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Anoplodactylus evansi

By Quinn Walker

Geographic Range

Anoplodactylus evansi is a species of sea spider (order Pantopoda). Its natural habitat includes the southern and eastern coasts of Australia, as well as the coasts of New South Wales and Tasmania. Local distributions of Anoplodactylus evansi are patchy, which may be in part due to its reproductive behavior of brooding its young. This behavior leads to resident populations at particular localities. (Mills, 2019; Patullo, 2017; Rogers, 2000; Rudman, 2010)

Habitat

Anoplodactylus evansi resides in coastal reefs, often on sponges, red algae, corals, or seaweeds. They primarily use algae for shelter, benthic algae for hunting, and nearby seaweeds for reproduction. (Mills, 2019; Patullo, 2017)

  • Range depth
    0 to 30 m
    0.00 to 98.43 ft

Physical Description

Anoplodactylus evansi is small, reaching up to 1 cm in length and weighing approximately 50 to 80 mg. It has relatively long legs, with a wingspan of around 3 cm. Anoplodactylus evansi has red and blue coloration with yellow markings on its joints. This allows it to camouflage well into its colorful coral environment.

Anoplodactylus evansi has 4 pairs of legs and a singular, four-part eye. It has a triradially symmetrical proboscis with a terminal mouth, three moveable lips, and strong musculature that allows for the suction and pumping of food to its pharyngeal filter. Next to its proboscis, Anoplodactylus evansi has a pair of pincer-bearing chelifores, which it uses to hunt prey. Both the proboscis and the chelifores of Anoplodactylus evansi are relatively short compared to other sea spider species. Sea spiders in the genus g. Anoplodactylus have absent or reduced palps. Anoplodactylus evansi males also have specialized egg carrying appendages called ovigers, which they also use for grooming outside of the breeding season. Anoplodactylus evansi has a body contained and supported by a non-calcareous exoskeleton that it molts multiple times throughout its life.

Sea spiders (order Pantopoda) have small abdomens and heads, with long, thin legs. As a result, sea spider species have a high surface area to body mass ratio. Anoplodactylus evansi has some of its midgut and genital anatomy contained in its legs because of its limited abdomen size. Furthermore, Anoplodactylus evansi lacks specialized respiratory and excretory structures. Instead, its large surface area to body mass ratio allows for diffusion of gases and wastes in and out of its cuticle, especially through its legs. Anoplodactylus evansi has a simple heart, an open circulatory system, and lacks gills or lungs. (Iwane, 2018; Mills, 2019; Patullo, 2017; Rogers, 2000; Simon, 2015; Taylor, 2021)

  • Sexual Dimorphism
  • sexes alike
  • female larger
  • Range mass
    0.05 to 0.08 g
    0.00 to 0.00 oz
  • Range length
    1 (high) cm
    0.39 (high) in
  • Range wingspan
    3 (high) cm
    1.18 (high) in

Development

Anoplodactylus evansi males use specialized appendages, known as ovigers, to carry fertilized eggs until they hatch. Anoplodactylus evansi larvae are small. Each newly hatched larva has a head with chelifores, a proboscis, and 2 pairs of undifferentiated appendages. As larvae grow and molt, more body segments develop and differentiate from each other, until they reach their adult stage with 4 pairs of appendages. Many larvae of species in the genus Anoplodactylus spend their first juvenile stage as parasites in the stomach cavities of cnidarians (phylum Cnidaria), after being placed there by their fathers. It is unclear whether this is also the case for Anoplodactylus evansi. ("Sea Spider", 2022; Simon, 2015; Taylor, 2021)

Reproduction

Anoplodactylus evansi is polygynandrous, meaning males and females have multiple mates. When mating, an individual male climbs on top of an individual female, then crawls underneath that female. The pair align the genital pores on their legs with those of their mate in order to copulate. No mating ritual or courtship are reported for sea spider species (order Pantopoda). Anoplodactylus evansi is solitary, with a relatively short lifespan, and thus individuals that experience multiple mating seasons are uncommon for this species. (Mills, 2019; "Sea Spider", 2022; Simon, 2015)

There is limited information on the breeding age, interval, and season of Anoplodactylus evansi.Most sea spider species (order Pantopoda) only survive to fulfill one breeding cycle. In fact, due to high predation rates, many do not survive to breeding age. When breeding, Anoplodactylus evansi males climb under females so that the genital pores located on their legs come into contact. Female then release their eggs onto the legs of males, that which point males combine eggs with their sperm to fertilize them. Males then carries the fertilized eggs on specialized appendages, called ovigers, until the eggs hatch. (Mills, 2019; "Sea Spider", 2022; Simon, 2015)

  • Breeding interval
    The breeding interval for Anoplodactylus evansi is unknown.
  • Breeding season
    The breeding season of Anoplodactylus evansi is unknown.

After Anoplodactylus evansi females release their eggs onto males and males fertilize the eggs, males use specialized appendages, called ovigers, to carry the fertilized eggs until they hatch. Anoplodactylus evansi males often brood their young on seaweed. Males also care for larvae until the end of their first juvenile stage, after which larvae are independent. Females exhibit no parental investment beyond the act of mating. (Mills, 2019; "Sea Spider", 2022; Simon, 2015)

  • Parental Investment
  • male parental care
  • pre-hatching/birth
    • provisioning
      • male
    • protecting
      • male
  • pre-weaning/fledging
    • provisioning
      • male
    • protecting
      • male

Lifespan/Longevity

There is limited information on the lifespan of Anoplodactylus evansi. On average, lifespans of sea spider species (order Pantopoda) are estimated between 3 and 12 months in the wild. Many sea spider individuals do not survive to maturity, due to high predation rates. Anoplodactylus evansi is not commonly kept in captivity, and thus there is no information on captive lifespan. (Mills, 2019)

  • Typical lifespan
    Status: wild
    3 to 12 months

Behavior

Anoplodactylus evansi hunts nocturnally and seeks shelter in algal blooms during the day. Anoplodactylus evansi hunts opisthobranchs, in the class Gastropoda, on benthic algae. Anoplodactylus evansi adults are solitary and remain close to seaweed, where they brood their young and hunt invertebrates. The tendency for Anoplodactylus evansi to live in such specific habitats limits its dispersal range. However, Anoplodactylus evansi can swim for extended periods of time. Anoplodactylus evansi is naturally solitary in the wild, but will hunt in groups when in captivity. Anoplodactylus evansi does not seem to exhibit any social heirarchies between individuals. (Mills, 2019; Patullo, 2017)

Home Range

There is limited information on home range sizes for Anoplodactylus evansi. No exact range has been reported.

Communication and Perception

There is limited information on the methods of communication and perception that Anoplodactylus evansi uses. Anoplodactylus evansi is primarily solitary, and the only observed social interactions occur while mating. Anoplodactylus evansi can sense toxin levels in prey items, and will avoid prey with high levels of secondary metabolites. (Mills, 2019; Rogers, 2000)

Food Habits

Anoplodactylus evansi is carnivorous, with the major portion of its diet consisting of body fluids from soft-bodied animals. Prey items of Anoplodactylus evansi include, but are not limited to segmented worms (phylum Annelida), sponges (phylum Porifera), cnidarians (phylum Cnidaria), bryozoans (phylum Bryozoa), and opisthobranchs (class Gastropoda). In captivity, Anoplodactylus evansi consumed 13 different types of opisthobranches, which are thought to be a primary component of its diet.

Anoplodactylus evansi prey on animals up to 6 times its size. They use a triradially symmetric proboscis to suck and pump primarily liquid food into their mouth. Anoplodactylus evansi posses moveable claws on the front two pairs of legs, which are used to immobilize prey before consuming them. Anoplodactylus evansi use these claws to grasp and hold prey while the hind pairs of legs stabilize Anoplodactylus evansi in the substrate. The digestive system of Anoplodactylus evansi is divided into three parts: foregut, midgut, and hindgut. The foregut is located within the proboscises of Anoplodactylus evansi individuals, and is responsible for processing and filtering food. The midgut is where food is digested and absorbed. Lastly, the hindgut is covered by cuticle in the reduced abdomens of Anoplodactylus evansi.

Many of the species consumed by Anoplodactylus evansi contain toxins. However, Anoplodactylus evansi typically consumes younger prey, which have not accumulated large amounts of toxins. Alternatively, Anoplodactylus evansi eats around the organs that produce toxic compounds. Anoplodactylus evansi can also tolerate low amounts of secondary metabolites in their diet. (Dietz, et al., 2018; Iwane, 2018; Mills, 2019; Patullo, 2017; Rogers, 2000; Rudman, 2010)

  • Animal Foods
  • body fluids
  • mollusks
  • cnidarians
  • other marine invertebrates

Predation

Sea stars (class Asteroidea), shorebirds (order Charadriiformes), rays (superorder Batoidea), crabs (infraorder Brachyura), and fishes are known to consume sea spider species (order Pantopoda). Specific predators of Anoplodactylus evansi are unknown. Anoplodactylus evansi has bright coloration that help camouflage with the typical coral and algae-rich habitats. ("Sea Spider", 2022; Patullo, 2017)

  • Anti-predator Adaptations
  • cryptic
  • Known Predators
    • Sea stars (class Asteroidea)
    • Shorebirds (order Charadriiformes)
    • Rays (superorder Batoidea)
    • Crabs (infraorder Brachyura)
    • Fishes

Ecosystem Roles

There is limited information regarding the ecosystem roles of Anoplodactylus evansi. Anoplodactylus evansi is predatory and may play a role in controlling populations of prey species. Anoplodactylus evansi also serves as prey for various marine species and shorebirds. (Rogers, 2000; Rudman, 2010)

Economic Importance for Humans: Positive

There are no known positive impacts of Anoplodactylus evansi on humans. (Mills, 2019)

Economic Importance for Humans: Negative

There are no known adverse effects of Anoplodactylus evansi on humans. (Mills, 2019)

Conservation Status

Little research or population data is available for Anoplodactylus evansi. This may be due to the limited range or the solitary behavior of Anoplodactylus evansi. Anoplodactylus evansi is not evaluated on the IUCN Red List and has no special status in the CITES appendices.

Other Comments

A main source of food for Anoplodactylus evansi are juvenile sea hares (order Anaspidea), which secrete ink that contains toxins when they are attacked. If a leg of an Anoplodactylus evansi individual comes into contact with the ink, it will vigorously wave the affected limb. (Mills, 2019; Rogers, 2000)

Sea spiders (order Pantapoda) are thought to have evolved over 500 million years ago. They are thought to share ancestors with crabs and spiders, but they have been evolving on their own for hundreds of millions of years. Over 1,300 species of sea spiders have been classified. Much remains unknown regarding sea spider phylogeny. ("Sea Spider", 2022)

Contributors

Quinn Walker (author), Colorado State University, Galen Burrell (editor), Special Projects.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

induced ovulation

ovulation is stimulated by the act of copulation (does not occur spontaneously)

male parental care

parental care is carried out by males

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

semelparous

offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

visual

uses sight to communicate

References

Monterey Bay Aquarium. 2022. "Sea Spider" (On-line). Monterey Bay Aquarium. Accessed March 28, 2022 at https://www.montereybayaquarium.org/animals/animals-a-to-z/sea-spider.

Colasanto, E., L. Galli. 2021. People’s contribution to the knowledge of Pycnogonida: citizen science in the case of a “problematic” taxon. Biogeographia – The Journal of Integrative Biogeography, 36: 1-11. Accessed February 13, 2022 at https://escholarship.org/uc/item/12r6m7r6.

Dietz, L., J. Dömel, F. Leese, T. Lehmann, R. Melzer. 2018. Feeding ecology in sea spiders (Arthropoda: Pycnogonida): what do we know?. Frontiers in Zoology, 15: 1-14. Accessed February 13, 2022 at https://link.springer.com/article/10.1186/s12983-018-0250-4#Bib1.

Harris, M., C. Arango. 2010. "WoRMS Photogallery" (On-line). World Register of Marine Species. Accessed February 13, 2022 at https://www.marinespecies.org/photogallery.php?album=677&pic=74223.

Iwane, T. 2018. "Observation of the Week, 2/23/18" (On-line). inaturalist. Accessed February 13, 2022 at https://www.inaturalist.org/blog/14427-observation-of-the-week-2-23-18.

Mills, E. 2019. "Pycnogonida (Sea Spiders)" (On-line). Accessed February 13, 2022 at https://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/pycnogonida-sea-spiders.

Patullo, B. 2017. "Anoplodactylus evansi Clark, 1963, Sea Spider" (On-line). MUSEUMS VICTORIA COLLECTIONS. Accessed February 13, 2022 at https://collections.museumsvictoria.com.au/species/8737.

Rogers, C. 2000. Predation of Juvenile Aplysia parvula and Other Small Anaspidean, Ascoglossan, and Nudibranch Gastropods by Pycnogonids. The Veliger, 43: 330-338. Accessed February 13, 2022 at https://www.biodiversitylibrary.org/item/134363#page/4/mode/2up.

Rudman, W. 2010. "Sea slug predators - Pycnogonids (Sea Spiders)" (On-line). Accessed February 13, 2022 at http://www.seaslugforum.net/find/pycnogon.

Simon, M. 2015. "Absurd Creature of the Week: This Isn’t a Spider, But It Does Have Genitals in Its Legs" (On-line). WIRED. Accessed February 13, 2022 at https://www.wired.com/2015/05/absurd-creature-of-the-week-sea-spider/.

Taylor, C. 2021. "Sea Spiders" (On-line). Accessed February 13, 2022 at http://coo.fieldofscience.com/2021/01/sea-spiders.html.

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