Showing papers in "Veliger in 2001"

Microhabitat segregation of co-existing gastropod species

Abstract: The formation of aggregations of four co-existing species of nerite gastropod was investigated on a tropical rocky shore in north Queensland, Australia. The results demonstrated that all species formed mono-specific aggregations, each of which had a strong fidelity for aggregating within a particular microhabitat type. Hence there was a distinct segregation of microhabitat usage among the four co-existing, ecologically similar species, and this segregation did not differ spatially or temporally. These results indicate that spatial and temporal fluctuations of abiotic conditions had little impact on the formation of aggregations, and that factors such as competition for microhabitats among species may play a greater role in the formation and maintenance of intertidal gastropod aggregations than previously thought.

Anatomy and histology of a new species of Enotepteron (Cephalaspidea: Gastropteridae) from tropical northeastern Australia

Abstract: The anatomy and histology of a new species of gastropterid cephalaspidean, Enotepteron heikeae, sp. nov., from tropical Australia is described. Enotepteron is the least documented of the gastropterid genera with only two previously recorded species, from Yellow Sea (North Pacific) and the Seychelles (Indian Ocean). The unique features of E. heikeae, within the genus, are the long thin tail (posterior end of the foot), cuticular penial armature, and a bilobed prostate. The investigation also reveals the presence of a very large anal gland. This gland maybe a useful taxonomic region, and its discovery considerably broadens the previously known geographical occurrence of the genus. Documentation and investigation of this species improves our knowledge of the morphological variation across the genus, and allows reassessment of the generic features to show that the presence of spheres to the posterior edge of the parapodia may be the only unifying character.

A new genus of aporrhaid gastropod from upper Paleocene rocks in southern California

Abstract: The family Aporrhaidae Gray, 1850, is a group of marine gastropods characterized by a highly modified apertural margin. It apparently originated near the end of the the Triassic and was an important component of the late Mesozoic marine-gastropod fauna (Roy, 1994). The end-Cretaceous mass-extinction removed about 76% of the aporrhaid genera (Roy, 1996). On the Pacific slope of North America, early Tertiary (Paleogene) aporrhaids represent a very minor component of the molluscan fauna. Aporrhaids previously reported from this region are Araeodactylus (?) costatus (Gabb, 1869), Tessarolax (?) inconspicua (Gabb, 1869), Drepanocheilus exilis (Gabb, 1864), and Drepanocheilus (?) transversus (Gabb, 1869). All of these species, which are illustrated by Stewart (1927), are late Paleocene in age and from California (Stewart, 1927; Weaver, 1953; Zinsmeister, 1983). The latter species is also known from upper? Paleocene rocks in Baja California, Mexico (Zinsmeister & Paredes, 1988). Tessarolax (?) inconspicua is based on poorly preserved material and might not even be an apporhaid. Drepanocheilus exilis and Drepanocheilus (?) transversus are also based on incomplete specimens, and future collecting might possibly reveal them to be conspecific. Recent collecting in upper Paleocene rocks in southern California revealed a single specimen of a very rare aporrhaid that represents a new genus. This new gastropod, Spinigeropsis, differs from most other aporrhaids by having digitations on both sides of the shell rather than only on one side. The specimen of the new gastropod was found at LACMIP locality 16869 in the upper part of thf Santa Susana Formation in the Palisades Highlands area just east of Santa Ynez Canyon in the east-central Santa Monica Mountains, Los Angeles County, southern C fornia (Figure 1). This locality is in a richly fossiliferous lens within a very fine-grained sandstone approximately 20 m stratigraphically below an algal-limestone interval. This locality and others in the immediate area are in rocks of late Paleocene age (Thanetian Stage) which were deposited in a protected bay (no deeper than 40 to 70 m) with warm-water, algal-limestone buildups associated with shoals on the bay floor (Squires & Kennedy, 1998). The following institutional acronym is used: Natural History Museum of Los Angeles County, Section of Invertebrate Paleontology, Los Angeles (LACMIP). 118°34' 118 o 32'30\