Sipunculus (Sipunculus) marcusi Ditadi, 1976
General description:
Holotype: Museu de Zoologia da Universidade de São Paulo, São Paulo, MZUSP006 (Ditadi, 1976).
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Sipunculus (Sipunculus) marcusi Ditadi, 1976
Sipunculus (Sipunculus) marcusi Ditadi, 1976
General description:This species was described from two specimens. Cutler and Cutler (1985) suggested that it might be an aberrant subset of the larger population of the sympatric species, S. phalloides phalloides. They point out that other than the peculiar arrangement of the basal union of the retractor muscles and the partially attached nephridia there are no clear distinctions. Despite their doubts, Cutler and Cutler (1985) retained this species as valid. Cutler (1994) declared that the interconnected retractor origins occur in other populations of Sipunculus species.
Sipunculus (Sipunculus) marcusi Ditadi, 1976
General description:This species was named to honor the memory of Prof. Ernest Marcus (Ditadi, 1976)
Sipunculus (Sipunculus) marcusi Ditadi, 1976
General description:This species is from the coast of the state of São Paulo, Brazil, and only two specimens have been collected. It is differs from the congeners mainly by the interconnection of the bases of the retractor muscles. The interconnected base spreads over the18 longitudinal muscles bands on both sides of the nerve cord around the inner periphery of the body wall.
Look alikes:Sipunculus phalloides phalloides, a sympatric species, is similar, but S. marcusi is distinguished by the peculiar basal union of the retractor muscles and the nephridial attachment to the body wall (Cutler, 1994).
Morphology:(From Ditadi, 1976; Cutler, 1994)
External anatomy
Introvert shorter than the trunk. Triangular papillae with blunt ends, arranged irregularly, covering the surface of the introvert.
Trunk is 250-325 mm in length. The surface of the trunk is divided into numerous small rectangles by the intersection of the longitudinal and circular muscles.
Tentacular crown consists of four leaf-like tentacles.
Internal anatomy
35-36 longitudinal muscles bands (LMBs).
A pair of nephridia attaches to the trunk wall for up to 25% of their length.
Brain with short leaf-like processes.
Two pairs of retractor muscles with a peculiar basal arrangement. The bases of the ventral retractor muscles arecontinuous with the bases of the dorsal retractor muscles, spreading over longitudinal muscle bands 1-18 on both sides of the nerve cord without interruption.
Spindle muscle arises anterior to the anus, makes contact with the rectal caecum and attaches internally within the gut coil.
Size:Only two specimens have been found, their trunks measuring 250 and 325 mm in length (Ditadi, 1976).
Distribution:Only found intertidally near São Paulo, Brazil (Cutler, 1994).
Habitat:This species was dug from a sandy beach between tidemarks at a depth of 30 cm (Ditadi, 1976).
Sipunculus (Sipunculus) marcusi Ditadi, 1976
General description:Praia da Siriúba, Ilha de São Sebastião, São Paulo, 22º 50’ S 45º 20’ W, 30 cm (Ditadi, 1976).