1 morphological characteristics
1.1 digestion
1.2 proboscis
1.3 size
1.4 skin
1.5 nervous system
1.6 reproduction
1.7 other features
morphological characteristics
some key features of acanthocephalan morphology
there several morphological characteristics distinguish acanthocephalans other phyla of parasitic worms.
digestion
acanthocephalans lack mouth or alimentary canal. feature share cestoda (tapeworms), although 2 groups not closely related. adult stages live in intestines of host , uptake nutrients have been digested host, directly, through body surface.
proboscis
scanning electron microscopy of proboscis of cathayacanthus spinitruncatus
the notable feature of acanthocephala presence of anterior, protrudible proboscis covered spiny hooks (hence common name: thorny headed worm). proboscis bears rings of recurved hooks arranged in horizontal rows, , means of these hooks animal attaches tissues of host. hooks may of 2 or 3 shapes, usually, longer, more slender hooks arranged along length of proboscis, several rows of more sturdy, shorter nasal hooks around base of proboscis. proboscis used pierce gut wall of final host, , hold parasite fast while completes life cycle.
like body, proboscis hollow, , cavity separated body cavity septum or proboscis sheath. traversing cavity of proboscis muscle-strands inserted tip of proboscis @ 1 end , septum @ other. contraction causes proboscis invaginated cavity. whole proboscis apparatus can be, @ least partially, withdrawn body cavity, , effected 2 retractor muscles run posterior aspect of septum body wall.
some of acanthocephalans (perforating acanthocephalans) can insert proboscis in intestine of host , open way abdominal cavity.
size
the size of these animals varies greatly, measured few millimetres in length gigantorhynchus gigas, measures 10 65 centimetres (3.9 25.6 in).
skin
the body surface of acanthocephala peculiar. externally, skin has thin tegument covering epidermis, consists of syncytium no cell walls. syncytium traversed series of branching tubules containing fluid , controlled few wandering, amoeboid nuclei. inside syncytium irregular layer of circular muscle fibres, , within again rather scattered longitudinal fibres; there no endothelium. in micro-structure muscular fibres resemble of nematodes.
except absence of longitudinal fibres skin of proboscis resembles of body, fluid-containing tubules of proboscis shut off of body. canals of proboscis open circular vessel runs round base. circular canal 2 sac-like projections called lemnisci run cavity of body, alongside proboscis cavity. each consists of prolongation of syncytial material of proboscis skin, penetrated canals , sheathed muscular coat. seem act reservoirs fluid used keep proboscis erect can withdraw when retracted, , fluid can driven out when wished expand proboscis.
nervous system
the central ganglion of nervous system lies behind proboscis sheath or septum. innervates proboscis , projects 2 stout trunks posteriorly supply body. each of these trunks surrounded muscles, , nerve-muscle complex called retinaculum. in male @ least there genital ganglion. scattered papillae may possibly sense-organs.
reproduction
the acanthocephala dioecious (an individual organism either male or female). there structure called genital ligament runs posterior end of proboscis sheath posterior end of body. in male, 2 testes lie on either side of this. each opens in vas deferens bears 3 diverticula or vesiculae seminales. male possesses 3 pairs of cement glands, found behind testes, pour secretions through duct vasa deferentia. these unite , end in penis opens posteriorly.
in female, ovaries found, testes, rounded bodies along ligament. ovaries, masses of ova dehisce body cavity, floating in fluids fertilization male s sperm. after fertilization, each egg contains developing embryo. (these embryos hatch first stage larva.) fertilized eggs brought uterus actions of uterine bell, funnel opening continuous uterus. @ junction of bell , uterus there second, smaller opening situated dorsally. bell swallows matured eggs , passes them on uterus. (immature embryos passed body cavity through dorsal opening.) uterus, mature eggs leave female s body via oviduct, pass host s alimentary canal , expelled host s body within feces.
other features
a curious feature shared both larva , adult large size of many of cells, e.g. nerve cells , cells forming uterine bell. polyploidy common, 343n having been recorded in species. acanthocephalans lack excretory system, although species have been shown possess flame cells (protonephridia).
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