BULLETIN OF MARINE SCIENCE, 60(2): 512-516, 1997

FUNCTIONAL MORPHOLOGY AND FEEDING BEHAVIOR OF VIRIDIS (POLYCHAETA: SPIONIDAE)

Daniel M. Dauer

ABSTRACT The functional morphology of the feeding palps, prostomium and peristomium of the spio- nid Marenzelleria viridis was studied based upon specimens from Delaware Bay, Delaware. The feeding palps of M. viridis were short in length compared to spionid species of similar total body length and were provided with two groups of cilia-frontal cilia lining the food groove and non-motile cirri on the lateral and abfrontal surface. M. I'iridi.\' is the first spionid polychaete known to have feeding palps with an asymmetrical arrangement of cilia, On the inner side of the frontal surface of the pa]p (relative to the palp held on the sediment surface) are distinct rows of cilia arranged perpendicular to the food groove. These rows are spaced 10 J.Lmapart while the frontal cilia of the food groove are densely packed with no distinct rows. The frontal cilia of the food groove transport particles to the pharynx for potential ingestion and the non-motile cirri of the palp were scattered along the length of the pa]p and projected directly from the surface of the palp. The prostomium and peristo- mium were provided with eversible cirri. When cirri were projected they were attached to a raised, circular mound. Cirri of the feeding palps, prostomium and peristomium were a~- sumed to be sensory.

Spionid inhabit a diverse variety of marine and estuarine habitats. Spionids use a pair of ciliated peristomial palps to capture particles either in sus- pension, bedload transport or deposited at the sediment-water interface (Taghon et al., 1980; Dauer et al., 1981). Six functional ciliary groups have been observed on spionid palps: frontal cilia, latero-frontal cirri, lateral cilia, non-motile cirri on papillae, non-motile cilia of the frontal surface and basal transverse cilia (Dauer, 1983, 1984, 1985, 1987, 1991, 1994; Dauer and Ewing, 1991). The feeding palp typically has a median ciliated food groove; however, and S. hutchingsae lack a median food groove and the cilia of the palps are non-motile and organized into numerous transverse rows (Dauer, 1983, 1987). Spionid polychaetes with a median ciliated food groove have one or more of the follow- ing five functional groups of cilia on their palps: (l) frontal cilia that line the median groove of the palp and transport captured particles to the pharynx (Dauer et aI., 1981); (2) lateral cilia that produce a current directed toward the frontal surface (Dauer, 1984, 1985); (3) latero-frontal cilia organized as compound cilia (cirri) that deflect or direct particles onto the frontal surface of the palp (Dauer, 1984, 1985, 1987); (4) non-motile cirri located at the tips of papillae that are sen- sory (Dauer, 1987, Dauer, 1991); and (5) basal transverse cilia that function in particle rejection from the pharynx (Dauer, 1985). The number of functional groups of cilia found on the palps of a single species varies from one to four. For example, Malacoceros indicus has only frontal cilia lining the food groove (Dauer and Ewing, 1991) and Paraprionospio pinnata has four ciliary groups-frontal cilia, latera-frontal cirri, lateral cilia and basal transverse cilia (Dauer, 1985). Di- rect deposit-feeding using the ciliated pharynx has been observed for ciliata (Daro and Polk, 1973) and elegans (Wilson, 1983). In this study the functional morphology of the feeding palps, prostomium, and peristomium of Marenzelleria viridis (=Scolecolepides viridis) (Verrill) from Delaware Bay, Delaware is described. M. viridis occupies both subitdal and in- tertidal habitats from tidal freshwater habitats to polyhaline habitats (George,

5]2 DAUER: FUNCTIONAL MORPHOLOGY OF MARENZELLERIA VIRIDIS 513

1966; Dauer et aI., 1980, 1982; Diaz and Schaffner, 1990; Sarda et aI., 1995a, 1995b). M. viridis was known to be distributed from Nova Scotia to Georgia on the east coast of North America (Dorges and Howard, 1975, Maciolek, 1984) un- til 1982 when this species was reported from the North Sea (McLuskey et aI., 1993). This species has recently been reported to be rapidly spreading throughout the North Sea and the Baltic Sea (Essink and K1eef, 1993); however, based upon genetic studies different species of Marenzelleria may occupy the North Sea and the Baltic Sea (Bastrop et a\., 1995). The feeding behavior of M. viridis from Cape Hcnlopen has been studied by Miller et aI. (1992) who observed this spe- cies to be an obligate deposit feeder.

MATERIAL AND METHODS

Individuals of Muren::elleriu viridis were collected from an intertidal, sandy, polyhaline habitat at Cape Henlopen, Delaware Bay, Delaware (38°47'N, 75°06'W) on 20 December 1994. The distribu- tion of cilia on the palps, prostomium and peristomium of M. viridis was studied on live and pre- served specimens using light and electron microscopy, respectively. Whole specimens and dissected palps of over 20 specimens were examined using a scanning electron microscope. Scanning electron micrographs were taken of specimens fixed in a 10% formalin solution, dried at the critical point in carbon dioxide, coated with gold and viewed with a JEOL JSM-35 scanning electron microscope.

RESULTS The feeding palps of Marenzelleria viridis contained two ciliary groups-fron- tal cilia lining the food groove and widely scattered cirri on the lateral and ab- frontal surface (Fig. 1, Fig. 2b). Frontal cilia were 3-5 /Lmin length (Fig. la, c); the food groove was 100-150 /Lm in depth as measured on live individuals. The frontal cilia extended out of the food groove on only one side of the palp (Fig. la, c). From the perspective of a palp with its food groove (frontal surface) held directly onto the sediment surface, the cilia of the food groove on the inner sur- face extended out approximately 100 /Lm on a flat lateral extension of the palp (Fig. Ib). The cilia on this inner portion of the food groove were in distinct rows approximately 10 /Lm apart. The cilia of the remainder of the food groove were densely packed with no rows discemable. Non-motile cirri projected directly from the palp surface on the lateral and abfrontal surface of the palp (Fig. 1b, d; Fig. 2b). The cilia of the palp cirri were 3-5 /Lm in length and 5-10 cilia per cirrus. The length of the palp on adult sized individuals (2-5 cm) ranged from 800-1,200 /Lm. Both the prostomium and peristomium were densely provided with cirri (Fig. 2a, c, d). Cirri appeared to be eversible and when everted were at the tip of a small papilJa (Fig. 2c, d). The cilia of these cirri were of the same size and num- ber per cirrus as those of the feeding palps.

DISCUSSION Marenzelleria viridis is the first spionid polychaete known to have feeding palps with an asymmetrical arrangement of cilia relative to the long axis of the feeding palp. The frontal cilia of M. viridis extend away from the food groove of the frontal surface in distinct rows on the inner surface of the palp as the palp is held in contact with the sediment surface. The functional significance of this arrangement is uncertain. These extended rows of frontal cilia may function in dislodging sur- face particles held together by mucus secretions of bacteria or diatoms. Such sur- face mats were readily observable on the intertidal sand flat during collection of individuals for this study. The relatively short palps of Marenzelleria viridis indicate that as an obligate 514 BULLETIN OF MARINE SCIENCE. VOL. 00. NO. ~. 1447

Figure 1. Scanning electron micrographs of Marellze/leria I'iridis. a. Frontal view of feeding palp showing rows of regularly spaced cilia on inner surface (bar = 500 J.Lm). b. Abfrontal view of feeding palp (bar = 500 J.Lm). c. View of regularly spaced frontal cilia of the inner surface of the palp (bar = 100 J.Lm). d. View of non-motile cirri of the abfrontal surface of feeding palp (bar = 100 J.Lm). deposit feeder the feeding radius of the species is small unless the extends its body outside of the burrow as observed in other spionids (Woodin, 1982). How- ever, extension outside of the burrow which subjects the individuals to greater browsing or predation may not be necessary if either the rate of transport of new sedimentary particles exceeds the feeding rate of the individual or if some sub- surface deposit feeding occurs. On the tidal flats of this study, waves and currents were significant in transporting sediment as indicated by ripple marks throughout the area. Direct observation of fecal rods of M. viridis indicated that most fecal rods had an oxygenated appearance indicative of sedimentary particles found at the surface. However many fecal rods also contained sections which had a much darker appearance possibly indicative of reducing conditions. Short feeding palps associated with a rapid replenishment of surface particles or supplementation with subsurface particles may reduce browsing and/or predation rates in M. viridis. Marenzelleria viridis has sensory cilia on the prostomium and peristomium which are located on eversible papillae. The feeding palps are also provided with non-motile cirri on the lateral and abfrontal surfaces of the palp. Non-motile cirri are believed to have a mechanosensory role in species of Polydora (Dauer 1991, 1994) and may be important in inter- and intraspecific encounters such as those observed in and Pseudopolydora paucibranchiata by Levin (1981). In contrast to other spionids the non-motile cirri of M. viridis project di- rectly from the palp surface and are not located at the tip of papillae (Dauer, 1994). These unpapillated non-motile cirri of the palps constitute a seventh group of cilia known from spionid polychaete feeding palps. DAUER: FUNCTIONAL MORPHOLOGY OF MARENZELLERIA VIRIDIS 515

Figure 2. Scanning electron micrographs of Marenzelleria viridis. a. View of prostomium with right feeding palp and food groove (bar = 200 /.Lm). b. Closeup of non-motile cirri of the feeding palp (bar = 10 /.Lm). c. View of cirri of prostomium (bar = 50 /.Lm). d. Closeup of cirri of prostomium (bar = 10 /.Lm).

ACKNOWLEDGMENTS

I thank A. J. Rodi, Jr. of the Benthic Ecology Laboratory of Old Dominion University, D. Miller and M. Brock of the University of Delaware and my wife, Chamie, for help in tleld collections. M. Adam of the Electron Microscopy Laboratory of the Department of Biological Sciences of Old Do- minion University prepared the specimens and plates of the electron micrographs.

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DATEAccEPTED: June 26, 1996.

ADDRESS: Department of Biological Sciences, Old Domionion University, Norfolk, Virginia 23529.