Haustrum haustorium, common name: the brown or dark rock shell, is a large species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of predatory sea snail

Snail

Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...

, a marine

Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 gastropod mollusc in the 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...

 Muricidae

Muricidae

Muricidae, common name murex snails or rock snails, is a large and varied taxonomic family of small to large predatory sea snails. With approximately 1,600 living species the Muricidae represent almost 10% of the Neogastropoda. Additionally, 1,200 fossil species have been recognised...

, the murex snails or rock snails.

Taxonomy

Haustrum haustorium used to be the only species in 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...

 Haustrum

Haustrum

Haustrum is a genus of sea snails, marine gastropod mollusks in the family Muricidae, the murex snails or rock snails.-Species:Species within the genus Haustrum include:* Haustrum baileyanum...

. However, Beu (2004) reclassified a number of New Zealand's whelks, considering species in the genus Lepsiella to be synonymous with the genus Haustrum.

Shell description

A reliable characteristic for distinguishing Haustum haustorium from its congeners is the angle by which the aperture

Aperture

In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are,...

 lip inserts on the shell: In Haustrum haustorium the angle is near-perpendicular

Perpendicular

In geometry, two lines or planes are considered perpendicular to each other if they form congruent adjacent angles . The term may be used as a noun or adjective...

, whereas in other species the angle is more acute (~45 degrees). Tan (2003) provides the most recent review.

Habitat

This rock snail's typical habitat is the mid and lower eulittoral zone of New Zealand's semi-exposed rocky intertidal shores. It is less common on algal-dominated sheltered shores.