Coast Watch 2012

Marine Invasives Overview

It's a new summer season in New England and the CZM launched its Marine Invasive Species Program for 2012.  This summer, I'll be working with the Provincetown Center for Coastal Studies monitoring marinas in Provincetown and Wellfleet.  There are no new species classified as invasvie this year.  The collection of MIMIC ID Cards gives detailed descriptions of the 16 marine invasive species and the 7 potentially new species that have not yet reached the New England coast.  Guidelines are listed for distinguishing MIS species from related native species. 

MIMIC ID Cards for MIS Species (16 ID cards)

MIMIC ID Cards for Potential Invasives whose geographic ranges are spreading (7 ID cards)

Recently, I was searching the internet for information on invasive species and I came across several Wikipedia listings that described some of the issues around terminology for invasive species.  They contrasted the terms "invasive, introduced, immigrant, naturalized, exotic, alien, foreign, non-native, and non-indigenous".  For example, "invasive" and "alien" have unintended negative connotations that may not apply to all species, and "exotic" is also used for rare or unusual pets.  Many native and formerly invasive species are also "fouling" organisms that have spread beyond their native habitat (usually because of human activities).  Many invasives are simply in the process of geographic range enlargement or globalization because of new opportunities created by humans.  Marinas help facilitate the spread of MIS, especially for species that prefer quiet waters, because they are so numerous along the coasts of many countries.  At some point in time, the invasive species will most likely reach an equilibrium and at some point may be considered established.

Here is this year's list of species featuring images from recent web searches, a few of my own micrographs, and my impressions of the species from last season's monitoring:

Ascidians:

• Didemnum vexillum (beige colonial tunicate).  This species aggressively grows over everything - any flat surface including docks, solitary ascidians, mussels, algae blades.  Have I forgotten anything?  If so, include it too.

  

• Diplosoma listerianum (grey/green colonial tunicate) - Diplosoma is also a rapid grower and shows seasonal and regional variability with Didemnum. It is also a member of the Didemnidae family but lacks spicules.  It is distinguished by its smooth, slimy texture - like the body of an anemone, but it grows in a flat sheet.



• Ascidiella aspersa (translucent solitary tunicate) - The translucent, bumpy solitary ascidian.  Distinct from Ciona, another related species, and distinguished by its placement of siphons, which are far apart.  Ascidiella and Ciona can easily to distinguished from Molgula by the internal organs which can be seen through the tunic in young specimens. 

• Styela clava (club solitary tunicate) - Very common but can be missed when small and large individuals are frequently covered by Didemnum with only the brown Styela siphons sticking out.

• Botryllus schlosseri (star colonial tunicate) - Probably the most commonly studied adult ascidian as a model for colonial growth and tissue rejection.  Numerous color and pattern variants.

• Botrylloides violaceus (orange colonial tunicate)  - One of the most beautiful invaders/foulers.  Comes in many different shades of red/orange/peach.  Not as aggressive as the Didemnid colonials. 

Bryozoa:

• Membranipora membranacea (lacy encrusting bryozoan, posted Feb 12, 2012) - common on any flat, sturdy surface.  Co-exists with the native encrusting bryozoan.  Helpful to have a 30X magnifier. 

• Bugula neritina (purple bushy bryozoan)  - Similar to red algae in growth form but calcareous and distinctly different in structure.  Individual zooids may be discerned with a 30x magnifier.  

Anemones:

• Diadumene lineata (orange striped anemone, posted Dec 22, 2011) - seen in the "murky" waters of Wellfleet but not in the "sparkling" waters of Provincetown.  They're tiny gems. 

Bivalves: 

• Ostrae edulis (European oyster) - Not likely to be seen on docks.

 

Crustacea:

• Carcinus maenus (green crab) - Vary in size on docks - usually smaller than the size of a quarter.  It is distinguished from the Asian crab by its color, shape of the carapace, and solid coloring on its legs. 

• Hemigrapsus sanguineus (asian shore crab) - Easily identified by its striped legs and body.

• Palaemon elegans (European rock shrimp) - Present in Salem Sound.  Difficult to distinguish from native shrimp, especially when small before the blue bands on its legs and body fully develop.  Best to confer with the crustacean or MIMIC experts.



• Caprella mutica (Caprellid amphipod a.k.a. skeleton shrimp) - Very common living on algae and bryozoa. These small amphipods look and act like miniature preying mantis.  They hold tight to surfaces and do not "swim around" like typical amphipods and shrimp.  Not very compatible with fine nets where they need to be hand-picked off. 

 Algae:

• Codium fragile (green fleece) - Common in mid-late summer along dock water lines where they grow in masses. Characterized by branching growth pattern (right).

 

• Grateloupia turuturu (leafy red algae) - Arrives late season in the Gulf of Maine due to cold temperatures.

Links:
Pappal, A, Pederson, J, and Smith JP. Marine Invaders in the Northeast. Rapid Assessment Survey of Non-native and Native Marine Species of Floating Dock Communities.
Non-Native Species Invasions, Marine Biodiversity Wiki
Invasion Biology Terminology, Wikipedia
Invasive Species, Wikipedia
Introduced Species, Wikipedia

Ascidian Filter Feeding Mechanism

Styela clava as the model

Ascidians are suspension feeder that filter food particles such as phytoplankton from the surrounding sea water.  They transport water through the branchial sac (pharynx) which is perforated with small, ciliated slits, the stigmata.  The ciliary tracts on each side of the stigmata create a water current that pulls water through the branchial siphon into the branchial sac, through the stigmata, and into the atrial cavity from which the water leaves the body as a stream through the atrial siphon. When the water is transported across the branchial wall, suspended particles are trapped on a mucous net that is created by the endostyle, a mucus secreting structure on the ventral wall. 

Diagram of the Ascidan Filter Feeding Process

Diagram of the ascidian filter-feeding process. From Woods Hole Oceanographic Institute Website, 2005

The feeding mechanism is similar in different ascidians regardless of the complexity of the structures. Styela clava belongs to a group of solitary ascidians with a structurally complex branchial sac that is folded.  The folding increases the internal surface area, thereby increasing the number of stigmata and filtration capacity.   A mucus secreting organ on the vental surface, the endostyle, secretes a mucus net that moves across the surface of the sac by cilia on the pharyngeal bars.  The mucus net with its retained food particles then moves toward the esophagus. Thus, the amount of food consumed is determined by the concentration of food particles in the sea water, the efficiency of particle retention, and the volume of water transported. At a structural level, the endostyle is a longitudinal ciliated groove on the ventral wall and is composed of 8 different types of cells, a single band at the base of the groove with very long cilia that extend toward the surface of the groove and 7 pairs of bands on each side of the endostyle wall.

Diagram of the Branchial Sac of S. clava in Relation to the Digestive Tract

 The digestive tract of Styela clava from the left side with the internal surface of the branchial sac exposed.   bs, branchial siphon;  bt, branchial tentancles;  en, endostyle;  bb, branchial bar;  s, stigmata; i, intestine;  as, atrial siphon;  dt, dorsal tubercle;  r, rectum;  dl, dorsal lamina;  es, esophagus;  rb, retropharyngeal band;  st, stomach.

 Cross Section through the Branchial Sac of Styela clava

Section passes through the tranverse bars and not the stigmata.  The endostyle is located on the ventral surface.  Mucus and entrapped food pass along the ciliated branchial bars towards the dorsal lamina and then towards the esophagus.  bf, branchial folds;  d, dorsal lamina;  en, endostyle;  lb, longitudinal bars;  sv, subendostyle vessel.  

View of the Internal Surface of the Branchial Basket of Styela clava

Internal surface of the branchial basket of Styela clava by scanning electron microscopy (SEM) showing branchial fold (left 1/3 of image) and direct view of rows of stigmata, major and minor trasverse folds, and longitudinal folds.

Internal View of 3 Stigmata in the Branchial Sac of Styela clava

 

Internal surface of the branchial sac of Styela clava by SEM showing 3 stigmata, a major transverse fold at the lower left and a minor transverse fold at the upper right.  Densely packed cilia are uniform in length. 

Section through the Stigmata and a Branchial Bar of Styela clava

Section through the stigmata and a branchial bar of Styela clava. Cilia prevent food particles from leaving the branchial cavity but allow filtered sea water to pass through.  Ciliated bars transport food-containing mucus along the longitudinal and transverse bars to the dorsal lamina and thereafter to the esophagus. The cilia on the bars actually pull the mucus net forward, whereas the stigmata cilia act only as filters. sb, stigmata bar, ve, ciliated ventral epithelium;  ue, unciliated epithelium. 

Histologic Section through the Stigmata of Styela clava

Semi-cross section through a group of about a dozen ciliated stigmata ending on the left at a branchial bar.  The ascidian had contracted and stopped feeding, so the branchial sac is not in its normally expanded, feeding configuration.  Hemotoxylin stain.  

Cross section of the Endostyle of Styela clava

  Cross-sectional diagram of the different cell types of the endostyle of Styela clava.   The cells at the base of the groove have very long, flagella-like cilia.  The remaining cells are paired with semi-alternating glandular and ciliated cells.  

Histological Section of the Endostyle of Styela clava

Cross section through the endostyle of Styela clava.  The long cilia in Zone 1 can be seen extending part-way up the depth of the groove.  Hemotoxylin stain. 

PUBLICATIONS:

Armsworthy, SL, MacDonald, BA, & Ward, JE. Feeding activity, absorption efficiency and suspension feeding processes in the ascidian, Halocynthia pyriformis (Stolidobranchia: Ascidiacea): responses to variations in diet quantity and quality.  J. Exp. Mar. Biol. Ecol. 260: 41–69, 2001.

Ermak, T.H. Cell proliferation in the digestive tract of Styela clava (Urochordata: Ascidiacea) as revealed by autoradiography with tritiated thymidine. J. Exp. Zool. 194: 449-465, 1975.
Godeaux, J.E.A. Functions of the endostyle in the tunicates.  Bull. Mar. Sci. 45: 228-242, 1989.
Holmes, N.  Water transport in the ascidians Styela clava Herdman and Ascidiella aspersa (Mueller).  J. Mar. Bio. Ecol. 11: 1-13, 1973.
MacGinitie, GE. The method of feeding of Tunicates.  Biol Bull 77: 443-447, 1939.
Petersen, J, & Svane, I. Filtration rate in seven Scandinavian ascidians: implications of the morphology of the gill sac. Mar. Biol. 140: 397-402, 2002.
Petersen, JK, Mayer, S, & Knudsen, MÅ. Beat frequency of cilia in the branchial basket of the ascidian Ciona intestinalis in relation to temperature and algal cell concentration. Mar. Biol. 133: 185-192, 1999.
Riisgird, HU.  The ascidian pump:  properties and energy costs.  Mar. Ecol. Prog. Ser. 47:129-134, 1988.  (Studied in Styela clava). 

WEB LINK:
Shimek, RL. Tunicates or Sea Squirts: A Wet Link. Reefkeeping Online Magazine.

The Invasive Club Tunicate

An Abundant Resource for Ascidian Research

Styela clava and its cousin Styela plicata have been getting some pretty bad press over the last 10 years due to their circumglobal distribution and classification as Marine Invasive Species.  As a Styela biologist, I'd like to spend some time discussing some of the positive aspects to the Styela story. They may be be ugly ducklings on the outside (literally), but because of their recent world-wide distribution, they have also been the subject of scientific investigation by several research labs.  They are an attractive research model because they are readily available to researchers around the temperate world (in both hemispheres), and they are an important group of ascidians biologically in terms of their relationships to colonial botryllid species and other solitary ascidians.  In Asia (Korea), S. clava is part of the regional cuisine (Mideodok-chim) and is grown in aquaculture. The biology of Styela has become important for understanding diseases that have threatened commercially-cultured ascidians (soft-tunic syndrome in Halocynthia roretzi).  Inside, they are fascinating to study because their internal organs are bright orange and easy to examine.   S. clava is particularly useful because it is slender with a relatively thin, easily-cut tunic, whereas S. plicata is globular in shape and has a thick, less pliable tunic.  S. clava cohabitates with S. plicata in bays where their ranges overlap on both the East and West US coasts. 

Successful MIS Species:  S. clava and S. plicata

Styela clava and Styela plicata have made a home in Marinas and Bays around the world and are two of the most commonly studied Styela species.  In North America, both species have been established on both coasts for several decades.  S. clava has a more northern distribution than S. plicata, and the two co-habitate where their ranges overlap.  

Native American Styelids (Pacific Coast):  S. montereyensis, and S. gibbssi.

 

Styela montereyensis and Styela gibbsii, two Styela species from the Pacific coast were the two Styela research species of choice before the two MIS species became established in North America and Europe.  S. montereyensis and S. gibbsii have stayed within their ranges in the North American Pacific and prefer the cooler waters of the open coast. 

Styela clava showing orange-colored internal organs

   

Dissection of Styela clava with branchial sac (bs) on left and digestive tract on the right.  All the internal organs are located in the upper portion of the individual and not in the stalk whose function is essentially to raise the siphons and body above the growth of encrusting invertebrates and algae.  st, stomach; int, intestine;  os, oral siphon. as, atrial excurrent siphon. 

Diagram of the internal organs of Styela clava

Diagram of the internal organs of Styela clava.  Branchial sac, digestive tract consisting of esophagus, stomach, and intestine; reproductive organs in the body wall (both sides); and heart.   en, endostyle; bf, branchial folds; dl, dorsal lamina; rb, retropharyngeal band; ht, heart; es, esophagus; st, stomach; in, intestine; ov, ovary; t, testis.

Styela clava has a number of advantages as a model system for the study of solitary ascidians.  It is abundant, grows up to 4-5 inches (12 cm), and is easy to dissect.  It is adaptable for a wide range of studies and has a firm, flexible tunic that supports the internal organs during dissection.  In coastal marinas, S. clava individuals on docks show a range of sizes depending on the season and whether the substrate has been recently cleared.  During my 2011 MIS monitoring from Cape Cod to Salem Harbor, the population density was kept at a moderate level by competition with other encrusting invertebrates and colonial ascidian species, especially Didemnum vexillum and Diplosoma listerianum, which can aggressively overgrow solitary ascidians.  When fully mature, large individuals are easy to spot (unless totally covered by Didemnum).  However, small, young individuals may not be counted in the field when if they are not recognized. This is particularly important in marinas with new or cleaned docks. 

Young and Fully-Grown Individuals of Styela clava

Size distribution of Styela clava (the field is approx 5 inches [12.5 cm] high). The 6 smallest individuals were covered with Diplosoma listerianum, which was manually removed, revealing a smooth, light-tan tunic. The 3 medium sized individuals show typical bumpy brown corrugated tunic. The 3 largest individuals are covered with colonial ascidians and other attaching invertebrates. Left, complete coverage with Didemnum vexillum except for the siphons.  Center, patch-work collection of orange Botrylloides and Botryllus. Right, coverage by Didemnum and Botrylloides. Siphons and the upper body can contract within the tunic of the colonial species maintaining water flow and inhibiting overgrowth.

Styela has been used as a model system for studying filter feeding, the anatomy, histology, and ultrastructure of tunicates, cell biology (such as the function of the endostyle), blood cell formation, and the production of anti-bacterial peptides (styelins, clavanins, and clavaspirin).  The ovaries and testes are located in the body wall on both sides of the body instead of along the digestive tract and are arranged in radiating rows that are ideal for morphological and developmental studies.  Styela is a good control solitary ascidian for the study of coloniality in botryllid ascidians and is therefore important from an evolutionary point of view.  The styelids are located at a cross road linking more distantly related solitary ascidians such as Ciona, Ascidia, and Ascidiella, and other more closely related advanced ascidians such as Pyura (on the West Coast), Halocynthia (sea peach), and Boltenia (sea potato).  Some of these topics will be discussed in more detail in upcoming posts.

Granulocytes in Blood-Forming Tissue of Styela clava

Granulated blood cells in ascidians contain antimicrobial peptides that are important in fighting off bacterial and fungal infections.  The peptides are made in the cytoplasm and are concentrated into secretion granules that are released from the cell when they detect microorganisms.  This process is a part of the innate immune response and serves a similar function to the granulated blood cells in vertebrates that fight infections.  

Antibacterial Peptides from Blood Cell Granules of Styela clava

Styelins share amino acid sequences with each other and with cecropins in the domestic pig Sus scrofa domesticus (P1) and Drosophila virilis (Dv1).  Clavanins also share similar amino acid sequences.   

WEB AND LITERATURE SEARCH TERMS:

Styela, branchial sac, filter feeding, endostyle, stigmata, cilia, mucus, digestive tract, stomach, blood cells, hemocytes, granulocytes, cell renewal, reproduction, ovary, testis, innate immunity, styelin, clavanin, etc.

REFERENCES:

1.  Ermak TH. Cell proliferation in the digestive tract of Styela clava (Urochordata: Ascidiacea) as revealed by autoradiography with tritiated thymidine. J. Exp. Zool., 194: 449-466, 1975.

2.  Ermak TH. The hematogenic tissues of tunicates. In, The Phylogeny of Thymus and Bone Marrow-Bursa Cells, RK Wright and EL Cooper, Eds., Elsevier/North Holland, Amsterdam, pp. 45-56, 1976.

3.  Ermak TH. The renewing cell populations of ascidians. Amer. Zool. 22: 795-805,1982.

4.  Jiang AI, Lin J, Wang CH. Physiological energetics of the ascidian Styela clava in relation to body size and temperature. Comp. Biochem. Physiol. 149: 129-136. 2006.

5.  Kumagai A, Suto A, Ito H, Tanabe T, Takahashi K, Kamaishi T, Miwa S. Mass mortality of cultured ascidians Halocynthia roretzi associated with softening of the tunic and flagellate-like cells. Dis. Aquat. Org. 90: 223-234, 2010.

6.  Lambert G. New records of ascidians form the NE Pacific: a new species of Trididemnum, range extension and redscription of Aplidiopsis pannosum (Ritter, 1899) including is larva, and several non-indigenous species. Zoosystema 25: 665-67X, 2003 (includes an updated description of Styela clava).
7.  Lee IH, Cho Y, and Lehrer RI.  Styelins, broad-spectrum antimicrobial peptides from the solitary tunicate, Styela clava.  Comp Biochem. Physiol. 118B: 515-521, 1997.
8.  Lehrer RI, Lee IH, Menzel L, Waring A, and Zhao C.  Clavanins and styelins, alpha-helical antimicrobial peptides from the hemocytes of Styela clava.  Adv. Exp. Med. Biol. 484: 71-76, 2001.

9.  Lehrer RI, Tincu JA, Taylor SW, Menzel LP, and Waring J.  Natural Peptide Antibiotics from Tunicates: Structures, Functions and Potential Uses. Integr. Comp. Biol. 43: 313-322, 2003.
10.  Menzel LP, Lee IH, Sjostrand B, and Lehrer RI.  Immunolocalization of clavanins in Styela clava hemocytes.  Dev. Comp. Immunol. 26: 505-515, 2002.
11.  Raftos DA, and Cooper EL. Proliferation of lymphocyte-like cells from the solitary tunicate, Styela clava, in response to allogeneic stimuli. J. Exp. Zool., 260: 391–400, 1991.
12.  Raftos DA, Stillman DL, and Cooper EL. In vitro culture of tissue from the tunicate Styela clava.  In Vitro Cell. Dev. Biol. 26, 962-970, 1990.
13. Sawada T, Zhang J, and Cooper EL. Classification and characterization of hemocytes in Styela clava. Biol. Bull. 184:87-96,1993.
14. Thorndyke MC. Observations on the gastric epithelium of ascidians with special reference to Styela clava.  Cell Tiss. Res. Volume 184, 539-550, 1977.

15. Thorndyke MC.  Comparative studies on the effects of cholecystokinins, caerulein, bombesin 6-14 nonapeptide, and physalaemin on gastric secretion in the ascidian Styela clava.  Gen. Comp. Endocrinol., 1984. 

LINKS:

National System for the Prevention and Management of Marine Pest Incursions

Korean Mideodok-chim (Steamed Styela with beef, clams, vegetables, and ground rice over noodles)
iTunicate Newsletter (Invasive Tunicate Network in Alaska):  Plate Watch.  Includes a recipe for steamed Mideodok-chim.

Botryllus: Burgundy Color Variants

At the beginning of the season, the typical star-shaped Botryllus schlosseri color variants with a burgundy body and white inter-siphon pigment bands forming an actual white star was one of the most prevalent color variants.  But as the summer progressed, the number and variations of color variants increased, including the burgundy colonies.  Their appearance in daylight or under incandescent light varied depending on substrate (light green sea lettuce, dark green Codium, brown algae, red algae, mussel shell, Styela) and background setting (on the dock, in collection containers, or on a black or white microscope stage). In this post, I show a few of the burgundy color variants collected from Provincetown and Salem Sound during the summer.

   Burgundy Botryllus schlosseri Variant on Green Algae - White Star

Botryllus schlosseri on Ulva, MacMillan Wharf, Provincetown, MA, September, 2011.  Green back-lighting through the algae clearly outlines the zooids.   White pigment cells form a pair of curved bands between the branchial and excurrent siphons giving the bands a daisy-star appearance.  Stereozoom 1.0 x 10x.  

Burgundy Variants with Inter-siphon White Shield

 

Botryllus schlosseri on Codium, MacMillan Wharf, September, 2011. White pigment cells form a shield-shaped pattern filling the space between the branchial and excurrent siphons of the cluster. The zooids also have a tiny patch of white cells on the opposite, outer side of the branchial siphon at the anterior end of the endostyle.  Othewise, the branchial siphons are burgundy like the rest of the zooid body. Stereozoom 3.0 x 10x.

 Burgundy Variant on Red Algae, White Branchial Crescent with Atrial Ring

 

Nine-zooid cluster of Botryllus schlosseri on red algae, MacMillan Wharf, October, 2011. Scattered white pigment cells encircle the orange-colored branchial siphon, more heavily on the outer side of the cluster. The common excurrent siphon is outlined by a dashed ring of white pigment cells formed by a short, white stripe at the atrial opening of each zooid.  Stereozoom 1.5 x 10x.

Ampullae of Burgundy Variant on Red Algae - White-Capped

 

Same colony of Botryllus schlosseri on red algae as shown above.   The zooids share a common vascular system that consists of blood vessels and enlarged club-shaped vascular ampullae along the periphery. The ampullae have the capacity to reconstruct the colony by vascular budding if all the zooids are lost.  Top, ampullae define the edge of the colony and separate clusters of zooids.    Bottom, white pigmented cells concentrate at the distal ends of burgundy ampullae like snow-capped boulders. 

Burgundy Variant on Red Algae - Diffuse White Branchial Stripe

Botryllus schlosseri on red algae, MacMillan Wharf, September, 2011.  White pigment cells form a short stripe through the branchial siphon above the endostyle and dorsal lamina.  Pigment cells also lightly speckle the body of the zooid.  Branchial siphons are orange-colored. Top, two 7-zooid and 10-zooid clusters.  Stereozoom 2.0 x 10x.  Bottom, close-up view of branchial siphons and diffuse white stripe.  Stereozoom 3.0 x 10x.  

LINK:

CE Carver, AL Mallet, and B Vercaemer, Biological Synopsis of the colonial tunicates, Botryllus schlosseri and Botrylloides violaceus

Identifying the Native Encrusting Bryozoan

Electra pilosa

Electra pilosa is a native encrusting Bryozoans found in the Gulf of Maine co-habitating with the cosmopolitan, MIS species Membranipora membranacea. Both of these encrusting colonies have a lacy appearance and are typically found on brown algae such as Laminaria sharing space on the same blade. Upon inspection, established colonies may look similar but they can be distinguished from each other by specific differential features. 

Colony growth pattern is an important clue to differentiating Electra from Membranipora.  Electra in its first stages of growth forms star-shaped colonies whereas Membranipora grows in a uniform, radial pattern (what Silén called "unitary multiserial", see LINK below).  In contrast, the colony of Electra is separated into sectors divided by radial axes that extend beyond the margins of the colony forming a multi-pointed star (what Silén called "composite multiserial" growth).  Each sector has a central growth axis composed of 2 or more parallel rows of rectangular zooids (approximately 0.33 by 0.5 mm in dimensions) flanked on each side by wings of oval or ovate zooids which fill in the area between the axes. The side walls of the calcified enclosure do not directly abut each other like in Membranipora (see February 12, 2012 post), but are separated by a translucent, calcareous surface membrane. Each enclosure is surrounded by several spines that vary in length. However, the median, proximal spine is larger than the rest and can be easily seen with a magnifing lens. 

The bottom line when identifying encrusting Bryozoans in New England is to check for growth pattern (composite vs. uniform), boundary morphology (jagged vs. smooth), zooid skeletal structure (ovate vs. rectangular), arrangement of spines (larger pointed, proximal spine vs. 6 short, blunt spines, 4 at each corner of the rectangular enclosure) for Electra vs Membranipora, respectively.  

Growth Pattern of Electra vs. Membranipora

Comparison of growth pattern of Electra vs. Membranipora in small colonies where the axial structure of Electra is most pronounced.  Modified image from Silén, 1987 (see LINK below).  

Axial Growth Pattern of Electra pilosa

Outer border of Electra pilosa colony growing on Laminaria collected from Hawthorne Cove, Salem Sound, MA.  The colony illustrates composite multiserial growth.  At the bottom, two axial strands of rectangular zooids curve toward each other encircling inter-axial ovate zooids. At the top, several axial strands join each other to form a single 5-zooid wide strand.   Stereozoom 1.0 x 10x objective. 

Calcareous Enclosures of Electra pilosa

Electra pilosa zooids showing axial (left and right) and inter-axial zooids (center) with conspicuous proximal spines and translucent calcareous membranes between walls of the enclosures.  Stereozoom 3.0 x 10x objective

LINKS:

L. Silén. Colony Growth Pattern in Electra pilosa (Linnaeus) and Comparable Encrusting Cheilostome Bryozoans. Act. Zool. 68: 17-34, 1987.

Electra pilosa: MarLIN - The Marine Life Information Network



Electra pilosa (Linnaeus, 1767): WoRMS - World Register of Marine Species