Overview

Brief Summary

Loriciferans are microscopic animals living between the particles of marine sediments. Discovered in 1983 off the coast of France by the Danish zoologist R. M. Kristensen, about 100 species have so far been collected, though (as of 2010) only a third of those have been described. Researchers continue to find new species, indicating that this is an abundant and cosmopolitan taxon, with worldwide distribution and occurring in sediments from shallow to deep water. Loricifera are interesting as “masters of miniturization” (Rundell & Leander 2010) but also as “the first evidence of a metazoan life cycle that is spent entirely in permanently anoxic sediments” (Danovaro et al 2010).

Loriciferans are similar in size to large single-celled protozoans (< 0.5 mm) but are multicellular, with about 10,000 specialized cells creating a tiny but complex body with a brain, digestive and excretory systems, specialized appendages, sense organs, musculature and locomotory functions, separate sexes, and a protective external cuticle (the “lorica”) into which the “introvert” containing the mouth cone and head can be retracted (Ruppert et al 2004).

Characteristics of the Phylum Loricifera KRISTENSEN 1983

Marine metazoans

ADULTS

  • Size: 115 to 425 micrometers long
  • Symmetry: bilateral
  • Autapomorphic characteristics:
    • body divided into 5 regions: mouth cone, heat (introvert), neck, thorax, abdomen
    • Internal buccal armature arranged in strict tri- or hexagonal pattern
    • Nine rows of sensory or locomotory appendages (scalids), each with muscles attached to introvert
    • First row of scalids consists of 8 multicellular club-shaped or blunt-tipped clavoscalids of various shapes and number
    • Second to ninth rows of scalids consist of spinoscalids of various shapes and numbers
    • Neck consists of 3 rows of basal plates and 1 row of trichoscalids
    • trichoscalids are flattened and serrated, with either 15 single or 7 double, alternating with 8 sincle trichoscalids
    • Thorax is accordion-like and without appendages
    • Abdomen covered with a more-or-less cuticularized lorica with 6 to 10 plates or 22 to 40 plicae
    • Mouth cone is not eversible but protrusible
    • Mouth cone and head can be retracted into the loricated abdomen

HIGGINS LARVAE

  • Size: 48 to 780 micrometers long
  • Body plan: same regions as adult
  • Autapomorphic characteristics:
    • Mouth cone sometimes with a midventral seta and/or 6 to12 oral stylets and, when present, internal armature in strict tri- or hexagonal pattern
    • Eversible introvert with 8 clavoscalids and up to 7 rows of spinoscalids
    • Neck used as closing apparatus
    • Accordion-shaped thorax has plated formed from transverse and longitudinal folds
    • Lorica is longitudinally folded
    • Two or 3 locomotory setae are present ventrally between thorax and abdomen
    • Toes located caudally
    • Two or 3 sensory setae present on posterior part of lorica
    • Several larval instars, growing by a series of molts

(summarized from Kristensen et al 2007)

Partial list of described Loricifera

Pliciloricidae

Nanaloricidae

  • Nanaloricus
    • Nanaloricus mysticus (1983) type species – in shelly gravel (Dentalium sand); 25-30 m depth; off Roscoff, France
    • Nanaloricus khaitatus (1998) – shallow intertidal and subtidal; Livorno, Italy
    • Nanaloricus gwenae (2007) – in coarse sand and shell habitats (Amphioxus sand); 15-17 m depth; 6-7 miles (9.7-11.3 km) off Fort Pierce, FL, USA
  • Armorloricus
  • Pheniciloricus
    • Phoeniciloricus simplidigitatus (2004) – 1813 m depth; near Kilinailau Trench off Papua New Guinea
  • Spinoloricus (2007)
    • Spinoloricus turbatio (2007) – from the “deep sea”; Galapagos Spreading Center
  • Australoricus (2009)
    • Australoricus oculatus (2009) – from submarine caves; New South Wales, Australia

(Higgins & Kristensen 1986, Heiner 2004, Gad & Arbizu 2005, Heiner 2005, Heiner & Neuhaus 2007, Kristensen et al 2007, Heiner et al 2009))

Undescribed species of obligate anaerobic Loricifera (Danovaro et al 2010): From anoxic hypersaline sediment; L’Atalante basin (Mediterranean Sea); >3000 m deep

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Comprehensive Description

Microscopic animals that live attached to the grains of marine sediments.

Key to Abbreviations Used in Higgins & Kristensen 1986

  • ac anal cone
  • ad apodeme on the mouth cone
  • af anal field
  • an anus
  • ap anal plate
  • ar anal ridge
  • at accessory tooth (cl)
  • ba bar-shaped structure of midventral plica
  • bc buccal canal
  • bg buccal canal gland
  • br brain
  • bt basal plate of toe
  • cl claw-tipped spinoscalid (sr4)
  • co collar
  • cp collar pore
  • cs clavoscalid (sr1)
  • cs1 ventral clavoscalid
  • cs2 dorsal clavoscalid
  • ct claw-tip
  • D dorsal
  • do double-organ
  • ed edge of lorica
  • ed1 edge of larval lorica
  • ed2 edge of adult lorica
  • es esophagus
  • ex larval exuvium
  • fl flosculus (Pliciloricus-type)
  • fl1 anterior flosculus
  • fl2 posterior flosculus
  • gu gut
  • ha hair
  • ho hook-shaped scalid of larval exuvium
  • ia internal armature of larval buccal canal
  • in introvert
  • in1 introvert of larval exuvium
  • in2 introvert of adult exuvium
  • lc larval closing apparatus
  • lo lorica
  • lo1 lorica of larval exuvium
  • lo2 lorica of adult exuvium
  • Ir1 primary double ridge of lorica
  • Ir2 secondary double ridge of lorica
  • Is1 anterolateral seta
  • Is2 anteroventral seta
  • mc mouth cone
  • mc1 first region of mouth cone
  • mc2 second region of mouth cone
  • mc3 third region of mouth cone
  • mh middorsal hook (modified sr9)
  • mo molting body
  • mp middorsal plate
  • mr mucro
  • ms midventral setae of mouth cone
  • mt mouth tube
  • mu muscle
  • mv midventral scalid
  • nf flosculus (Nanaloricus-type)
  • ne nephridiopore(?)
  • or oral ridge
  • os oral stylet
  • ot oral tooth
  • ph pharynx bulb
  • pi1 plica
  • pi2 midventral modified plica
  • po pore on trichoscalid plate
  • ps penile spine(?)
  • pt toe gland pore
  • re ridge
  • ri transverse ridge of lorica
  • ro rosette structure
  • ru ruff
  • sc scalid
  • se1 posterodorsal seta
  • se2 posterolateral seta
  • se3 posteroterminal seta
  • sp spine on spinoscalid
  • sr1-sr9 scalid row 1-9
  • ss spinoscalid
  • su sculpture of lorica
  • te testis
  • th thorax
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