Group Chitinozoa

Because Chitinozoa are invariably opaque with their internal structure obscured, classification has concentrated

Oral pole

Fig. 11.1 (a) Desmochitina (Operculatifera), longitudinal section through two welded vesicles.

(b) Desmochitina, exterior view.

(c) Lagenochitina (Prosomatifera), longitudinal section. (d) Lagenochitina exterior view. (Based partly on Jansonius 1970.)

Operculum

Outer wall

Inner wall

Operculum

Recessed .operculum

Oral pole

Outer wall

Inner wall

"Base Aboral pole

Rough wall

"Base Aboral pole

Rough wall

Aperture

Recessed .operculum

Fig. 11.1 (a) Desmochitina (Operculatifera), longitudinal section through two welded vesicles.

(b) Desmochitina, exterior view.

(c) Lagenochitina (Prosomatifera), longitudinal section. (d) Lagenochitina exterior view. (Based partly on Jansonius 1970.)

Fig. 11.2 Prosomatifera (diagrammatic). (a) Ancyrochitina, longitudinal section. (b) Ancyrochitina, exterior view. (c) Velatachitina, longitudinal section. (d) Velatachitina, exterior view. (Based partly on Jansonius 1970.)

largely on form genera defined on their outline shape (i.e. silhouette). Chitinozoa are generally arranged alphabetically under a version of the suprageneric classification proposed by Eisenack (1972). Orders are the highest taxonomic category used. The Operculati-fera are characterized by an operculum, reduced oral tubes (usually with a collarette, but lacking a neck). This order contains one family, the Desmochitinidae, and six subfamilies; for example Desmochitina (L. Ord.-U. Sil; Fig. 11.1a,b) had a relatively small subspherical vesicle with short lips but no neck and was commonly united in chains.

The Prosomatifera have a prosome and well-developed necks. This order contains two families, the Conochitinidae and the Lagenochitinidae, distinguished by the relationship between the chamber and the neck. The operculum is recessed within the neck of Lagenochitina (L. Ord.-L. Sil., Fig. 11.1c,d) which had a relatively large vesicle with a cylindrical neck. Twelve subfamilies are distinguished by the type and distribution of the ornament and the morphology of basal edge structures. The Complexoperculati bear a recessed operculum provided with a sleeve-like extension, the flange, which together are called the prosome (Fig. 11.2). This prosome is simple in the Sphaerochitinidae, whose vesicles lack aboral sleeves and copulae, as for example in Ancyrochitina (Ord.-Dev., Fig. 11.2a,b) which has a flask-shaped vesicle with a ring of spines around the base. The Tanuchi-tinidae display elaborate differentiation at the aboral end and their vesicles are often tubular. Velatachitina (L. Ord.-L. Sil., Fig. 11.2c,d) is subcylindrical with a sleeve at either end, formed from the outer wall. The inner wall is produced aborally into a copula, whilst

Provisional chitinozoan phylogeny. (Redrawn from Miller in Jansonius & McGregor 1996 after Paris.)

Provisional chitinozoan phylogeny. (Redrawn from Miller in Jansonius & McGregor 1996 after Paris.)

the prosome has an orally extended tube with ring-like markings (annulations).

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