Learning Bio-Etymology- Part 7 – NEMERTEA
‘Making Biology students interested in Etymologies’ !!!
The episode of ‘Bio-etymology’ is devoted to analyzing the hidden meanings derived from the Names of various Animal Phyla and Classes, along with the terms specifically used to describe their respective diagnostics, important examples (Genus or species) etc.
At any level, may it be animals in general or Man in particular, there is some structured or indicative or behavioural system of communication. It is simply referred to as a kind of ‘Language’. In a broader sense, ‘Language’ is the method of communication that involves the use of various languages (in various countries) spoken by man. Articulation of words in a definite sequence is the basic of formulating a Language and knowledge of words forming it and their ‘sense’ is of utmost importance. Accumulation of a treasure of words constitutes what is called ‘Vocabulary’ defined variously as follows:
1. The words of a language.
2. The body of words used in a particular language.
3. All the words that exist in a particular language or subject.
4. A list or collection of the words or phrases of a language, technical field etc
5. A listing either selective or exhaustive, containing the words and phrases of a language, with meaning or translations into another language.
Over a period of time in past centuries, Science is general and Biology in particular has accumulated a vast array of words to communicate fact(s) or phenomena through deriving their meanings.
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PHYLUM : NEMERTEA
[= Nemertini, Nemertinea or Rhynchocoela]
The animals commonly known as ‘ribbon worms’, ‘bootlace worms’ or ‘proboscis worms’ are among about 1,149 species belonging to about 250 Genera, included under Phylum- Nemertea, with a well-defined ‘bilateral symmetry’ and ‘tissue organ grade of body organization’.
Explanation: In Greek mythology sea-nymph Nemertes was one of the daughters of Nereus (> Nereis) and Doris. The name Nereis is also akin to the name of an Annelidan Genus Nereis having sharp retractable or protractible jaws; showing similarity with the protractible ‘Proboscis’ of ‘Nemerteans’.
Unique to the Phylum, the ‘Proboscis’ is an elongate, eversible, blind tube, surrounded by rhynchocoel (a fluid-filled hydrostatic cavity) and additional muscle layers, including proboscis retractor muscle at the posterior wall of the rhynchocoel. It is either connected directly to the foregut or opens through a proboscis pore. In many species, the proboscis is provided with nail-shaped, piercing barbs or stylets, typically used to trap prey. The stylet may also be used for burrowing; in land-dwelling species it may be used for rapid movement.
The first hitherto known report of a Nemertean is by William Borlase (1758), who described a ‘Sea Long Worm’. The species was named by Gunnerus (1770) as Ascaris longissima while Sowerby (1806) was the first to use its present name, Lineus longissimus. For quite long, in historical accounts Nemerteans were included under Genus Planaria (Phylum – Platyhelminthes), until 1817 when the French naturalist Georges Cuvier recognized their differences and unaware of the previous names applied to the species, placed Lineus longissimus in Genus Nemertes, from which the name of the Phylum takes its origin. In 1859, German Anatomist Karl Gegenbaur (1826 – 1903) coined the term ‘Platyhelminthes’ and included 4 Classes viz., Turbellaria, Trematoda, Cestoda and Nimertea but Charles Sedgwick Minot (1876) excluded Nemerteans from Platyhelminthes.
Free living (marine, freshwater or terrestrial) or parasitic (on crustaceans, mollusks and sea-squirts), Carnivorous, Triploblastic, Vermiform, Bilaterally symmetrical. Body (5.0 mm – 55.0 m) highly contractile, cylindrical anteriorly and dorso-ventrally flattened posteriorly. Acoelomate (rhynchocoel often considered a true coelom). Digestive system complete & tubular. Blood vascular system well-formed of longitudinal trunks. Respiration by diffusion. Brain 4-lobed, connected to paired longitudinal nerves. A sensory and regulatory organ called ‘cerebral organ’ closely associated with brain. Eyes 2 – 250, pigment-cup type. Excretory system made of two coiled canals and branched flame-cells. Dioecious (sexes separate) or Monoecious. Gonads numerous. Fertilization external. Development direct or indirect with a ciliated helmet-shaped Pilidium larva (Gk. pilidion = a small felt night cap) or *Desor’s larva (named after Swiss scientist E. Desor, 1811 – 1882; a pelagic or benthic larva that develops without Pilidium stage), Asexual reproduction by fragmentation (= regeneration).
Often uniformly coloured, but various forms exhibit stripes, bands, speckles or geometric shapes.
There is no coelom, as embryonic mesoderm remains as a solid mass (layer) and the space between the endoderm (gut wall) and the ectoderm (body wall) remains filled with mesodermal tissue called mesenchyme [Gk. mesos = middle + enkhyma = infusion] i.e., a layer infused in the middle; often called ‘packing tissue’ or parenchyma [Gk. para = beside + enkhyma = infusion] i.e., something poured in beside].
The ‘ribbon worms’ are classified into 2 Classes on the basis of the presence or absence of a stylet (or stylets) on the proboscis, the position of brain relative to mouth and the position of lateral nerves relative to the muscle layers.
Order – Palaeonemertea: [Gk. palaios = ancient + nemertea] i.e., primitive worms with brain not divided into lobes. Muscles arranged in two or three layers; if three, the innermost is of circular fibres. Dermis gelatinous.
Order – Heteronimertea: [Gk. heteros = different (other party or another)] i.e., the Nemerteans which are ‘different’ in having a proboscis being divided into many ‘proboscides’ which appear as a mass of worm-like structures when everted.
Body muscles arranged in three layers of longitudinal fibres. Dermis fibrous.
2. Class – Enopla [Gk. enoplos = armed] i.e., the Nemertean worms with stylets (one to many) on proboscis. Mouth located underneath but ahead of the brain. Nerve cords running inside body-wall muscles.
Order – Hoplonemertea [Gk. hoplos = tool, weapon; a wooden shield carried by some warriors in ancient Greece + nemertea] i.e., worms armed with stylet(s) [ = Enopla and Hoplonemertea are synonyms]. Most are benthic commensals or parasites.
The Nimertean worm (Geonimertes sp.), crawling gently on the wet floor close to home garden. Cilia on the ventral surface move the animal in a gliding fashion. The animal secretes copious amount of mucus in which it glides, leaving a trail of mucus behind. The worm is negatively photoklinotactic and thus the swaying lateral movements of head are peculiar to watch. Watch the pointed anterior end exhibiting shortening and widening due to muscular action. Contactions of circular muscles are making the worm thinner and more elongated whereas contractions of longitudinal muscles are making the animal shorter and wider. When crawling across a solid surface (as shown in the video) worm is moving in a manner similar to earthworm by peristaltic waves of muscle contraction alternately shortening and elongating the body.
[Video by SK Gupta using Sony Cyber-Shot DSC-H10]
The Nimertean worm (Geonimertes sp.), stuck to a vertical surface (pillar of gate), showing gentle crawling movements. Watch the anterior pointed and posterior club-shaped end.
Order – Bdellonemertea [Gk. bdella = leech + nemertea] i.e., the body of these Nemerteans is ‘leech-like’, with a posterior sucker, used for locomotion. Stylets on proboscis absent.
A FIELD NOTE ON Geonemertes (?)
[from the ‘back-yard’ (garden) of SK Gupta, the content contributor of this website ‘fishboppedia.com’]
The distribution of ‘terrestrial Nemerteans’ is of particular interest in that they primarily occupy oceanic islands. Geonimertes palaensis, the most widespread species, is recorded from Islands in the Pacific and Indian Oceans and the Caribbean, as well as Florida, USA and Japan. In 1943, a land Nemertine (Geonemertes dengyi) was recorded from Western Australia. In 1969, all terrestrial Nemertines were assigned to one Genus – Geonemertes.
There appear to be three groups of species identified from Indopacific, Australia and New Zealand and three separate species from Atlantic Islands. In the Indopacific, G. palaensis was the first land nemeretine ever found on the Pelew Islands (Republic of Palau in Pacific Ocean, consisting of more than 250 islands, southeast of Philippines, in Oceania) and has since been recorded from Kei, Celebes, Samoa, the Caroline Islands, Sri Lanka, Samurai, New Guinea, Mahe in the Seychelles, Mauritius and the Philippines.
Their mode of dispersal on land had been quite interesting. The most probable mode of dispersal has been found to be by human activities through transport of exotic plants used in gardening and nurseries.
The specimens noticed by the author (SK Gupta) are probably the lineage of the same Geonemertes (?) which have invaded the Indian soil through human activities as narrated in the following publications:
● The Distribution and Evolution of Terrestrial Nemertines’ by Janet Moore, Amer. Zool., 25:15-21 (1985)
● ‘First record of the terrestrial Nemertean Geonemertes palaensis Semper, 1893 (Hoplonemertea: Prosorhochmidae) for Cuba’ by Jans Morffel et al., BioInvasions Records, 9(2):399-407’(2020)
Learning process is an on-going process:
Keep on venturing more into the fantastic world of Etymology and feel NEMERTEAN– friendly!!!