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A picture of a sea spider would really go a long way to making the text of this article much clearer, but the only picture of a sea spider I've ever seen (which made this clear to me) is a drawing in Fingerman's Animal Diversity textbook, and the drawing is copyright-encumbered. If you've got access to an image of a sea spider that isn't so encumbered, please put it up here. --arkuat(talk) 06:28, 16 August 2005 (UTC)[reply]
Sea spiders do seem to be as primitive as they look. Unlike spider fangs, both chelifores and their nerves sprout from the cells that form the front most part of sea spiders' brains, the team reports 19 October in Nature. This supports the theory that sea spiders belong to their own ancient lineage that predates the origin of all other modern arthropods. It also suggests that all of today's other arthropods inherited their heads from a subsequent ancestor that gave up such up-front appendages.
Nature articles at [2] and [3]; editorial summary at [4]. kwami 07:57, 20 October 2005 (UTC)[reply]
Indeed, and the page on Chelicerata does not list them as a member (citing those reasons), so this page should probably be edited to reflect that (it currently lists them as a member) —Preceding unsigned comment added by 210.215.140.180 (talk) 04:27, 27 January 2009 (UTC)[reply]
No coelom?
I read somewhere that the sea spiders don't have any coelom. Is this correct?
"Pycnogonids possessed a coelom at one point, but it was eventually lost through evolution". IronChris | (talk) 20:50, 22 August 2006 (UTC)[reply]
I think what was meant was a drawing, showing more details of the head and nervous system. Personally I would very much like if some pictures also showed a species with more then 4 pair of legs, since there are species there with 5 of 6 pairs, and a discussion whether 4 pairs is a reduction of the original plan or 5 and 6 is a novelty that arose later. --Codiv (talk) 11:33, 9 July 2022 (UTC)[reply]
Do they or don't they?
The article contradicts itself: "Sea spiders do not swim but rather walk along the bottom with their stilt-like legs." Then in the next paragraph:
"They crawl slowly along (although some do swim), feeding." I'm no expert, but both cannot be true. RandyKaelber 20:51, 22 September 2006 (UTC)[reply]
According to Deep Sea News[1]:
Also interesting, and also noticed by Kevin, is an error occurs in the video. The announcer discusses giant sea spiders, while what is shown is a swimming crinoid. Accordingly, I'm going to take the link to video down.
This link doesn't work anymore, perhaps somebody can add a working link? Also it would be nice to have some more info on the within/without the Chelicerata debate. Looking at their rather different bodyplan, the head looking more like euanthropods, they probably form a separate lineage, one can easily imagine them descending from lobopodians like Paucipodia. It would be great of somebody with specialized knowledge could elaborate on the fossil evidence--Codiv (talk) 11:33, 9 July 2022 (UTC)[reply]
References to small size of sea spiders vs lead
There are multiple references to details of pycnogonid anatomy explained by their supposed small size; e.g.:
“
Because of their small size and slender body and legs, no respiratory system is necessary, with gases moving by diffusion.
”
“
Pycnogonids are so small that each of their tiny muscles consists of only one single cell, surrounded by connective tissue.
”
However the lead says:
“
There are over 1300 known species, ranging in size from 1 to 10 millimetres (0.039 to 0.39 in) to over 90 cm (35 in) in some deep water species. Most are toward the smaller end of this range in relatively shallow depths, however, they can grow to be quite large in Antarctic waters.
”
(emphasis mine).
So there are large pycnogonids. I suspect that some of the explanation in the article can be only partially correct (i.e. good for smaller ones but not for large ones). Anyone knows how to solve this discrepancy? Good reviews on pycnogonid anatomy? --Cyclopiatalk 13:30, 17 August 2010 (UTC)[reply]
Assessment comment
The comment(s) below were originally left at Talk:Sea spider/Comments, and are posted here for posterity. Following
several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.
Last edited at 17:51, 4 January 2007 (UTC).
Substituted at 05:39, 30 April 2016 (UTC)
Error in illustration
The caption for the figure at the top of the Description section (copied here, right) belongs to a different illustration: clearly the list of marked items in the caption doesn't match the marks on the illustration.
Anatomy of a pycnogonid: A: head; B: thorax; C: abdomen 1: proboscis; 2: chelifores; 3: palps; 4: ovigers; 5: egg sacs; 6a–6d: four pairs of legs
The referenced body divisions A, B, and C are not present on the illustration.
The labelled leg segments L1–L4 are not discussed in the caption, but marks 6a–6d (legs) are not in the illustration.
I believe that item 5, the egg sac in the caption, is not in fact what 5 in the illustration points to on the right side. The yellow cluster on the left side of the illustration, grasped in a minor leg, seems to be illustration's egg sac.
The illustration has a marked item 7, but no 7 is discussed in the caption.
A great admirer of Sherlock Holmes, I deduce that there was a prior illustration for which the caption was written. Some hasty edit (possibly done because of copyright issues) failed to transfer the new caption along with a new illustration. The edit needs to be repaired.
As far as the remedy for the problem goes, my grandmother often said If enough is good, then too much must be better. I think that she would agree that two illustrations have to be better than one, and that both illustrations should be re-joined with their correct captions, and restored to the article – perhaps placed in widely separated locations, where the reader might wish to refer to vocabulary for strange body parts.
Could someone please find the original illustration, and put it back?
Could someone please take the current illustration and replace the caption with a caption that matches? (Perhaps from the original source.)
, although specifically about about mollusc (mollusk) digestion, is more relevant as the same mechanism is in play here. Thus, I'm changing the link to Diverticulum (mollusc) with an eye to expanding the mollusc article to acknowledge that similar mechanisms are found elsewhere in the animal kingdom RATHER THAN to try to rewrite the medically oriented one to include sea-spider anatomy.
Do the smallest sea spiders have only one cell per muscle?
This is fascinating, if it is true. Could really do with a reference — Preceding unsigned comment added by 150.143.245.181 (talk) 18:53, 31 October 2018 (UTC)[reply]
Pycnogonids are a particularly strange, obscure group of animals that can often be easily mistaken for spiders due to their resemblances. But, are they crustaceans?
Pycnogonids, or sea spiders, are a unique group of animals that live in every ocean around the world and belong to the Pycnogonida class of animals. They are generally between 0.2 inches and 1.2 inches in length and have long, thin legs with no claws or other complex body parts. They also have a single pair of eyes and a small proboscis projecting from the head.
Their relationship to crustaceans has long been a subject of debate. While their body structure is not dissimilar to that of crabs, lobsters, and other crustaceans, their appearance and behavior are much more spider-like. For example, they don’t have any claws or other visible defense mechanisms like crustaceans do.
Based on the recent molecular analysis of sea spiders, it appears that pycnogonids are not related to crustaceans, but instead belong to a separate branch of the arthropod family tree. In fact, some experts now believe that these peculiar ocean-dwellers have been around for more than 450 million years, making them one of the oldest surviving animal phyla on the planet.
Despite their lack of a true classification, pycnogonids remain an enigmatic group of animals. They may not be crustaceans, but they exhibit behavior and structure that is unique among all other species in the animal kingdom. So, while they may not be related to crustaceans, their strange biology and history still make them one of the most interesting creatures on the planet, they are different to spiders, but they are in the same family as crustaceans and spiders. .Underline2A02:C7C:DB71:7900:C5DF:FBA1:2788:5F02 (talk) 11:05, 17 September 2023 (UTC)[reply]
for more here’s the rest: Pycnogonids (sea spiders) and crustaceans may appear similar, but there are unique characteristics that differentiate them from one another.
Pycnogonids are considered to be the most ancient of the arthropods and few in number. They vary in size from 0.5cm to 15cm in body length, and have four pairs of jointed appendages filamentous in form. These appendages have not been modified into legs, antennae, mouthparts, and other specialized structures like other arthropods, but are instead used for locomotion and capture of prey. They also have no mandibles and their mouths take the form of a proboscis that is used to suck their food.
Crustaceans, on the other hand, are much more diverse than pycnogonids. They have five or more pairs of jointed appendages which have been modified into specialized structures, such as legs, antennae, and mandibles. Crustaceans also have a chitinous exoskeleton which can be composed of multiple parts, such as the head, thorax, and abdomen. This exoskeleton provides protection and support for the body, as well as waterproofing. They also have secondary gills which are used for respiration, as well as their antennae which are used for smelling and feeling.
The differences between pycnogonids and crustaceans are significant and directly influence the way they interact with their environments. Both species are humblingly diverse, and understanding the differences between them helps us gain a fuller appreciation of the complexity of the arthropod group. 2A02:C7C:DB71:7900:C5DF:FBA1:2788:5F02 (talk) 11:08, 17 September 2023 (UTC)[reply]
Last one, are Pycnogonida arachnids
Pycnogonida, are among the most unusual members of the arthropod phylum. With their spindle-shaped bodies and eight legs, they bear a strong resemblance to traditional spiders. However, while these creatures may look like spiders, much of their anatomy and biology indicate that they differ from spiders in many important ways. So, are Pycnogonida arachnids?
The answer depends on how one defines an arachnid. Traditionally, the term “arachnid” is used to refer to any member of the class Arachnida, which includes spiders, mites, ticks, scorpions, and certain parasitic worms. But in a broader sense, “arachnid” can refer to any member of the larger taxonomic group Arthropoda, which includes insects, crustaceans, centipedes, and millipedes in addition to the members of the class Arachnida.
According to this definition, Pycnogonida are indeed arachnids. Though they differ from spiders in some respects—for example, they lack spinnerets for producing silk, and their heads are fused with their thoraxes—they share many characteristics with spiders, such as eight jointed legs, two-segmented abdomens, and exoskeletons made of chitin. These traits, and the fact that Pycnogonida belongs to the same taxonomic class as spiders, make Pycnogonida clear arachnids in a wider sense.
That said, it’s worth noting that Pycnogonida represent a distinct sub-group of arachnids that contain some features not found in other members of the class. For instance, Pycnogonida possess a unique slit-like structure in their legs, which is believed to help them absorb dissolved oxygen from the marine environment. It is also thought that they may have evolved from “primitive” spiders, though this has yet to be confirmed by further scientific study.
In summary, Pycnogonida may look like spiders, but this alone isn't enough to confirm that they are true arachnids. However, evidence from their anatomy and biology supports the view that Pycnogonida belong to the larger group of Arthropods, making them members of the class Arachnida and thus arachnids in a wider sense. 2A02:C7C:DB71:7900:C5DF:FBA1:2788:5F02 (talk) 11:11, 17 September 2023 (UTC)[reply]
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