MEMORIES OF 2004

Walter Dioni Cancun, Mexico

(Part 2)
A mysterious worm
Key words: polychaeta, trochophore, metatrochophore, Sabellidae, Sabellinae, Fabriciinae

Pictures included here have been taken with the 0.4 MP camera included on my "digital" National Optical microscope, using light background, dark background, oblique illumination and Rheinberg illumination. Backgrounds were cleaned, or replaced when needed, using ACDSee and Corel PhotoPaint.

The picture below is the last image in my First Part of these Memories on the materials collected by accident after a storm on a beach in Cancun. Gliding between the smooth grains of sand, under the low power of my microscope, this little worm doesn't know that it would open a long journey through my books and the Web to identify its characteristics, and discover its identity.

The little worm glided smoothly, without contractions of its small body, probably driven by a thin layer (invisible at the low power, but predictable, according to my experience with worms) of ventral cilia. At low power the appearance and movements remind me of a turbellarian.

( http://es.wikipedia.org/wiki/Turbellaria , http://en.wikipedia.org/wiki/Turbellaria , http://fr.wikipedia.org/wiki/Turbellaria ) www. earthlife.net /inverts/ turbellaria .html

What makes it different was, above all, the opacity, the rigidity of its cylindrical body, the faint suggestion of segmentation, according to some side indentations, and the two dark areas it had on both ends.

It was evident, not only by the direction of the movement, but by the presence of two black eyes, that it had a differentiated cephalic end, but I could not see any mouth, not any other specific organ.

I soon found other specimens, a few gliding on the surface but most in the mass of the gelatinous cylinders that had been collected along with the algae. Were they inhabitants, or consumers of the jelly? Many different species of bacteria and protozoa shared the transparent substrate.

Worms in righthand image glide over the jelly. Those on the left are navigating within the same, as the steles that they make when "drilling" through the transparent substrate indicates. (Rheinberg illumination).

But, apart from some areas now empty, suggesting that they had hosted some ovoidal bodies, I also found what obviously was a resting egg .

A logical inference was that the many, blunt ended, small, and mobile cylindrical worms, with ventral cilia, were born recently from eggs housed in the jelly like cylinders that were naturally floating on the surface, or were uprooted from the bottom by the storm surge of the previous night.

Those were the "bad waters" (jellyfish) that my grandchildren suspected in the morning!!!

The most important detail seemed to me the production of those jelly 'egg-carriers'. And, if I remember right from my old teaching on invertebrates, I taught that those marine worms that could produce jelly were the polychaetes .

(It's not possible to describe here the polychaetes and relatives. So, for those who do not have enough knowledge of basic zoology, but would continue to read, I would advise them to open now SOME OF THE INTERNET ARTICLES I suggest at the end of this article.)

But, I also taught that these worms develop from eggs that produce trochophore larvae . Do you want to know what a trochophore larva is?
These are planktonic larvae with a very characteristic shape, (generally like a very transparent inverted pear or a child's spinning top even taking into account variations between different species. What follows is my conceptual syntesis of a generalized trochophore larva

Trochophores, then , are pelagic larvae that swim in the plankton until they evolve by the production of successive segments, becoming planktonic metatrochophores , which produce several segments behind the prototroch (and ahead of the telotroch ), and then fall to the bottom where they finish their metamorphosis and give rise to the adult worm . See the new "trochophore" article in WIKIPEDIA .

Here is a short review of the terms applicable to trochophores and metatrochophores

A - episphere, is the front conical part of the trochophore , above the prototroch (see later). This would be the first segment, or prostomium , of the future worm.
1 - apical tuft, a handful of cilia at the apex of the episphere, linked to a sensory nerve ganglion

2 - apical ganglion, probably sensory, at the base of the apical tuft
3 - eyes (ocelli) - two dorsal pigmented photosensitive areas, linked to the primordium of the brain
4 - prototroch , a belt of cilia around the equator of the trochophore, ahead of the mouth, when this exists. Its function (in species with a mouth) is to capture and drive the food to the mouth collaborating with the metatroch (see below). In species without a mouth the prototroch is thick and wide and its primary function is locomotion.

B - hyposphere, is an inverted cone (usually slightly larger than the episphere) which is at the bottom of the trochophore.

5 - metatroch , is a belt of cilia similar to the prototroch, and placed below the mouth, when this exists. Works together with the prototroch to capture and ingest food. In species that have no mouth the metatroch can not exist, and the prototroch is more developed.

6 - gastrointestinal tract , with a mouth (not always existing) opening in the adoral band of cilia that exist between the proto and the metatrocha, a stomach and a gut that opens through the anus at the lower end of the trochophore, even in species with no mouth this gastrointestinal primordial exist even if there is not functional.

7 - mesodermal primordium, a group of cells that later differentiate to produce the internal organs of the juvenile and adult polychaete

8 - telotroch , the ciliary belt formed above the anus, especially in benthonic forms. When new segments are built they appear above the telotroch.
9 - pigidium, the area that bears the anus and remains below the telotroch
10 - gastrotroch or neurotroch, a ciliary band that stretches from the mouth to the anus, and defines the ventral side of the larva.
11 - nephridium, a primordium of what will be the future excretory system  of the Polychaete.

http://www.diatomloir.eu/Siteplancton/Vers.html ON THIS SITE you can see various kinds of metatrochophores , planktonic of course. What can be seen easily is the amount of long bristles that they own. These are just aids that increase the surface of the worm without significantly increasing its weight, to give the little larva an easy float.

Nereids , for example, met with that typical life cycle. This is a short description for Nereis virens

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2440741

The special formatting is mine:

The trochophore (early, middle, and late) is an unsegmented spherical larva comprising two hemispheres, the episphere and the hyposphere, whose border is marked by a belt of ciliated cells, the prototroch. The metatrochophore (early, middle, and late) larva has signs of external segmentation. The trochophore and metatrochophore are non-feeding swimming planktonic larvae. The late metatrochophore falls to the sea floor where it transforms into a benthic larva, the nectochaete, and starts feeding. The nectochaete has parapodia that it uses for crawling

Obviously this is not about my little worms. These were born from eggs, without having even the aspect of a trochophore and they were never pelagic.

But as you have seen trochophores have an interesting feature. Its body is divided into 3 parts, by the presence of two bands of cilia, and I thought seeing two bands of cilia, an anterior and a posterior one in my little worms. See them here:

Little worm showing the prostomium, derived from the episphere, eyes, the prototroch ciliary band, the medium body with signs of segmentation (derived from the hiposfere). This segmentation begins in the dark zone immediately above the telotroch. Behind the telotroch, is the terminal segment called pigidium. (Rheinberg Illumination, dark field).

The closest thing I found was this picture, labeled as "metatrochophores", whose address I did not file, for over-confidence, and which despite my later long searches I do not find again. (If the author, or a web surfer more fortunate than I, falls on this page, please, tell me the address to be included here)

Therefore I devoted myself for a while to find descriptions and pictures of trochophores of different shapes, and, above all, an indication that some of them might be fully benthic trochophores . It was absolutely obvious that some of my little animals had left the egg recently, and, yet, they have exactly the same structure and behavior of the elderly. But I never found a reference to a benthic " trochophore ", or one with that shape. So could these be metatrochophores , without a trocophore stage? They had the basic structures.

a) head , lateral view, b) head, top view, c) the prototroch d) the telotroch; e) and f) the neurotroch. The compact body and the low proportion of cilia clearly indicate that this is a benthic worm.

Therefore I left my books and surfed the Web. Just as in my books, also here I found references to the production of a gelatinous mass with included eggs. For example:

Description of the masses of eggs from three sedentary species of polychaetes
from the Mediterranean Sea

A.OCA�A (1), L. S�NCHEZ TOCINO (1) & G. SAN MART�N (2)

Zool . baetica, 16: 165-169, 2005

Eupolymnia nebulosa (Montagu, 1818);

The batch (fig. 1B) consists of a transparent ovoid gelatinous mass in which it is possible to see the distinct individual orange- coloured eggs. After a few days, the batch loses its consistency

Polycirrus sp.

The batch (fig. 2B) is observed associated with the mouth among the set of tentacles. It consists of a translucent gelatinous mass, glassy grey or even with green tones, with the form of a small lemon.

Spionidae gen. sp.

The batch consists of a mucous mass coming out of the mouth of the tube, translucent foggy white in colour and somewhat ovoid.

But they are not jelly cylinders, and apparently they are small.

One of the things I discovered is that apparently the original works on polychaetes reproduction published on the Web, are very few. But there are a huge number of replicas of each one, sometimes published as if they were original works, without the slightest indication of the source that produced the data. One gets tired, opening page through page, which essentially repeated the same data and sometimes even the same phrases. Or which simply cite the same work.
The previous cited 'Mediterranean' reference accumulated dozens of citations that do not add a single supplementary data.

The other thing I discovered was that from over more than 400 read citations I could barely pick up less than ten useful references.

But yes!, I found a few references of several worms that produce eggs enclosed in gelatinous cylinders:

1) Diopatra
http://www.mbl.edu/BiologicalBulletin/EGGCOMP/pages/38.html

The naturally-fertilized eggs are surrounded by a gelatinous substance, and are deposited on the sand in long, slender, cylindrical egg-masses (Hartman, 1945). Various stages of embryonic development are contained within the jelly; when a freshly-laid string is placed in a culture tank, the larvae leave the jelly and seek the upper, light side of the container (Hartman, 1945). Ordinarily, however, they remain within the jelly-mass for a period of several days.

2) Sabella Spallanzani
http://www.marine.csiro.au/crimp/nimpis/spGeneralNotes.asp?txa=6129

    Broadcast spawner. The females extend the thorax and upper abdomen from the tube and release
    long mucus strings (~1m length) containing eggs (180-220um diameter.) (Currie et al., 2000).

At last! Two genera that produce mucous cylinders loaded with eggs as those that arrived in my hands. There may be more, but at least I could now search data more efficiently.

The Natural History Museum in London has most interesting and informative web pages. Included is a visual key for the families of polychaetes . Diopatra belongs to the family Onuphidae , and Sabella to the family Sabellidae. In addition to pictures of the adults, each plate shows the type of bristles typical for the family.

With a little torturing of my metatrochophores I managed to see still included in its interior, without having even outlines of parapodia , the famous chaetae, which, according to my photos, are of 3 types in this species.

Obviously the chaetae I show have nothing to do with the Onuphidae and they are very similar to those of Sabellidae. Please confirm that visiting THIS SITE

http://www.nhm.ac.uk/research-curation/research/projects/taxinfo/browse/family/family_browser.htm

And the trochophore ? None of my specimens, even the smaller ones, seemed to be a trochophore. According to my material I should assume that this never existed, or that (only to comply conceptually with the known cycles of life of polychaetes), had a fleeting life inside the egg, and that the larvae are born directly as metatrochophores .

Placed in shallow aquariums, with some of the algae, the metatrochophores survived several days. In its fifth day of development I could take a series of pictures that allowed me to assemble a patchwork ( mosaique ) of one small polychaete that already may be regarded as a juvenile.

Dr. Maria Ana Tovar, a researcher at the ' Colegio de la Frontera Sur advanced research institute based in the south of the Mexican Quintana Roo state, to whom I made some consultations, had the courtesy to communicate the Pernet, B et al. Chapter 12 of the "Atlas of Marine Invertebrate Larvae" on the larval development of 21 polychaeta families, beautifully illustrated with photographs of larvae obtained with Scanning Electronic Microscope. I could see there that portrayed metatrocophores are all very different from those here illustrated. But 21 is only a quarter of the 81 families that are recognized for the polychaeta . And the pictures are for only a representative species of each treated family....

Nevertheless the most interesting thing is that, definitely, the chaetae on my young worms match well with the illustrated for Sabellidae in the plates of the Natural History Museum at London, and also with published papers on genera in the family Sabellidae such as these

http://scientiamarina.revistas.csic.es/index.php/scientiamarina/article/view/11/11 (PDF, 1.4 MB)

http://www.mapress.com/zootaxa/2006f/zt01168p058.pdf

Of course I can not identify either the genus or the species, and is a gift of a single publication on the Internet, that it has brought me near the family, giving a little more peace of mind to my conscience. The systematic location, of the larvae, according to the categories often used in classic taxonomy would be as follows:

Domain: Eukaryota Whittaker & Margulis,1978

Kingdom: Animalia Linnaeus, 1758

Subkingdom: Bilateria (Hatschek, 1888) Cavalier-Smith, 1983

Branch: Protostomia Grobben, 1908

Superphylum : Eutrochozoa

Phylum: Annelida Lamarck, 1809

Class: Polychaeta Grube, 1850

Subclass: Palpata

Order: Canalipalpata

Family: Sabellidae (Malmgren, 1867)

An interesting fact: Canalipalpata refers to the fact that the 'feathers' that make up the 'duster' that gives a so striking appearance to these species have its top surface grooved and ciliated. The movement of the cilia, capture and guides the food along these grooves, channeling it into the mouth, that wait in the center of the showy duster.

So, probably we can believe with some confidence that what we present here is the benthic metatrochophore larva, with direct development of a Sabellid that, as we shall see right away may probably belong to the subfamily Fabriciinae, if were not that ... well we can discuss this in a moment. Now take note of this :

Sabellid annelids are sessile, tube-dwelling worms often known as "feather-duster worms" because of the crown of tentacles they extend from their organic, unmineralized tubes for suspension feeding. The family includes about 490 species that fall into two clades, the subfamilies Fabriciinae and Sabellinae ( Rouse and Pleijel, 2001 ). All fabriciins whose reproduction has been studied (about 15 of 75 species) brood embryos that undergo direct development. Sabellins are more variable in reproductive biology, with some species brooding embryos and larvae through the juvenile stage; others brooding embryos and larvae for most of their development, releasing larvae for a brief planktonic phase before settlement; and still others releasing gametes directly into the sea where they are fertilized and develop into planktonic larvae. No sabellid larvae are known to feed ( Rouse and Fitzhugh, 1994 ).

http://www.biolbull.org/cgi/content/full/205/3/295

I highlighted in bold the more interesting text

Well!! That also explains why my little worms had no mouth.

This also explains the size of the eggs, which must to host an abundant supply of yolk (larval food). These are called 'lecitothrophic' larvae for opposition to the 'planktotrophic' ones that feed on the plankton. And also explains the opacity of the body of the newborn, with the tissues still filled with yolk.

The problem that I find to allocate with confidence my metatrochophores to Fabriciinae , which apparently had all a direct development, is that all the descriptions I found assign to them just a few millimeters (2 to 4 mm, can you credit that?) in size ... and the cylinders of gelatin had at least 10 to 15 mm in diameter.
See for example:

http://scientiamarina.revistas.csic.es/index.php/scientiamarina/article/view/73/70 (PDF, 1.6 Mb)

Dr Maria Ana Tovar informed me that the more primitive Sabelliinae (to which such genus as Chone pertains, and descriptions and pictures of adults of whom, and their chaetae, can be found in one of the works mentioned above) have a direct style of reproduction like Fabriciinae .

Therefore it is clear to me that I should stop here my attempts for a closer taxonomic approach. I have no more data to continue. I just want to stress that my 5 day young worms have no cephalic differentiations as palpes or radiolae, and that this is different from all that can be seen in the bibliography (printed or electronic) at my reach. I hope that at some time they can fall into the hands of a qualified specialist (which can dive and work in the underwater world that is forbidden to me) which can link the larvae with its adult parents and so be able to assign to them an identity .

As the Sabelids are really beautiful animals, although seafarers and port workers may find it annoying because of "unduly" building their colonies of intertwined parchment tubes on the structures they wanted to see clean (ships, port structures, buoys, etc.), I show here, to reward those that have followed this arid investigation, a picture of an Antarctic Sabelid, (could it be that my larvae ends as this?) on loan courteously by Dr. Dirk Schories , who manages a beautiful SERIES OF PAGES on marine life:

http://guiamarina.com/gallery/main.php

SOME COMMENTS

Surely those who work with marine polychaeta, especially if they do so on reproduction and in the laboratory, must have seen many times some larvae as those presented in this article. They might therefore consider them so well known and common, that it's not worth uploading an image to the Web.

But I took a couple of days to identify conceptually the specimens I had in my hands, a few weeks to find one or two more or less coincident images, and months to collect scientific information, that never came to be defining, not even dependable, about the family and their reproductive habits.

An interesting exercise for the reader would be to put in his browser search: "Polychaetes", "Trochophore" and "Metatrochophore" to see the harvest of images they get. If you search for Sabellidae (now that we have an idea of whose family can be our metatrochophores) you will be rewarded by the harvest of many beautiful illustrations ... of the adults.

I believe that, only thanks to a single pair of works happily located (almost by accident) I was able to greatly reduce the options for identification. All other articles published on the Web, including on-line scientific work were lost in the same generalizations of all textbooks, and focus on the adult. The scientific references to the reproduction and development, apart from almost nonexistent, are purely wordy ones, dedicated only to the most well-known and most common behaviors, or the more striking, such as palolos. They do not allow more than inferences without much support.

This refers of course to the investigation of the Web Those who live in a city with good academic libraries might have better opportunities to document on this subject, especially if they had access to a specialist in polychaeta at some research institute, or a university.

That's why I add multiple addresses of sites that are introductory but particularly informative, and that everyone who wants to deepen a little in this issue should review as a start:

In Spanish

http://www.hydronauta.com/temas/biologia/vertebrados-infe/anelidos/poliquetos.htm#morfologia

http://es.wikipedia.org/wiki/Polychaeta

In english

http://en.wikipedia.org/wiki/Polychaete

http://www.earthlife.net/inverts/polychaeta.html

In French

http://fr.wikipedia.org/wiki/Polychaeta

http://www.darse.org/v1/sciences/plan_annelides.html

http://www.cg66.fr/environnement/espaces_naturels/reserve_marine/especes/annelides/index.html

the latter has also a magnificent collection of pictures of worms.

Comments to the author, Walter Dioni , are welcomed.

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