Crustaceans - familiar to the average person as shrimp, lobsters, crabs, krill, barnacles, and their many relatives-are easily one of the most important and diverse groups of marine life. Poorly understood, they are among the most numerous invertebrates on earth. Most crustaceans start life as eggs and move through a variety of morphological phases prior to maturity. In Atlas of Crustacean Larvae, more than 45 of the world's leading crustacean researchers explain and illustrate the beauty and complexity of the many larval life stages. Revealing shapes that are reminiscent of aliens from other worlds - often with bizarre modifications for a planktonic life or for parasitization, including (in some cases) bulging eyes, enormous spines, and aids for flotation and swimming - the abundant illustrations and photographs show the detail of each morphological stage and allow for quick comparisons. The diversity is immediately apparent in the illustrations: spikes that deter predators occur on some larvae, while others bear unique specializations not seen elsewhere, and still others appear as miniature versions of the adults. Small differences in anatomy are shown to be suited to the behaviors and survival mechanisms of each species. Destined to become a key reference for specialists and students and a treasured book for anyone who wishes to understand "the invertebrate backbone of marine ecosystems," Atlas of Crustacean Larvae belongs on the shelf of every serious marine biologist.

Atlas of Crustacean Larvae

Putative sensory structures, called lattice organs, were studied with scanning electron microscopy from ascothoracid or cypris larvae representing a wide range of families of the Ascothoracida and Cirripedia. These organs, situated dorsally on the carapace were, with few exceptions, always found in two anterior and three posterior pairs. The lattice organ morphology displayed by the Ascothoracida, a seta–like structure with a terminal pore, is believed to be the most plesiomorphic condition. Within the Cirripedia lattice organ morphology varied from types resembling the Ascothoracida in the Acrothoracica and the lepadomorph Capitulum mitella, to an elongate pore field with a larger terminal pore in most Thoracica and Rhizocephala. Akentrogonid Rhizocephala seem to display the most apomorphic condition. While lattice organ morphology was generally constant at the family level, cases were seen where closely related species such as Chthamalus stellatusand Chthamalus montaguishowed minor, but clear cut differences.



Lattice organs in 2 + 3 pairs are argued to represent a synapomorphy for the Ascothoracida and the Cirripedia. The results confirm that the cyprid morphology at the ultrastructural level will prove to be of high value in estimating phylogeny within the Cirripedia.

Comparative SEM Studies of Lattice Organs: Putative Sensory Structures on the Carapace of Larvae from Ascothoracida and Cirripedia (Crustacea Maxillopoda Thecostraca)

Hoeg, J.T. and Kolbasov G.A. 2002. Lattice organs in y-cyprids of the Facetotecta and their significance in the phylogeny of the Crustacea Thecostraca. — Acta Zoologica (Stockholm) 83 : 67‐79 Scanning and transmission electron microscopy (SEM and TEM) were used to study lattice organs in facetotectan y-cyprids from the White Sea and from Norwegian and Bahamian waters. The larvae represent at least four and possibly five different species of Facetotecta. Y-cyprids have five pairs of lattice organs in the head shield (carapace) organized into two anterior pairs and three posterior pairs. Both groups of lattice organs are arranged around a large central pore. The facetotectan lattice organs are elongate areas with a longitudinal keel, just as in the Ascothoracida and some Cirripedia Acrothoracica. The terminal pore of the organs is situated posteriorly in all five pairs. TEM confirms that the organs have the same general morphology as in the Cirripedia and Ascothoracida, namely, a cuticular chamber into which project ciliary segments from the chemosensory cells. Unlike Cirripedia the cuticular roof of the chamber lacks any pores. We conclude that five pairs of lattice organs represent an autapomorphy for the Thecostraca, which supports the monophyly of this taxon. In the ground pattern the terminal pore is posterior in all five pairs. The anterior position of the pore in lattice organ pair 2 is apomorphic for the Cirripedia, while within this taxon an anterior position also in pair 1 is apomorphic for a monophylum comprising the Thoracica and the Rhizocephala. Minute pores in the roof of the organs is another apomorphy of the Cirripedia, but its elaboration into pores visible with SEM may have been subject to some homoplasy. Since lattice organs are omnipresent in the settling instar of the Thecostraca they probably serve a critical role for the function of these cypris or cypris-like larvae.

/pdf/lattice-organs-in-y-cyprids-of-the-facetotecta-and-their-15x8f7r8ia.pdf

Lattice organs in y-cyprids of the Facetotecta and their significance in the phylogeny of the Crustacea Thecostraca

The plesiomorphic mode of crustacean development is widely accepted to be via a larva called the nauplius. Extant taxa like the Cephalocarida, Branchiopoda, Ostracoda, Mystacocarida, Copepoda, Cirripedia, Ascothoracida, Facetotecta, Euphausiacea and Penaeidea hatch from an egg as a free-living nauplius. Other crustaceans show an embryonic phase of development suggestive of a naupliar organization. Several features of the nauplius larva have been proposed as diagnostic characters for the Crustacea: a median (nauplius) eye; at least three pairs of head appendages (antennules, antennae, mandibles); a posteriorly directed fold (the labrum) extending over the mouth and a cephalic (nauplius) shield. The relationship between trilobite protaspis with at least four appendages and the crustacean nauplius remains unclear, but reports of a copepod orthonauplius with four appendages are rejected. Swimming is suggested to represent the underived mode of locomotion for the crustacean nauplius, and that naupliar swimming directly results in naupliar feeding which also is underived.

Phylogenetic implications of the Crustacean nauplius

SEM investigations of laboratory-reared larvae of Briarosaccus tenellus Boschma, 1970, revealed five naupliar instars, one more than previously described for the Rhizocephala. The external features of these and the cypris larva are described in detail. The youngest instar (NO) is characterised by a better developed furca than in subsequent stages and one additional antennulary seta. Differences in outline, shape of antennulae, and hind-body denticulation, offer the potential of individual discrimination. All the nauplii possess a transparent, hollow cuticular ring around their body. This ‘flotation collar’ represents the bulged margin of the larval head shield and is attached to the body along a delicate ridge. Three pairs of tiny pores in contact with the ridge possibly regulate inflation of the ring, but details of this mechanisms remain unknown. Due to total lecithotrophy, the nauplii of B. tenellus have limbs setation reduced to that needed for swimming only, and other feeding structures such as the labrum are also highly reduced. In the antennulae, the morphological changes in form and setation were followed from nauplius to cypris and shown to largely resemble events in ontogeny of the thoracican barnacle Semibalanus balanoides. On this basis we establish a homology scheme between antennulary setae in these two species. In both B. tenellus and S. balanoides, a naupliar seta, apically on the fourth antennulary segment develops into a conspicuous aesthetasc while one (B. tenellus) or two (S. balanoides) subapical and postaxially sited setae on the same segment develops into into four short setae in the cypris. Our study reveals that the terminology used in describing cirripede nauplius and cypris larvae is often misleading or even erroneous and improvements are suggested. Notably replacing ‘cypris carapace’ with the ontogenetically and phylogenetically more informative term ‘head shield’.

Larval development of the rhizocephalan cirripede Briarosaccus tenellus (Maxillopoda: Thecostraca) reared in the laboratory: a scanning electron microscopy study

Description and complete larval development of a new species of Baccalaureus (Crustacea: Ascothoracida) parasitic in a zoanthid from Tanabe Bay, Honshu, Japan.

Mark J. Grygier

Papers

Description and complete larval development of a new species of Baccalaureus (Crustacea: Ascothoracida) parasitic in a zoanthid from Tanabe Bay, Honshu, Japan.