The Numerate are look like ribbon worms
The Numerate are look like ribbon worms. Some species of phylum Nemertea are live in mud, There are 900 species of nemertea. nemertea are found in freshwater and terrestrial habitats as well. Most nemertea are carnivores, feed on worms, clams, they have commensalism relationships with some mollusks. Some species have fish like characters of clams and crumbs. Nemertea are not predators. They are few millimeters and several kinds are centimeter in length. They have different coloures such as yellow, orange, red and green.
Reference from: biology for majors
Fig: 1.1
Characteristics
Characteristics of Phylum Nemertea
? They have Bilateral symmetry and have highly contractile body
? Nemertea have three germ layers
? Epidermis is present with cilia and gland cells
? Body spaces are also present with a parenchyma, it may be gelatinous
? An eversible proboscis, is also present in it which lies free in a cavity) on upper side of alimentary canal
? It has Complete digestive system (mouth and anus is present
? Outer body layer is circular and inner layer is longitudinal with diagonal fibers
? Blood-vascular system have two or three longitudinal trunks
? Nervous system usually have four-lobed brain linked to paired longitudinal nerve trunks
? Excretory system also have two coiled canals, which are connected with flame cells
? Sex cells are separate with simple gonads; asexual and sexual reproduction present asexual reproduction by fragmentation .
? They have no proper respiratory system
Fig 1.2
Reproduction and life cycle
In this phylum the reproduction can occur by fragmentation some parts f body breaks and form new individual but some remain attach and grow like the tail. Sexes are separate. The species which are living in water are hermaphroditic.
The nemertea have gonads. Some are arise from oval or from sperm .One gonad is built when the sperm and oval ready. The eggs are produce inside the body. Some lay eggs in tube and some protect their egg from water from injury and some lays their egg in female body.
The zygote can divide by spiral cleavage. Some embryos are develop when they form juveniles or to form planuliform larvae. The larva is along the axis. The planuliform larva have short life cycle before to lecithotrophic when become juvenile. These are swimming for eating the large molecule we can see in microscope. Their some species of heteronemertean and palaeonemertean belong to family hubrechtideae form palladium larva. It can capture the unicellular algae having the ear cap to capture the algae. It has a mouth near the ear flap but it does not have anus. Small ducts are formed to form to developing ducts when these ducts completely the juvenile bursts. this life cycle is very important because there is no HOX GENES.
The life span of this phylum is 18 months.
Fig: 1.3
Phylogenetic considerations
The phylogenetic analysis based on studying the different genes of this phylum.
Differentiating elucidations of morphology as laid out in the prior dialog fundamentally prompt contrasting temporary homology proclamations and represent the premise of clashing theories of nemerteans and, by augmentation, metazoan phylogeny. In light of the relative scarcity of perceived useful morphological characters for gathering metazoan phylogeny, elective elucidations of even 1 or 2 characters can prompt elective arrangement of taxa in a phylogeny. The impact of clashing from the earlier character understandings on the arrangement of nemerteans can be outlined by thinking about the accompanying model. Nielsen’s (2001) examination of an informational index containing 64 morphological characters places nemerteans as the sister taxon to the Platyhelminthes, framing the basal subclade of the Spiralia This speculation is bolstered by a solitary unambiguous synapomorphy, lessened hyposphere of polyclad flatworm hatchlings and pilidium hatchlings of heteronemerteans. From the earlier elucidation of this character as a homologue expect that the ground-example of the nemerteans and flatworms displays aberrant advancement and besides, that the hatchlings of polyclad flatworms and heteronemerteans are adjusted trochophores (Nielsen, 2001). In spite of the fact that platyhelminth phylogeny is disrupted, none of the distributed elective phylogenies (e.g.,Ax, 1995; Haszprunar, 1996; Ruiz-Trillo et al., 1999; Peterson and Eernisse, 2001) bolsters circuitous improvement as the plesiomorphic condition. A starter phylogenetic investigation of nemerteans recommend that the pilidium hatchling is an inferred highlight of a Heteronemertea + Hubrechtella clade (Norenburg, 1993; J. L. Norenburg, individual correspondence) as opposed to a crude component of the phylum. Besides, information supporting homology of the trochophore prototroch and the ciliary groups of the pilidium hatchlings are uncertain (Henry and Martindale, 1998), however it is essential to take note of that Maslakova and Norenburg (2001) as of late gave primer confirmation from an “immediate creating” animal types recommending that a trochophore might be plesiomorphic for nemerteans (see page 694). Be that as it may, regardless of whether Nielsen’s speculation is acknowledged, the consideration of only two potential homologues, schizocoelous coelom and gliointerstitial cell framework in his unique network results in profoundly extraordinary situation of the nemerteans, in particular as the sister taxon to the coelomate spiralians (Fig. 3B). The evaluated phylogeny recommends that the larval similitude are homoplastic. Other cladistic investigations of morphology that included either of these characters are consistent with the outcome exhibited.
Fig 1.4
