The document summarizes the larval forms of trematodes (flukes), including miracidium, sporocyst, redia, cercaria, and metacercaria larvae. It describes the key characteristics and developmental process of each larval stage, where the miracidium hatches from an egg and penetrates a snail host, transforming into a sporocyst which produces germ balls that develop into redia larvae, then the redia produce cercaria larvae that infect the final host, and the cercaria sheds its tail to become an encysted metacercaria larva.

1. LARVAL FORMS OF
TREMATODES
DR. SHAMPA JAIN
PROFESSOR
DEPARTMENT OF ZOOLOGY & BIOTECHNOLOGY GOVT. M.H. COLLEGE
OF HOME SCIENCE & SCIENCE FOR WOMEN, AUTONOMOUS,
JABALPUR, M.P. INDIA
S

2. MIRACIDIUM
• WHEN THE EGG HATCHES, A MINUTE, ELONGATE OVOID LARVA COVERED WITH
FLATTENED CILIATED EPIDERMAL PLATES ESCAPES.
• BENEATH THE EPIDERMAL PLATES ARE FOCUSED WELL-DEVELOPED CIRCULAR
AND LONGITUDINAL MUSCLES
• AT THE ANTERIOR TIP OF THE MIRACIDIUM IS A MOBILE APICAL PAPILLA
• A MULTINUCLEATED APICAL GLAND, LOCATED IN THE PARENCHYMA, EMPTIES
TO THE OUTSIDE NEAR THE TEREBRATORIUM
• THE SECRETION OF THIS GLAND AIDS IN DISSOLVING THE HOST’S TISSUE
DURING THE MIRACIDIUM’S PENETRATION PROCESS
• THE SENSORY ORGANS OF THE MIRACIDIUM ALSO MAY INCLUDE TWO,
SOMETIMES THREE, EYESPOTS AND LATERAL PAPILLAE, ONE ON EACH SIDE OF
THE BODY BETWEEN THE FIRST AND SECOND TIERS OF CILIATED PLATES.

3. MIRACIDIUM
• . THE BRAIN OF THE MIRACIDIUM IS A LARGE CEPHALIC GANGLION LYING IN THE
PARENCHYMA BEHIND THE APICAL REGION
• THE BODY FLUIDS CONTAINING WASTES ARE COLLECTED BY TWO OR THREE
PAIRS OF FLAME CELLS AND ARE DEPOSITED TO THE EXTERIOR THROUGH TWO
LATERALLY SITUATED EXCRETORY PORES
• DURING THE DIFFERENTIATION OF THE MIRACIDIUM WITHIN THE EGG SHELL,
CERTAIN GERMINAL CELLS BECOME TRAPPED IN THE PARENCHYMA.
• THESE DEVELOP INTO GERM BALLS BY INCREASING IN SIZE AND NUMBER AND
BECOMING ENVELOPED. THESE GERM BALLS EVENTUALLY DIFFERENTIATE INTO
THE NEXT LARVAL GENERATION. THEY ARE USUALLY LOCATED IN THE
POSTERIOR PORTION OF THE BODY
• THE NAKED MIRACIDIUM DEVELOPS INTO A SPOROCYST

4. MIRACIDIUM

5. SPOROCYST
• IT LOOKS LIKE AN ELONGATED SAC, ABOUT 0.7 MM LONG.
• GLANDS, BRAIN , EYE SPOTS AND APICAL PAPILLA OF MIRACIDIUM DEGENERATE
AND DISAPPEAR IN SPOROCYST.
• PROTONEPHRIDIUM OF EACH SIDE DIVIDES INTO TWO FLAME CELLS WHICH OPEN
OUTSIDE BY A COMMON EXCRETORY PORE.
• IN ADDITION, THE SPOROCYST CONTAINS GERM BALLS.SPOROCYST MOVES
ABOUT IN THE TISSUE OF HOST, ABSORBING NUTRITION FROM IT.
• ITS GERM BALLS DEVELOP INTO THE NEXT LARVAL GENERATION, THE REDIAE.
• EACH SPOROCYST PRODUCES 5 TO 8 REDIAE.

6. SPOROCYST

7. REDIA LARVA
• REDIAE EMERGES FROM THE SPOROCYST BY RUPTURE OF ITS BODY WALL. EACH
REDIA IS AN ELONGATED AND CYLINDRICAL CREATURE ABOUT 1.3 MM TO 1.6
MM LONG.
• REDIA MOVES THROUGH THE HOST’S TISSUES ON WHICH IT ALSO FEEDS.
• DURING SUMMER MONTHS, WHEN SUFFICIENT NOURISHMENT IS AVAILABLE, THE
GERM BALLS OF REDIAE GICE RISE TO A SECOND GENERATION OF REDIAE,
MORPHOLOGICALLY IDENTICAL TO THE PARENTS.
• DURING WINTER, GERM BALLS OF REDIAE OF SECOND GENERATION DEVELOP
INTO THE LARVAE OF THE NEXT STAGE, KNOWN AS CERCARIA LARVAE.

9. CERCARIA LARVAE
• EACH REDIA PRODUCES 14 TO 20 CERCACARIA LARVAE. THEY LEAVE THE BODY
OF REDIA THROUGH ITS BIRTH PORE AND ENTERS THE SNAIL’S DIGESTIVE
GLAND. MORPHOLOGICALLY, CERCARIA BEARS A CLOSE RESEMBLANCE WITH
THE THE ADULT FLUKE. IT HAS AN OVAL BODY 0.25 MM TO 0.35 MM LONG,
WITH A LONG SIMPLE TAIL FOR SWIMMING.
• BELOW BODY WALL LIE NUMEROUS CYSTOGENOUS GLAND CELLS,WHICH
SECRETE CYST FOR THE NEXT LARVA( METACERCARIA)

11. METACERCARIA LARVA
• AS MANY AS A THOUSAND METACERCARIA MAY BE FOUND ATTACHED TO A
SINGLE GRASS BLADE.
• THEY HAVE A ROUNDED FORM WITH A DIAMETER OF ABOUT 0.2 MM.
• GERM CELLS OR THE GENITALS RUDIMENTS ARE PRESENT AS SUCH.
• CYST PROVIDES PROTECTION AGAINST SHORT PERIODS OF DESICCATION.

13. REFERENCES
•
MODERN TEXT BOOK OF ZOOLOGY: INVERTEBRATES ( RL KOTPAL)
• HTTP://ZOOLOGY.UOK.EDU.IN/FILES/CAE2D08F-4F62-428E-B6EA-
CF46CDCCBF42/CUSTOM/2.GENERAL%20LIFE%20CYCLE%20PATTERNS%20AND
%20LARVAL%20FORMS%20IN%20TREMATODE...%20(AUTOSAVED).PDF