Pamela Roe

TRANSFER OF NEMERTEAN EGG PREDATORS DURING HOST MOLTING AND COPULATION

Juvenile nemertean egg predators were able to efficiently transfer from the premolt cuticle to the postmolt cuticle of male and female crabs when the host molted. These worms also efficiently transferred from male to female hosts at copulation. The synchronized responses of the nemertean worms to host physiology and behavior dramatically concentrate the nemertean population on the sole food source required for worm reproduction: crab eggs. The efficient location of reproductive crabs by juvenile worms increased the likelihood that these worms can have significant effects on crab fisheries when worm population density is high.

Aspects of the biology of Pantinonemertes californiensis , a high intertidal nemertean

I studied the distribution, feeding biology, and reproductive biology of Pantinonemertes californiensis, described as a semi-terrestrial nemertean, along the central California coast. At the sites used in this study, maximal tidal height is about 2 m, and P. californiensis typically occurred under boulders between 1.3 and 1.7 m tidal height. Worms fed primarily on the semi-terrestrial amphipod Traskorchestia traskiana. Distribution of nemerteans was similar to that of the prey, although prey extended higher on the beach than did the worms. Nemerteans were largest and most abundant at the site with highest abundance of T. traskiana and smallest and least abundant at the lowest prey abundance site. In laboratory feeding trials, nemerteans from the site with lowest prey abundance fed most readily. Non-reproductive nemerteans lived for at least a week when submerged in sea water; some prey died within a week of being submerged. Nemerteans only lived minutes when submerged in fresh water; 50% of prey lived 4.5 h. Eggs are approximately 90–100 µm in diameter and hundreds to thousands are shed per female. Larvae are planktonic and apparently planktotrophic, and are morphologically similar to other marine hoplonemertean larvae. At the sites studied life history characteristics of P. californiensis provided little evidence of adaptations to terrestrial life in these worms and were not helpful in elucidating the role of semi-terrestrial nemerteans in the evolution of terrestrial nemerteans.

Observations on musculature in pelagic nemerteans and on pseudostriated muscle in nemerteans

Histological study of 43 pelagic polystiliferans showsthat a pseudostriated, or obliquely striated,musculature is a common characteristic of therhychocoel wall of seven of eight polystiliferanspecies examined, representing four of five supposedlywidely divergent genera. This kind of muscle tissuewas previously reported from pelagic hoplonemerteansby Korotkevich, in 1955, but without a cleardescription. Both her report and the existence ofthis muscle type have gone unnoticed in subsequentliterature. We also document an earlier, unpublished,ultrastructural discovery of pseudostriation in thebody wall of a pelagic polystiliferan and reportseveral more instances in our light microscopicmaterial. We describe an overlooked aspect of theproboscis insertion; that is, the inner longitudinalmusculature of the proboscis is confluent with thelongitudinal musculature of the rhynchocoel, whereasthe outer longitudinal muscle of the proboscis extendsto the body wall as proboscis fixators. We note thatthe so-called circular muscle of the rhynchocoel insome species actually comprises crossed diagonalfibers. We report, for the first time, the presenceof crossed diagonal musculature in the body wall ofsome pelagic polystiliferans.

Ecological implications of the reproductive biology of symbiotic nemerteans

A major problem for parasites is to ensure that offspring will reach a correct host. Responses to this problem include several reproductive adaptations. This review paper shows that Carcinonemertes has several such adaptations, including increased number of gonads and offspring, synchrony of hatching with host larval hatching, facultative parthenogenesis, and mating. Other nemerteans show different, but comparably adaptive, reproductive modifications for parasitism. In contrast, reproductive biology of the commensal Malacobdella resembles that of free-living nemerteans, being timed to coincide with plankton blooms that are food for settling young.It has been thought that nemerteans found in association with other animals usually have only causal relationships with those animals, and that actual parasitism is rare among nemerteans. However, it is being found that parasitism is both well developed and more common among nemerteans than was previously thought. Nemerteas show in their reproductive biology that they are adapted to the selective factors that are important in their ways of life, and we should be able to predict the life styles of these worms by knowing their reproductive ecology.

Reproductive biology of several species of recently collected pelagic nemerteans

The reproductive biology and morphology of six polystiliferous and onemonostiliferous species of pelagic nemerteans was studied in specimensrecently collected off California. Depth distributions for these specimensranged from 250 m to 3250 m, with most specimens obtained between 700 m and1750 m. Length of sexually mature individuals ranged from 2 mm for themonostiliferan to 61 mm for a male Phallonemertes cf. murrayi. Among P. cf.murrayi and Nectonemertes cf. mirabilis, which yielded the largest specimensstudied, mature males were larger than mature females and mature animalswere larger than those in which gonads were not apparent. Females typicallyoutnumbered males, although N. cf. mirabilis approached a 1:1 sex ratio. Inthe polystiliferans studied by light microscopy, accessory ovarian cellsappeared to translocate yolk or yolk precursors to oocytes via cytoplasmicbridges, a mechanism typically associated with nurse cells and notpreviously reported from nemerteans. Mature oocytes 0.5–1 mm indiameter were common, making them very large compared to those of benthicnemerteans. Sperm possessed elongated heads and nuclei. In general, thepelagic nemerteans studied appeared: a) to produce relatively few maturegametes at a time, b) spawn in close proximity to each other, c) undergoiteroparous reproduction, and d) display moderately long-lived life cycles.In addition, data for P. cf. murrayi and possibly N. cf. mirabilisdemonstrates potential seasonal peaks in reproductive activity.

PARTHENOGENESIS IN CARCINONEMERTES SPP. (NEMERTEA: HOPLONEMERTEA)

When juveniles of Carcinonemertes spp. are removed from male crabs and raised in the laboratory, a 50:50 sex ratio is obtained. Isolated females produce egg strings typical of Carcinonemertes, except that the embryos are haploid, with about 13 chromosomes per cell. Larvae develop at least to hatching, and some do hatch. Nearly all of the 146 females so raised produced egg strings. Larvae of all females raised in isolation were haploid while larvae of females put with males were diploid. Females from both U.S. west coast species, Carcinonemertes epialti and C. errans, and from three hosts, Cancer magister, C. antennarius, and Hemigrapsus oregonensis, produced these haploid larvae by parthenogenesis.

Morphology and taxonomic distribution of a newly discovered feature, postero-lateral glands, in pelagic nemerteans

A variety of pelagic nemerteans from our collections off California and Hawaii between 1992 and 1997 have a pair of epidermal structures, usually visible on the intact specimens, located on the ventro-lateral margins near the caudal end of the body. The only previous reports of similar structures from pelagic or any other nemerteans are for two species of the genus Plotonemertes. Histological serial sections of at least one specimen from each of about 16 morpho-species demonstrate that these are specialized glandular regions of the epidermis, which we broadly term postero-lateral glands. The objects of this study are to describe these glands at the level of light microscopy and to consider their systematic implications and possible functions. Most of the glands consist of two more or less spatially segregated types of secretory cells. One type is usually at the anterior end of the gland and resembles typical mucous goblet cells. The other type usually is the more abundant, and resembles a nemertean serous cell, with secretion that probably is relatively proteinaceous. The glands of one of the Plotonemertes specimens have two additional types of secretory cells that are relatively abundant. This study reports on postero-lateral glands from 30 specimens: three specimens of Plotonemertes in the family Protopelagonemertidae, 18 in at least three genera of the family Pelagonemertidae, six in the monotypic family Balaenanemertidae, and three of Proarmaueria in the family Armaueriidae. The glands are relatively large, with large quantities of secretory vesicles, indicating that they must be of considerable importance to the animals. However, neither structure nor location offer self-evident clues to function of these glands. We also report on different forms of regional specialization in the epidermis of Crassonemertes and Nectonemertes, both of which lack postero-lateral glands.

SELECTIVITY IN TRANSMISSION TO CRAB HOSTS BY THE SYMBIOTIC NEMERTEAN, CARCINONEMERTES EPIALTI

Three species of crabs, Hemigrapsus oregonensis, H. nudus, and Cancer magister, were held in cages in Elkhorn Slough, Monterey Bay, California, to measure rates of infestation by the egg predator Carcinonemertes epialti and to determine whether host preference was displayed. Larval worms showed a clear preference for both species of Hemigrapsus over Cancer magister. Worm larvae also selected H. oregonensis at a rate approx- imately twice that for H. nudus.

Dietary immunoassay of pelagic nemerteans by use of cross-reacting polyclonal antibodies: preliminary findings

With little data on the diet of pelagic nemerteans, apreliminary immunoassay survey of the gut contents ofthree species from the Pacific Ocean was performedusing non-specific, cross-reacting polyclonalantibodies. Results suggest that Nectonemertescf. mirabilis, Phallonemertes cf. murrayi, and Cuneonemertes elongata containedsomewhat different types of prey. Worms elicitedstrong responses when probed with antibodies tosquid-like mollusks and to mysids and shrimp. Heteropods are more likely ingested than pteropods. Additional studies must be done to confirm thesehighly suggestive results.