Cirratulidae Ryckholt, 1851

Blake, James A., 2018, Bitentaculate Cirratulidae (Annelida, Polychaeta) collected chiefly during cruises of the R / V Anton Bruun, USNS Eltanin, USCG Glacier, R / V Hero, RVIB Nathaniel B. Palmer, and R / V Polarstern from the Southern Ocean, Antarctica, and off Western South America, Zootaxa 4537 (1), pp. 1-130 : 7-8

Family Cirratulidae Ryckholt, 1851

Diagnosis. Body elongate with numerous short segments; not divided into distinct regions, but anterior and/or posterior segments sometimes expanded with crowded segments. Prostomium narrow and conical or broad and wedge-shaped, without appendages; eyespots present or absent; paired dorsolateral nuchal organs present. Peristomium achaetous, smooth or with two or more distinct annuli. Grooved dorsal tentacles arise as single pair or as multiple groups of filaments on posterior margin of peristomium or on one or more anterior chaetigerous segments. Branchiae long, filamentous, usually occurring over numerous segments. Parapodia biramous with rudimentary podial lobes. Chaetae simple, including capillaries, acicular spines, or bidentate hooks. Pygidium a simple lobe sometimes with sub-anal disk, or terminal cirrus. Pharynx ventral, unarmed. Sexual and asexual reproduction may occur.

Remarks. During preparation of the 1996 publication on cirratulid polychaetes ( Blake 1996) for the “Taxonomic Atlas of the Santa Maria Basin and Western Santa Barbara Channel,” the late Dr. Mary E. Petersen informed me that the authorship for the Cirratulidae should be Ryckholt, 1851, rather than Carus, 1863, as was then in usage. Her position was based on a publication by Rosenberg & Petit (1987) who reviewed the little known and seldom cited monographs on fossil invertebrates by Baron Philippe de Ryckholt entitled “Mélanges Paléontologiques,” published in three volumes between 1851 and 1862. These authors noted that Ryckholt’s work had been largely unavailable because only six copies were known to exist; they listed the locations of these copies. They also noted that Ryckholt’s monographs contained numerous new taxa, mostly Mollusca, at the genus level, which they demonstrated were well described and available according to the International Code of Zoological Nomenclature (ICZN). These authors also attributed several non-molluscan taxa including the family-level polychaete name Cirratulidae to Ryckholt with a publication date of 1851. This predated the better-known reference by Carus (1863). Following the initial usage of Ryckholt, 1851 as the author of Cirratulidae in Blake (1996) , the change has been widely used and was recently reviewed and accepted by the World Register of Marine Species (WoRMS) ( Read & Fauchald 2018a).

The diagnosis of the Family Cirratulidae presented here, encompasses characters as understood sensu stricto. At present, there are three major groups of Cirratulidae with 12 genera currently recognized:

The multitentaculate species are those cirratulids with a wedge-shaped prostomium and numerous dorsal tentacles that occur in two groups on the anterior part of the body; setae include capillaries and spines, with Protocirrineris species having only capillaries. The multitentaculate species are more common in intertidal and nearshore habitats and are rarely encountered in deep water. There are five genera currently assigned to this category: Cirratulus , Cirriformia , Fauvelicirratulus , Protocirrineris , and Timarete .

The bitentaculate sediment-dwelling species are those cirratulids with a pre-setigerous region consisting of a distinct prostomium and peristomium; a single pair of long dorsal tentacles usually arises from the posterior margin of the peristomium; branchiae are present along most of the body. The bitentaculate species occur from the intertidal to abyssal depths. There are five genera currently assigned to this category: Aphelochaeta , Caulleriella , Chaetozone , Kirkegaardia , and Tharyx . A sixth genus, Chaetocirratulus n. gen., is described as part of this study.

The bitentaculate shell- or rock-boring species belong to a single genus, Dodecaceria . These cirratulids bore into or otherwise inhabit burrows in calcareous substrates; the paired tentacles are lateral rather than dorsal and branchiae are limited to a few anterior segments. Most species of Dodecaceria are limited to nearshore habitats.

This diagnosis excludes several closely related taxa currently included in the Acrocirridae , Ctenodrilidae , and Cossuridae . However, recent phylogenetic studies strongly suggest that the ctenodrilids are closely related to Dodecaceria ( Weidhase et al. 2016; Blake & Magalhães 2017).

Bitentaculate cirratulids in general do not have distinct body regions. However, the pre-setiger area, anterior or thoracic segments, middle or abdominal segments, and the posterior segments differ in appearance from one another and are usually characterized separately.

The pre-setiger area includes the prostomium, peristomium, and usually the dorsal tentacles. The peristomium may be divided into annular rings and may be surmounted by a dorsal crest. The last peristomial ring may sometimes be interpreted as separate achaetous segment. The first pair of branchiae often occurs in close proximity to the dorsal tentacles on the peristomium, or on setiger 1.

An expanded anterior segmental region often called the thorax is best developed in the genera Aphelochaeta and Kirkegaardia . In species of those genera, the anterior segments are often expanded, individually crowded, narrow, and bear expanded parapodia that are variously developed into prominent shoulders that in some cases, are elevated over the dorsum producing a mid-dorsal channel or groove. Ventrally, conspicuous yellow glands often occur across individual anterior segments; these may stain intensely with Methyl Green. In other genera, however, the anterior segments are not overly expanded and are not readily differentiated from middle body segments. In contrast to Aphelochaeta and Kirkegaardia , species of Caulleriella and Chaetocirratulus n. gen., have little or no difference in the appearance of anterior and middle body setigers.

Middle body or abdominal segments are typically longer and sometimes moniliform in shape. In a few species, the middle body segments are expanded, usually due to the presence of gametes or to an enlarged stomach between the esophagus and intestine. Far posterior segments of Aphelochaeta species are sometimes expanded or inflated; other species have narrow or tapering posterior ends.

The present study is limited to five of the six sediment-dwelling bitentaculate genera; the genus Kirkegaardia was treated earlier ( Blake 2016). The multitentaculate genera and Dodecaceria will be treated in a separate contribution. A recent review of the Cirratulidae including diagnoses of the genera is found in Blake & Magalhães (2017). The following key to all genera of Cirratulidae is provided to help readers and users of this study better orient themselves in the family.