Table of Contents
Last Updated: October 22, 2025
Estimated reading time: ~7 minutes
Branching off from the Monopisthocotylea previously discussed, the Polyopisthocotylea represent another major suborder of monogenetic trematodes.
These fascinating parasites primarily utilize complex clamps, rather than large hooks, for attachment to their fish hosts, often targeting the gills. This exploration focuses on several key polyopisthocotylean families and genera described in Dr. R. K. Sharma’s 1980 thesis, highlighting their unique morphology and presence in Indian waters.
- Polyopisthocotylean trematodes attach using multiple clamps, often arranged symmetrically or asymmetrically on the haptor.
- Families like Microcotylidae, Gastrocotylidae, and Diplozoidae exhibit diverse clamp structures and reproductive strategies.
- The genus *Microcotyle* typically has numerous clamps arranged along two margins of the haptor.
- Genera within Gastrocotylidae, such as *Gastrocotyle* and *Pricea*, often show asymmetrical haptors or specialized clamp features.
- *Diplozoon* species are unique, involving the permanent fusion of two individuals.
Family Microcotylidae: The Genus *Microcotyle*
This family is characterized by a symmetrical or asymmetrical haptor bearing numerous clamps, typically lacking a terminal lappet with anchors.
“Family – Microcotylidae Taschenberg, 1879 / Subfamily – Microcotylinae Monticelli, 1892 / Genus Microcotyle van Beneden et Hesse, 1863…” (Sharma, 1980, p. iii, vi)
Species of *Microcotyle* generally possess an elongated body with a posterior haptor bearing many clamps arranged along its lateral margins. The clamps themselves have a characteristic skeletal structure (“microcotylid type”) involving median and lateral sclerites. The anterior end usually has a pair of buccal suckers near the mouth.
The reproductive system features numerous post-ovarian testes and often a genital atrium armed with spines or hooks near the anterior end. Sharma (1980) describes new species *M. microlepidotusi*, *M. simhai*, and *M. stunkardi*. [span_0](start_span)Key distinguishing features include the number of clamps (e.g., 46-65 on one side, 53-87 on the other in *M. microlepidotusi, the number of testes (15-21 in *M. microlepidotusi*, 39 in *M. simhai*, 19-27 in *M. stunkardi, the specific arrangement and types of spines in the genital atrium, and the presence or absence of adhesive glands near the anterior end (*M. microlepidotusi*, *M. simhai*, *M. stunkardi* possess them[span_5](end_span)).
Student Note: When identifying Microcotylidae, pay attention to the symmetry of the haptor, the total number and range of clamps, the number and distribution of testes, and the precise structure and armature (spines/hooks) of the genital atrium.
Family Axinidae: The Genus *Megamicrocotyle*
Axinids often exhibit highly asymmetrical haptors, with clamps concentrated along one elongated edge.
“Family – Axinidae Unnithan, 1957 / Subfamily – Lintaxininae Price, 1962 / Genus – Megamicrocotyle Tripathi, 1956…” (Sharma, 1980, p. vi)
The genus Megamicrocotyle, as described by Tripathi (1956) and represented by the new species M. manteri in Sharma’s thesis, showcases this asymmetry. The body is long and slender, and the opisthohaptor is elongated with two unequal rows of clamps.One side bears numerous small, sessile clamps (40-63 in M. manteri), while the other side has fewer, larger, pedunculated clamps (27-31 in M. manteri).
clamp structure itself is detailed, involving median and lateral sclerites with specific accessory piecesThe reproductive system features numerous testes (30-49 in M. manteri) located posteriorly, a tubular, recurved ovary, and a genital atrium armed with hooks and distinct plates The presence of anterior adhesive glands is also noted. This distinct haptor asymmetry is a key characteristic of many Axinidae.
Exam Tip: Asymmetry of the haptor is a major clue for identifying families like Axinidae. Note the difference between the small, sessile clamps on one side and the larger, pedunculated clamps on the other in genera like *Megamicrocotyle*.
Family Gastrocotylidae: Diversity in *Gastrocotyle*, *Pricea*, and *Pseudothoracocotyla*
This family includes genera with varied haptor morphology, often asymmetrical and sometimes featuring specialized clamp structures or terminal lappets with anchors.
“Family Gastrocotylidae Price, 1943 / Subfamily Gastrocotylinae Sproston, 1946 / Genus Gastrocotyle van Beneden et Hesse, 1863…” (Sharma, 1980, p. vi)
Sharma (1980) describes new species within several Gastrocotylidae genera. Gastrocotyle* (*G. sprostoni*, *G. mandapami*) typically has a unilateral haptoral frill with clamps (“gastrocotylid type”) and a terminal lappet bearing anchors. features include the number of clamps (21-34 in *G. sprostoni*, 29 in *G. mandapami, the number of anchor pairs on the lappet (2 pairs in *G. sprostoni*, 3 pairs in *G. mandapami, the presence of haptoral glands (3 pairs in both, and the number of hooks in the genital atrium (12 in *G. sprostoni*, 11 in *G. mandapami
The genus *Pricea* (*P. thapari*, *P. fotedari*) also has clamps in two rows, often pedunculated, and a distinct clamp structure involving multiple lateral pieces and a three-pronged central piece Key features include the clamp count (90-100 in *P. thapari*, 128-164 in *P. fotedari, testes number (16-18 in *P. thapari*, 38-44 in *P. fotedari, and armature of the genital atrium and vagina[span_21](end_span).
Pseudothoracocotyla* (*P. kanyakumarii*) features an elliptical haptor extending far forward ventrally, numerous clamps with rib-like sclerites and median sclerites bearing thorns, and a terminal lappet with 3 anchor pairsTestes are numerous (104-140, and the genital pore is sclerotized but unarmed.
Student Note: Gastrocotylidae is a diverse family. Focus on how the haptor is organized (unilateral frill vs. symmetrical rows), the specific structure of the clamps (presence of ribs, thorns, additional sclerites), the number/arrangement of anchors on the terminal lappet (if present), and the details of reproductive organs (testes number, genital/vaginal armature). Table 1: Comparison of New Gastrocotylidae Species Described
| Genus/Species | Host (Example) | Clamp Count | Haptor Type | Anchor Pairs (Lappet) | Testes Count | Genital Atrium Armature |
|---|---|---|---|---|---|---|
| Gastrocotyle sprostoni | Pseudosciaena diacanthus | 21-34 | Unilateral Frill | 2 | ~1 (elongate) | 12 Hooks |
| Gastrocotyle mandapami | Ilisha feligera | 29 | Unilateral Frill | 3 | ~1 (elongate) | 11 Hooks |
| Pricea thapari | Cybium guttatum | 90-100 | Bilateral Rows | 1 | 16-18 | 12 Hooks |
| Pricea fotedari | Scomber microlepidotus | 128-164 | Bilateral Rows | 1 | 38-44 | 14 Hooks |
| Pseudothoracocotyla kanyakumarii | Scomber microlepidotus | 37-47 | Bilateral Rows (ventral) | 3 | 104-140 | Unarmed (sclerotized pore) |
Families Discocotylidae and Diplozoidae: Unique Adaptations
These families also belong to Polyopisthocotylea but show distinct features, including specialized clamps or life cycles.
“Family Discocotylidae Price, 1936… Family Diplozoidae Tripathi, 1959 / Genus Diplozoon Nordman, 1832…” (Sharma, 1980, p. iii)
Within the Discocotylidae, Sharma describes new species in genera like *Allodiscocotyla* and *Gemmaecaputia*. Allodiscocotyla mackiewiczi* has an asymmetrical triangular haptor with four pairs of clamps; those on one side are embedded in muscular cushions, while those on the other are not
It also possesses a terminal lappet with three pairs of anchors Gemmaecaputia indicum* features four pairs of pedunculated clamps and distinct preoral gland cells. The family Diplozoidae is particularly notable for the genus *Diplozoon*. Species like *D. lucknowensis* and *D. gomatii* exhibit a unique life history where two larval individuals permanently fuse in the shape of an ‘X’ to form the mature adult. Each fused individual develops its own reproductive systems. The haptor of each individual typically bears four pairs of specialized clamps This permanent fusion is a hallmark of the Diplozoidae.
Exam Tip: Remember the unique characteristic of *Diplozoon* – the permanent fusion of two individuals into one functional adult unit. Discocotylids like *Allodiscocotyla* can show asymmetry in how clamps are associated with muscular pads.
Key Takeaways
- Polyopisthocotylean fish parasites are characterized by haptors bearing multiple clamps, contrasting with the anchor-based haptors of Monopisthocotylea.
- Families like Microcotylidae (*Microcotyle*) often have numerous clamps in symmetrical or asymmetrical rows and armed genital atria.
- Axinidae (*Megamicrocotyle*) frequently display highly asymmetrical haptors with morphologically distinct clamps on opposite sides.
- Gastrocotylidae (*Gastrocotyle*, *Pricea*, *Pseudothoracocotyla*) show diverse haptor arrangements (unilateral frills or bilateral rows) and clamp structures, sometimes with terminal anchors.
- Diplozoidae (*Diplozoon*) are unique due to the permanent fusion of two individuals during maturation.
- Detailed study of clamp structure, testes number, ovary shape, and reproductive armature is essential for classifying these diverse parasites.
Multiple Choice Questions (MCQs)
- Which family often exhibits a highly asymmetrical haptor with small sessile clamps on one side and larger pedunculated clamps on the other?
- (a) Microcotylidae
- (b) Diplozoidae
- (c) Axinidae
- (d) Discocotylidae
- The genus *Diplozoon* is unique among Monogenea because:
- (a) It lacks a haptor
- (b) It infects mammals
- (c) Two individuals permanently fuse to form the adult
- (d) It has only one pair of clamps
- What type of armature is commonly found in the genital atrium of *Microcotyle* species?
- (a) A single large hook(b) Numerous small spines or hooks(c) A sclerotized ring(d) Usually unarmed
Frequently Asked Questions (FAQs)
- What is a “clamp skeleton”? It refers to the complex arrangement of hardened sclerites that form the structural framework of a polyopisthocotylean clamp, enabling it to grip host tissue.
- Do all Polyopisthocotylea lack large anchors? While clamps are their primary attachment organs, some families/genera retain small anchors, often on a posterior terminal lappet (e.g., Gastrocotylidae).
- What does “pedunculated” vs. “sessile” mean for clamps? Pedunculated clamps are attached to the haptor by stalks (peduncles), while sessile clamps are attached directly without a stalk.
- What is a genital atrium? It’s a common chamber near the anterior end into which the male (cirrus) and female (uterus) reproductive ducts open before leading to the external genital pore.
- Are Polyopisthocotyleans generally larger than Monopisthocotyleans? There’s considerable size variation in both groups, but many polyopisthocotyleans with numerous clamps can reach larger body sizes than typical dactylogyrids.
Lab / Practical Note
Observing the detailed structure of polyopisthocotylean clamps often requires careful preparation and high magnification. Dissecting individual clamps from the haptor and mounting them separately can allow for better orientation and visualization of the different sclerites. Using stains that highlight sclerotized structures or employing phase contrast/DIC microscopy is highly beneficial for resolving the intricate clamp components.
External Resources
- NCBI PMC: Phylogeny of Polyopisthocotylea
- ScienceDirect: Fish Diseases and Disorders, Volume 1: Protozoan and Metazoan Infections (Chapter on Monogenea)
Author: Raj Kishore Sharma, M.Sc., Department of Zoology, University of Lucknow (as of 1980).
Reviewed and edited by the Professor of Zoology editorial team. Except for direct thesis quotes, all content is original work prepared for educational purposes.
Note: This article summarizes research from 1980. Parasite classifications may have been revised; always consult current taxonomic resources for definitive identification.
Sources & Citation
Primary Source: Sharma, R. K. (1980). Monogenetic Trematodes of Fishes (Doctoral Thesis). Department of Zoology, University of Lucknow, Lucknow. Excerpt pages used: Cover, Contents (i-vii), 141-142, 145-161, 165-181, 183-186, 188-190, 192-193, 195, 197-200, 202, 205-209, 211-214.
Note: Full verification of every species name against current taxonomic databases was not performed as part of this summarization.
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