pourquoi les sangsues ils ont pas de vrai vaisseaux sanguins comme les autres vers mais ils ont quelque chose d'autre à la place c'est quoi ce truc
Anatomy and physiology

Leeches show a remarkable similarity to each other in morphology, very different from typical annelids which are cylindrical with a fluid-filled space, the coelom (body cavity). In leeches, most of the coelom is filled with botryoidal tissue, a loose connective tissue composed of clusters of cells of mesodermal origin. The remaining body cavity has been reduced to four slender longitudinal channels. Typically, the body is dorso-ventrally flattened and tapers at both ends. Longitudinal and circular muscles in the body wall are supplemented by diagonal muscles, giving the leech the ability to adopt a large range of body shapes and show great flexibility. Most leeches have a sucker at both the anterior (front) and posterior (back) ends, but some primitive leeches have a single sucker at the back.

Like most annelids, with a few exceptions like Sipuncula, Echiura and Diurodrilus, the leech is a segmented animal, but unlike other annelids, the segmentation is masked by secondary external ring markings (annuli). The number of annulations varies, both between different regions of the body and between species. In one species, the body surface is divided into 102 annuli. All leech species, however, have 32 segments, called somites, (34 if two head segments, which have different organization, are counted). Of these segments, the first five are designated as the head and include the anterior brain, several ocelli (eyespots) dorsally and the sucker ventrally. The following 21 mid-body segments each contain a nerve ganglion, and between them contain two reproductive organs, a single female gonopore and nine pairs of testes. The last seven segments contain the posterior brain and are fused to form the animal's tail sucker. The septa that separates the body segments—and the mesenteries which in turn separates each segment into a left and right half—in the majority of annelids, have been lost in leeches except for the primitive genus Acanthobdella, which still have some septa and mesenteries.

The body wall consists of a cuticle, an epidermis and a thick layer of fibrous connective tissue in which are embedded the circular muscles, the diagonal muscles and the powerful longitudinal muscles. There are also dorso-ventral muscles. In leeches the original blood vascular system has been lost and replaced by the modified coelom known as the haemocoelomic system, and the coelomic fluid, called the haemocoelomic fluid, has taken over the role as blood. The haemocoelomic channels run the full length of the body, the two main ones being on either side. Part of the lining epithelium consists of chloragogen cells which are used for the storage of nutrients and in excretion. There are 10 to 17 pairs of metanephridia (excretory organs) in the mid-region of the leech. From these, ducts typically lead to a urinary bladder, which empties to the outside at a nephridiopore.
Les vaisseaux sanguins sont les structures du système circulatoire qui transportent le sang dans tout le corps humain. Ces vaisseaux transportent les cellules sanguines, les nutriments et l'oxygène vers les tissus du corps. Ils éliminent également les déchets et le dioxyde de carbone des tissus. Les vaisseaux sanguins sont essentiels à la vie, car tous les tissus du corps dépendent de leur fonctionnalité. Il existe cinq types de vaisseaux sanguins : les artères, qui transportent le sang loin du cœur ; les artérioles ; les capillaires, où les échanges d'eau et de produits chimiques entre le sang et les tissus ont lieu ; les vénules ; et les veines, qui ramènent le sang des capillaires vers le cœur. Le mot « vasculaire », signifiant relatif aux vaisseaux sanguins, est dérivé du latin « vas », qui signifie vaisseau. Certaines structures – comme le cartilage, l'épithélium, ainsi que le cristallin et la cornée de l'œil – ne contiennent pas de vaisseaux sanguins et sont qualifiées d'avasculaires.
### Query ###
pourquoi les sangsues ils ont pas de vrai vaisseaux sanguins comme les autres vers mais ils ont quelque chose d'autre à la place c'est quoi ce truc

### Main Text ###
Anatomy and physiology

Leeches show a remarkable similarity to each other in morphology, very different from typical annelids which are cylindrical with a fluid-filled space, the coelom (body cavity). In leeches, most of the coelom is filled with botryoidal tissue, a loose connective tissue composed of clusters of cells of mesodermal origin. The remaining body cavity has been reduced to four slender longitudinal channels. Typically, the body is dorso-ventrally flattened and tapers at both ends. Longitudinal and circular muscles in the body wall are supplemented by diagonal muscles, giving the leech the ability to adopt a large range of body shapes and show great flexibility. Most leeches have a sucker at both the anterior (front) and posterior (back) ends, but some primitive leeches have a single sucker at the back.

Like most annelids, with a few exceptions like Sipuncula, Echiura and Diurodrilus, the leech is a segmented animal, but unlike other annelids, the segmentation is masked by secondary external ring markings (annuli). The number of annulations varies, both between different regions of the body and between species. In one species, the body surface is divided into 102 annuli. All leech species, however, have 32 segments, called somites, (34 if two head segments, which have different organization, are counted). Of these segments, the first five are designated as the head and include the anterior brain, several ocelli (eyespots) dorsally and the sucker ventrally. The following 21 mid-body segments each contain a nerve ganglion, and between them contain two reproductive organs, a single female gonopore and nine pairs of testes. The last seven segments contain the posterior brain and are fused to form the animal's tail sucker. The septa that separates the body segments—and the mesenteries which in turn separates each segment into a left and right half—in the majority of annelids, have been lost in leeches except for the primitive genus Acanthobdella, which still have some septa and mesenteries.

The body wall consists of a cuticle, an epidermis and a thick layer of fibrous connective tissue in which are embedded the circular muscles, the diagonal muscles and the powerful longitudinal muscles. There are also dorso-ventral muscles. In leeches the original blood vascular system has been lost and replaced by the modified coelom known as the haemocoelomic system, and the coelomic fluid, called the haemocoelomic fluid, has taken over the role as blood. The haemocoelomic channels run the full length of the body, the two main ones being on either side. Part of the lining epithelium consists of chloragogen cells which are used for the storage of nutrients and in excretion. There are 10 to 17 pairs of metanephridia (excretory organs) in the mid-region of the leech. From these, ducts typically lead to a urinary bladder, which empties to the outside at a nephridiopore.

### Supplementary Text ###
Les vaisseaux sanguins sont les structures du système circulatoire qui transportent le sang dans tout le corps humain. Ces vaisseaux transportent les cellules sanguines, les nutriments et l'oxygène vers les tissus du corps. Ils éliminent également les déchets et le dioxyde de carbone des tissus. Les vaisseaux sanguins sont essentiels à la vie, car tous les tissus du corps dépendent de leur fonctionnalité. Il existe cinq types de vaisseaux sanguins : les artères, qui transportent le sang loin du cœur ; les artérioles ; les capillaires, où les échanges d'eau et de produits chimiques entre le sang et les tissus ont lieu ; les vénules ; et les veines, qui ramènent le sang des capillaires vers le cœur. Le mot « vasculaire », signifiant relatif aux vaisseaux sanguins, est dérivé du latin « vas », qui signifie vaisseau. Certaines structures – comme le cartilage, l'épithélium, ainsi que le cristallin et la cornée de l'œil – ne contiennent pas de vaisseaux sanguins et sont qualifiées d'avasculaires.

### Draft ###

Query breakdown: "pourquoi les sangsues ils ont pas de vrai vaisseaux sanguins" → why don't leeches have true blood vessels. "ils ont quelque chose d'autre" → they have something else instead.

Translation issues: "vrais vaisseaux" = "real/true blood vessels" - loaded term suggesting inferior system. User assumes vessels = normal, whatever leeches have = abnormal.

Information retrieval task. ● High confidence domain: invertebrate physiology, annelid morphology.

### Core anatomical facts:

Leeches ≠ typical annelids. Coelom largely replaced by **botryoidal tissue** → loose connective clusters. 

Original coelomic cavity → reduced to **4 longitudinal channels** (not vessels, but fluid-filled spaces).

Key substitution: **haemocoelomic system** replaces traditional circulatory system.
- Coelomic fluid = **haemocoelomic fluid** 
- Functions as blood
- Flows through modified channels

∴ No "real" vessels because entire system rewired evolutionarily.

### Evolutionary context:

Primitive annelids: separate coelom + vessels
Leeches: coelom → haemocoelomic fluid
Vessels → obsolete/lost

? Why this adaptation?
→ Likely for flexibility, space efficiency
→ Flattened body shape requirements
→ Specialized blood-sucking lifestyle needs

### Verification against physical constraints:

✓ Body flattened dorso-ventrally → space for vessels?
✓ Channel system allows flexibility → movement requirements
✓ Haemocoelomic fluid maintains pressure → circulation needs

NB: User's "autre truc" = haemocoelomic system. Not replacement, but evolutionary innovation.

⟨H≈0.8⟩ Fascinating how form follows function... flattened leech body, space constraints, specialized feeding... coelom becomes fluid-filled channels rather than traditional vessels... efficient, flexible, adapted to their world ⟨/H⟩

Answer structure:
1. Direct response to "vrai vaisseaux" misconception
2. Explain botryoidal tissue replacement
3. Detail haemocoelomic system function
4. Evolutionary context

◐ Missing: specific advantages of haemocoelomic system vs traditional vessels in leeches

### Answer###
Les sangsues ne possèdent pas de vrais vaisseaux sanguins comme les autres animaux car leur système circulatoire a été complètement modifié au cours de leur évolution. Contrairement aux annélides typiques, qui ont un espace fluide appelé coelome, les sangsues ont remplacé la majorité de leur coelome par un tissu conjonctif lâche appelé tissu botryoïdal, composé de clusters de cellules d'origine mésodermique.

Le coelome restant a été réduit à seulement quatre canaux longitudinaux étroits. Ce qui était initialement le système vasculaire sanguin original a ainsi été perdu et remplacé par ce que l'on appelle le système hémocéloïque. Cette modification consiste en un fluide cœlomique spécialisé appelé fluide hémocéloïque qui remplit les canaux longitudinaux et joue le rôle du sang dans l'organisme.

Les sangsues présentent donc ce système évolutif unique où le fluide dans les canaux hémoélics circule à travers le corps à la place des vaisseaux sanguins traditionnels. Cette adaptation anatomique particulière explique pourquoi les sangsues n'ont pas de vaisseaux sanguins conventionnels, mais utilisent plutôt ce système de canaux remplis de fluide hémoélic qui fonctionne comme leur système circulatoire.