PORT PHILLIP BAY


Pycnogonid 

Achelia assimilis (Haswell, 1884)

View scientific description and taxonomy

Scientific Details

Family level characters.
TRUNK: Variably fused or articulated. Often compact and almost circular in outline.
SCAPE: 1or 2-segmented or absent.
CHELA: fingers generally reduced in adults but maybe chelate, atrophied or absent.
PALPS: 1-10 segments, usually 8-9 segments. Present in both sexes.
OVIGERS: 3-10 segments, both sexes but larger in males. No terminal claw. In some genera the number of oviger segments is fewer in the female. No apophysis. Terminal spines are compound.
LEGS: Eight only. Propodal heel usually well developed. Auxiliary claws present or absent. Dorsodistal femoral cement glands present.

Genus level characters.
TRUNK: Small, variably fused or articulated. General appearance circular or discoid, lateral processes touching or narrowly separated. Without dorsal transverse ridges.
ABDOMEN: Unsegmented.
EYES: Four.
PROBOSCIS: Barrel-shaped to spindle-shaped.
SCAPES: 1-segmented.
CHELAE: Vestigial, fingers atrophied.
PALPS: 7-9 segments; usually 8 segments.
OVIGERS: 10-segments in both sexes but larger in males; no strigilis; compound spines
present; no terminal claw, no apophysis.
LEGS: Eight. Propodal heel usually well developed.
TARSUS: shorter than propodus
AUXILIARY.CLAWS: present, usually long.

Taxonomy

Phylum:
Arthropoda
Subphylum:
Cheliceriformes
Class:
Pycnogonida
Order:
Pantopoda
Family:
Ammotheidae
Genus:
Achelia
Species:
assimilis

General Description

Body with proboscis projecting outward from front, with the mouth at the tip. Central body (trunk) behind the proboscis, with a raised, rounded area (tubercle) bearing four eyes. Eight segmented walking legs attached to the sides of the trunk. Small abdomen behind trunk, unsegmented. Leg span about 5 mm.

Biology

While this species has been mainly collected from algae, particularly brown seaweed and seagrass, the association is most probably with epiphytic hydroids which live on or near the algae. Current records of this species in Victoria most likely include more than one species, yet to be determined. Males carry the eggs, holding them between body parts called ovigers that hang under the animal.

Habitat

Usually on seaweed or seagrass, to depths greater than 400 m.

Seagrass meadows

Reefs

Distribution guide

Worldwide. Southern Australia.

Species Group

Sea spiders

Depth

Shallow (1-30 m)
Deep ( > 30 m)

Water Column

On or near sea floor

Max Size

5 mm

Commercial Species

No

Global Dispersal

Recorded in Australia.

Species Code

MoV 1791

Conservation Status

  • DSE Advisory List : Not listed
  • EPBC Act 1999 : Not listed
  • IUCN Red List : Not listed

Author

article author Staples, D.

David Staples is a consultant with expertise in pycnogonid taxonomy.

citation

Cite this page as:
Staples, D., 2011, Pycnogonid, Achelia assimilis, in Taxonomic Toolkit for marine life of Port Phillip Bay, Museum Victoria, accessed 23 Oct 2017, http://portphillipmarinelife.net.au:8098/species/6243

Text: creative commons cc by licence