Arenicolidae is a family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 of marine polychaete worms. They are commonly known as lugworms and the little coils of sand they produce are commonly seen on the beach. Arenicolids are found worldwide, mostly living in burrows in sandy substrates. Most are deposit feeders

Detritivore

Detritivores, also known as detritophages or detritus feeders or detritus eaters or saprophages, are heterotrophs that obtain nutrients by consuming detritus . By doing so, they contribute to decomposition and the nutrient cycles...

 but some graze on algae

Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

.

Description

The arenicolids are characterised by an elongated cylindrical body separated into two or three distinct regions. The prostomium

Prostomium

Prostomium is the first body segment in annelid worms. It is in front of the mouth, being usually a small shelf- or lip-like extension over the dorsal side of the mouth. It sometimes bears antennae and eyes. It often functions like a kind of overlip when the animal is feeding...

 has no appendage

Appendage

In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...

s or palps. There are one or two anterior segments without setae. On the other segments, all the setae are unbranched, including the capillary setae and the rostrate

Rostrum (anatomy)

The term rostrum is used for a number of unrelated structures in different groups of animals:*In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes....

 uncini. The notopodia

Parapodium

Parapodia , singular parapodium, are paired, un-jointed lateral outgrowths from the bodies of two different invertebrate groups, which are primarily marine in habitat...

 are bluntly truncate and the neuropodia

Parapodium

Parapodia , singular parapodium, are paired, un-jointed lateral outgrowths from the bodies of two different invertebrate groups, which are primarily marine in habitat...

 are elongated tori forming long transverse welts in some of the setigers. The notosetae

Parapodium

Parapodia , singular parapodium, are paired, un-jointed lateral outgrowths from the bodies of two different invertebrate groups, which are primarily marine in habitat...

 have either a capillary function or act as limbs and the neurosetae

Parapodium

Parapodia , singular parapodium, are paired, un-jointed lateral outgrowths from the bodies of two different invertebrate groups, which are primarily marine in habitat...

 are rostrate hooks. There are branchiae

Gill

A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

 present on some of the setigers in the middle or posterior regions.

Apart from the genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Branchiomaldane, the lugworms are not easy to confuse with other polychaetes. Their tough cuticle and their distinct branchial region with strongly tufted branchiae are characteristic.

Genera

• Abarenicola Wells, 1959
• Arenicola Lamarck, 1801
• Arenicolides Mesnil, 1898
• Branchiomaldane Langerhans, 1881
• Clymenides
• Eruca
• Protocapitella