“Hey, everyone likes spiders, right?”

“Well, uh…”

“Of course they do. Spiders are cute, and they keep the insect population under control.”

“They sure do, evolution.”

“Anyway, I was thinking of making something similar, but for the ocean. Like a… sea spider.”

“A sea spider.”

“Mmm hmm. Only it’ll barely need a body, because I’m going to stuff most of its organs and its digestive tract down its legs. And instead of eating insects, it’ll stick its long proboscis into sea anemones and suck their insides out. What do you think?”


“I think everybody’s going to love it.”

“Yes, evolution, I’m sure.”

Source: NOAA Ocean Today / Creatures of the Deep: Sea Spider (click for video)

Yellow Kneed Sea Spider

Despite their appearance, the so called Sea spiders are not actually true spiders, they are marine arthropods belonging to the Class Pycnogonida, but in fact their relationships are enigmatic. They may represent a very early branching of the chelicerate lineage. There are approximately 1000 described species of pycnogonids, all of which are marine.

Pycnogonids vaguely resemble spiders, with small bodies and relatively long, hinged legs. Unique characteristics include an unusual proboscis (mouthparts), which varies in size and shape among species. The body itself is not divisible into neatly- organized tagmata or regions as it is in most other arthropods. An anterior region bears, besides the proboscis, three or four pairs of appendages, including the first pair of walking legs. Some species have more than four pairs of walking legs. 

The photo shows a showy pycnogonid in the Family Callipallenidae. 

Reference: [1]

Photo credit: ©Sylke Rohrlach

Locality: New South Wales, Australia

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Other Evolution Topics:

The Cambrian Explosion
Darwin’s finches, decent with modification and natural selection
Puntuated Equilibrium

Appearance and Origins of Life

Chemotrophs and the Origins of Life
Archaeans - The Most Ancient Life
Endosymbiosis - A Primary Evolutionary Milstone

Evolution of Various Taxa:

Cambrian Explosion
Transitional Fossils
The evolutionary arms race - examples among trilobites
Evolutionary Placement of the Enigmatic Carpoids (Stylophorans)
Fossil Chelicerates and Evolution of Chelicerata
Evolution of Insects
Archaeopteryx with Dinosaur Affinity


9/3/15             Spider of the Day

Kingdom Animalia (Animals) Phylum Arthropoda (Arthropods) Subphylum Chelicerata (Chelicerates) Class Arachnida (Arachnids) Order Araneae (Spiders) Infraorder Araneomorphae (True Spiders) No Taxon  (Entelegynes ) Family Araneidae (Orb Weavers) Genus Micrathena Species sagittata (Arrowshaped Micrathena) 

Explanation of Names Latin: “arrowed, in the form of an arrow” Size Female 8-9mm, Male 4-5mm (1) Identification Female: three pairs of pointed tubercles on the abdomen, with the rear pair large and spreading to give the abdomen a triangular look. Tubercles are black-tipped and red at the base. The center of the dorsum is yellow. Male adomen does not have spines, widest at rear. (1) Range Eastern U.S. west to Texas and Nebraska. (1) Habitat Builds webs in open woods. (1) Remarks Web often has a short stabilimentum above the hub. (1)

This spider does not pose a danger to humans (and neither do any others in this family).


Scorpiones, Scorpio, Scorpion…

It’s hard to get a good picture of a scorpion - they’ve just got so much going on. Here, at least, are four images that show some key features: chelicerate mouth-parts, claws (chela) like an unrelated lobster, and tail with a sting segment (telson) and sting (aculeus). Fun creatures…

Scorpions have been on our little planet for an awful long time with the earliest evidence, fossils from the Silurian, around 450 million years ago, long before vertebrates began their land invasion. Some of these were real beasts up to about one metre (three feet) long, unlike today’s well over 1000 species which are usually less than 10 cm (3 in) long. Thankfully.

Here the images show two species and there’s an obvious difference in two of the images that clearly differentiates them. Know what it is?

Scorpions are one of the Many Little ancient Things.

Red and Black Spider - Ambicodamus sp.

Due to their typical coloration, spiders of the Australian genus Ambicodamus belong to the family Nicodamidae, whose members are commonly known as red and black spiders. They are small to medium-sized spiders found in small sheet webs close to the ground in eucalypt forests. They have eight eyes, small, in two straight rows. The single cheliceral tooth is highly unusual amongst spiders. 

Reference: [1]

Photo credit: ©Simon Grove | Locality: Flinders Island, Tasmania (2014)

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The Yohoia (1912)

Phylum : Arthropoda
Class : Megacheira
Family : Yohoiidae
Genus : Yohoia
Species : T. tenuis

  • Middle Cambrian (500 Ma)
  • 2 cm long (size)
  • Burgess shale, Canada (map)

Yohoia is a tiny, extinct animal from the Cambrian period that has been found as fossils in the Burgess Shale formation of British Columbia, Canada. It has been placed among the arachnomorphs, a group of arthropods that includes the chelicerates and trilobites. Their sizes range from 7 to 23 mm. 711 specimens of Yohoia are known from the Greater Phyllopod bed, where they comprise 1.35% of the community.

Specimens of Yohoia have a head shield which is followed by 13 trunk tergites, or plates. On both sides, the bottom side of the first 10 of these ended in backward-pointing, triangular points or projections. The last three plates were complete tubes, circling the entire trunk. At the end of the trunk was a paddle-like tail. There were also a pair of large extensions at the front of the head shield. They had a pronounced “elbow” and ended in four long spines, looking rather like fingers. There were three appendages on the bottom of the head shield on each side, and these are assumed to have supported the creature on the sandy or silty sea bottom. There were also single appendages hanging down under the body plates which were flap-like and fringed with setae, probably used for swimming and respiration. Specimens also show some bulbous formations at the front of the head shield that may have served as eyes.

Yohoia is assumed to been a mainly benthic (bottom-dwelling) creature that swam just above the muddy ocean floor and using its appendages to scavenge or capture prey.


4/2/2016               Spider of the Day Rabidosa  punctulata Gravid adult 

Kingdom Animalia (Animals) Phylum Arthropoda (Arthropods) Subphylum Chelicerata (Chelicerates) Class Arachnida (Arachnids) Order Araneae (Spiders) Infraorder Araneomorphae (True Spiders) No Taxon  (Entelegynes ) Family Lycosidae (Wolf Spiders) Genus Rabidosa Species punctulata (Dotted Wolf Spider)

Explanation of Names The genus name was formed by adding -osa to the species name for which the genus is based, rabida (Lycosa rabida).(1) Numbers 5 species in bugguide’s range.  Identificatin:  Rabidosa punctulata - Venter of abdomen very pale brownish yellow (beige) with few-to-many scattered, variably-sized dark spots. Occasionally the venter is all dark brown or black. ( no horizontal lines through the posterior portion of the abdominal stripe.)
              Family Lycosidae (Wolf Spiders) Pronunciation ley-KO-si-dee(1) Explanation of Names Named after the genus Lycosa, itself from the Greek word “lycosa” meaning “wolf”.   Size 2.2-35.0 mm

The names of several of the genera follow a pattern: the Greek name of a mammalian carnivore has an “a” or “cosa” added to the end:
Lycos- Wolf
Alopex- Fox
Arctos- Bear
Pardos- Panther Numbers Approx. 240 species in 21 genera in North America north of Mexico. Exact numbers and recognized genera are subject to change. Note that at the time of this writing the World Spider Catalog(2) lists 9 species of Lycosa in North America, these are not included here because they likely all belong to other genera. It is noted in “Spiders of North America: An Identification Manual” By D. Ubick, P. Paquin, P.E. Cushing and V. Roth (eds)(1) that “the genus Lycosa Lᴀᴛʀᴇɪʟʟᴇ 1840b is properly restricted to a group of large burrowing wolf spiders in the Mediterranean region. Consequently this genus is not represented in North America, and the species listed from this continent by Platnick (2005) require revision and placement.” One species of Paratrochosina is also not included here as in SoNA(1) it is suspected of being a misidentification of the highly variable Alopecosa hirtipes, more information is needed. Identification Eight dark eyes of unequal size arranged in three rows, the first having four eyes (see below). The abdomen and the cephalothorax are usually as long as wide. The long legs have three microscopic claws at each tip.Range Widespread from the Arctic to the Subtropics.(1) Found throughout North America. Habitat Preferred habitat varies between species but includes open grasslands, suburban lawns, deciduous forests, deserts, coastal dunes, sandy soil and wet terrain such as marshes and swamps.(1)(6) Food Mainly insects. Life Cycle Most wolf spiders live on the ground and hunt for prey at night. Their dark mottled colors help camouflage them among the leaves. Except for those in the genus Sosippus, wolf spiders do not spin webs. Some dig burrows in the ground, others make holes under rocks, and many have no retreat at all.  
The mating rituals of wolf spiders can vary depending on the species, as is true for most spider groups. Adult males follow silk and chemical cues left by females. Generally, males then use a combination of visual and seismic (vibratory) behaviors to court their potential mate. They often wave and rhythmically thump their pedipalps and/or abdomen on the ground. Most species also create sounds (usually inaudible to humans) by quickly rubbing together two corresponding parts of their body, known as “stridulatory files.” The female spins a spherical egg sac, attaches it to her spinnerets, and drags it about until the spiderlings emerge. The young clamber about on the female’s back and are carried until they are ready to disperse
All information from BugGuide: