Phylum Kinorhyncha
Phylum
Kinorhyncha
Kinorhyncha (kin´o-ring´ka) (Gr. kinein, to move, + rhynchos, beak) are marine worms a little larger than rotifers and gastrotrichs but usually not more than 1 mm long. The phylum has also been called Echinodera, meaning spiny necked. About 75 species have been described.
Kinorhynchs are cosmopolitan, living from pole to pole, from intertidal areas to 6000 m in depth. Most live in mud or sandy mud, but some have been found in algal holdfasts, sponges, or other invertebrates. They feed mainly on diatoms. About 100 species have been reported. Among the best-known genera of the Kinorhyncha are Echinoderes, Pycnophyes, and Kinorhynchus.
Form and Function
The body of the kinorhynch is divided into 13 segments, which bear spines but have no cilia (Figure 15-7).
The
retractile head has a circlet of spines
with a small retractile proboscis.
The
body is flat ventrally and arched dorsally.
The body wall is made up of a
cuticle, a syncytial epidermis, and longitudinal
epidermal cords, much like
those of nematodes. The arrangement
of the muscles is correlated with the
segments, and circular, longitudinal,
and diagonal muscle bands are all
represented.
A kinorhynch cannot swim. In the silt and mud where it commonly lives, it burrows by extending the head into the mud and anchoring it with spines. It then draws its body forward until its head is retracted into its body. When disturbed, a kinorhynch draws in its head and protects it with a closing apparatus of cuticular plates (Figure 15-7).
The digestive system is complete, with a mouth at the tip of a proboscis, a pharynx, an esophagus, a stomachintestine, and an anus. Kinorhynchs feed on diatoms or on organic material in the mud where they burrow.
The pseudocoel is filled with amebocytes containing fluid. The excretory system is made up of a multinucleated solenocyte protonephridium on each side of the tenth and eleventh segments. Each solenocyte has one long and one short flagellum.
The nervous system is in contact with the epidermis, with a multilobed brain encircling the pharynx, and with a ventral ganglionated nerve cord extending throughout the body. Sense organs are represented by eyespots in some and by the sensory bristles.
Sexes are separate, with paired gonads and gonoducts. There is a series of about six juvenile stages and a definitive, nonmolting adult.
Kinorhyncha (kin´o-ring´ka) (Gr. kinein, to move, + rhynchos, beak) are marine worms a little larger than rotifers and gastrotrichs but usually not more than 1 mm long. The phylum has also been called Echinodera, meaning spiny necked. About 75 species have been described.
Kinorhynchs are cosmopolitan, living from pole to pole, from intertidal areas to 6000 m in depth. Most live in mud or sandy mud, but some have been found in algal holdfasts, sponges, or other invertebrates. They feed mainly on diatoms. About 100 species have been reported. Among the best-known genera of the Kinorhyncha are Echinoderes, Pycnophyes, and Kinorhynchus.
Form and Function
The body of the kinorhynch is divided into 13 segments, which bear spines but have no cilia (Figure 15-7).
 |
| Figure 15-7 Echinoderes, a kinorhynch, is a minute marine worm. Segmentation is superficial. The head, with its circle of spines, is retractile. |
A kinorhynch cannot swim. In the silt and mud where it commonly lives, it burrows by extending the head into the mud and anchoring it with spines. It then draws its body forward until its head is retracted into its body. When disturbed, a kinorhynch draws in its head and protects it with a closing apparatus of cuticular plates (Figure 15-7).
The digestive system is complete, with a mouth at the tip of a proboscis, a pharynx, an esophagus, a stomachintestine, and an anus. Kinorhynchs feed on diatoms or on organic material in the mud where they burrow.
The pseudocoel is filled with amebocytes containing fluid. The excretory system is made up of a multinucleated solenocyte protonephridium on each side of the tenth and eleventh segments. Each solenocyte has one long and one short flagellum.
The nervous system is in contact with the epidermis, with a multilobed brain encircling the pharynx, and with a ventral ganglionated nerve cord extending throughout the body. Sense organs are represented by eyespots in some and by the sensory bristles.
Sexes are separate, with paired gonads and gonoducts. There is a series of about six juvenile stages and a definitive, nonmolting adult.
Support our developers
