Loriciferans (phylum Loricifera) are meiofauna - tiny organisms which occupy the spaces between sediment
particles (the meiobenthic habitat). Loriciferans are fee-living and dwell in coarse sediments. They are
so-called because of the cuticular tunic or lorica which invests much of the body (loricifera literally means
"corset-bearing"). They were only officially discovered in 1983, largely because adhere so strongly to the
sediment particles that normal extraction methods failed to dislodge them. Consequently, there is still relatively
little known about this group.
Loriciferans are microscopic (about 0.1 to 0.4 mm long) but contain over 10 000 cells. The body is divided into
a head (introvert), thorax (part or all of which is sometimes called the neck) and abdomen. The lorica encloses
the abdomen and is made of 6 plates (some sources say 4) which end in forward-projecting spikes or scales
anteriorly. Longitudinal muscle bands can retract the anterior parts into the lorica, in telescopic fashion. Larval
stages (the feeding Higgins larva) have two toes at their tail end. These toes are muscular and are probably
adhesive and similar to those of rotifers. Loriciferans are often considered to be aschelminths, along with the
nematodes, rotifers, gastrotrichs and kinorhynchs.
The mouth is situated on the end of the oral cone, which may be surrounded by 8 or 9 protrusible oral
stylets. There are nine rings of spinelike appendages, called scalids (which typically number between 200
and 400 in total). The first ring consists of forward-pointed scalids, called clavoscalids which are broader
towards their apex than at their base. In loriciferans such as Piciloricus, the scalids have jointed bases. Behind
the clavoscalids are 8 rings of bacjward-projecting spinelike spinoscalids.
Above: a 3D Pov-Ray model of a loriciferan of the Pliciloricus
Above: a view of the anterior end of our model, showing the mouth at
the end of the oral cone and the clavoscalids. Loriciferans are
dioecious (separate sexes) and males and females differ in the
number of scalids, including the clavoscalids.
The mouth, borne on the end of the oral cone, leads into a long tube, the buccal tube, which connects to a
pharynx consisting of a muscular pharyngeal bulb which in turn connects to the oesophagus. These
structures form the foregut and are lined by cuticle. One pair of salivary glands open into the buccal tube.
The oesophagus leads into the midgut which is not lined by true cuticle. The midgut in turn which connects to
a short rectum, which is lined by cuticle and so constitutes a hindgut and opens to the outside via the
terminal anus which may be on top of a short anal cone at the rear of the animal.
The 'brain' consists of a circular ganglion ( a group of 8 circumoral ganglia and associated dorsal ganglia)
around the pharynx, the circumpharyngeal ganglion. There is a large ganglionated ventral nerve cord
and peripheral ganglia are present. Micropapillae, and some of the scalids are probably sensory. The larva has
sensory bristles or setae.
Reproduction and Growth
Males have two dorsal testes in the abdominal body cavity (which is probably some sort of coelom), the female
has a pair of ovaries. Mention has already been made of the Higgins larva, which resembles the adult but has
two muscular toes, which are joined to the abdomen by ball and socket joints and are said to be used in
swimming. During growth the cuticle is periodically molted. The larva may molt into a juvenile, which resembles
the adult but lacks ovaries, or else it may molt directly into an adult. The larva also has three pairs of spines
which are used like legs.
There is one pair of monoflagellate protonephridia situated within the gonads.