SYNOPTIC DESCRIPTION OF THE SUBPHYLUM TRILOBITOMORPHA

SYNOPTIC DESCRIPTION OF THE SUBPHYLUM TRILOBITOMORPHA (MOORE 1959)

EUKARYA> UNIKONTA> OPISTHOKONTA> ANIMALIA> BILATERIA> PROTOSTOMATA> ECDYSOZOA> PANARTHROPODA> ARTHROPODA> TRILOBITOMORPHA

SUBPHYLUM TRILOBITOMORPHA LINKS

Introduction

Hierarchical Classification

The following information came from Margulis and Schwartz (1998), Brusca and Brusca (2003), Fortey (1997, 2001), Hickman (1973), Nielsen (2001), Storer and Usinger (1965), and Tudge (2000).

I. SYNONYMS: trilobites.

II. NUMBER: ~4,000 species known, all extinct.

III. SUBPHYLUM CHARACTERISTICS:
- A. Structure
  - Symmetry: Bilateral; segmented body regions organized into cephalon (head), thorax and pygidium.
  - Body Cavity: Presumably, they were like other arthropods and had a true coelom that was reduced and absent in adults. Haemocoel the only body cavity.
  - Body Covering: Covered by chitinous exoskeleton, reinforced by calcium carbonate.
  - Support: Hardened exoskeleton.
  - Digestive System: Food tube simple. Mouth at anterioventral end. Likely they tore apart their food by spiny processes on their thoracic legs. The pieces, thus rendered, were passed forward to the mouth for ingestion.
  - Circulatory System: Likely, they had an open system. Haemocoel of blood sinuses with a dorsal circulatory vessel (heart).
  - Locomotion: A pair of biramous walking legs per thoracic segment.
  - Excretory System: Not known.
  - Nervous System: Probably with circumesophagial ring and ventral cords ganglionated at each segment. The cephalon had a pair of sensory antennae. Compound eyes of unusual structure. Lenses of calcium carbonate crystals. At least one group had sensory cerci.
  - Endocrine System: Not known.
  - Respiratory System The exopodites of the biramous walking leg likely functioned as gills.
- B. Reproduction:
  - Reproductive System: Likely they were oviparous.
  - Development: The development of trilobites occurred through successive molts in three periods: Protaspid Period (in this period the larvae have no segmentation), Meraspid Period (in this period the larvae have segments and add them through successive molts until they achieve the adult number), Holaspid Period (the stage at which the animal has achieved the adult number of segments and molts as it increases in size).
- C. Ecology: Mostly free-living scavenger-predators, benthic marine (though a few seem to have been adapted to swimming in the open water).

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By Jack R. Holt and Carlos A. Iudica. Last revised: 02/03/2013

SYNOPTIC DESCRIPTION OF THE SUBPHYLUM TRILOBITOMORPHA (MOORE 1959)

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