INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM TRUE MULTICELLULAR ANIMALS (EUMETAZOA)

SECTION TRIPLOBLASTIC (TRIPLOBLASTICA) OR BILATERAL (BILATERIA) ANIMALS

SUBSECTION MOLTING ANIMALS (ECDYSOZOA)

PHYLUM ARTHROPODS (ARTHROPODA)

SUBPHYLUM TRACHEATES (TRACHEATA)

SUPERCLASS MYRIAPODS (MYRIAPODА)

CLASS SYMPHYLA (SYMPHYLA)

Small (up to 8 mm) animals with a very delicate cuticle. They range from sea coasts to high mountains (3,000 m above sea level); they inhabit soil, decaying plant debris, and leaf litter under stones. Symphylans are highly sensitive to moisture deficiency and live only in conditions of relative humidity close to 100%. This accounts for their complex seasonal and daily Migrations within the soil. About 150 species have been described, with five known in Ukraine.

Morphology. The HEAD is covered by a true head capsule resembling that of insects. The antennae are unbranched, and there are three pairs of mouthparts, with the second pair of maxillae fused into an unpaired gnathochilarium. Eyes are absent. The trunk shows differentiation between the ventral and dorsal sides. The ventral side always bears 12 sternites and 12 pairs of legs, while the dorsal side has a variable number of tergites depending on the species, but always more than 12 (up to 24). The last segment bears a pair of appendages—cerci, which contain the ducts of silk glands (Fig. 354).

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Fig. 354. Symphylan

Scolopendrella immaculata (after Gilyarov)

The Digestive System is similar to that of diplopods. Symphylans feed on dead and living plant Tissues. Some species, such as Scolopendrella immaculata, can cause significant damage to young shoots of field and greenhouse crops.

The excretory system is represented by a pair of Malpighian tubules, and in addition, they may possess one or two pairs of maxillary glands.

Respiratory Organs. Unlike all other myriapods, the tracheal system opens via a single pair of spiracles located on the head behind the antennae. The tracheae extending from the spiracles are weakly branched, with their branches reaching only the head and the first three body segments; thus, symphylans respire primarily through the integument.

The Nervous system is typical of Arthropods, with the ventral nerve cord consistently bearing 12 ganglia.

Sense Organs, particularly those of Touch, are represented by numerous sensilla in the form of fine setae. Near the first leg segment on all body segments, there are peculiar sac-like structures that protrude under Blood pressure and are subsequently retracted into the body through muscular contractions. There are various opinions regarding their Functions: some researchers consider them to be accessory organs where gas exchange takes place, while others view them as organs enabling the animal to respond to changes in Temperature and humidity.

The Reproductive System of symphylans is similar to that of pauropods, but the genital opening is unpaired and situated on the third trunk segment.

Reproduction. Males deposit spermatophores in the burrows through which symphylans move. Females pick up the spermatophores with their mouthparts, and the seminal fluid enters specialized reservoirs on the inner surface of the mouthparts. As the female catches the egg emerging from the genital opening with her mouthparts, it is fertilized by the spermatozoa. The fertilized egg is attached to the walls of burrows in the soil, and after 10 days, a larva with an incomplete number of legs hatches (anamorphosis). Symphylans exhibit a remarkable ability to regenerate lost antennal segments—a phenomenon very rare among terrestrial arthropods.