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Related to Sipuncula: Chaetognatha, Phoronida, Echiura, peanut worms


A phylum of sedentary marine vermiform coelomates that are unsegmented, but possibly distantly related to the annelids; they are commonly called peanut worms. Two classes are defined: Sipunculidea and Phascolosomatidea. In all there are 17 genera and approximately 150 species living in a wide variety of oceanic habitats within the sediment or inside any protective shelter such as a discarded mollusk shell, foraminiferan test, or crevice in rock or coral.

Adult sipunculans range in trunk length from 2 to over 500 mm (0.08 to over 20 in.). The shape of the body ranges from almost spherical to a slender cylinder. Sipunculans have a variety of epidermal structures (papillae, hooks, or shields). Many species lack color, but shades of yellow or brown may be present. Internal anatomy is relatively simple. The digestive tract has a straight esophagus and a double-coiled intestine extending toward the posterior end of the body and back terminating in a rectum, sometimes bearing small cecum. A ventral nerve cord with lateral nerves and circumenteric connectives to the pair of cerebral ganglia are present. Two or four pigmented eyespots may be present on the cerebral ganglia, and a chemoreceptor (nuchal organ) is usually present.

Knowledge of the reproductive biology of sipunculans is scanty, and good information on breeding cycles is unavailable for most genera. Most sipunculans are dioecious and lack any sexual dimorphism. These worms play a part in the recycling of detritus and probably consume smaller invertebrates in the process. They are in turn preyed on by fishes and probably other predators (including humans).

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
The Brachiopoda and Hemichordata are considered two separate groups each with the category of Phylum, while the Sipuncula is presently grouped by some authors within the Phylum Annelida based on molecular evidence (Brusca, Moore, & Shuster, 2016).
Squalus blainville showed a less diverse diet, composed of 30 different prey item types, grouped into six taxonomical categories: Sipuncula, Annelida, Crustacea, Mollusca, Echinodermata, and Teleostei, as well as unidentified materials (Table 2).
The next most important items were amphipods (6.7%) and Echiura (5.7%) for the [is greater than] 30 cm group, and Sipuncula (21.7%) and amphipods (11.6%) for the [is less than] 30 cm group.
Spring Summer GI GII GIII GI GII GIII Polychaeta Chone insularis 351 22 Exogone arenosa 1 316 2 3 205 Aricidea taylori 9 10 142 3 115 Neanthes bruaca 12 78 32 12 16 Magelona posterenlongata 27 75 Lumbrinereis tetraura 24 96 Cirrophorus americanus 36 32 135 Mollusca Caecum striatum 601 8 Caecum pulchellum 462 8 Corbula caribea 2 78 8 75 131 Sipuncula Aspidosiphon gosnoldi 42 84 Crustacea Microphoxus cornutus 13 1 30 Phoxocephalopsis zimmeri 1 33 11 1 Ampelisciphotis podophthalma Apanthura sp.
(pea crab) 68.2 8.4 3.2 Sipuncula (marine worm) 0.8 0.0 0.6 Echiura (marine worm) 24.0 1.4 6.6 Ophiuroidea (basket and brittle star) 9.3 0.7 0.1 Chaetognatha (arrow worm) 1.6 0.2 0.0 Rajidae (skate) 2.3 0.1 0.4 Osteichthyes Teleostei (fish) 12.4 1.1 0.6 Nongadoid fish remains 47.3 6.5 2.3 Gadidae (unidentified) 1.6 0.1 0.4 Theragra chalcogramma (walleye pollock) 2.3 0.1 1.4 Zoarcidae (eelpout) 16.3 0.9 14.0 Cottoidei (Sculpin) 2.3 0.1 0.2 Dasycottus setiger (spinyhead sculpin) 0.8 0.0 0.2 Stichaeidae (prickleback) 8.5 1.5 0.6 Lumpenus sp.
Currently, Sipuncula is one of the most hotly debated lophotroehozoan assemblages: in some recent molecular phylogenetic analyses it even loses its status as a phylum and is downgraded to a subtaxon within (polychaete) annelids (Struck et al, 2007; Dunn et al, 2008).
Recent number of species of some zoobenthic groups in the whole Mediterranean Sea was as follows: 1 000 Polychaeta species, 2 000 Mollusca, 154 Echinodermata, 1 935 Arthropoda (Amphipoda 451, Decapoda 340, Isopoda 165, Anisopoda 43, Cumacea 91 and miscellaneous 845 species), 33 Sipuncula, 500 Bryozoa and 622 Porifera (UNEP/MAP 2004).
Cnidaria, Turbellaria, Sipuncula, Gastrotricha) during delay phase (2-7 months) between collection and observation of samples, and (ii) low efficiency of sampling strategy (i.e.