Setae sentence example
The setae vary much in form and are often longer and stronger than in the Oligochaetes.
I more comp complicated in the In all the figures the nephridial pores are indicated by dots and the setae by larger forms than in the strokes.
They are disposed in two groups on either side, corresponding in the Polychaeta to the parapodia; the two bundles are commonly reduced among the earthworms to two pairs of setae or even to a single seta.
On the other hand, in certain Polychaeta the bundles of setae are so extensive that they nearly form a complete circle surrounding the body; and in the Oligochaet genus Perichaeta (=Pheretima), and some allies, there is actually a complete circle of setae in each segment broken only by minute gaps, one dorsal, the other ventral.
Setae always present and often very large, much varied in form and very numerous, borne by the dorsal and ventral parapodia (when present).Advertisement
As in the Oligochaeta the peristomial segment is often without setae; but this character is not by any means so constant as in the Oligochaeta.
Typically, the parapodium consists of two processes of the body on each side, each of which bears a bundle of setae; these two divisions of the "limb" are termed.
In some genera the setae are in vertical rows, and in certain Capitellidae these rows so nearly meet that an arrangement occurs reminiscent of the continuous circle of setae in the perichaetous Oligochaeta.
In Syllis there is also a "Heterosyllid" form in which the gonads are limited to a posterior region of the body which is further marked off from the anterior non-sexual segments by the oak-like setae.
The chief modifications of this form are seen in the Mitraria larva of Ammochares with only the preoral band, which is much folded and which has provisional and long setae; the a.trochous larva, where the covering of cilia is uniform and not split into bands; and the polytrochous larva where there are several bands surrounding the body.Advertisement
The setae, which are always absent from the peristomial segment, are also sometimes absent from a greater number of the FIG.
When present they are either arranged in four bundles of from one to ten or even more setae, or are disposed in continuous lines completely encircling each segment of the body.
The varying forms of the setae are illustrated in fig.
The external segments are usually definable by the setae; and if the setae are absent, as in the anterior segments a, Penial seta of Perichaeta ceylonica.
Associated with these glands are frequently to be found bundles or pairs of long and variously modified setae which are termed penial setae,to distinguish them from other setae sometimes but not always associated with rather similarglandswhich are found anteriorly to these, and often in the immediate neighbourhood of the spermathecae; the latter are spoken of as genital setae.Advertisement
The setae are either entirely capillary or there are in addition some sigmoid setae even with bifid free extremities.
There are no setae and apparently only two pairs of nephridia, of which the anterior pair open commonly by a common pore on the third segment after the head, whose segments have not been accurately enumerated.
The absence of setae and the great secondary annulation render the mapping of the segments a subject of some difficulty.
The free edges of the mantle often bear chitinous bristles or setae which project beyond the shell.
In it the hairs are confined to the dorsal middle line and the creeping setae are hooked, of a finer structure than in Chaetosoma, and situated so far forward that the vagina opens amongst them.Advertisement
The body-wall is highly muscular and, except in a few probably specialized cases, possesses chitinous spines, the setae, which are secreted by the ectoderm and are embedded in pits of the skin.
The " postabdomen," marked off by the two postabdominal setae, usually has teeth or spines, and ends in two denticulate or ciliate claws, or it may be rudimentary, as in Polyphemus.
The former, with the feet for the most part concealed by the carapace, is subdivided into two tribes, the Ctenopoda, or " comb-feet," in which the six pairs of similar feet, all branchial and nonprehensile, are furnished with setae arranged like the teeth of a comb, and the Anomopoda, or " variety-feet," in which the front feet differ from the rest by being more or less prehensile, without branchial laminae.
Above this point springs the large median dorsal limb, which terminates in groups of long setae.
Saccocirrus, which also lives in sand, and more closely resembles the Polychaeta, has throughout the greater length of its body on each segment a pair of small uniramous parapodia bearing a bunch of simple setae.Advertisement
No other member of the group is known to have any trace of setae or parapodia at any stage of development.
The male of the cochineal insect is half the size of the female, and, unlike it, is devoid of nutritive apparatus; it has long white wings, and a body of a deep red colour, terminated by two diverging setae.
As in Arthropoda, the hairs or setae on the surface of the body are important organs of sense and are variously modified for special sensory functions.
When feathered or provided with secondary barbs the setae will respond to movements or vibrations in the surrounding water, and have been supposed to have an auditory function.
In the majority of the Decapoda there is a saccular invagination of the integument in the basal segment of the antennular peduncle having on its inner surface " auditory " setae of the type just described.Advertisement
Another modification of sensory setae is supposed to be associated with the sense of smell.
The dorsal surface is smooth; ventrally there are five pairs of parapodia, armed with supporting and hooked setae, by means of which the worm adheres to its host.
The larva is provided with postoral and perianal ciliated bands, and on either side with a bunch of long provisional setae.
In Lacaze-Duthiers's highly-elaborated memoir it should be noticed that he uses the term " cirrhes " rather misleadingly, not for cirrhiform feet, but as the equivalent of setae.
Special olfactory or tactile hairs called setae cover the body surface.Advertisement
Its rear legs have very long setae near its claws.
It is a remarkable and newly-ascertained fact that in regeneration (in Potamilla) the thorax is not replaced by the growth of uninjured thoracic segments; but that the anterior segments of the abdomen take on the same characters, the setae dropping out and being replaced in accordance with the plan of the setae in the thorax of uninjured worms. Among the Oligochaeta the sexually mature worm is distinguished from the immature worm by the clitellum and by the development of genital setae.
The first antennae, according to the family, may assist in walking, swimming, burrowing, climbing, grasping, and besides they carry sensory setae, and sometimes they have suckers on their setae (see Brady and Norman on Cypridina norvegica).
Dark brown setae were frequently observed on PDA and ranged up to 100 mom in length.
They possess (save for certain Archiannelida, most Hirudinea, and other very rare exceptions) setae or chaetae implanted in epidermal pits.Advertisement
The setae are implanted metamerically in accordance with the metamerism of the body, which consists of a prostomium followed by a number of segments.
The setae are organs of locomotion, though their large size and occasionally jagged edges in some of the Polychaeta suggest an aggressive function.
In these forms the bundles of setae are either capilliform or uncinate, and the dorsal setae of the thorax are like the ventral setae of the abdomen.
The genital ducts are limited to one segment (the 8th in Capitella capitata), and there are genital setae on this and the next FIG.
The furca is, as a rule, a powerful motor organ, and has its laminae edged with strong teeth (ungues) or setae or both.Advertisement
On either side is attached a dorsolateral and ventro-lateral appendage, each with a fan-like plumose termination consisting of compound hairs or setae, found elsewhere only among arthropods (q.v.); each of these is moved by muscles running upwards towards the neck and arising immediately under the trochal disk, the inferior ventro-lateral pair also presenting muscles which form a girdle in the hind region of the body.
The peristomium has no setae, and the setae generally are hair-like or uncinate, often forming almost complete rings.