyi, T. trachydermum, and A. pacificum are all gonochores that reproduce in late summer; in contrast, T. coronatum appears to reproduce in the spring. D. rudyi and T. coronatum brood larvae internally to a late planula stage. A key to species is presented for all shallow-water soft corals known to occur in the northeastern Pacific Ocean.

Additional key words: octocoral, Alcyonium, Discophyton, Thrombophyton


Invertebrate Biology 122(2):114-125
© 2003 American Microscopical Society, Inc.

Phylogeny of the Cocculinoidea (Mollusca, Gastropoda) Abstract. The superfamily Cocculinoidea is a group of marine, deep-water, limpet-like gastropods. Recent speculation surrounding their affinities has concentrated on their placement within the Gastropoda. However, phylogenetic relationships within the Cocculinoidea, especially the monophyly of families and genera within the group, remain poorly understood. Phylogenetic analysis of 31 morphological characters for 15 cocculinoidean taxa and 2 outgroups resulted in a single most parsimonious tree, length=70, CI=0.62, and RI=0.71. Monophyly of the Cocculinoidea, Cocculinidae, and the genera Cocculina and Coccopigya was supported; Paracocculina and Coccocrater were found to be paraphyletic. Character optimization demonstrates that many characters often cited as diagnostic of various taxa, are often homoplastic and/or synapomorphies at different hierarchical levels.

Additional key words: morphology, cladistics, deep-sea


Invertebrate Biology 122(2):126-137
© 2003 American Microscopical Society, Inc.

Apoptotic-like morphology associated with annual synchronized death in kleptoplastic sea slugs (Elysia chlorotica) Abstract. Certain digestive cells of the opisthobranch mollusc, Elysia chlorotica, contain functional chloroplasts which it steals from the filamentous alga, Vaucheria litorea. The adult portion of the life cycle of the slug lasts for ~10 months and is completely synchronized between individuals. All the adults die each year within a few weeks of each other. We have examined the microscopic morphology of the slugs near the end of the life cycle. Light microscopy demonstrated an absence of chloroplasts in most of the digestive epithelial cells, the appearance of many crypt cells containing residual bodies and an invasion of the blood sinuses by neoplastic morula-like cells as the animals die. Electron microscopy revealed a degeneration of the digestive diverticulum which had several morphological characteristics in common with apoptosis: expansion of the endoplasmic reticulum and Golgi apparatus, DNA fragmentation, formation of primary lysosomes, and condensation of chromatin. These are followed by fragmentation of the nucleus and cytoplasm into autosomes merging to form a large central autolysosome. In addition in the aging slugs, the plastids begin to degenerate until none were left in the digestive epithelial cells and the central autolysosome contained numerous viral particles.

Additional key words: chloroplast symbiosis, Vaucheria litorea, apoptosis, virus


Invertebrate Biology 122(2):138-151
© 2003 American Microscopical Society, Inc.

Effects of biofilms on zebra mussel postveliger attachment to artificial surfaces Abstract. The zebra mussel is an introduced fouling organism in North American inland waters. This field study tested whether natural biofilms, formed by covering substrata with a 100-µm mesh that allows microorganisms to attach and films to develop in the absence of postveligers influenced the attachment of zebra mussel postveligers to artificial surfaces. Low-wettable polycarbonate and wettable glass surfaces were used in the experiments over four field seasons to study biofilm formation (1997--1998) and mussel attachment (1998--2000). The presence of the mesh did not quantitatively affect biofilm development on either substratum as determined by microscopic direct counts and colony-forming units on R2A agar. Natural biofilms on polycarbonate surfaces positively influenced postveliger attachment compared to substrata that initially had no film (ANOVA, p-values ranged from <.05 to <.001). Biofilms did not influence postveliger attachment to glass surfaces (ANOVA, p>.05). Attachment to both substrata was similar on surfaces with and without previously settled postveligers. Based on these results, we conclude that biofilms can enhance postveliger attachment to some but not all artificial surfaces, as previously reported.

Additional key words: biofouling, biofilms, Dreissena polymorpha


Invertebrate Biology 122(2):152-157
© 2003 American Microscopical Society, Inc.

Gametogenesis and reproduction in Hormogaster elisae (Oligochaeta, Hormogastridae) Abstract. The gametogenesis of the earthworm Hormogaster elisae, an endemic species of central Spain, was studied over a 12-month period. The ovaries, seminal vesicles, male funnels, and spermathecae of 156 specimens were removed by dissection. Microscopic analysis of these organs allowed the study of the gametogenic cycle, and provided information on copulation method and reproductive cycle. Individuals of H. elisae have two pairs of spermathecae, the posterior of which is more important for the storage of sperm. In summer, the earthworms enter quiescence, and oogenesis and spermatogenesis are interrupted. The gametogenic processes occur mainly during autumn and winter. Ovules are produced during all months except August and September, and the spermathecae contain sperm over the full 12-month period. There is a reproductive peak in spring, when most ovules are produced and the clitellum is most developed.

Additional key words: Annelida, earthworms, copulation, seasonality


Invertebrate Biology 122(2):158-165
© 2003 American Microscopical Society, Inc.

Description of intracerebral ocelli in two species of North American crayfish: Orconectes limosus (Cambaridae) and Pacifastacus leniusculus (Astacidae) Abstract. Among malacostracan crustaceans, intracerebral ocelli were first discovered in Isopoda, but they have been more recently reported from a crayfish (Cherax destructor) and a sandhopper (Talitrus saltator). This electron microscopic study increases the number of crayfish taxa in which intracerebral ocelli are now known to occur by two: Astacidae and Cambaridae. These photoreceptors are always integrated into the anteromedio-dorsal part of the brain and are not visible externally. Each ocellus is made up of 4--5 photoreceptor cells and is characterized by the presence of a fused rhabdom. The occurrence of different kinds of lysosomes in the cytoplasm is indicative of metabolic activity and perhaps membrane turnover. One typical feature of crayfish ocelli is their extraordinary variability in number. This trait is exemplified by individuals of Pacifastacus leniusculus, where as many as 14 ocelli were identified in a single brain. The arrangement of the ocelli is often not symmetrical with regard to the brain's midline and the ocelli always lack dioptric structures. Thus, it is difficult to see how they are involved in image formation. However, further research is needed to determine the precise role of these "hidden" receptors.

Additional key words: eye, vision, rhabdom, brain (protocerebrum), crayfish


Invertebrate Biology 122(2):166-176
© 2003 American Microscopical Society, Inc.

Effects of variable water motion on regeneration of Hemipholis elongata (Echinodermata, Ophiuroidea) Abstract. To determine whether increased water motion affects patterns of regeneration in the subtidal burrowing brittlestar Hemipholis elongata (phylum Echinodermata), individuals were subjected to laboratory-controlled turbulence conditions. Half of each replicate aquarium experienced oscillatory (wave-like) turbulence while the other half had no turbulence. Individual brittlestars from which arm-tips had been removed were allowed to burrow and to regenerate. Regenerated arm-tip length and weight were tested for differences between organisms in calm and turbulent conditions. Regenerated arm-tip length differed significantly between control and treatment, but arm-tip dry weight and skeleton/tissue ratio of regenerated arm-tips did not. To quantify plasticity in the skeleton, 15 morphological measurements made on the proximal face of vertebral ossicles (using scanning electron microscopy) were integrated as an index of overall ossicle size. We found a significant difference in the overall size index of the vertebral ossicles between treatments, but could not determine which of the measurements contributed most to the difference. The results indicate that regeneration in H. elongata is a complex process that can be modified by environmental conditions.

Additional key words: phenotypic plasticity, brittlestar


Invertebrate Biology 122(2):177-185
© 2003 American Microscopical Society, Inc.

Peptidergic and serotonergic immunoreactivity in the metamorphosing ophiopluteus of Ophiactis resiliens (Echinodermata, Ophiuroidea) Abstract. Antibodies against the echinoderm-specific neuropeptide S1 and against 5HT were used to examine the fate of the larval nervous system during metamorphosis in the ophiuroid Ophiactis resiliens. In contrast to most echinoderms, the onset of peptidergic and serotonergic expression was delayed to the advanced ophiopluteus stage, in particular for 5HT. In advanced ophioplutei, peptidergic immunoreactivity was located in simple fibres associated with the ciliated bands, a stomach nerve ring, and cells along the antero-lateral arms. 5HT immunoreactivity was concentrated in 2 oral ganglia in the adoral projections, located at the posterior rim of the mouth. Clusters of 5HT-positive cells were also found along the antero-lateral arms. The ophiopluteus lacked a serotonergic (or peptidergic) anterior ganglion. In echinoids, holothuroids, and crinoids, anterior ganglia are thought to have a sensory role in settlement and metamorphosis. Given that ophioplutei metamorphose in the plankton and that larval structures degenerate before settlement, the absence of apical ganglia correlates with the lack of a functional role for larval structures in substrate selection and settlement. Although most of the larval nervous system degenerated during metamorphosis, the adoral projections and associated oral ganglia appeared to be incorporated into the juvenile mouth, suggesting a potential role for larval neurons in contributing to oral neuronal structures in the adult. S1-positive neurons and fibres in the rudiment developed de novo and in parallel with development of the epineural canal. This structure gives rise to the primordia of the adult circumoral nerve ring and radial nerves, indicating that differentiation of the adult nervous system begins in the early stages of metamorphosis.

Additional key words: larval nervous system, neuropeptides