Haplodrili
Encyclopedia
Haplodrili, or Archiannelida, is a primitive marine worm
part of the annelid
phylum
. Zoologist Ray Lankester
gave it its name of Haplodrili, while zoologist Berthold Hatschek named it Archiannelida. Following five families were included in Haplodrili: Dinophilidae, Nerillidae
, Polygordiidae, Prorodrilidae and Saccocirridae
.
is small and resembles polychaete
larva
e, epidermis ciliated, the number of segments varies from five and up or can be completely absent, small prostomium with or without appendages, parapodia absent, septa reduced or absent, the nervous system consists of a brain and longitudinal ventral nerve cords closely connected with the epidermis (withotit distinct ganglia), widely separated in Saccocirrus, closely approximated in Protodrilus, fused together in Polygordius; the coelom is well developed and the dorsal and ventral longitudinal mesenteries are complete; the nephridia are simple, and open into the coelom. Polygordius differs from Protodrilus and Saccocirrus in the absence of a distinct suboesophageal muscular pouch, and in the absence of a peculiar closed cavity in the head region, which is especially well developed in Saccocirrus, and probably represents the specialized coelom of the first segment.
Moreover, in Saccocirrus the genital organs of a transverse section of Saccocirrus showing on the left side the organs in a genital segment of a male, and on the right side the organs in a genital segment of a female.
Marine worm
Any worm that lives in a marine environment is considered a marine worm. Marine worms are found in several different phyla, including the Platyhelminthes, Nematoda, Annelida , Chaetognatha, Hemichordata, and Phoronida....
part of the annelid
Annelid
The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...
phylum
Phylum
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....
. Zoologist Ray Lankester
Ray Lankester
Sir E. Ray Lankester KCB, FRS was a British zoologist, born in London.An invertebrate zoologist and evolutionary biologist, he held chairs at University College London and Oxford University. He was the third Director of the Natural History Museum, and was awarded the Copley Medal of the Royal...
gave it its name of Haplodrili, while zoologist Berthold Hatschek named it Archiannelida. Following five families were included in Haplodrili: Dinophilidae, Nerillidae
Nerillidae
Nerillida is a family of invertebrates containing the following genera:* Meganerilla* Mesonerilla* Nerilla* Nerillidium* Nerillidopsis* Paranerilla* Psammoriedlia* Thalassochaetus* Troglochaetus...
, Polygordiidae, Prorodrilidae and Saccocirridae
Saccocirridae
The Saccocirridae are small interstitial polychaetes common in coarse sand, reflective, surf beaches, usually within the zone of retention. The Saccociridae are members of the clade Protodrilida, which is in turn part of the clade Canalipalpata. Saccocirridae have a world wide distribution and it...
.
Overview
Polygordius and Protodrilus live in sand, but while the former moves by means of the contraction of its body-wall muscles, Protodrilus can progress by the action of the bands of cilia surrounding its segments, and of the longitudinal ciliated ventral groove. Saccocirrus, which also lives in sand, and more closely resembles the Polychaeta, has throughout the greater length of its body on each segment a pair of small uniramous parapodia bearing a bunch of simple setae. No other member of the group is known to have any trace of setae or parapodia at any stage of development.Commonality
These three genera have the following characters in common. The bodyBody
With regard to living things, a body is the physical body of an individual. "Body" often is used in connection with appearance, health issues and death...
is small and resembles polychaete
Polychaete
The Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000...
larva
Larva
A larva 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...
e, epidermis ciliated, the number of segments varies from five and up or can be completely absent, small prostomium with or without appendages, parapodia absent, septa reduced or absent, the nervous system consists of a brain and longitudinal ventral nerve cords closely connected with the epidermis (withotit distinct ganglia), widely separated in Saccocirrus, closely approximated in Protodrilus, fused together in Polygordius; the coelom is well developed and the dorsal and ventral longitudinal mesenteries are complete; the nephridia are simple, and open into the coelom. Polygordius differs from Protodrilus and Saccocirrus in the absence of a distinct suboesophageal muscular pouch, and in the absence of a peculiar closed cavity in the head region, which is especially well developed in Saccocirrus, and probably represents the specialized coelom of the first segment.
Moreover, in Saccocirrus the genital organs of a transverse section of Saccocirrus showing on the left side the organs in a genital segment of a male, and on the right side the organs in a genital segment of a female.