''Zaitzevia elongata'' is a species of

riffle beetle Elmidae, commonly known as riffle beetles, is a family of beetles in the superfamily Byrrhoidea described by John Curtis in 1830. Both adults and larvae are usually aquatic, living under rocks in fast-flowing shallow areas of streams, such as r ...

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 Geography of Taiwan, Taiwan: the Ryukyu Islands are divided into the Satsunan Islands (Ōsumi Islands, Ōsumi, Tokara Islands, Tokara and A ...

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

in the gravel substrate of streams.

Description

Larvae

The mature

larvae A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect developmental biology, development such as insects, some arachnids, amphibians, or cnidarians typical ...

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 (: thoraces or thoraxes) or chest is a part of the anatomy of 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 di ...

(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 (: tracheae or tracheas), 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 animals' lungs. The trachea extends from ...

, 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) ...

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 The fus ...

and

ventral Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. 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 (; seta ; ) are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Depending partly on their form and function, protostome setae may be called macrotrichia, chaetae ...

(bristles). The head of the larvae are 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 ...

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

clypeus The clypeus is one of the sclerites that make up the face of an arthropod. In insects, the clypeus delimits the lower margin of the face, with the labrum articulated along the ventral margin of the clypeus. The mandibles bracket the labrum, but ...

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

stemmata A simple eye or ocellus (sometimes called a pigment pit) is a form of eye or an optical arrangement which has a single lens without the sort of elaborate retina that occurs in most vertebrates. These eyes are called "simple" to distinguish them ...

. Each antenna has three antennomeres (segments). The thorax of the larvae are 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 gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...

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 Parameres ('side parts') are part of the external reproductive organs of male insects and the term was first used by Verhoeff in 1893 for the lateral genital lobes in Coleoptera. The primary phallic lobes which appear in the nymph or larval stag ...

are membraneous.

Distribution and habitat

''Zaitzevia elongata'' is found in the

. Specimens have been collected from the islands of

Amami Ōshima , also known as Amami, is the largest island in the Amami Islands, Amami archipelago between Kyūshū and Okinawa Prefecture, Okinawa. It is one of the Satsunan Islands, all of which belong to Kagoshima Prefecture, Japan. The island, 712.35 ...

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 administrative t ...

, and

Okinawa most commonly refers to: * Okinawa Prefecture, Japan's southernmost prefecture * Okinawa Island, the largest island of Okinawa Prefecture * Okinawa Islands, an island group including Okinawa itself * Okinawa (city), the second largest city in th ...

Ecology

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

References

{{Taxonbar, from=Q2072227 Elmidae Fauna of Japan