''Zaitzevia elongata'' is a species of

riffle beetle Elmidae, commonly known as riffle beetles, is a family (biology), family of beetles in the superfamily Byrrhoidea described by John Curtis (entomologist), John Curtis in 1830. Both adults and larvae are usually aquatic, living under rocks in fas ...

which is wingless and flightless. It is found on several of the

Ryukyu Islands The , also known as the or the , are a chain of Japanese islands that stretch southwest from Kyushu to Taiwan: the Ōsumi, Tokara, Amami, Okinawa, and Sakishima Islands (further divided into the Miyako and Yaeyama Islands), with Yona ...

in Japan in the gravel substrate of streams.

Description

Larvae

The mature

larvae A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. T ...

of ''Zaitzevia elongata'' have a body length of approximately 4 millimeters (mm) long and are black or dark brown with orange appendages. Their bodies are longer than they are wide, and gradually become more narrow from the

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the ...

(center) to the apex (front). When viewed from the side, the larvae form a rough semi-circular shape. The spiracles, which are openings that allow air to enter the

trachea The trachea, also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends from th ...

, are found on the

mesothorax The mesothorax is the middle of the three segments of the thorax of hexapods, and bears the second pair of legs. Its principal sclerites (exoskeletal plates) are the mesonotum (dorsal), the mesosternum (ventral), and the mesopleuron (lateral) on ...

and the first eight abdominal segments. Their

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal co ...

and

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

(top and bottom) surfaces are not smooth, and have flat granules (bumps) and various

setae In biology, setae (singular seta ; from the Latin word for " bristle") are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Annelid setae are stiff bristles present on the body. ...

(bristles). The head of the larvae is visible from above and is clearly separated from the front segment of the thorax, the

prothorax The prothorax is the foremost of the three segments in the thorax of an insect, and bears the first pair of legs. Its principal sclerites (exoskeletal plates) are the pronotum (dorsal), the prosternum (ventral), and the propleuron (lateral) on e ...

. It is about as long as it is wide. The

clypeus Clypeus may refer to: * ''Clypeus'' (echinoderm), a fossil genus of echinoid * Clypeus Grit, a stratum in the Jurassic Inferior Oolite named for the echinoid * Clypeus (arthropod anatomy), a sclerite in an insect's exoskeleton * Clypeus (fungal) C ...

(frontal tooth) is transverse and lacks spines on either side. The eyes are large, but lack the lens of

stemmata A simple eye (sometimes called a pigment pit) refers to a form of eye or an optical arrangement composed of a single lens and without an elaborate retina such as occurs in most vertebrates. In this sense "simple eye" is distinct from a multi-le ...

. Each

antenna Antenna ( antennas or antennae) may refer to: Science and engineering * Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves * Antennae Galaxies, the name of two collid ...

has three antennomeres (segments). The thorax of the larvae is not serrated on the sides, and the dorsum has similar granules and setae to the rest of the body. The segment of the thorax closest to the head, the prothorax, is wider than it is long and is twice as long as the middle segment of the thorax, the mesothorax. Along the ventral side of the prothorax are seven

sclerites A sclerite (Greek , ', meaning " hard") is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instead it refers most commonly ...

, while along the ventral side of the meso- and metathorax there are five sclerites. The larval

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the tors ...

has nine segments, all of which have the same type of granules and setae to the rest of the body. The first eight segments are of similar size and form, all having pleural sclerites. The last segment is longer than it is wide, and gradually narrows to an apex at the rear of the beetle. The apex is notched and ventrally flat, having opercular claws and anal gills.

Adults

The male genitalia of ''Zaitzevia elongata'' is about 2.2 times as long as the median lobe, and the parameres are membraneous.

Distribution and habitat

''Zaitzevia elongata'' is found in the

of Japan. Specimens have been collected from the islands of

Amami Ōshima , also known as Amami, is the largest island in the Amami archipelago between Kyūshū and Okinawa. It is one of the Satsunan Islands. The island, 712.35 km2 in area, has a population of approximately 73,000 people. Administratively it is ...

Tokunoshima , also known in English as is an island in the Amami archipelago of the southern Satsunan Islands of Kagoshima Prefecture, Japan. The island, in area, has a population of approximately 27,000. The island is divided into three administrativ ...

, and

Okinawa is a prefecture of Japan. Okinawa Prefecture is the southernmost and westernmost prefecture of Japan, has a population of 1,457,162 (as of 2 February 2020) and a geographic area of 2,281 km2 (880 sq mi). Naha is the capital and largest city ...

Ecology

Larvae of the species have been recorded as residing among the moss species ''Fissidens nagasakinus''.

References

{{Taxonbar, from=Q2072227 Elmidae Fauna of Japan